Streptococcus pneumoniae, or pneumococcus, is a Gram-positive, alpha-hemolytic or beta-hemolytic, facultative anaerobic member of the genus Streptococcus. They are found in pairs and do not form spores and are nonmotile; as a significant human pathogenic bacterium S. pneumoniae was recognized as a major cause of pneumonia in the late 19th century, is the subject of many humoral immunity studies. S. pneumoniae resides asymptomatically in healthy carriers colonizing the respiratory tract and nasal cavity. However, in susceptible individuals with weaker immune systems, such as the elderly and young children, the bacterium may become pathogenic and spread to other locations to cause disease, it spreads by direct person-to-person contact via respiratory droplets and by autoinoculation in persons carrying the bacteria in their upper respiratory tracts. It can be a cause of neonatal infections. S. Pneumoniae is the main cause of community acquired pneumonia and meningitis in children and the elderly, of septicemia in those infected with HIV.
The organism causes many types of pneumococcal infections other than pneumonia. These invasive pneumococcal diseases include bronchitis, acute sinusitis, otitis media, meningitis, osteomyelitis, septic arthritis, peritonitis, pericarditis and brain abscess. S. Pneumoniae can be differentiated from the viridans streptococci, some of which are alpha-hemolytic, using an optochin test, as S. pneumoniae is optochin-sensitive. S. pneumoniae can be distinguished based on its sensitivity to lysis by bile, the so-called "bile solubility test". The encapsulated, Gram-positive, coccoid bacteria have a distinctive morphology on Gram stain, lancet-shaped diplococci, they have a polysaccharide capsule. In 1881, the organism, known in 1886 as the pneumococcus for its role as a cause of pneumonia, was first isolated and independently by the U. S. Army physician the French chemist Louis Pasteur; the organism was termed Diplococcus pneumoniae from 1920 because of its characteristic appearance in Gram-stained sputum.
It was renamed Streptococcus pneumoniae in 1974 because it was similar to streptococci. S. Pneumoniae played a central role in demonstrating that genetic material consists of DNA. In 1928, Frederick Griffith demonstrated transformation of life turning harmless pneumococcus into a lethal form by co-inoculating the live pneumococci into a mouse along with heat-killed virulent pneumococci. In 1944, Oswald Avery, Colin MacLeod, Maclyn McCarty demonstrated that the transforming factor in Griffith's experiment was not protein, as was believed at the time, but DNA. Avery's work marked the birth of the molecular era of genetics; the genome of S. pneumoniae is a closed, circular DNA structure that contains between 2.0 and 2.1 million base pairs depending on the strain. It has a core set of 1553 genes, plus 154 genes in its virulome, which contribute to virulence and 176 genes that maintain a noninvasive phenotype. Genetic information can vary up to 10% between strains. Natural bacterial transformation involves the transfer of DNA from one bacterium to another through the surrounding medium.
Transformation is a complex developmental process requiring energy and is dependent on expression of numerous genes. In S. pneumoniae, at least 23 genes are required for transformation. For a bacterium to bind, take up, recombine exogenous DNA into its chromosome, it must enter a special physiological state called competence. Competence in S. pneumoniae is induced by DNA-damaging agents such as mitomycin C, fluoroquinolone antibiotics, topoisomerase inhibitors. Transformation protects S. pneumoniae against the bactericidal effect of mitomycin C. Michod et al. summarized evidence that induction of competence in S. pneumoniae is associated with increased resistance to oxidative stress and increased expression of the RecA protein, a key component of the recombinational repair machinery for removing DNA damages. On the basis of these findings, they suggested that transformation is an adaptation for repairing oxidative DNA damages. S. pneumoniae infection stimulates polymorphonuclear leukocytes to produce an oxidative burst, lethal to the bacteria.
The ability of S. pneumoniae to repair the oxidative DNA damages in its genome, caused by this host defense contributes to this pathogen’s virulence. Consistent with this premise, Li et al. reported that, among different transformable S. pneumoniae isolates, nasal colonization fitness and virulence depend on an intact competence system. S. pneumoniae is part of the normal upper respiratory tract flora. As with many natural flora, it can become pathogenic under the right conditions when the immune system of the host is suppressed. Invasins, such as pneumolysin, an antiphagocytic capsule, various adhesins, immunogenic cell wall components are all major virulence factors. After S. pneumoniae colonizes the air sacs of the lungs, the body responds by stimulating the inflammatory response, causing plasma and white blood cells to fill the alveoli. This condition is called pneumonia, it is susceptible to clindamycin. Pneumonia is the most common of the S. pneumoniae diseases which include symptoms such as fever and chills, rapid breathing, difficulty breathing, chest pain.
For the elderly, they may include confusion, low alertness, the former listed symptoms to a lesser degree. Pneumococcal me
Bacteria are a type of biological cell. They constitute a large domain of prokaryotic microorganisms. A few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. Bacteria were among the first life forms to appear on Earth, are present in most of its habitats. Bacteria inhabit soil, acidic hot springs, radioactive waste, the deep portions of Earth's crust. Bacteria live in symbiotic and parasitic relationships with plants and animals. Most bacteria have not been characterised, only about half of the bacterial phyla have species that can be grown in the laboratory; the study of bacteria is known as a branch of microbiology. There are 40 million bacterial cells in a gram of soil and a million bacterial cells in a millilitre of fresh water. There are 5×1030 bacteria on Earth, forming a biomass which exceeds that of all plants and animals. 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 dead bodies. In the biological communities surrounding hydrothermal vents and cold seeps, extremophile bacteria provide the nutrients needed to sustain life by converting dissolved compounds, such as hydrogen sulphide and methane, to energy. Data reported by researchers in October 2012 and published in March 2013 suggested that bacteria thrive in the Mariana Trench, 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—they're adaptable to conditions, survive wherever they are."The famous notion that bacterial cells in the human body outnumber human cells by a factor of 10:1 has been debunked. There are 39 trillion bacterial cells in the human microbiota as personified by a "reference" 70 kg male 170 cm tall, whereas there are 30 trillion human cells in the body.
This means that although they do have the upper hand in actual numbers, it is only by 30%, not 900%. The largest number exist in the gut flora, a large number on the skin; the vast majority of the bacteria in the body are rendered harmless by the protective effects of the immune system, though many are beneficial in the gut flora. However several species of bacteria are pathogenic and cause infectious diseases, including cholera, anthrax and bubonic plague; the most common fatal bacterial diseases are respiratory infections, with tuberculosis alone killing about 2 million people per year in sub-Saharan Africa. In developed countries, antibiotics are used to treat bacterial infections and are used in farming, making antibiotic resistance a growing problem. In industry, bacteria are important in sewage treatment and the breakdown of oil spills, the production of cheese and yogurt through fermentation, the recovery of gold, palladium and other metals in the mining sector, as well as in biotechnology, the manufacture of antibiotics and other chemicals.
Once regarded as plants 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 harbour membrane-bound organelles. Although the term bacteria traditionally included all prokaryotes, the scientific classification changed after the discovery in the 1990s that prokaryotes consist of two different groups of organisms that evolved from an ancient common ancestor; these evolutionary domains are called Archaea. The word bacteria is the plural of the New Latin bacterium, the latinisation of the Greek βακτήριον, the diminutive of βακτηρία, meaning "staff, cane", because the first ones to be discovered were rod-shaped; the ancestors of modern bacteria were unicellular microorganisms that were the first forms of life to appear on Earth, about 4 billion years ago. For about 3 billion years, most organisms were microscopic, bacteria and archaea were the dominant forms of life. Although bacterial fossils exist, such as stromatolites, their lack of distinctive morphology prevents them from being used to examine the history of bacterial evolution, or to date the time of origin of a particular bacterial species.
However, gene sequences can be used to reconstruct the bacterial phylogeny, these studies indicate that bacteria diverged first from the archaeal/eukaryotic lineage. The most recent common ancestor of bacteria and archaea was a hyperthermophile that lived about 2.5 billion–3.2 billion years ago. Bacteria were involved in the second great evolutionary divergence, that of the archaea and eukaryotes. Here, eukaryotes resulted from the entering of ancient bacteria into endosymbiotic associations with the ancestors of eukaryotic cells, which were themselves related to the Archaea; this involved the engulfment by proto-eukaryotic cells of alphaproteobacterial symbionts to form either mitochondria or hydrogenosomes, which are still found in all known Eukarya. Some eukaryotes that contained mitochondria engulfed cyanobacteria-like organisms, leading to the formation of chloroplasts in algae and plants; this is known as primary endosymbiosis. Bacteria display a wide diversity of sizes, called morphologies.
Bacterial cells are about one-tenth the size of eukaryotic cells
In human anatomy, the head is at the top of the human body. It is maintained by the skull, which itself encloses the brain; the human head consists of a fleshy outer portion. The brain is enclosed within the skull; the head rests on the neck, the seven cervical vertebrae support it. The human head weighs between 5 and 11 pounds The face is the anterior part of the head, containing the eyes and mouth. On either side of the mouth, the cheeks provide a fleshy border to the oral cavity; the ears sit to either side of the head. The head receives blood supply through the external carotid arteries; these supply the area outside of the inside of the skull. The area inside the skull receives blood supply from the vertebral arteries, which travel up through the cervical vertebrae; the twelve pairs of cranial nerves provide the majority of nervous control to the head. The sensation to the face is provided by the branches of the trigeminal nerve, the fifth cranial nerve. Sensation to other portions of the head is provided by the cervical nerves.
Modern texts are in agreement about which areas of the skin are served by which nerves, but there are minor variations in some of the details. The borders designated by diagrams in the 1918 edition of Gray's Anatomy are similar but not identical to those accepted today; the cutaneous innervation of the head is as follows: Ophthalmic nerve Maxillary nerve Mandibular nerve Cervical plexus Dorsal rami of cervical nerves and others are in picture which show following in upper column The head contains sensory organs: two eyes, two ears, a nose and tongue inside of the mouth. It houses the brain. Together, these organs function as a processing center for the body by relaying sensory information to the brain. Humans can process information faster by having this central nerve cluster. For humans, the front of the head is the main distinguishing feature between different people due to its discernible features, such as eye and hair colors, shapes of the sensory organs, the wrinkles. Humans differentiate between faces because of the brain's predisposition toward facial recognition.
When observing a unfamiliar species, all faces seem nearly identical. Human infants are biologically programmed to recognize subtle differences in anthropomorphic facial features. People who have greater than average intelligence are sometimes depicted in cartoons as having bigger heads as a way of notionally indicating that they have a "larger brain". Additionally, in science fiction, an extraterrestrial having a big head is symbolic of high intelligence. Despite this depiction, advances in neurobiology have shown that the functional diversity of the brain means that a difference in overall brain size is only to moderately correlated to differences in overall intelligence between two humans; the head is a source for many metaphors and metonymies in human language, including referring to things near the human head, things physically similar to the way a head is arranged spatially to a body and things that represent some characteristics associated with the head, such as intelligence. Ancient Greeks had a method for evaluating sexual attractiveness based on the Golden ratio, part of which included measurements of the head.
Headpieces can signify status, religious/spiritual beliefs, social grouping, team affiliation, occupation, or fashion choices. In many cultures, covering the head is seen as a sign of respect; some or all of the head must be covered and veiled when entering holy places or places of prayer. For many centuries, women in Europe, the Middle East, South Asia have covered their hair as a sign of modesty; this trend has changed drastically in Europe in the 20th century, although is still observed in other parts of the world. In addition, a number of religions require men to wear specific head clothing—such as the Islamic Taqiyah, Jewish yarmulke, or the Sikh turban; the same goes for Christian nun's habit. A hat is a head covering. Hats may be worn as part of a uniform or used as a protective device, such as a hard hat, a covering for warmth, or a fashion accessory. Hats can be indicative of social status in some areas of the world. While numerous charts detailing head sizes in infants and children exist, most do not measure average head circumference past the age of 21.
Reference charts for adult head circumference generally feature homogeneous samples and fail to take height and weight into account. One study in the United States estimated the average human head circumference to be 55 centimetres in females and 57 centimetres in males. A British study by Newcastle University showed an average size of 55.2 cm for females and 57.2 cm for males with average size varying proportionally with height Macrocephaly can be an indicator of increased risk for some types of cancer in individuals who carry the genetic mutation that causes Cowden syndrome. For adults, this refers to head sizes greater than 58 centimeters in men or greater than 57 centimeters in women. Human body Head and neck anatomy 8. Human head Campbell, Bernard Grant. Human Evolution: An Introduction to Man's Adaptations, 4th edition
Neutrophils are the most abundant type of granulocytes and the most abundant type of white blood cells in most mammals. They form an essential part of the innate immune system, their functions vary in different animals. They are formed from stem cells in the bone marrow and differentiated into subpopulations of neutrophil-killers and neutrophil-cagers, they are short-lived and motile, or mobile, as they can enter parts of tissue where other cells/molecules cannot. Neutrophils may be banded neutrophils, they form part of the polymorphonuclear cells family together with eosinophils. The name neutrophil derives from staining characteristics on hematoxylin and eosin histological or cytological preparations. Whereas basophilic white blood cells stain dark blue and eosinophilic white blood cells stain bright red, neutrophils stain a neutral pink. Neutrophils contain a nucleus divided into 2–5 lobes. Neutrophils are a type of phagocyte and are found in the bloodstream. During the beginning phase of inflammation as a result of bacterial infection, environmental exposure, some cancers, neutrophils are one of the first-responders of inflammatory cells to migrate towards the site of inflammation.
They migrate through the blood vessels through interstitial tissue, following chemical signals such as Interleukin-8, C5a, fMLP, Leukotriene B4 and H2O2 in a process called chemotaxis. They are the predominant cells in pus, accounting for its whitish/yellowish appearance. Neutrophils are recruited to the site of injury within minutes following trauma and are the hallmark of acute inflammation; when adhered to a surface, neutrophil granulocytes have an average diameter of 12–15 micrometers in peripheral blood smears. In suspension, human neutrophils have an average diameter of 8.85 µm. With the eosinophil and the basophil, they form the class of polymorphonuclear cells, named for the nucleus' multilobulated shape; the nucleus has the separate lobes connected by chromatin. The nucleolus disappears as the neutrophil matures, something that happens in only a few other types of nucleated cells. In the cytoplasm, the Golgi apparatus is small and ribosomes are sparse, the rough endoplasmic reticulum is absent.
The cytoplasm contains about 200 granules, of which a third are azurophilic. Neutrophils will show increasing segmentation. A normal neutrophil should have 3–5 segments. Hypersegmentation occurs in some disorders, most notably vitamin B12 deficiency; this is noted in a manual review of the blood smear and is positive when most or all of the neutrophils have 5 or more segments. Neutrophils are the most abundant white blood cells in humans; the stated normal range for human blood counts varies between laboratories, but a neutrophil count of 2.5–7.5 x 109/L is a standard normal range. People of African and Middle Eastern descent may have lower counts. A report may divide neutrophils into segmented bands; when circulating in the bloodstream and inactivated, neutrophils are spherical. Once activated, they change shape and become more amorphous or amoeba-like and can extend pseudopods as they hunt for antigens. Neutrophils have a preference to engulf refined carbohydrates over bacteria. In 1973 Sanchez et al. found that the neutrophil phagocytic capacity to engulf bacteria is affected when simple sugars are digested, that fasting strengthens the neutrophils' phagocytic capacity to engulf bacteria.
However, the digestion of normal starches has no effect. It was concluded that the function, not the number, of phagocytes in engulfing bacteria was altered by the ingestion of sugars. In 2007 researchers at the Whitehead Institute of Biomedical Research found that given a selection of sugars, neutrophils engulf some types of sugar preferentially; the average lifespan of inactivated human neutrophils in the circulation has been reported by different approaches to be between 5 and 90 hours. Upon activation, they marginate and undergo selectin-dependent capture followed by integrin-dependent adhesion in most cases, after which they migrate into tissues, where they survive for 1–2 days. Neutrophils are much more numerous than the longer-lived monocyte/macrophage phagocytes. A pathogen is to first encounter a neutrophil; some experts hypothesize. The short lifetime of neutrophils minimizes propagation of those pathogens that parasitize phagocytes because the more time such parasites spend outside a host cell, the more they will be destroyed by some component of the body's defenses.
Because neutrophil antimicrobial products can damage host tissues, their short life limits damage to the host during inflammation. Neutrophils will be removed after phagocytosis of pathogens by macrophages. PECAM-1 and phosphatidylserine on the cell surface are involved in this process. Neutrophils undergo a process called chemotaxis via amoeboid movement, which allows them to migrate toward sites of infection or inflammation. Cell surface receptors allow neutrophils to detect chemical gr
Macrophages are a type of white blood cell, of the immune system, that engulfs and digests cellular debris, foreign substances, cancer cells, anything else that does not have the type of proteins specific to healthy body cells on its surface in a process called phagocytosis. These large phagocytes are found in all tissues, where they patrol for potential pathogens by amoeboid movement, they take various forms throughout the body. Besides phagocytosis, they play a critical role in nonspecific defense and help initiate specific defense mechanisms by recruiting other immune cells such as lymphocytes. For example, they are important as antigen presenters to T cells. In humans, dysfunctional macrophages cause severe diseases such as chronic granulomatous disease that result in frequent infections. Beyond increasing inflammation and stimulating the immune system, macrophages play an important anti-inflammatory role and can decrease immune reactions through the release of cytokines. Macrophages that encourage inflammation are called M1 macrophages, whereas those that decrease inflammation and encourage tissue repair are called M2 macrophages.
This difference is reflected in their metabolism. However, this dichotomy has been questioned as further complexity has been discovered. Human macrophages are about 21 micrometres in diameter and are produced by the differentiation of monocytes in tissues, they can be identified using flow cytometry or immunohistochemical staining by their specific expression of proteins such as CD14, CD40, CD11b, CD64, F4/80 /EMR1, lysozyme M, MAC-1/MAC-3 and CD68. Macrophages were first discovered by Élie Metchnikoff, a Russian zoologist, in 1884. A majority of macrophages are stationed at strategic points where microbial invasion or accumulation of foreign particles is to occur; these cells together as a group are known as the mononuclear phagocyte system and were known as the reticuloendothelial system. Each type of macrophage, determined by its location, has a specific name: Investigations concerning Kupffer cells are hampered because in humans, Kupffer cells are only accessible for immunohistochemical analysis from biopsies or autopsies.
From rats and mice, they are difficult to isolate, after purification, only 5 million cells can be obtained from one mouse. Macrophages can express paracrine functions within organs that are specific to the function of that organ. In the testis for example, macrophages have been shown to be able to interact with Leydig cells by secreting 25-hydroxycholesterol, an oxysterol that can be converted to testosterone by neighbouring Leydig cells. Testicular macrophages may participate in creating an immune privileged environment in the testis, in mediating infertility during inflammation of the testis. Cardiac resident macrophages participate in electrical conduction via gap junction communication with cardiac myocytes. Macrophages can be classified on basis of the fundamental activation. According to this grouping there are classically activated macrophages, wound-healing macrophages and regulatory macrophages. Macrophages that reside in adult healthy tissues either derive from circulating monocytes or are established before birth and maintained during adult life independently of monocytes.
By contrast, most of the macrophages that accumulate at diseased sites derive from circulating monocytes. When a monocyte enters damaged tissue through the endothelium of a blood vessel, a process known as leukocyte extravasation, it undergoes a series of changes to become a macrophage. Monocytes are attracted to a damaged site by chemical substances through chemotaxis, triggered by a range of stimuli including damaged cells and cytokines released by macrophages at the site. At some sites such as the testis, macrophages have been shown to populate the organ through proliferation. Unlike short-lived neutrophils, macrophages survive longer in the body, up to several months. Macrophages are professional phagocytes and are specialized in removal of dying or dead cells and cellular debris; this role is important in chronic inflammation, as the early stages of inflammation are dominated by neutrophils, which are ingested by macrophages if they come of age. The neutrophils are at first attracted to a site, where they proliferate, before they are phagocytized by the macrophages.
When at the site, the first wave of neutrophils, after the process of aging and after the first 48 hours, stimulate the appearance of the macrophages whereby these macrophages will ingest the aged neutrophils. The removal of dying cells is, to a greater extent, handled by fixed macrophages, which will stay at strategic locations such as the lungs, neural tissue, bone and connective tissue, ingesting foreign materials such as pathogens and recruiting additional macrophages if needed; when a macrophage ingests a pathogen, the pathogen becomes trapped in a phagosome, which fuses with a lysosome. Within the phagolysosome and toxic peroxides digest the pathogen. However, some bacteria, such as Mycobacterium tuberculosis, have become resistant to these methods of digestion. Typhoidal Salmonellae induce their own phagocytos
Legionella pneumophila is a thin, pleomorphic, non-spore-forming, Gram-negative bacterium of the genus Legionella. L. pneumophila is the primary human pathogenic bacterium in this group and is the causative agent of Legionnaires' disease known as legionellosis. In nature, L. pneumophila infects freshwater and soil amoebae of the genera Acanthamoeba and Naegleria. The mechanism of infection is similar in amoeba and human cells. L. pneumophila is a Gram-negative, aerobic bacillus with a single, polar flagellum characterized as being a coccobacillus. It is unable to hydrolyse gelatin or produce urease, it is nonfermentative. L. pneumophila does it autofluoresce. It is oxidase- and catalase-positive, produces beta-lactamase. L. pneumophila colony morphology is gray-white with a cut-glass appearance. It grows on yeast extract in "opal-like" colonies. While L. pneumophila is categorized as a Gram-negative organism, it stains poorly due to its unique lipopolysaccharide content in the outer leaflet of the outer cell membrane.
The bases for the somatic antigen specificity of this organism are located on the side chains of its cell wall. The chemical composition of these side chains both with respect to components and arrangement of the different sugars, determines the nature of the somatic or O-antigen determinants, which are important means of serologically classifying many Gram-negative bacteria. At least 35 different serovars of L. pneumophila have been described, as well as several other species being subdivided into a number of serovars. Sera have been used both for slide agglutination studies and for direct detection of bacteria in tissues using fluorescent-labelled antibody. Specific antibody in patients can be determined by the indirect fluorescent antibody test. ELISA and microagglutination tests have been applied. Legionella stains poorly with Gram stain, stains positive with silver, is cultured on charcoal yeast extract with iron and cysteine. L. pneumophila is a facultative intracellular parasite that can invade and replicate inside amoebae in the environment species of the genera Acanthamoeba and Naegleria, which can thus serve as a reservoir for L. pneumophila.
These hosts provide protection from environmental stresses, such as chlorination. In the United States, about 2 infections with L. pneumophila appear per 100,000 residents per year. The infections peak in the summer. Within endemic regions, about 4% to 5% of pneumonia cases are caused by L. pneumophila.. In humans, L. pneumophila replicates inside macrophages. The internalization of the bacteria can be enhanced by the presence of antibody and complement, but is not required. Internalization of the bacteria appears to occur through phagocytosis. However, L. pneumophila is capable of infecting nonphagocytic cells through an unknown mechanism. A rare form of phagocytosis known as coiling phagocytosis has been described for L. pneumophila, but this is not dependent on the Dot/Icm secretion system and has been observed for other pathogens. Once internalized, the bacteria surround themselves in a membrane-bound vacuole that does not fuse with lysosomes that would otherwise degrade the bacteria. In this protected compartment, the bacteria multiply.
The bacteria use a type IVB secretion system known as Dot/Icm to inject effector proteins into the host. These effectors are involved in increasing the bacteria's ability to survive inside the host cell. L. pneumophila encodes for over 330 "effector" proteins, which are secreted by the Dot/Icm translocation system to interfere with host cell processes to aid bacterial survival. It has been predicted that the genus Legionella encodes more than 10,000 and up to ~18,000 effectors that have a high probability to be secreted into their host cells. One key way in which L. pneumophila uses its effector proteins is to interfere with fusion of the Legionella-containing vacuole with the host's endosomes, thus protect against lysis. Knock-out studies of Dot/Icm translocated effectors indicate that they are vital for the intracellular survival of the bacterium, but many individual effector proteins are thought to function redundantly, in that single-effector knock-outs impede intracellular survival; this high number of translocated effector proteins and their redundancy is a result of the bacterium having evolved in many different protozoan hosts.
For Legionella to survive within macrophages and protozoa, it must create a specialized compartment known as the Legionella-containing vacuole. Through the action of the Dot/Icm secretion system, the bacteria are able to prevent degradation by the normal endosomal trafficking pathway and instead replicate. Shortly after internalization, the bacteria recruit endoplasmic reticulum-derived vesicles and mitochondria to the LCV while preventing the recruitment of endosomal markers such as Rab5 and Rab7. Formation and maintenance of the vacuoles are crucial for pathogenesis. Once inside the host cell, Legionella needs nutrients to reproduce. Inside the vacuole, nutrient availability is low. To improve the availability of amino acids, the parasite promotes the host mechanisms of proteasomal degradation; this generates an excess of free amino acids in the cytoplasm of L. pneumophila-infected cells that can be used for intravacuolar proliferation of the parasite
Parenchyma is the bulk of a substance. In animals, a parenchyma comprises the functional parts of an organ and in plants parenchyma is the ground tissue of nonwoody structures; the term "parenchyma" is New Latin from word Greek παρέγχυμα parenchyma, "visceral flesh" from παρεγχεῖν parenkhein, "to pour in" from παρα- para-, "beside", ἐν en-, "in" and χεῖν khein, "to pour". Erasistratus and other anatomists used it to refer to certain human tissues, it was applied to some plant tissues by Nehemiah Grew. The parenchyma is the functional parts of an organ in the body; this is in contrast to the stroma, which refers to the structural tissue of organs, the connective tissues. In the brain, the parenchyma refers to the functional tissue in the brain, made up of the two types of brain cell and glial cells. Damage or trauma to the brain parenchyma results in a loss of cognitive ability or death. Lung parenchyma is the substance of the lung outside of the circulation system, involved with gas exchange and includes the alveoli and respiratory bronchioles.
In cancer, the parenchyma refers to "The portion of a tissue that lies outside the circulatory system and is responsible for carrying out the specialized functions of the tissue". In plants, "parenchyma" is one of the three main types of ground tissue, the most common, it can be distinguished through their thin cell wall as compared to other cells. Parenchyma cells make up the bulk of the soft parts of plants, including the insides of leaves and fruits; the dictionary definition of parenchyma at Wiktionary