Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the outer surfaces of organs and blood vessels throughout the body, as well as the inner surfaces of cavities in many internal organs. An example is the outermost layer of the skin. There are three principal shapes of epithelial cell: squamous and cuboidal; these can be arranged in a single layer of cells as simple epithelium, either squamous, columnar, or cuboidal, or in layers of two or more cells deep as stratified, either squamous, columnar or cuboidal. In some tissues, a layer of columnar cells may appear to be stratified due to the placement of the nuclei; this sort of tissue is called pseudostratified. All glands are made up of epithelial cells. Functions of epithelial cells include secretion, selective absorption, transcellular transport, sensing. Epithelial layers contain no blood vessels, so they must receive nourishment via diffusion of substances from the underlying connective tissue, through the basement membrane.
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 and columnar. Squamous epithelium has cells; this is found as the lining of the mouth, the blood vessels and in the alveoli of the lungs. Cuboidal epithelium has cells whose height and width are the same. Columnar epithelium has cells taller. By layer, epithelium is classed as either simple epithelium, only one cell thick or stratified epithelium having two or more cells in thickness or multi-layered – as stratified squamous epithelium, stratified cuboidal epithelium, stratified columnar epithelium, both types of layering can be made up of any of the cell shapes. However, when taller simple columnar epithelial cells are viewed in cross section showing several nuclei appearing at different heights, they can be confused with stratified epithelia; this kind of epithelium is therefore described as pseudostratified columnar epithelium.
Transitional epithelium has cells that can change from squamous to cuboidal, depending on the amount of tension on the epithelium. 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 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 squamous. Simple cuboidal: these cells may have secretory, absorptive, or excretory functions. Examples include small collecting ducts of kidney and salivary gland. Simple columnar. Non-ciliated epithelium can possess microvilli; some tissues are referred to as simple glandular columnar epithelium. These secrete mucus and are found in stomach and rectum. Pseudostratified columnar epithelium; the ciliated type is called respiratory epithelium as it is exclusively confined to the larger respiratory airways of the nasal cavity and bronchi.
Stratified epithelium differs from simple epithelium. 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, cuboidal or columnar. Stratified epithelia can have the following specializations: The basic cell types are squamous and columnar classed by their shape. Cells of epithelial tissue are scutoid shaped packed and form a continuous sheet, they have no intercellular spaces. All epithelia is separated from underlying tissues by an extracellular fibrous basement membrane; the lining of the mouth, lung alveoli and kidney tubules are all made of epithelial tissue. The lining of the blood and lymphatic vessels are of a specialised form of epithelium called endothelium. Epithelium lines both the outside and the inside cavities and lumina of bodies; the outermost layer of human skin is composed of dead stratified squamous, keratinized epithelial cells.
Tissues that line the inside of the mouth, the esophagus, the vagina, part of the rectum are composed of nonkeratinized stratified squamous epithelium. Other surfaces that separate body cavities from the outside environment are lined by simple squamous, columnar, or pseudostratified epithelial cells. Other epithelial cells line the insides of the lungs, the gastrointestinal tract, the reproductive and urinary tracts, make up the exocrine and endocrine glands; the outer surface of the cornea is covered with fast-growing regenerated epithelial cells. A specialised form of epithelium – endothelium forms the inner lining of blood vessels and the heart, is known as vascular endotheliu
The pylorus, or pyloric part, connects the stomach to the duodenum. The pylorus is considered as having the pyloric antrum and the pyloric canal; the pyloric canal ends as the pyloric orifice, which marks the junction between the stomach and the duodenum. The orifice is surrounded by a band of muscle, called the pyloric sphincter; the word pylorus comes via Latin. The word pylorus in Greek means "gatekeeper", related to "gate" and is thus linguistically related to the word "pylon"; the pylorus is the furthest part of the stomach. It is divided into two parts, the antrum, which connects to the body of the stomach, the pyloric canal, which connects to the duodenum; the pyloric antrum is the initial portion of the pylorus. It is near the bottom of the stomach, proximal to the pyloric sphincter, which separates the stomach and the duodenum, it may temporarily become or shut off from the remainder of the stomach during digestion by peristaltic contraction of the prepyloric sphincter. The canal is the opening between the duodenum.
The pyloric sphincter, or valve, is a strong ring of smooth muscle at the end of the pyloric canal which lets food pass from the stomach to the duodenum. It controls the outflow of gastric contents into the duodenum, it receives sympathetic innervation from the celiac ganglion. Under microscopy, the pylorus contains numerous glands, including gastric pits, which constitute about half the depth of the pyloric mucosa, they consist of three short closed tubes opening into a common duct or mouth. These tubes are wavy, are about one-half the length of the duct; the duct is lined by columnar cells, continuous with the epithelium lining the surface of the mucous membrane of the stomach, the tubes by shorter and more cubical cell which are finely granular. The glands contain mucus cells and G cells; the pylorus contains scattered parietal cells and neuroendocrine cells. These endocrine cells including D cells. Unstriated muscles which are involuntary are located in at the (Pylorus The pylorus is one component of the gastrointestinal system.
Food from the stomach, as chyme, passes through the pylorus to the duodenum. The pylorus, through the pyloric sphincter, regulates entry of food from the stomach into the duodenum. In such conditions as stomach cancer, tumours may block the pyloric canal. A special tube can be implanted surgically to connect the stomach to the duodenum so as to facilitate the passage of food from one to the other; this tube is called a gastroduodenostomy. Pyloric stenosis refers to a pylorus, narrow; this is due to congenital hypertrophy of the pyloric sphincter. The lumen of the pylorus is narrower, less food is able to pass through; this problem is detected in the early weeks of life. When it is present, a newborn baby may projectile vomit after eating, but despite vomiting remain hungry. Pyloric stenosis may be managed by the insertion of a stent, or through surgical cutting of the pyloric sphincter, a pyloromyotomy. Pyloric tumors Pyloric gland adenoma Human gastrointestinal tract Stomach Duodenum Digestion "Pylorus", Stedman's Online Medical Dictionary at Lippincott Williams and Wilkins Anatomy photo:37:06-0105 at the SUNY Downstate Medical Center - "Abdominal Cavity: The Stomach" Anatomy photo:38:07-0102 at the SUNY Downstate Medical Center - "Stomach and Liver: The Pylorus" Anatomy image:8150 at the SUNY Downstate Medical Center
Dissection is the dismembering of the body of a deceased animal or plant to study its anatomical structure. Autopsy is used in forensic medicine to determine the cause of death in humans. Less extensive dissection of plants and smaller animals preserved in a formaldehyde solution is carried out or demonstrated in biology and natural science classes in middle school and high school, while extensive dissections of cadavers of adults and children, both fresh and preserved are carried out by medical students in medical schools as a part of the teaching in subjects such as anatomy and forensic medicine. Dissection is conducted in a morgue or in an anatomy lab. Dissection has been used for centuries to explore anatomy. Objections to the use of cadavers have led to the use of alternatives including virtual dissection of computer models. Plant and animal bodies are dissected to analyze the function of its components. Dissection is practised by students in courses of biology, botany and veterinary science, sometimes in arts studies.
In medical schools, students dissect human cadavers to learn anatomy. Dissection is used to help to determine the cause of death in autopsy and is an intrinsic part of forensic medicine. A key principle in the dissection of human cadavers is the prevention of human disease to the dissector. Prevention of transmission includes the wearing of protective gear, ensuring the environment is clean, dissection technique and pre-dissection tests to specimens for the presence of HIV and Hepatitis viruses. Specimens are dissected in morgues or anatomy labs; when provided, they are evaluated for use as a "fresh" or "prepared" specimen. A "fresh" specimen may be dissected within some days, retaining the characteristics of a living specimen, for the purposes of training. A "prepared" specimen may be preserved in solutions such as formalin and pre-dissected by an experienced anatomist, sometimes with the help of a diener; this preparation is sometimes called prosection. Most dissection involves the careful isolation and removal of individual organs, called the Virchow technique.
An alternative more cumbersome technique involves the removal of the entire organ body, called the Letulle technique. This technique allows a body to be sent to a funeral director without waiting for the sometimes time-consuming dissection of individual organs; the Rokitansky method involves an in situ dissection of the organ block, the technique of Ghon involves dissection of three separate blocks of organs - the thorax and cervical areas and abdominal organs, urogenital organs. Dissection of individual organs involves accessing the area in which the organ is situated, systematically removing the anatomical connections of that organ to its surroundings. For example, when removing the heart, connects such as the superior vena cava and inferior vena cava are separated. If pathological connections exist, such as a fibrous pericardium this may be deliberately dissected along with the organ. Human dissections were carried out by the Greek physicians Herophilus of Chalcedon and Erasistratus of Chios in the early part of the third century BC.
During this period, the first exploration into full human anatomy was performed rather than a base knowledge gained from'problem-solution' delving. While there was a deep taboo in Greek culture concerning human dissection, there was at the time a strong push by the Ptolemaic government to build Alexandria into a hub of scientific study. For a time, Roman law forbade dissection and autopsy of the human body, so physicians had to use other cadavers. Galen, for example, dissected the Barbary macaque and other primates, assuming their anatomy was the same as that of humans; the ancient societies that were rooted in India left behind artwork on how to kill animals during a hunt. The images showing how to kill most depending on the game being hunted relay an intimate knowledge of both external and internal anatomy as well as the relative importance of organs; the knowledge was gained through hunters preparing the captured prey. Once the roaming lifestyle was no longer necessary it was replaced in part by the civilization that formed in the Indus Valley.
There is little that remains from this time to indicate whether or not dissection occurred, the civilization was lost to the Aryan people migrating. Early in the history of India, the Arthashastra described the 4 ways that death can occur and their symptoms: drowning, strangling, or asphyxiation. According to that source, an autopsy should be performed in any case of untimely demise; the practice of dissection flourished during the 8th century. It was under their rule; this created a need to better understand human anatomy, so as to have educated surgeons. Dissection was limited by the religious taboo on cutting the human body; this changed the approach taken to accomplish the goal. The process involved the loosening of the tissues in streams of water before the outer layers were sloughed off with soft implements to reach the musculature. To perfect the technique of slicing, the prospective students used gourds and squash; these techniques of dissection gave rise to an advanced understanding of the anatomy and the enabled them to complete procedures used today, such as rhinoplasty.
During medieval times the anatomical teachings from India spread throughout the known world however the practice of dissection was stunted by Islam. The practice of dissection at a university level was not seen again until 1827, when it was performed by the student Pandit Madhusudan Gupta. Through the 1900s
Microscopy is the technical field of using microscopes to view objects and areas of objects that cannot be seen with the naked eye. There are three well-known branches of microscopy: optical and scanning probe microscopy, along with the emerging field of X-ray microscopy. Optical microscopy and electron microscopy involve the diffraction, reflection, or refraction of electromagnetic radiation/electron beams interacting with the specimen, the collection of the scattered radiation or another signal in order to create an image; this process may be carried out by wide-field irradiation of the sample or by scanning a fine beam over the sample. Scanning probe microscopy involves the interaction of a scanning probe with the surface of the object of interest; the development of microscopy revolutionized biology, gave rise to the field of histology and so remains an essential technique in the life and physical sciences. X-ray microscopy is three-dimensional and non-destructive, allowing for repeated imaging of the same sample for in situ or 4D studies, providing the ability to "see inside" the sample being studied before sacrificing it to higher resolution techniques.
A 3D X-ray microscope uses the technique of computed tomography, rotating the sample 360 degrees and reconstructing the images. CT is carried out with a flat panel display. A 3D X-ray microscope employs a range of objectives, e.g. from 4X to 40X, can include a flat panel. The field of microscopy dates back to at least the 17th-century. Earlier microscopes, single lens magnifying glasses with limited magnification, date at least as far back as the wide spread use of lenses in eyeglasses in the 13th century but more advanced compound microscopes first appeared in Europe around 1620 The earliest practitioners of microscopy include Galileo Galilei, who found in 1610 that he could close focus his telescope to view small objects close up and Cornelis Drebbel, who may have invented the compound microscope around 1620 Antonie van Leeuwenhoek developed a high magnification simple microscope in the 1670's and is considered to be the first acknowledged microscopist and microbiologist. Optical or light microscopy involves passing visible light transmitted through or reflected from the sample through a single lens or multiple lenses to allow a magnified view of the sample.
The resulting image can be detected directly by the eye, imaged on a photographic plate, or captured digitally. The single lens with its attachments, or the system of lenses and imaging equipment, along with the appropriate lighting equipment, sample stage, support, makes up the basic light microscope; the most recent development is the digital microscope, which uses a CCD camera to focus on the exhibit of interest. The image is shown on a computer screen, so eye-pieces are unnecessary. Limitations of standard optical microscopy lie in three areas. Diffraction limits resolution to 0.2 micrometres. This limits the practical magnification limit to ~1500x. Out-of-focus light from points outside the focal plane reduces image clarity. Live cells in particular lack sufficient contrast to be studied since the internal structures of the cell are colorless and transparent; the most common way to increase contrast is to stain the different structures with selective dyes, but this involves killing and fixing the sample.
Staining may introduce artifacts, which are apparent structural details that are caused by the processing of the specimen and are thus not legitimate features of the specimen. In general, these techniques make use of differences in the refractive index of cell structures. Bright field microscopy is comparable to looking through a glass window: one sees not the glass but the dirt on the glass. There is a difference, as glass is a denser material, this creates a difference in phase of the light passing through; the human eye is not sensitive to this difference in phase, but clever optical solutions have been devised to change this difference in phase into a difference in amplitude. In order to improve specimen contrast or highlight certain structures in a sample, special techniques must be used. A huge selection of microscopy techniques are available to label a sample. Four examples of transillumination techniques used to generate contrast in a sample of tissue paper. 1.559 μm/pixel. Bright field microscopy is the simplest of all the light microscopy techniques.
Sample illumination is via transmitted white light, i.e. illuminated from below and observed from above. Limitations include low contrast of most biological samples and low apparent resolution due to the blur of out-of-focus material; the simplicity of the technique and the minimal sample preparation required are significant advantages. The use of oblique illumination gives the image a three-dimensional appearance and can highlight otherwise invisible features. A more recent technique based on this method is Hoffmann's modulation contrast, a system found on inverted microscopes for use in cell culture. Oblique illumination suffers from the same limitations as bright field microscopy. Dark field microscopy is a technique for improving the contrast of transparent specimens. Dark field illumination uses a aligned light source to minimize the quantity of direct
Peristalsis is a radially symmetrical contraction and relaxation of muscles that propagates in a wave down a tube, in an anterograde direction. In much of a digestive tract such as the human gastrointestinal tract, smooth muscle tissue contracts in sequence to produce a peristaltic wave, which propels a ball of food along the tract. Peristaltic movement comprises relaxation of circular smooth muscles their contraction behind the chewed material to keep it from moving backward longitudinal contraction to push it forward. Earthworms use a similar mechanism to drive their locomotion, some modern machinery imitates this design; the word comes from New Latin and is derived from the Greek peristellein, "to wrap around," from peri-, "around" + stellein, "draw in, bring together. After food is chewed into a bolus, it is moved through the esophagus. Smooth muscles contract behind the bolus to prevent it from being squeezed back into the mouth. Rhythmic, unidirectional waves of contractions work to force the food into the stomach.
The migrating motor complex helps trigger peristaltic waves. This process works in one direction only and its sole esophageal function is to move food from the mouth into the stomach. In the esophagus, two types of peristalsis occur: First, there is a primary peristaltic wave, which occurs when the bolus enters the esophagus during swallowing; the primary peristaltic wave forces the bolus down the esophagus and into the stomach in a wave lasting about 8–9 seconds. The wave travels down to the stomach if the bolus of food descends at a greater rate than the wave itself, continues if for some reason the bolus gets stuck further up the esophagus. In the event that the bolus gets stuck or moves slower than the primary peristaltic wave, stretch receptors in the esophageal lining are stimulated and a local reflex response causes a secondary peristaltic wave around the bolus, forcing it further down the esophagus, these secondary waves continue indefinitely until the bolus enters the stomach; the process of peristalsis is controlled by the medulla oblongata.
Esophageal peristalsis is assessed by performing an esophageal motility study. During vomiting, the propulsion of food up the esophagus and out the mouth comes from contraction of the abdominal muscles. Once processed and digested by the stomach, the milky chyme is squeezed through the pyloric sphincter into the small intestine. Once past the stomach, a typical peristaltic wave only lasts for a few seconds, travelling at only a few centimeters per second, its primary purpose is to mix the chyme in the intestine rather than to move it forward in the intestine. Through this process of mixing and continued digestion and absorption of nutrients, the chyme works its way through the small intestine to the large intestine. In contrast to peristalsis, segmentation contractions result in that churning and mixing without pushing materials further down the digestive tract. Although the large intestine has peristalsis of the type that the small intestine uses, it is not the primary propulsion. Instead, general contractions called mass movements occur one to three times per day in the large intestine, propelling the chyme toward the rectum.
Mass movements tend to be triggered by meals, as the presence of chyme in the stomach and duodenum prompts them. The human lymphatic system has no central pump. Instead, lymph circulates through peristalsis in the lymph capillaries, as well as valves in the capillaries, compression during contraction of adjacent skeletal muscle, arterial pulsation. During ejaculation, the smooth muscle in the walls of the vas deferens contracts reflexively in peristalsis, propelling sperm from the testicles to the urethra; the earthworm is a limbless annelid worm with a hydrostatic skeleton. Its hydrostatic skeleton consists of a fluid-filled body cavity surrounded by an extensible body wall; the worm moves by radially constricting the anterior portion of its body, resulting in an increase in length via hydrostatic pressure. This constricted region propagates posteriorly along the worm's body; as a result, each segment is extended forward relaxes and re-contacts the substrate, with hair-like setae preventing backwards slipping.
A peristaltic pump is a positive-displacement pump in which a motor pinches advancing portions of a flexible tube to propel a fluid within the tube. The pump isolates the fluid from the machinery, important if the fluid is abrasive or must remain sterile. Robots have been designed. Catastalsis is a related intestinal muscle process. Aperistalsis refers to a lack of propulsion, it can result from achalasia of the smooth muscle involved. Basal electrical rhythm is a slow wave of electrical activity. Ileus is a disruption of the normal propulsive ability of the gastrointestinal tract caused by the failure of peristalsis. Retroperistalsis, the reverse of peristalsis Interactive 3D display of swallow waves at menne-biomed.de Peristalsis at the US National Library of Medicine Medical Subject Headings Essentials of Human Physiology by Thomas M. Nosek. Section 6/6ch3/s6ch3_9. Overview at colostate.edu