1.
Colloid
–
A colloid, in chemistry, is a mixture in which one substance of microscopically dispersed insoluble particles is suspended throughout another substance. Sometimes the dispersed substance alone is called the colloid, the colloidal suspension refers unambiguously to the overall mixture. Unlike a solution, whose solute and solvent constitute only one phase, a colloid has a dispersed phase, to qualify as a colloid, the mixture must be one that does not settle or would take a very long time to settle appreciably. The dispersed-phase particles have a diameter between approximately 1 and 1000 nanometers, such particles are normally easily visible in an optical microscope, although at the smaller size range, an ultramicroscope or an electron microscope may be required. Homogeneous mixtures with a phase in this size range may be called colloidal aerosols, colloidal emulsions, colloidal foams, colloidal dispersions. The dispersed-phase particles or droplets are affected largely by the surface chemistry present in the colloid, some colloids are translucent because of the Tyndall effect, which is the scattering of light by particles in the colloid. Other colloids may be opaque or have a slight color, Colloidal suspensions are the subject of interface and colloid science. This field of study was introduced in 1861 by Scottish scientist Thomas Graham, because of the size exclusion, the colloidal particles are unable to pass through the pores of an ultrafiltration membrane with a size smaller than their own dimension. The smaller the size of the pore of the ultrafiltration membrane, the measured value of the concentration of a truly dissolved species will thus depend on the experimental conditions applied to separate it from the colloidal particles also dispersed in the liquid. This is particularly important for solubility studies of readily hydrolyzed species such as Al, Eu, Am, Cm, the colloid particles are attracted toward water. They are also called reversible sols, hydrophobic colloids, These are opposite in nature to hydrophilic colloids. The colloid particles are repelled by water and they are also called irreversible sols. In some cases, a colloid suspension can be considered a homogeneous mixture and this is because the distinction between dissolved and particulate matter can be sometimes a matter of approach, which affects whether or not it is homogeneous or heterogeneous. The following forces play an important role in the interaction of particles, Excluded volume repulsion. Electrostatic interaction, Colloidal particles often carry a charge and therefore attract or repel each other. The charge of both the continuous and the phase, as well as the mobility of the phases are factors affecting this interaction. Van der Waals forces, This is due to interaction between two dipoles that are permanent or induced. Even if the particles do not have a permanent dipole, fluctuations of the electron density gives rise to a dipole in a particle
Colloid
–
Milk is an
emulsified colloid of liquid
butterfat globules dispersed within a
water -based solution.
2.
Antiseptic
–
Antiseptic are antimicrobial substances that are applied to living tissue/skin to reduce the possibility of infection, sepsis, or putrefaction. Disinfectants do not kill bacterial spores e. g. on surgical instruments, even sterilization may not destroy prions. Some antibiotics are true germicides, capable of destroying microbes, while others are bacteriostatic, antibacterials are antiseptics that have the proven ability to act against bacteria. Microbicides which destroy virus particles are called viricides or antivirals, antisepsis was recommended by Hungarian physician Ignaz Semmelweis in 1847 but, tragically, he was ignored. In this paper, Lister advocated the use of acid as a method of ensuring that any germs present were killed. Some of this work was anticipated by, Ancient Greek physicians Galen and Hippocrates and their theories were bitterly opposed by Galenist Guy de Chauliac and others trained in the classical tradition. Joseph Smith alluded to the use of alcohol as an antiseptic in February 1833, specifically, verse 7 states, And, again, strong drinks are not for the belly, but for the washing of your bodies. More commonly, 3% solutions of hydrogen peroxide have been used in household first aid for scrapes, however, the strong oxidization causes scar formation and increases healing time during fetal development. Iodine is usually used in a solution or as Lugols iodine solution as a pre-. Some people do not recommend disinfecting minor wounds with iodine because of concern that it may induce scar tissue formation, however, concentrations of 1% iodine or less have not been shown to increase healing time and are not otherwise distinguishable from treatment with saline. Polyhexanide is a compound suitable for clinical use in critically colonized or infected acute. The physicochemical action on the bacterial envelope prevents or impedes the development of resistant bacterial strains, balsam of Peru is a mild antiseptic. By continued exposure to antibiotics, bacteria may evolve to the point where they are no longer harmed by these compounds, bacteria can also develop a resistance to antiseptics, but the effect is generally less pronounced. The mechanism by which bacteria evolve may vary in response to different antiseptics, low concentrations of an antiseptic may encourage growth of a bacterial strain that is resistant to the antiseptic, where a higher concentration of the antiseptic would simply kill the bacteria. In addition, use of a high concentration of an antiseptic may cause tissue damage or slow the process of wound healing
Antiseptic
–
Joseph Lister
Antiseptic
–
A bottle of ethanol (95%) – an antiseptic
3.
Lysozyme
–
Lysozyme, also known as muramidase or N-acetylmuramide glycanhydrolase is an antimicrobial enzyme produced by animals that forms part of the innate immune system. This hydrolysis in turn compromises the integrity of cell walls causing lysis of the bacteria. Lysozyme is abundant in a number of secretions, such as tears, saliva, human milk and it is also present in cytoplasmic granules of the macrophages and the polymorphonuclear neutrophils. Large amounts of lysozyme can be found in egg white, c-type lysozymes are closely related to alpha-lactalbumin in sequence and structure, making them part of the same family. In humans, the enzyme is encoded by the LYZ gene. Lysozyme is thermally stable, with a melting point reaching up to 72 ℃ at pH5.0, however, in human milk it loses activity very fast at that temperature. In a large range of pH lysozyme can survive, the enzyme functions by attacking, hydrolyzing, and breaking glycosidic bonds in peptidoglycans. The enzyme can also break glycosidic bonds in chitin, although not as effective as true chitinases, the ability to break down both oligosaccharides suggests a similar mechanism between the breakdown of the two molecules. Lysozymes active site binds the peptidoglycan molecule in the prominent cleft between its two domains and it attacks peptidoglyans, its natural substrate, between N-acetylmuramic acid and the fourth carbon atom of N-acetylglucosamine. Shorter saccharides like tetrasaccharide have also shown to be viable substrates, chitin has also been show to be a viable lysozyme substrate. Artificial substrates have also developed and used in lysozyme. The Phillips Mechanism proposed that the enzymes catalytic power came from both steric strain on the substrate and electrostatic stabilization of the oxo-carbenium intermediate. From x-ray crystallography data, Phillips proposed the lysozymes active site binds to a hexasaccharide, the lysozyme distorts the fourth sugar in hexasaccharide into a half-chair conformation. In this stressed state, the bond is more easily broken. An ionic intermediate containing an oxo-carbenium is created as a result of the glycosidic bond breaking, thus distortion causing the substrate molecule to adopt a strained conformation similar to that of the transition state will lower the energy barrier of the reaction. This oxo-carbonium intermediate was proposed to be electrostatically stabilized by Arieh Warshel in 1978. Residues in the site, such as aspartate and glutamate are able to stabilize this intermediate. The electrostatic stabilization argument was based on comparison to bulk water, in Warshels model, the enzyme acts as a super-sovlent, which fixes the orientation of ion pairs and provides super-solvation, and especially lower the energy when to ions are close to each other
Lysozyme
Lysozyme
–
Lysozyme crystals stained with
methylene blue.
Lysozyme
Lysozyme
4.
Immunoglobulin
–
An antibody, also known as an immunoglobulin, is a large, Y-shaped protein produced mainly by plasma cells that is used by the immune system to neutralize pathogens such as bacteria and viruses. The antibody recognizes a molecule of the harmful agent, called an antigen. Each tip of the Y of an antibody contains a paratope that is specific for one particular epitope on an antigen, allowing these two structures to bind together with precision. Using this binding mechanism, an antibody can tag a microbe or a cell for attack by other parts of the immune system. Depending on the antigen, the binding may impede the process causing the disease or may activate macrophages to destroy the foreign substance. The ability of an antibody to communicate with the components of the immune system is mediated via its Fc region. The production of antibodies is the function of the humoral immune system. Antibodies are secreted by B cells of the immune system. In most cases, interaction of the B cell with a T helper cell is necessary to produce full activation of the B cell and, therefore, soluble antibodies are released into the blood and tissue fluids, as well as many secretions to continue to survey for invading microorganisms. Antibodies are glycoproteins belonging to the immunoglobulin superfamily and they constitute most of the gamma globulin fraction of the blood proteins. They are typically made of basic structural units—each with two heavy chains and two small light chains. There are several different types of heavy chains that define the five different types of crystallisable fragments that may be attached to the antigen-binding fragments. The five different types of Fc regions allow antibodies to be grouped into five isotypes, each Fc region of a particular antibody isotype is able to bind to its specific Fc Receptor, thus allowing the antigen-antibody complex to mediate different roles depending on which FcR it binds. The ability of an antibody to bind to its corresponding FcR is further modulated by the structure of the present at conserved sites within its Fc region. The ability of antibodies to bind to FcRs helps to direct the immune response for each different type of foreign object they encounter. For example, IgE is responsible for an allergic response consisting of mast cell degranulation, igEs Fab paratope binds to allergic antigen, for example house dust mite particles, while its Fc region binds to Fc receptor ε. The allergen-IgE-FcRε interaction mediates allergic signal transduction to induce conditions such as asthma and this region is known as the hypervariable region. Each of these variants can bind to a different antigen and this enormous diversity of antibody paratopes on the antigen-binding fragments allows the immune system to recognize an equally wide variety of antigens
Immunoglobulin
–
Immunofluorescence image of the eukaryotic
cytoskeleton.
Actin filaments are shown in red,
microtubules in green, and the
nuclei in blue.
Immunoglobulin
–
Each antibody binds to a specific
antigen; an interaction similar to a lock and key.
Immunoglobulin
–
Example of tissue cross-reactivity on human
tissue microarray
Immunoglobulin
–
Angel of the West (2008) by
Julian Voss-Andreae is a sculpture based on the antibody structure published by E. Padlan. Created for the Florida campus of
the Scripps Research Institute, the antibody is placed into a ring referencing
Leonardo da Vinci's Vitruvian Man thus highlighting the similarity of the antibody and the human body.
5.
Glycoprotein
–
Glycoproteins are proteins that contain oligosaccharide chains covalently attached to polypeptide side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification and this process is known as glycosylation. Secreted extracellular proteins are often glycosylated, in proteins that have segments extending extracellularly, the extracellular segments are also often glycosylated. Glycoproteins are also often important integral membrane proteins, where they play a role in cell–cell interactions and it is important to distinguish endoplasmic reticulum-based glycosylation of the secretory system without reversible cytosolic-nuclear glycosylation. In contrast, classical secretory glycosylation can be structurally essential, for example, inhibition of asparagine-linked, i. e. N-linked, glycosylation can prevent glycoprotein folding and full inhibition can be toxic to an individual cell. In contrast, perturbation of terminal processing, which occurs in the Golgi apparatus, is dispensable for isolated cells but can lead to human disease, a famous example of this latter effect is the ABO blood system. There are several types of glycosylation, although the first two are the most common, in N-glycosylation, sugars are attached to nitrogen, typically on the amide side-chain of asparagine. In O-glycosylation, sugars are attached to oxygen, typically on serine or threonine, in P-glycosylation, sugars are attached to phosphorus on a phosphoserine. In C-glycosylation, sugars are attached directly to carbon, such as in the addition of mannose to tryptophan, in glypiation, a GPI glycolipid is attached to the C-terminus of a polypeptide, serving as a membrane anchor. Monosaccharides commonly found in eukaryotic glycoproteins include, The sugar group can assist in protein folding or improve proteins stability, one example of glycoproteins found in the body is mucins, which are secreted in the mucus of the respiratory and digestive tracts. The sugars when attached to give them considerable water-holding capacity. Glycoproteins are important for blood cell recognition, especially in mammals. Examples of glycoproteins in the system are, molecules such as antibodies. Molecules of the major histocompatibility complex, which are expressed on the surface of cells, sialyl Lewis X antigen on the surface of leukocytes. H antigen of the ABO blood compatibility antigens, other examples of glycoproteins include, glycoprotein IIb/IIIa, an integrin found on platelets that is required for normal platelet aggregation and adherence to the endothelium. Components of the zona pellucida, which surrounds the oocyte, and is important for sperm-egg interaction, structural glycoproteins, which occur in connective tissue. These help bind together the fibers, cells, and ground substance of connective tissue and they may also help components of the tissue bind to inorganic substances, such as calcium in bone. Glycoprotein-41 and glycoprotein-120 are HIV viral coat proteins, soluble glycoproteins often show a high viscosity, for example, in egg white and blood plasma
Glycoprotein
–
N-linked protein glycosylation (N-glycosylation of N-glycans) at Asn residues (Asn-x-Ser/Thr motifs) in glycoproteins.
6.
Lactoferrin
–
Lactoferrin, also known as lactotransferrin, is a multifunctional protein of the transferrin family. Lactoferrin is a glycoprotein with a molecular mass of about 80 kDa that is widely represented in various secretory fluids, such as milk, saliva, tears. Lactoferrin is also present in secondary granules of PMN and is secreted by some acinar cells, Lactoferrin can be purified from milk or produced recombinantly. Human colostrum has the highest concentration, followed by human milk, Lactoferrin is one of the components of the immune system of the body, it has antimicrobial activity and is part of the innate defense, mainly at mucoses. In particular, lactoferrin provides antibacterial activity to human infants, Lactoferrin interacts with DNA and RNA, polysaccharides and heparin, and shows some of its biological functions in complexes with these ligands. Its first detailed studies were reported around 1960 and they documented the molecular weight, isoelectric point, optical absorption spectra and presence of two iron atoms per protein molecule. The protein was extracted from milk, contained iron and was structurally and chemically similar to serum transferrin, therefore, it was named lactoferrin in 1961, though the name lactotransferrin was used in some earlier publications, and later studies demonstrated that the protein is not restricted to milk. The antibacterial action of lactoferrin was also documented in 1961, and was associated with its ability to bind iron, at least 60 gene sequences of lactoferrin have been characterized in 11 species of mammals. In most species, stop codon is TAA, and TGA in Mus musculus, deletions, insertions and mutations of stop codons affect the coding part and its length varies between 2,055 and 2,190 nucleotide pairs. Gene polymorphism between species is more diverse than the intraspecific polymorphism of lactoferrin. There are differences in amino acid sequences,8 in Homo sapiens,6 in Mus musculus,6 in Capra hircus,10 in Bos taurus and 20 in Sus scrofa and this variation may indicate functional differences between different types of lactoferrin. In humans, lactoferrin gene LTF is located on the chromosome in the locus 3q21-q23. In oxen, the sequence consists of 17 exons and has a length of about 34,500 nucleotide pairs. Exons of the gene in oxen have a similar size to the exons of other genes of the transferrin family. Similarity in the size of exons and their distribution in the domains of the protein indicates that the evolutionary development of lactoferrin gene occurred by duplication. Study of polymorphism of genes that encode lactoferrin helps selecting livestock breeds that are resistant to mastitis, Lactoferrin is one of the transferrin proteins that transfer iron to the cells and control the level of free iron in the blood and external secretions. Concentration of lactoferrin in the milk varies from 7 g/L in the colostrum to 1 g/L in mature milk, x-ray diffraction reveals that lactoferrin is based on one polypeptide chain that contains about 700 amino acids and forms two homologous globular domains named N-and C-lobes. N-lobe corresponds to amino acid residues 1–333 and C-lobe to 345–692, each lobe consists of two subdomains, N1, N2 and C1, C2, and contains one iron binding site and one glycosylation site
Lactoferrin
Lactoferrin
–
Richardson diagram of recombinant human lactoferrin. Based on
PDB: 1b0l .
Lactoferrin
Lactoferrin
7.
Mucins
–
Mucins are a family of high molecular weight, heavily glycosylated proteins produced by epithelial tissues in most organisms of Kingdom Animalia. They often take an inhibitory role, some mucins are associated with controlling mineralization, including nacre formation in mollusks, calcification in echinoderms and bone formation in vertebrates. They bind to pathogens as part of the immune system, overexpression of the mucin proteins, especially MUC1, is associated with many types of cancer. At least 20 human mucin genes have been distinguished by cDNA cloning — MUC1, MUC2, MUC3A, MUC3B, MUC4, MUC5AC, MUC5B, MUC6, MUC7, MUC8, MUC12, MUC13, MUC15, MUC16, MUC17, MUC19, and MUC20. A recently identified human mucin gene is MUC21, previously known as chromosome 6 open reading frame 205, the major secreted airway mucins are MUC5AC and MUC5B, while MUC2 is secreted mostly in the intestine but also in the airway. Mature mucins are composed of two regions, The amino- and carboxy-terminal regions are very lightly glycosylated, but rich in cysteines. The cysteine residues participate in establishing disulfide linkages within and among mucin monomers, a large central region formed of multiple tandem repeats of 10 to 80 residue sequences in which up to half of the amino acids are serine or threonine. This area becomes saturated with hundreds of O-linked oligosaccharides, n-linked oligosaccharides are also found on mucins, but in less abundance than O-linked sugars. Mucin genes encode mucin monomers that are synthesized as rod-shape apomucin cores that are modified by exceptionally abundant glycosylation. The dense sugar coating of mucins gives them considerable water-holding capacity and also makes them resistant to proteolysis, mucins are secreted as massive aggregates of proteins with molecular masses of roughly 1 to 10 million Da. Within these aggregates, monomers are linked to one another mostly by non-covalent interactions, upon stimulation, MARCKS protein coordinates the secretion of mucin from mucin-filled vesicles within the specialized epithelial cells. Fusion of the vesicles to the membrane causes release of the mucin. The result is a product of interwoven molecules which, combined with other secretions, is called mucus. Increased mucin production occurs in many adenocarcinomas, including cancers of the pancreas, lung, breast, ovary, colon, mucins are also overexpressed in lung diseases such as asthma, bronchitis, chronic obstructive pulmonary disease or cystic fibrosis. Two membrane mucins, MUC1 and MUC4 have been studied in relation to their pathological implication in the disease process. Mucins are under investigation as possible diagnostic markers for malignancies and other processes in which they are most commonly over- or mis-expressed. Abnormal deposits of mucin are responsible for the non-pitting facial edema seen in untreated hypothyroidism and this edema is seen in the pretibial area as well. Bovine Submaxillary Mucin Coatings Verotoxin-producing Escherichia coli Ali M, Hutton D, Wilson J, otolaryngology - Head and Neck Surgery
Mucins
–
Micrograph showing cells with prominent mucin -containing intra
cytoplasmic vacuoles.
Pap stain.
8.
Goblet cell
–
A goblet cell is a glandular, modified simple columnar epithelial cell whose function is to secrete gel-forming mucins, the major components of mucus. The goblet cells mainly use the method of secretion, secreting vesicles into a duct, but may use apocrine methods, budding off their secretions. The goblet cell is highly polarised with the nucleus and other organelles concentrated at the base of the cell, the remainder of the cells cytoplasm is occupied by membrane-bound secretory granules containing mucin. The goblet shape is due to the mucus laden granules in the apical part expanding, causing part of the cell to balloon. The apical plasma membrane projects microvilli to give a surface area for secretion. Goblet cells are scattered among the epithelial lining of organs, such as the intestinal. They are found inside the trachea, bronchi, and larger bronchioles in the tract, small intestines, the large intestine. In the conjunctiva goblet cells are a source of mucin in tears, in the lacrimal glands, mucus is synthesized by acinar cells instead. Goblet cells are modified simple columnar epithelial cells, having a height of four times that of their width and this gives the basal part of the cell a basophilic staining because of nucleic acids within the nucleus and rough endoplasmic reticulum staining with hematoxylin. Mucin within the granules stains pale in routine histology sections, primarily because these proteins are washed out in the preparation of microscopy samples. However, they stain easily with the PAS staining method, which colours them magenta, in mucicarmine stains, deep red mucin is found within goblet cell bodies. Goblet cells can be seen in the examples below as the larger, the main role of goblet cells is to secrete mucus in order to protect the mucous membranes where they are found. Goblet cells accomplish this by secreting mucins, large glycoproteins formed mostly by carbohydrates, the gel-like properties of mucins are given by its glycans attracting relatively large quantities of water. On the inner surface of the intestine, it forms a 200 µm thick layer that lubricates. Distinct forms of mucin are produced in different organs, while MUC2 is prevalent in the intestine, MUC5AC, mucins are stored in granules inside the goblet cells before being released to the lumen of the organ. Secretion may be stimulated by irritants such as dust and smoke, other stimuli are microbes such as viruses and bacteria. A paper published in Nature in 2012 has shed light on the process. Goblet cell carcinoids are a class of rare tumors that form as a result of a proliferation of both goblet and neuroendocrine cells
Goblet cell
–
Schematic illustration of a goblet cell in close up, illustrating different internal structures of the cell.
Goblet cell
–
Transverse section of a
villus, from the human
intestine. X 350. a.
Basement membrane, here somewhat shrunken away from the epithelium. b.
Lacteal. c.
Columnar epithelium. d. Its striated border. e. Goblet cells. f.
Leucocytes in epithelium. f’. Leucocytes below epithelium. g.
Blood vessels. h.
Muscle cells cut across.
Goblet cell
–
Goblet cell in
ileum
Goblet cell
–
Section of mouse intestine, mucus of goblet cells in blue
9.
Epithelium
–
Epithelial is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of blood vessels and organs throughout the body, there are three principal shapes of epithelial cell, squamous, columnar, and cuboidal. All glands are made up of epithelial cells, functions of epithelial cells include secretion, selective absorption, protection, transcellular transport, and sensing. Epithelial layers contain no blood vessels, so they must receive nourishment via diffusion of substances from the connective tissue. Cell junctions are well-employed in epithelial tissues, in general, epithelial tissues are classified by the number of their layers and by the shape and function of the cells. The three principal shapes associated with epithelial cells are—squamous, cuboidal and columnar, squamous epithelium has cells that are wider than their height. Cuboidal epithelium has cells whose height and width are approximately the same, columnar epithelium has cells taller than they are wide. However, when taller simple columnar epithelial cells are viewed in cross section showing several nuclei appearing at different heights and this kind of epithelium is therefore described as pseudostratified columnar epithelium. Transitional epithelium has cells that can change from squamous to cuboidal, Simple epithelium is a single layer of cells with every cell in direct contact with the basement membrane that separates it from the underlying connective tissue. In general, it is found where absorption and filtration occur, the thinness of the epithelial barrier facilitates these processes. In general, simple epithelial tissues are classified by the shape of their cells, the four major classes of simple epithelium are, simple squamous, simple cuboidal, simple columnar, pseudostratified. Simple squamous, which is found lining areas where passive diffusion of gases occur, E. g. skin, walls of capillaries, linings of the pericardial, pleural, and peritoneal cavities, as well as the linings of the alveoli of the lungs. Simple cuboidal, these cells may have secretory, absorptive, or excretory functions, examples include small collecting ducts of kidney, pancreas and salivary gland. Simple columnar, cells can be secretory, absorptive, or excretory, Simple columnar epithelium can be ciliated or non-ciliated, ciliated columnar is found in the reproductive tract. Non-ciliated epithelium can also possess microvilli, pseudostratified columnar epithelium, can be ciliated or non-ciliated. The ciliated type is called respiratory epithelium as it is almost exclusively confined to the larger respiratory airways of the nasal cavity, trachea. Stratified epithelium differs from simple epithelium in that it is multilayered and it is therefore found where body linings have to withstand mechanical or chemical insult such that layers can be abraded and lost without exposing subepithelial layers. Cells flatten as the layers become more apical, though in their most basal layers the cells can be squamous, stratified epithelia can have the following specializations, The basic cell types are squamous, cuboidal, and columnar classed by their shape
Epithelium
–
Types of epithelium
Epithelium
–
Different forms of secretion are possible in epithelial tissue or in glands.
Epithelium
–
Summary showing different epithelial cells/tissues and their characteristics.
Epithelium
–
Different characteristics of glands of the body.
10.
Respiratory
–
The respiratory system is a biological system consisting of specific organs and structures used for the process of respiration in an organism. The respiratory system is involved in the intake and exchange of oxygen, in air-breathing vertebrates like human beings, respiration takes place in the respiratory organs called lungs. In humans and other mammals, the features of the respiratory system include trachea, bronchi, bronchioles, lungs. Molecules of oxygen and carbon dioxide are exchanged, by diffusion. This exchange process occurs in the alveoli in the lungs, in fish and many invertebrates, respiration takes place through the gills. Other animals, such as insects, have respiratory systems with very simple anatomical features, plants also have respiratory systems but the directionality of gas exchange can be opposite to that in animals. The respiratory system in plants also includes features such as holes on the undersides of leaves known as stomata. The elephant is the animal known to have no pleural space. Rather, the parietal and visceral pleura are both composed of connective tissue and joined to each other via loose connective tissue. The respiratory system of birds differs significantly from that found in mammals, the lungs of birds also do not have the capacity to inflate as birds lack a diaphragm and a pleural cavity. Gas exchange in birds occurs between air capillaries and blood capillaries, rather than in alveoli, the anatomical structure of the lungs is less complex in reptiles than in mammals, with reptiles lacking the very extensive airway tree structure found in mammalian lungs. Gas exchange in reptiles still occurs in alveoli however, reptiles do not possess a diaphragm, thus, breathing occurs via a change in the volume of the body cavity which is controlled by contraction of intercostal muscles in all reptiles except turtles. In turtles, contraction of specific pairs of flank muscles governs inspiration or expiration, both the lungs and the skin serve as respiratory organs in amphibians. The ventilation of the lungs in amphibians uses positive pressure ventilation, muscles lower the floor of the oral cavity, enlarging it and drawing in air through the nostrils. While the lungs are of importance to breathing control, the skins unique properties aid rapid gas exchange when amphibians are submerged in oxygen-rich water. In most fish, respiration takes place through gills, lungfish, however, do possess one or two lungs. The labyrinth fish have developed an organ that allows them to take advantage of the oxygen of the air. Some species of crab use an organ called a branchiostegal lung
Respiratory
–
A complete, schematic view of the human respiratory system with their parts and functions.
11.
Gastrointestinal
–
Gastrointestinal is an adjective meaning of or pertaining to the stomach and intestines. A tract is a collection of related anatomic structures or a series of connected body organs, the mouth, oesophagus, stomach, and intestines are part of the human alimentary canal. All bilaterians have a gastrointestinal tract, also called a gut or an alimentary canal and this is a tube that transfers food to the organs of digestion. In large bilaterians, the gastrointestinal tract generally also has an exit, some small bilaterians have no anus and dispose of solid wastes by other means. The gastrointestinal tract contains thousands of different bacteria in their gut flora, the human gastrointestinal tract consists of the esophagus, stomach, and intestines, and is divided into the upper and lower gastrointestinal tracts. In contrast, the digestive system comprises the gastrointestinal tract plus the accessory organs of digestion. The tract may also be divided into foregut, midgut, and hindgut, the whole human GI tract is about nine metres long at autopsy. The GI tract releases hormones from enzymes to help regulate the digestive process, the structure and function can be described both as gross anatomy and as microscopic anatomy or histology. The tract itself is divided into upper and lower tracts, the upper gastrointestinal tract consists of the buccal cavity, pharynx, esophagus, stomach, and duodenum. The exact demarcation between the upper and lower tracts is the muscle of the duodenum. Upon dissection, the duodenum may appear to be an organ, but it is divided into four segments based upon function, location. The four segments of the duodenum are as follows, bulb, descending, horizontal, the suspensory muscle attaches the superior border of the ascending duodenum to the diaphragm. The suspensory muscle is an important anatomical landmark which shows the division between the duodenum and the jejunum, the first and second parts of the small intestine. This is a muscle which is derived from the embryonic mesoderm. The lower gastrointestinal tract includes most of the intestine and all of the large intestine. In humans, the intestine is further subdivided into the duodenum, jejunum and ileum while the large intestine is subdivided into the cecum, colon, rectum. The small intestine begins at the duodenum, which receives food from the stomach and it is a tubular structure, usually between 6 and 7 m long. The area of the human, adult small intestinal mucosa is about 30 m2 and its main function is to absorb the products of digestion into the bloodstream
Gastrointestinal
–
Stomach colon rectum diagram
12.
Amphibians
–
Amphibians are ectothermic, tetrapod vertebrates of the class Amphibia. They inhabit a variety of habitats, with most species living within terrestrial, fossorial, arboreal or freshwater aquatic ecosystems. Thus amphibians typically start out as larvae living in water, the young generally undergo metamorphosis from larva with gills to an adult air-breathing form with lungs. Amphibians use their skin as a respiratory surface and some small terrestrial salamanders and frogs lack lungs. They are superficially similar to lizards but, along with mammals and birds, reptiles are amniotes, the earliest amphibians evolved in the Devonian period from sarcopterygian fish with lungs and bony-limbed fins, features that were helpful in adapting to dry land. They diversified and became dominant during the Carboniferous and Permian periods, over time, amphibians shrank in size and decreased in diversity, leaving only the modern subclass Lissamphibia. The three modern orders of amphibians are Anura, Urodela, and Apoda, the number of known amphibian species is approximately 7,000, of which nearly 90% are frogs. The smallest amphibian in the world is a frog from New Guinea with a length of just 7.7 mm. The largest living amphibian is the 1.8 m Chinese giant salamander, the study of amphibians is called batrachology, while the study of both reptiles and amphibians is called herpetology. The word amphibian is derived from the Ancient Greek term ἀμφίβιος, the term was initially used as a general adjective for animals that could live on land or in water, including seals and otters. Traditionally, the class Amphibia includes all tetrapod vertebrates that are not amniotes, the numbers of species cited above follows Frost and the total number of known amphibian species is over 7,000, of which nearly 90% are frogs. With the phylogenetic classification, the taxon Labyrinthodontia has been discarded as it is a group without unique defining features apart from shared primitive characteristics. Classification varies according to the phylogeny of the author and whether they use a stem-based or a node-based classification. The phylogeny of Paleozoic amphibians is uncertain, and Lissamphibia may possibly fall within groups, like the Temnospondyli or the Lepospondyli. If the common ancestor of amphibians and amniotes is included in Amphibia, all modern amphibians are included in the subclass Lissamphibia, which is usually considered a clade, a group of species that have evolved from a common ancestor. The three modern orders are Anura, Caudata, and Gymnophiona, although the fossils of several older proto-frogs with primitive characteristics are known, the oldest true frog is Prosalirus bitis, from the Early Jurassic Kayenta Formation of Arizona. It is anatomically similar to modern frogs. The oldest known caecilian is another Early Jurassic species, Eocaecilia micropodia, the earliest salamander is Beiyanerpeton jianpingensis from the Late Jurassic of northeastern China
Amphibians
–
Triadobatrachus massinoti, a proto-frog from the Early Triassic of Madagascar
Amphibians
Amphibians
–
Top: Restoration of Eusthenopteron, a fully aquatic lobe-finned fish Bottom: Restoration of
Tiktaalik, an advanced tetrapodomorph fish
Amphibians
13.
Gills
–
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water and excretes carbon dioxide. The gills of species, such as hermit crabs, have adapted to allow respiration on land provided they are kept moist. The microscopic structure of a gill presents a surface area to the external environment. Many microscopic aquatic animals, and some larger but inactive ones, can absorb oxygen through the entire surface of their bodies. However, more complex or more active aquatic organisms usually require a gill or gills, Gills usually consist of thin filaments of tissue, branches, or slender, tufted processes that have a highly folded surface to increase surface area. A high surface area is crucial to the gas exchange of aquatic organisms, a cubic meter of air contains about 250 grams of oxygen at STP. The concentration of oxygen in water is lower than in air, in fresh water, the dissolved oxygen content is approximately 8 cm3/L compared to that of air which is 210 cm3/L. Water is 777 times more dense than air and is 100 times more viscous, oxygen has a diffusion rate in air 10,000 times greater than in water. The use of sac-like lungs to remove oxygen from water would not be efficient enough to sustain life, rather than using lungs, aseous exchange takes place across the surface of highly vascularised gills over which a one-way current of water is kept flowing by a specialised pumping mechanism. The density of the water prevents the gills from collapsing and lying on top of each other, with the exception of some aquatic insects, the filaments and lamellae contain blood or coelomic fluid, from which gases are exchanged through the thin walls. The blood carries oxygen to other parts of the body, carbon dioxide passes from the blood through the thin gill tissue into the water. Gills or gill-like organs, located in different parts of the body, are found in groups of aquatic animals, including mollusks, crustaceans, insects, fish. The gills of vertebrates typically develop in the walls of the pharynx, most species employ a countercurrent exchange system to enhance the diffusion of substances in and out of the gill, with blood and water flowing in opposite directions to each other. The gills are composed of filaments, the gill lamellae. When a fish breathes, it draws in a mouthful of water at regular intervals, then it draws the sides of its throat together, forcing the water through the gill openings, so it passes over the gills to the outside. Fish gill slits may be the ancestors of the tonsils, thymus glands. Adjacent slits are separated by a gill arch from which projects a cartilaginous gill ray. This gill ray is the support for the sheet-like interbranchial septum, the base of the arch may also support gill rakers, projections into the pharyngeal cavity that help to prevent large pieces of debris from damaging the delicate gills
Gills
–
The red gills of this
common carp are visible as a result of a
gill flap birth defect.
Gills
–
Freshwater Fish Gills magnified 400 times
Gills
–
The red gills inside a detached
tuna head (viewed from behind)
Gills
–
An
Alpine newt larva showing the
external gills, which flare just behind the head
14.
Fish
–
A fish is any member of a group of animals that consist of all gill-bearing aquatic craniate animals that lack limbs with digits. They form a group to the tunicates, together forming the olfactores. Included in this definition are the living hagfish, lampreys, and cartilaginous, tetrapods emerged within lobe-finned fishes, so cladistically they are fish as well. However, traditionally fish are rendered obsolete or paraphyletic by excluding the tetrapods, because in this manner the term fish is defined negatively as a paraphyletic group, it is not considered a formal taxonomic grouping in systematic biology. The traditional term pisces is considered a typological, but not a phylogenetic classification, the earliest organisms that can be classified as fish were soft-bodied chordates that first appeared during the Cambrian period. Although they lacked a true spine, they possessed notochords which allowed them to be more agile than their invertebrate counterparts, fish would continue to evolve through the Paleozoic era, diversifying into a wide variety of forms. Many fish of the Paleozoic developed external armor that protected them from predators, the first fish with jaws appeared in the Silurian period, after which many became formidable marine predators rather than just the prey of arthropods. Fish are abundant in most bodies of water and they can be found in nearly all aquatic environments, from high mountain streams to the abyssal and even hadal depths of the deepest oceans. With 33,100 described species, fish exhibit greater species diversity than any group of vertebrates. Fish are an important resource for humans worldwide, especially as food, commercial and subsistence fishers hunt fish in wild fisheries or farm them in ponds or in cages in the ocean. They are also caught by fishers, kept as pets, raised by fishkeepers. Fish have had a role in culture through the ages, serving as deities, religious symbols, fish do not represent a monophyletic group, and therefore the evolution of fish is not studied as a single event. Early fish from the record are represented by a group of small, jawless. Jawless fish lineages are mostly extinct, an extant clade, the lampreys may approximate ancient pre-jawed fish. The first jaws are found in Placodermi fossils, the diversity of jawed vertebrates may indicate the evolutionary advantage of a jawed mouth. It is unclear if the advantage of a hinged jaw is greater biting force, improved respiration, fish may have evolved from a creature similar to a coral-like sea squirt, whose larvae resemble primitive fish in important ways. The first ancestors of fish may have kept the form into adulthood. Fish are a group, that is, any clade containing all fish also contains the tetrapods
Fish
–
Giant grouper swimming among
schools of other fish
Fish
Fish
–
Leedsichthys (left) the largest known fish.
Fish
–
Dunkleosteus was a gigantic, 10 meter (33 feet) long
prehistoric fish.
15.
Fungi
–
A fungus is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from the other eukaryotic life kingdoms of plants, a characteristic that places fungi in a different kingdom from plants, bacteria and some protists, is chitin in their cell walls. Similar to animals, fungi are heterotrophs, they acquire their food by absorbing dissolved molecules, growth is their means of mobility, except for spores, which may travel through the air or water. Fungi are the principal decomposers in ecological systems and this fungal group is distinct from the structurally similar myxomycetes and oomycetes. The discipline of biology devoted to the study of fungi is known as mycology, in the past, mycology was regarded as a branch of botany, although it is now known fungi are genetically more closely related to animals than to plants. Abundant worldwide, most fungi are inconspicuous because of the size of their structures. Fungi include symbionts of plants, animals, or other fungi and they may become noticeable when fruiting, either as mushrooms or as molds. Fungi perform a role in the decomposition of organic matter and have fundamental roles in nutrient cycling. Since the 1940s, fungi have been used for the production of antibiotics, Fungi are also used as biological pesticides to control weeds, plant diseases and insect pests. Many species produce bioactive compounds called mycotoxins, such as alkaloids and polyketides, the fruiting structures of a few species contain psychotropic compounds and are consumed recreationally or in traditional spiritual ceremonies. Fungi can break down manufactured materials and buildings, and become significant pathogens of humans, losses of crops due to fungal diseases or food spoilage can have a large impact on human food supplies and local economies. The fungus kingdom encompasses a diversity of taxa with varied ecologies, life cycle strategies. However, little is known of the biodiversity of Kingdom Fungi. Advances in molecular genetics have opened the way for DNA analysis to be incorporated into taxonomy, phylogenetic studies published in the last decade have helped reshape the classification within Kingdom Fungi, which is divided into one subkingdom, seven phyla, and ten subphyla. The English word fungus is directly adopted from the Latin fungus, used in the writings of Horace, a group of all the fungi present in a particular area or geographic region is known as mycobiota, e. g. the mycobiota of Ireland. Like plants, fungi grow in soil and, in the case of mushrooms, form conspicuous fruit bodies. The fungi are now considered a kingdom, distinct from both plants and animals, from which they appear to have diverged around one billion years ago. Fungi have membrane-bound cytoplasmic organelles such as mitochondria, sterol-containing membranes and they have a characteristic range of soluble carbohydrates and storage compounds, including sugar alcohols, disaccharides, and polysaccharides
Fungi
Fungi
–
Omphalotus nidiformis, a bioluminescent mushroom
Fungi
–
Bracket fungi on a tree stump
Fungi
–
Two types of edible fungi
16.
Bacteria
–
Bacteria constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods, Bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit soil, water, acidic hot springs, radioactive waste, Bacteria also live in symbiotic and parasitic relationships with plants and animals. Most bacteria have not been characterised, and only half of the bacterial phyla have species that can be grown in the laboratory. The study of bacteria is known as bacteriology, a branch of microbiology, There are typically 40 million bacterial cells in a gram of soil and a million bacterial cells in a millilitre of fresh water. There are approximately 5×1030 bacteria on Earth, forming a biomass which exceeds that of all plants, Bacteria are vital in many stages of the nutrient cycle by recycling nutrients such as the fixation of nitrogen from the atmosphere. The nutrient cycle includes the decomposition of bodies and bacteria are responsible for the putrefaction stage in this process. In March 2013, data reported by researchers in October 2012, was published and it was suggested that bacteria thrive in the Mariana Trench, which with a depth of up to 11 kilometres is the deepest known part of the oceans. Other researchers reported related studies that microbes thrive inside rocks up to 580 metres below the sea floor under 2.6 kilometres of ocean off the coast of the northwestern United States. According to one of the researchers, You can find microbes everywhere—theyre extremely adaptable to conditions, the vast majority of the bacteria in the body are rendered harmless by the protective effects of the immune system, though many are beneficial particularly in the gut flora. However several species of bacteria are pathogenic and cause diseases, including cholera, syphilis, anthrax, leprosy. The most common fatal diseases are respiratory infections, with tuberculosis alone killing about 2 million people per year. In developed countries, antibiotics are used to treat infections and are also used in farming, making antibiotic resistance a growing problem. Once regarded as constituting the class Schizomycetes, bacteria are now classified as prokaryotes. Unlike cells of animals and other eukaryotes, bacterial cells do not contain a nucleus and these evolutionary domains are called Bacteria and Archaea. The ancestors of modern bacteria were unicellular microorganisms that were the first forms of life to appear on Earth, for about 3 billion years, most organisms were microscopic, and bacteria and archaea were the dominant forms of life. In 2008, fossils of macroorganisms were discovered and named as the Francevillian biota, however, gene sequences can be used to reconstruct the bacterial phylogeny, and these studies indicate that bacteria diverged first from the archaeal/eukaryotic lineage. Bacteria were also involved in the second great evolutionary divergence, that of the archaea, here, eukaryotes resulted from the entering of ancient bacteria into endosymbiotic associations with the ancestors of eukaryotic cells, which were themselves possibly related to the Archaea
Bacteria
–
Had'n
Bacteria
Bacteria
–
A
biofilm of thermophilic bacteria in the outflow of
Mickey Hot Springs,
Oregon, approximately 20 mm thick.
Bacteria
–
Helicobacter pylori electron micrograph, showing multiple flagella on the cell surface
17.
Osteichthyes
–
Osteichthyes /ˌɒstiːˈɪkθi. iːz/, popularly referred to as the bony fish, is a diverse taxonomic group of fish that have skeletons primarily composed of bone tissue, as opposed to cartilage. The vast majority of fish are members of Osteichthyes, which is a diverse and abundant group consisting of 45 orders. It is the largest class of vertebrates in existence today, the group Osteichthyes is divided into the ray-finned fish and lobe-finned fish. The oldest known fossils of fish are about 420 million years ago. Osteichthyes can be compared to Euteleostomi, in paleontology, the terms are synonymous. However, recently published phylogenetic trees treat the Osteichthyes as a clade, bony fish are characterized by a relatively stable pattern of cranial bones, rooted, medial insertion of mandibular muscle in the lower jaw. The head and pectoral girdles are covered with large dermal bones, the eyeball is supported by a sclerotic ring of four small bones, but this characteristic has been lost or modified in many modern species. The labyrinth in the ear contains large otoliths. The braincase, or neurocranium, is divided into anterior and posterior sections divided by a fissure. Early bony fish had simple lungs which helped them breathe in low-oxygen water, in many bony fish these have evolved into swim bladders, which help the body create a neutral balance between sinking and floating. They do not have fin spines, but instead support the fin with lepidotrichia and they also have an operculum, which helps them breathe without having to swim. Bony fish have no placoid scales, most have smooth and overlapping ganoid, cycloid or ctenoid scales. Traditionally, Osteichthyes is considered a class, recognised on having a swim bladder, under this classification systems, the Osteichthyes are paraphyletic with regard to land vertebrates as the common ancestor of all Osteichthyes includes tetrapods amongst its descendants. The largest subclass, the Actinopterygii are monophyletic, but with the inclusion of the smaller sub-class Sarcopterygii and this has led to an alternative classification, splitting the Osteichthyes into two full classes. Paradoxically, Sarcopterygii is under this scheme monophyletic, as it includes the tetrapods, most bony fish belong to the ray-finned fish. The phylogeny of living bony fishes is shown in the cladogram, for the majority this is their sole or main means of respiration. Lungfish and other species are capable of respiration through lungs or vascularized swim bladders. Other species can respire through their skin, intestines, and/or stomach, Osteichthyes are primitively ectothermic, meaning that their body temperature is dependent on that of the water
Osteichthyes
–
Blue runner
Osteichthyes
–
Guiyu oneiros, the earliest known bony fish, lived during the
Late Silurian, 419 million years ago). It has the combination of both
ray-finned and
lobe-finned features, although analysis of the totality of its features place it closer to lobe-finned fish.
Osteichthyes
–
ray-finned fish
18.
Hagfish
–
Hagfish, the class Myxini, are eel-shaped, slime-producing marine fish. They are the known living animals that have a skull. Along with lampreys, hagfish are jawless, they are the group to vertebrates. The classification of hagfish has been controversial, the issue is whether the hagfish is a degenerate type of vertebrate-fish, or represents a stage that precedes the evolution of the vertebral column. The original scheme groups hagfish and lampreys together as cyclostomes, as the oldest surviving class of vertebrates alongside gnathostomes, an alternative scheme proposed that jawed vertebrates are more closely related to lampreys than to hagfish, and introduces the category craniata to group vertebrates near hagfish. Recent DNA evidence has supported the original scheme, Hagfish average about 0.5 m in length. The largest known species is Eptatretus goliath with a recorded at 127 cm, while Myxine kuoi. Hagfish have elongated, eel-like bodies, and paddle-like tails, the skin is naked and covers the body like a loosely fitting sock. They have cartilaginous skulls and tooth-like structures composed of keratin, colors depend on the species, ranging from pink to blue-grey, and black or white spots may be present. Eyes are simple eyespots, not compound eyes that can resolve images, Hagfish have no true fins and have six or eight barbels around the mouth and a single nostril. Instead of vertically articulating jaws like Gnathostomata, they have a pair of horizontally moving structures with tooth-like projections for pulling off food, the mouth of the hagfish has two pairs of horny, comb-shaped teeth on a cartilaginous plate that protracts and retracts. These teeth are used to food and draw it toward the pharynx. Hagfish are long and vermiform, and can exude copious quantities of a milky, the typical species Myxine glutinosa was named for this slime. When captured and held, e. g. by the tail, they secrete the microfibrous slime, which expands into up to 20 litres of sticky, gelatinous material when combined with water. This singular behavior may assist them in extricating themselves from the jaws of predatory fish or from the interior of their own prey, recently, the slime was reported to entrain water in its microfilaments, creating a slow-to-dissipate, viscoelastic substance, rather than a simple gel. It has been proven to impair the function of a predator fishs gills, in this case, the hagfishs mucus would clog up the predators gills, disabling their ability to breathe. The predator would release the hagfish as it focused less on eating and it is because of the mucus that there are very few marine predators that target the hagfish. The other known predators of hagfish are varieties of birds or mammals, free-swimming hagfish also slime when agitated and later clear the mucus off by way of the same travelling-knot behavior
Hagfish
–
Hagfish
Hagfish
–
Pacific hagfish at 150 m depth,
California,
Cordell Bank National Marine Sanctuary
Hagfish
–
Drawing of
Eptatretus polytrema
Hagfish
–
Two Pacific hagfish feeding on a dead sharpchin rockfish, Sebastes zacentrus, while one remains in a curled position at the left of the photo
19.
Snail
–
Snail is a common name that is applied most often to land snails, terrestrial pulmonate gastropod molluscs. However, the common name snail is also applied to most of the members of the molluscan class Gastropoda that have a shell that is large enough for the animal to retract completely into. When the word snail is used in this most general sense, it not just land snails but also thousands of species of sea snails. Occasionally a few other molluscs that are not actually gastropods, such as the Monoplacophora, snail-like animals that naturally lack a shell, or have only an internal shell, are mostly called slugs, and land snails that have only a very small shell are often called semi-slugs. Even a few species have lungs. Snails can be found in a wide range of environments, including ditches, deserts. Although land snails may be familiar to laymen, marine snails constitute the majority of snail species, and have much greater diversity. Numerous kinds of snail can also be found in fresh water, most snails have thousands of microscopic tooth-like structures located on a banded ribbon-like tongue called a radula. The radula works like a file, ripping food into small pieces, many snails are herbivorous, eating plants or rasping algae from surfaces with their radulae, though a few land species and many marine species are omnivores or predatory carnivores. Several species of the genus Achatina and related genera are known as giant African land snails, some grow to 15 in from snout to tail, and weigh 1 kg. The largest living species of sea snail is Syrinx aruanus, its shell can measure up to 90 cm in length, and the whole animal with the shell can weigh up to 18 kg. The snail Lymnaea makes decisions by using two types of neuron, one deciding whether the snail is hungry, and the other deciding whether there is food in the vicinity. Named Gee Geronimo, this snail was owned by Christopher Hudson of Hove, East Sussex, UK, gastropods that lack a conspicuous shell are commonly called slugs rather than snails. Some species of slug have a red shell, some have only a vestige that serves mainly as a calcium repository. Other than that there is little difference between slugs and snails. There are however important differences in habitats and behavior, slugs squeeze themselves into confined spaces such as under loose bark on trees or under stone slabs, logs or wooden boards lying on the ground. In such retreats they are in danger from either predators or desiccation. Slugs as a group are far from monophyletic, biologically speaking slug is a term of convenience with little taxonomic significance, the reduction or loss of the shell has evolved many times independently within several very different lineages of gastropods
Snail
–
Snail
Snail
–
Helix pomatia sealed in its shell with a
calcareous epiphragm.
Snail
–
Helix aspersa - garden snail
Snail
–
French cooked snails
20.
Slugs
–
Slug, or land slug, is a common name for any apparently shell-less terrestrial gastropod mollusc. The word slug is often used as part of the common name of any gastropod mollusc that has no shell. Various taxonomic families of land slugs form part of quite different evolutionary lineages. Thus, the families of slugs are not closely related. The shell-less condition has arisen many times independently during the evolutionary past, of the six orders of Pulmonata, two – the Onchidiacea and Soleolifera – solely comprise slugs. A third family, the Sigmurethra, contains various clades of snails, the taxonomy of this group is in the process of being revised in light of DNA sequencing. It appears that pulmonates are paraphyletic and basal to the opisthobranchs, the family Ellobiidae are also polyphyletic. E. The upper pair is light sensing and has eyespots at the ends, mantle On top of the slug, behind the head, is the saddle-shaped mantle, and under this are the genital opening and anus. On one side of the mantle is an opening, which is easy to see when open. This opening is known as the pneumostome, tail The part of a slug behind the mantle is called the tail. Keel Some species of slugs, for example Tandonia budapestensis, have a prominent ridge running over their back along the middle of the tail and this ridge is called a keel. Foot The bottom side of a slug, which is flat, is called the foot, like almost all gastropods, a slug moves by rhythmic waves of muscular contraction on the underside of its foot. It simultaneously secretes a layer of mucus that it travels on, around the edge of the foot in some taxa is a structure called the foot fringe. Vestigial shell Most slugs retain a remnant of their shell, which is usually internalized and this organ generally serves as storage for calcium salts, often in conjunction with the digestive glands. An internal shell is present in the Limacidae and Parmacellidae, adult Philomycidae, Onchidiidae and Veronicellidae lack shells. Slugs bodies are made up mostly of water and, without a full-sized shell and they must generate protective mucus to survive. Many species are most active just after rain because of the moist ground, in drier conditions, they hide in damp places such as under tree bark, fallen logs, rocks and man-made structures, such as planters, to help retain body moisture. Like all other gastropods, they undergo torsion during development, Slugs produce two types of mucus, one is thin and watery, and the other thick and sticky
Slugs
Slugs
–
Various species of
British land slugs, including (from the top) the larger drawings:
Arion ater,
Kerry slug,
Limax maximus and
Limax flavus
Slugs
–
An active
Ambigolimax slug in
Fremont, California
Slugs
–
Deroceras juvenile with eggs
21.
Invertebrates
–
Invertebrates are animals that neither possess nor develop a vertebral column, derived from the notochord. This includes all animals apart from the subphylum Vertebrata, familiar examples of invertebrates include insects, crabs, lobsters and their kin, snails, clams, octopuses and their kin, starfish, sea-urchins and their kin, jellyfish, and worms. The majority of species are invertebrates, one estimate puts the figure at 97%. Many invertebrate taxa have a number and variety of species than the entire subphylum of Vertebrata. Some of the invertebrates, such as the Tunicata and Cephalochordata are more closely related to the vertebrates than to other invertebrates. This makes the term invertebrate paraphyletic and hence almost meaningless for taxonomic purposes, the word invertebrate comes from the form of the Latin word vertebra, which means a joint in general, and sometimes specifically a joint from the spinal column of a vertebrate. In turn the jointed aspect of vertebra derived from the concept of turning, coupled with the prefix in-, meaning not or without. The term invertebrates is not always precise among non-biologists since it does not accurately describe a taxon in the way that Arthropoda. Each of these describes an valid taxon, phylum, subphylum or family. Invertebrata is a term of convenience, not a taxon, it has very little circumscriptional significance except within the Chordata, the Vertebrata as a subphylum comprises such a small proportion of the Metazoa that to speak of the kingdom Animalia in terms of Vertebrata and Invertebrata has limited practicality. That would at least circumscribe the Chordata, however, even the notochord would be a less fundamental criterion than aspects of embryological development and symmetry or perhaps bauplan. The following text reflects earlier scientific understanding of the term and of animals which have constituted it. According to this understanding, invertebrates do not possess a skeleton of bone and they include hugely varied body plans. Many have fluid-filled, hydrostatic skeletons, like jellyfish or worms, others have hard exoskeletons, outer shells like those of insects and crustaceans. The most familiar invertebrates include the Protozoa, Porifera, Coelenterata, Platyhelminthes, Nematoda, Annelida, Echinodermata, Mollusca, Arthropoda include insects, crustaceans and arachnids. By far the largest number of described species are insects. The following table lists the number of described extant species for major invertebrate groups as estimated in the IUCN Red List of Threatened Species,2014.3. The IUCN estimates that 66,178 extant vertebrate species have been described, the trait that is common to all invertebrates is the absence of a vertebral column, this creates a distinction between invertebrates and vertebrates
Invertebrates
–
The common fruit fly,
Drosophila melanogaster, has been used extensively for research
Invertebrates
–
Insects
Invertebrates
–
Molluscs
Invertebrates
–
Crustaceans
22.
Predator
–
In an ecosystem, predation is a biological interaction where a predator feeds on its prey. Predators may or may not kill their prey prior to feeding on it, but the act of predation often results in the death of the prey, thus predation is often, though not always, carnivory. Other categories of consumption are herbivory, fungivory, and detritivory, all of these are consumer-resource systems. It can often be difficult to separate various types of feeding behaviors. For example, some parasites prey on their host and then lay their eggs on it, for their offspring to feed on it while it continues to live, the key characteristic of predation is the predators direct impact on the prey population. Selective pressures imposed on one another leads to an evolutionary arms race between prey and predator, resulting in various antipredator adaptations. Ways of classifying predation include grouping by trophic level or diet, by specialization, Predators can be classified by their interactions with their prey. Two factors are considered here, how close the predator and prey are, and whether the prey is killed by the predator. A true predator is one that kills and eats another living thing, Predators may hunt actively for prey in pursuit predation, or sit and wait for prey to approach within striking distance, as in ambush predators. Some predation entails venom that subdues a prey before the predator ingests it, as in the box jellyfish, or disables it, in some cases, the venom contributes to the digestion of the prey, as in rattlesnakes and some spiders. In contrast, baleen whales eat millions of microscopic plankton at once, seed and egg predation are true predation, as seeds and eggs are potential organisms. Predators need not eat prey entirely, for example, some predators cannot digest bones, some may eat only part of an organism, but still consistently cause its death. Grazing organisms do not often kill their prey, while some herbivores like zooplankton live on unicellular phytoplankton and therefore, by the individualized nature of the organism, kill their prey, many others only eat a small part of the plant. Grazing livestock may pull some grass out at the roots, but most is simply grazed upon, kelp is frequently grazed in subtidal kelp forests, but regrows at the base of the blade continuously to cope with browsing pressure. Animals may also be grazed upon, female mosquitos land on hosts briefly to gain sufficient proteins for the development of their offspring, starfish may be grazed on, being capable of regenerating lost arms. Parasites can at times be difficult to distinguish from grazers and their feeding behavior is similar in many ways, however they are noted for their close association with their host species. This close living arrangement may be described by the symbiosis, living together. Parasitic organisms range from the mistletoe, a parasitic plant
Predator
–
A
South China tiger (Panthera tigris amoyensis) as the predator feeding on the
blesbuck as the prey
Predator
–
Indian python swallowing a small
chital deer at
Mudumalai National Park
Predator
–
Meat ants feeding on a
cicada; some species can
prey on individuals of far greater size, particularly when working cooperatively.
Predator
–
Leopard (Panthera pardus pardus) killing a young
bushbuck (Tragelaphus sylvaticus) in
Kruger National Park.
23.
Communication
–
Communication is the act of conveying intended meanings from one entity or group to another through the use of mutually understood signs and semiotic rules. The main steps inherent to all communication are, The forming of communicative motivation or reason, transmission of the encoded message as a sequence of signals using a specific channel or medium. Noise sources such as forces and in some cases human activity begin influencing the quality of signals propagating from the sender to one or more receivers. Reception of signals and reassemblying of the message from a sequence of received signals. Decoding of the encoded message. Interpretation and making sense of the original message. The channel of communication can be visual, auditory, tactile and haptic, olfactory, electromagnetic, human communication is unique for its extensive use of abstract language. Development of civilization has been linked with progress in telecommunication. Nonverbal communication describes the process of conveying information in the form of non-linguistic representations, examples of nonverbal communication include haptic communication, chronemic communication, gestures, body language, facial expressions, eye contact, and how one dresses. Nonverbal communication also relates to intent of a message, examples of intent are voluntary, intentional movements like shaking a hand or winking, as well as involuntary, such as sweating. Speech also contains nonverbal elements known as paralanguage, e. g. rhythm, intonation, tempo and it affects communication most at the subconscious level and establishes trust. Likewise, written texts include nonverbal elements such as handwriting style, spatial arrangement of words, Nonverbal communication demonstrates one of Wazlawicks laws, you cannot not communicate. Once proximity has formed awareness, living creatures begin interpreting any signals received, Nonverbal cues are heavily relied on to express communication and to interpret others’ communication and can replace or substitute verbal messages. There are several reasons as to why non-verbal communication plays a role in communication. Written communication can also have non-verbal attributes, e-mails and web chats allow individual’s the option to change text font colours, stationary, emoticons, and capitalization in order to capture non-verbal cues into a verbal medium. Many different non-verbal channels are engaged at the time in communication acts. “Non-verbal behaviours may form a language system. ”Smiling, crying, pointing, caressing. Such non-verbal signals allow the most basic form of communication when verbal communication is not effective due to language barriers, Verbal communication is the spoken or written conveyance of a message
Communication
–
Communication major dimensions scheme
Communication
–
Shannon and Weaver Model of Communication
Communication
–
Berlo's Sender-Message-Channel-Receiver Model of Communication
Communication
–
Transactional model of communication
24.
Respiratory system
–
The respiratory system is a biological system consisting of specific organs and structures used for the process of respiration in an organism. The respiratory system is involved in the intake and exchange of oxygen, in air-breathing vertebrates like human beings, respiration takes place in the respiratory organs called lungs. In humans and other mammals, the features of the respiratory system include trachea, bronchi, bronchioles, lungs. Molecules of oxygen and carbon dioxide are exchanged, by diffusion. This exchange process occurs in the alveoli in the lungs, in fish and many invertebrates, respiration takes place through the gills. Other animals, such as insects, have respiratory systems with very simple anatomical features, plants also have respiratory systems but the directionality of gas exchange can be opposite to that in animals. The respiratory system in plants also includes features such as holes on the undersides of leaves known as stomata. The elephant is the animal known to have no pleural space. Rather, the parietal and visceral pleura are both composed of connective tissue and joined to each other via loose connective tissue. The respiratory system of birds differs significantly from that found in mammals, the lungs of birds also do not have the capacity to inflate as birds lack a diaphragm and a pleural cavity. Gas exchange in birds occurs between air capillaries and blood capillaries, rather than in alveoli, the anatomical structure of the lungs is less complex in reptiles than in mammals, with reptiles lacking the very extensive airway tree structure found in mammalian lungs. Gas exchange in reptiles still occurs in alveoli however, reptiles do not possess a diaphragm, thus, breathing occurs via a change in the volume of the body cavity which is controlled by contraction of intercostal muscles in all reptiles except turtles. In turtles, contraction of specific pairs of flank muscles governs inspiration or expiration, both the lungs and the skin serve as respiratory organs in amphibians. The ventilation of the lungs in amphibians uses positive pressure ventilation, muscles lower the floor of the oral cavity, enlarging it and drawing in air through the nostrils. While the lungs are of importance to breathing control, the skins unique properties aid rapid gas exchange when amphibians are submerged in oxygen-rich water. In most fish, respiration takes place through gills, lungfish, however, do possess one or two lungs. The labyrinth fish have developed an organ that allows them to take advantage of the oxygen of the air. Some species of crab use an organ called a branchiostegal lung
Respiratory system
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A complete, schematic view of the human respiratory system with their parts and functions.
25.
Phlegm
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Phlegm /ˈflɛm/ is a liquid secreted by the mucous membranes of mammals. Its definition is limited to the produced by the respiratory system, excluding that from the nasal passages. Phlegm is in essence a water-based gel consisting of glycoproteins, immunoglobulins, lipids and its composition varies depending on climate, genetics, and state of the immune system. Its color can vary from transparent to pale or dark yellow and green, from light to dark brown, contrary to popular misconception and misuse, mucus and phlegm are not always the same. Mucus is a protective layering around the airway, eye, nasal turbinate. Mucus is a viscoelastic gel produced in the airway by submucosal glands. It also contains high-molecular weight mucous glycoproteins that form linear polymers, phlegm is more related to disease than is mucus and can be troublesome for the individual to excrete from the body. Phlegm is a secretion in the airway during disease and inflammation, phlegm usually contains mucus with virus, bacteria, other debris, and sloughed-off inflammatory cells. Once phlegm has been expectorated by a cough it becomes sputum, there are multiple factors that can contribute to an excess of phlegm in the throat or larynx. Vocal abuse, Vocal abuse is the misuse or overuse of the voice in an unhealthy fashion such as clearing the throat, yelling, screaming, talking loudly, or singing incorrectly. Clearing the throat, Clearing the throat removes or loosens phlegm but the vocal cords hit together causing inflammation, yelling/screaming, Yelling and screaming both cause the vocal cords to hit against each other causing inflammation and phlegm. Nodules, Excessive yelling, screaming, and incorrect singing as well as other vocal abusive habits can cause vocal nodules, see vocal fold nodule for more information on nodules. Smoking, Smoke is hot, dry, polluted air which dries out the vocal cords, with each breath in of smoke, the larynx is polluted with toxins that inhibit it from rehydrating for about 3 hours. The vocal cords need a fair amount of lubrication and swell from inflammation when they do not have enough of it, a major illness associated with excess phlegm is acute bronchitis. A major symptom of acute bronchitis is an amount of phlegm and is usually caused by a viral infection, and only bacterial infections. Hay fever, asthma, In hay fever and asthma, inner lining in bronchioles become inflamed, air pollution, In studies of children, air pollutants have been found to increase phlegm by drying out and irritating parts of the throat. Humourism is an ancient theory that the body is filled with four basic substances, called the four humours. It is closely related to the ancient theory of the four elements and states that all diseases and disabilities result from an excess or deficit in black bile, yellow bile, phlegm, hippocrates, an ancient Greek medical doctor, is credited for this theory, about 400 BC
Phlegm
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For the humor in ancient medicine, see
Humorism. For the British artist, see
Phlegm (artist).
26.
Bronchioles
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The bronchioles or bronchioli are the passageways by which air passes through the nose or mouth to the alveoli of the lungs, in which branches no longer contain cartilage or glands in their submucosa. They are branches of the bronchi, and are part of the zone of the respiratory system. A pulmonary lobule is the portion of the lung ventilated by one bronchiole, bronchioles are approximately 1mm or less in diameter and their walls consist of ciliated cuboidal epithelium and a layer of smooth muscle. Bronchioles divide into smaller bronchioles, called terminal, which are 0. 5mm or less in diameter. Terminal bronchioles in turn divide into smaller respiratory bronchioles which divide into alveolar ducts, the diameter of the bronchioles plays an important role in air flow. The bronchioles change diameter to either increase or reduce air flow, an increase in diameter is called bronchodilation and is stimulated by either epinephrine or sympathetic nerves to increase air flow. A decrease in diameter is called bronchoconstriction and is stimulated by histamine, parasympathetic nerves, cold air, chemical irritants, the primary bronchi, in each lung, which are the left and right bronchus, give rise to secondary bronchi. These in turn give rise to tertiary bronchi, the tertiary bronchi subdivide into the bronchioles. They are histologically distinct from the tertiary bronchi in that their walls do not have hyaline cartilage, the epithelium starts as a simple ciliated columnar epithelium and changes to simple ciliated cuboidal epithelium as the bronchioles decreases in size. The diameter of the bronchioles is often said to be less than 1 mm, as stated, these bronchioles do not have hyaline cartilage to maintain their patency. Instead, they rely on elastic fibers attached to the lung tissue for support. The inner lining of these bronchioles is thin with no glands present, as the bronchioles get smaller they divide into terminal bronchioles. These bronchioles mark the end of the zone, which covers the first division through the sixteenth division of the respiratory tract. Alveoli only become present when the conducting zone changes to the respiratory zone, the terminal bronchiole is the most distal segment of the conducting zone. It branches off the lesser bronchioles, each of the terminal bronchioles divides to form respiratory bronchioles which contain a small number of alveoli. Terminal bronchioles are lined with simple cuboidal epithelium containing club cells, terminal bronchioles contain a limited number of ciliated cells and no goblet cells. Club cells are non-ciliated, rounded protein secreting cells and their secretions are a nonsticky, proteinaceous compound to maintain the airway in the smallest bronchioles. The secretion, called surfactant, reduces surface tension, allowing for bronchioles to expand during inspiration, club cells, a stem cell of the respiratory system, produce enzymes that detoxify substances dissolved in the respiratory fluid
Bronchioles
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Bronchiole
Bronchioles
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Diagram of the
alveoli with both cross-section and external view.
Bronchioles
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Cross sectional cut of primary bronchiole
Bronchioles
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1.
Trachea 2.
Mainstem bronchus 3.
Lobar bronchus 4.
Segmental bronchus 5. Bronchiole 6.
Alveolar duct 7.
Alveolus
27.
Goblet cells
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A goblet cell is a glandular, modified simple columnar epithelial cell whose function is to secrete gel-forming mucins, the major components of mucus. The goblet cells mainly use the method of secretion, secreting vesicles into a duct, but may use apocrine methods, budding off their secretions. The goblet cell is highly polarised with the nucleus and other organelles concentrated at the base of the cell, the remainder of the cells cytoplasm is occupied by membrane-bound secretory granules containing mucin. The goblet shape is due to the mucus laden granules in the apical part expanding, causing part of the cell to balloon. The apical plasma membrane projects microvilli to give a surface area for secretion. Goblet cells are scattered among the epithelial lining of organs, such as the intestinal. They are found inside the trachea, bronchi, and larger bronchioles in the tract, small intestines, the large intestine. In the conjunctiva goblet cells are a source of mucin in tears, in the lacrimal glands, mucus is synthesized by acinar cells instead. Goblet cells are modified simple columnar epithelial cells, having a height of four times that of their width and this gives the basal part of the cell a basophilic staining because of nucleic acids within the nucleus and rough endoplasmic reticulum staining with hematoxylin. Mucin within the granules stains pale in routine histology sections, primarily because these proteins are washed out in the preparation of microscopy samples. However, they stain easily with the PAS staining method, which colours them magenta, in mucicarmine stains, deep red mucin is found within goblet cell bodies. Goblet cells can be seen in the examples below as the larger, the main role of goblet cells is to secrete mucus in order to protect the mucous membranes where they are found. Goblet cells accomplish this by secreting mucins, large glycoproteins formed mostly by carbohydrates, the gel-like properties of mucins are given by its glycans attracting relatively large quantities of water. On the inner surface of the intestine, it forms a 200 µm thick layer that lubricates. Distinct forms of mucin are produced in different organs, while MUC2 is prevalent in the intestine, MUC5AC, mucins are stored in granules inside the goblet cells before being released to the lumen of the organ. Secretion may be stimulated by irritants such as dust and smoke, other stimuli are microbes such as viruses and bacteria. A paper published in Nature in 2012 has shed light on the process. Goblet cell carcinoids are a class of rare tumors that form as a result of a proliferation of both goblet and neuroendocrine cells
Goblet cells
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Schematic illustration of a goblet cell in close up, illustrating different internal structures of the cell.
Goblet cells
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Goblet cell in
ileum
Goblet cells
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Section of mouse intestine, mucus of goblet cells in blue
28.
Pollutant
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A pollutant is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resource. A pollutant may cause long- or short-term damage by changing the rate of plant or animal species, or by interfering with human amenities, comfort, health. Some pollutants are biodegradable and therefore will not persist in the environment in the long term, however the degradation products of some pollutants are themselves polluting such as the products DDE and DDD produced from degradation of DDT. Pollutants, towards which the environment has little or no absorptive capacity are called stock pollutants, stock pollutants accumulate in the environment over time. The damage they cause increases as more pollutant is emitted, stock pollutants can create a burden for future generations, by passing on damage that persists well after the ‘benefits received from incurring that damage, have been forgotten. Fund pollutants are those for which the environment has some absorptive capacity, fund pollutants do not cause damage to the environment unless the emission rate exceeds the receiving environments absorptive capacity. Fund pollutants are not destroyed, but rather converted into less harmful substances and it also encompasses ecological light pollution which describes the effect of artificial light on individual organisms and on the structure of ecosystems as a whole. Pollutants can also be defined by their zones of influence, both horizontally and vertically, the horizontal zone refers to the area that is damaged by a pollutant. Local pollutants cause damage near the emission source, regional pollutants cause damage further from the emission source. The vertical zone is referred to whether the damage is ground-level or atmospheric, surface pollutants cause damage by concentrations of the pollutant accumulating near the Earths surface Global pollutants cause damage by concentrations in the atmosphere. Pollutants can cross borders and therefore international regulations are needed for their control. The Stockholm Convention on Persistent Organic Pollutants, which entered force in 2004, is an international legally binding agreement for the control of persistent organic pollutants. Pollutant Release and Transfer Registers are systems to collect and disseminate information on releases and transfers of toxic chemicals from industrial. The National Emissions Standards for Hazardous Air Pollutants are additional emission standards that are set by EPA for toxic air pollutants, under the Clean Water Act, EPA promulgated national standards for municipal sewage treatment plants, also called publicly owned treatment works, in the Secondary Treatment Regulation. National standards for industrial dischargers are called Effluent guidelines and New Source Performance Standards, in addition, the Act requires states to publish water quality standards for individual water bodies to provide additional protection where the national standards are insufficient. The Resource Conservation and Recovery Act regulates the management, transport and disposal of solid waste, hazardous waste. A tank or piping network that has at least 10 percent of its volume underground is known as a storage tank. They often store substances such as petroleum, that are harmful to the environment should it become contaminated
Pollutant
–
Surface runoff, also called
nonpoint source pollution, from a farm field in Iowa, United States during a rain storm. Topsoil as well as farm fertilizers and other potential pollutants run off unprotected farm fields when heavy rains occur.
29.
Allergen
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An allergen is a type of antigen that produces an abnormally vigorous immune response in which the immune system fights off a perceived threat that would otherwise be harmless to the body. In technical terms, an allergen is a capable of stimulating a type-I hypersensitivity reaction in atopic individuals through Immunoglobulin E responses. Most humans mount significant Immunoglobulin E responses only as a defense against parasitic infections, however, some individuals may respond to many common environmental antigens. This hereditary predisposition is called atopy, in atopic individuals, non-parasitic antigens stimulate inappropriate IgE production, leading to type I hypersensitivity. Sensitivities vary widely from one person to another, a very broad range of substances can be allergens to sensitive individuals. Allergens can be found in a variety of sources, such as dust mite excretion, pollen, Food allergies are not as common as food sensitivity, but some foods such as peanuts, nuts, seafood and shellfish are the cause of serious allergies in many people. Officially, the United States Food and Drug Administration does recognize eight foods as being common for reactions in a large segment of the sensitive population. These include peanuts, tree nuts, eggs, milk, shellfish, fish, wheat and their derivatives, see the FDA website for complete details. Canada recognizes all eight of the allergens recognized by the US, and also recognizes sesame seeds, the European Union additionally recognizes celery. Various trees and wood products such as paper, cardboard, MDF etc. can also cause mild to severe allergy symptoms through touch or inhalation of sawdust such as asthma, other common causes of serious allergy are wasp, fire ant and bee stings, penicillin, and latex. An extremely serious form of a reaction is called anaphylaxis. This depends on the kind of tree or grass, for instance, some trees such as oak, elm, and maple pollinate in the spring, while grasses such as Bermuda, timothy and orchard pollinate in the summer. Grass allergy is generally linked to hay fever because their symptoms, symptoms include rhinitis, which causes sneezing and a runny nose, as well as allergic conjunctivitis, which includes watering and itchy eyes. Also an initial tickle on the roof of the mouth or in the back of the throat may be experienced, also, depending on the season, the symptoms may be more severe and people may experience coughing, wheezing, and irritability. A few people even become depressed, lose their appetite, or have problems sleeping, moreover, since the sinuses may also become congested, some people experience headaches. The immune system also has influence on seasonal allergies, since it reacts differently to diverse allergens like pollen. When an allergen enters the body of an individual that is predisposed to allergies, it triggers an immune reaction and these allergen antibodies migrate to mast cells lining the nose, eyes and lungs. Some symptoms that differentiate allergies from a cold include, No fever, mucous secretions are runny and clear
Allergen
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SEM of miscellaneous plant pollens. Pollens are very common allergens.
Allergen
–
The
house dust mite, its feces and
chitin are common allergens around the home
30.
Tissue (biology)
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In biology, tissue is a cellular organizational level intermediate between cells and a complete organ. A tissue is an ensemble of similar cells from the origin that together carry out a specific function. Organs are then formed by the grouping together of multiple tissues. The study of tissue is known as histology or, in connection with disease, the classical tools for studying tissues are the paraffin block in which tissue is embedded and then sectioned, the histological stain, and the optical microscope. In the last couple of decades, developments in microscopy, immunofluorescence. With these tools, the appearances of tissues can be examined in health and disease. Animal tissues are grouped into four types, connective, muscle, nervous. Collections of tissues joined in structural units to serve a common function compose organs, while all animals can generally be considered to contain the four tissue types, the manifestation of these tissues can differ depending on the type of organism. For example, the origin of the cells comprising a particular type may differ developmentally for different classifications of animals. By contrast, a true epithelial tissue is present only in a layer of cells held together via occluding junctions called tight junctions. This tissue covers all surfaces that come in contact with the external environment such as the skin, the airways. It serves functions of protection, secretion, and absorption, and is separated from other tissues below by a basal lamina and they are made up of cells separated by non-living material, which is called an extracellular matrix. This matrix can be liquid or rigid, for example, blood contains plasma as its matrix and bones matrix is rigid. Connective tissue gives shape to organs and holds them in place, blood, bone, tendon, ligament, adipose and areolar tissues are examples of connective tissues. One method of classifying tissues is to divide them into three types, fibrous connective tissue, skeletal connective tissue, and fluid connective tissue. Muscle cells form the active contractile tissue of the known as muscle tissue or muscular tissue. Muscle tissue functions to force and cause motion, either locomotion or movement within internal organs. Cells comprising the nervous system and peripheral nervous system are classified as nervous tissue
Tissue (biology)
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Microscopic view of a histologic specimen of human
lung tissue stained with
hematoxylin and
eosin.
Tissue (biology)
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Cross section of sclerenchyma fibers in plant
ground tissue
Tissue (biology)
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PAS diastase showing the fungus
Histoplasma.
Tissue (biology)
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Diving medicine:
. PMID 20805871. doi:10.1371/journal.pone.0012238.
