Lymph node
A lymph node or lymph gland is an ovoid or kidney-shaped organ of the lymphatic system, of the adaptive immune system, present throughout the body. They are linked by the lymphatic vessels as a part of the circulatory system. Lymph nodes are major sites of B and T lymphocytes, other white blood cells. Lymph nodes are important for the proper functioning of the immune system, acting as filters for foreign particles and cancer cells. Lymph nodes do not have a detoxification function, dealt with by the liver and kidneys. In the lymphatic system the lymph node is a secondary lymphoid organ. A lymph node is enclosed in a fibrous capsule and is made up of an outer cortex and an inner medulla. Lymph nodes have clinical significance, they become inflamed or enlarged in various diseases which may range from trivial throat infections, to life-threatening cancers. The condition of the lymph nodes is important in cancer staging, which decides the treatment to be used, determines the prognosis; when swollen, inflamed or enlarged, lymph nodes can be hard, tender.
Lymph nodes are oval shaped and range in size from a few millimeters to about 1 -- 2 cm long. Each lymph node is surrounded by a fibrous capsule, which extends inside the lymph node to form trabeculae; the substance of the lymph node is divided into the inner medulla. The cortex is continuous around the medulla except where the medulla comes into direct contact with the hilum. Thin reticular fibers of reticular connective tissue, elastin form a supporting meshwork called a reticulin inside the node. B cells are found in the outer cortex where they are clustered together as follicular B cells in lymphoid follicles and the T cells are in the paracortex; the lymph node is divided into compartments called lymph nodules each consisting of a cortical region of combined follicle B cells, a paracortical region of T cells, a basal part of the nodule in the medulla. The number and composition of follicles can change when challenged by an antigen, when they develop a germinal center. Elsewhere in the node, there are only occasional leukocytes.
As part of the reticular network there are follicular dendritic cells in the B cell follicle and fibroblastic reticular cells in the T cell cortex. The reticular network not only provides the structural support, but the surface for adhesion of the dendritic cells and lymphocytes, it allows exchange of material with blood through the high endothelial venules and provides the growth and regulatory factors necessary for activation and maturation of immune cells. Lymph enters the convex side of the lymph node through multiple afferent lymphatic vessels, flows through spaces called sinuses. A lymph sinus which includes the subcapsular sinus, is a channel within the node, lined by endothelial cells along with fibroblastic reticular cells and this allows for the smooth flow of lymph through them; the endothelium of the subcapsular sinus is continuous with that of the afferent lymph vessel and with that of the similar sinuses flanking the trabeculae and within the cortex. All of these sinuses drain the filtered lymphatic fluid into the medullary sinuses, from where the lymph flows into the efferent lymph vessels to exit the node at the hilum on the concave side.
These vessels are smaller and don't allow the passage of the macrophages so that they remain contained to function within the lymph node. In the course of the lymph, lymphocytes may be activated as part of the adaptive immune response; the lymph node capsule is composed of dense irregular connective tissue with some plain collagenous fibers, from its internal surface are given off a number of membranous processes or trabeculae. They pass inward, radiating toward the center of the node, for about one-third or one-fourth of the space between the circumference and the center of the node. In some animals they are sufficiently well-marked to divide the peripheral or cortical portion of the node into a number of compartments, but in humans this arrangement is not obvious; the larger trabeculae springing from the capsule break up into finer bands, these interlace to form a mesh-work in the central or medullary portion of the node. In these trabecular spaces formed by the interlacing trabeculae is contained the proper lymph node substance or lymphoid tissue.
The node pulp does not, however fill the spaces, but leaves, between its outer margin and the enclosing trabeculae, a channel or space of uniform width throughout. This is termed the subcapsular sinus. Running across it are a number of finer trabeculae of reticular connective tissue, the fibers of which are, for the most part, covered by ramifying cells; the subcapsular sinus is the space between the capsule and the cortex which allows the free movement of lymphatic fluid and so contains few lymphocytes. It is continuous with the similar lymph sinuses; the lymph node contains lymphoid tissue, i.e. a meshwork or fibers called reticulum with white blood cells enmeshed in it. The regions where there are few cells within the meshwork are known as lymph sinus, it is lined by reticular cells and fixed macrophages. The subcapsular sinus has clinical importance as it is the most location where the earliest manifestations of a metastatic carcinoma in a lymph node would be found; the cortex of the lymph node is the outer portion of the node, underneath the capsule and the subcapsular sinus.
It has a deeper part known as the paracortex. The subcapsular sinus drains to the trabecul sinuses, the lymph flows into the medullary sinuses; the outer cortex consists of the B c
Venomous snake
Venomous snakes are species of the suborder Serpentes that are capable of producing venom, which they use for killing prey, for defense, to assist with digestion of their prey. The venom is delivered by injection using hollow or grooved fangs, although some venomous snakes lack well-developed fangs. Common venomous snakes include the families Elapidae, Viperidae and some of the Colubridae; the toxicity of venom is indicated by murine LD50, while multiple factors are considered to judge the potential danger to humans. Other important factors for risk assessment include the likelihood that a snake will bite, the quantity of venom delivered with the bite, the efficiency of the delivery mechanism, the location of a bite on the body of the victim. Snake venom may have both hemotoxic properties; the evolutionary history of venomous snakes can be traced back to as far as 25 million years ago. Snake venom is modified saliva used for prey immobilization and self-defense and is delivered through specialized teeth, hollow fangs, directly into the bloodstream or tissue of the target.
Evidence has been presented for the Toxicofera hypothesis, but venom was present in the ancestors of all snakes as "toxic saliva" and evolved to extremes in those snake families classified as venomous by parallel evolution. The Toxicofera hypothesis further implies that "nonvenomous" snake lineages have either lost the ability to produce venom, or do produce venom in small quantities sufficient to help capture small prey but causing no harm to humans when bitten. There is not a single or special taxonomic group for venomous snakes that comprise species from different families; this has been interpreted to mean venom in snakes originated more than once as the result of convergent evolution. Around a quarter of all snake species are identified as being venomous. Venomous snakes are said to be poisonous, but poison and venom are not the same thing. Poisons must be ingested, inhaled or absorbed, while venom must be injected into the body by mechanical means. While unusual, there are a few species of snake which are poisonous.
Rhabdophis keelback snakes are both venomous and poisonous – their poisons are stored in nuchal glands and are acquired by sequestering toxins from poisonous toads the snakes eat. Certain garter snakes from Oregon can retain toxins in their livers from ingesting rough-skinned newts. LD50, Mostly on Rodents, is a common indicator of snakes' toxicity with a smaller resultant value indicating a higher level of toxicity. There have been numerous studies on snake venom with a variability of potency estimates. There are four methods in which the LD50 test is conducted, which are injections to subcutis, vein and peritoneum; the former is most applicable to actual bites as only vipers with large fangs, such as large Bitis, Crotalus, or Daboia specimens, would be able to deliver a bite, intramuscular, snakebites cause IV envenomation. Testing using dry venom mixed with 0.1% bovine serum albumin in saline, gives more consistent results than just saline alone. Belcher's sea snake, which many times is mistakenly called the hook-nosed Sea Snake, has been erroneously popularized as the most venomous snake in the world, due to the first edition of Ernst and Zug's book, Snakes in Question: The Smithsonian Answer Book, published in 1996.
Prominent venom expert Associate Professor Bryan Grieg Fry has clarified the error: "The hook nosed myth was due to a fundamental error in a book called Snakes in Question. In there, all the toxicity testing results were lumped in together, regardless of the mode of testing; as the mode can influence the relative number, venoms can only be compared within a mode. Otherwise, it's apples and rocks." Belcher's sea snake's actual LD50 is 0.155 mg/kg. Studies on mice and human cardiac cell culture show that venom of the inland taipan, drop by drop, is the most toxic among all snakes; the toxicity of snake venom is sometimes used to gauge the extent of danger to humans, but this is not enough. Many venomous snakes are specialized predators whose venom may be adapted to incapacitate their preferred prey. A number of other factors are critical in determining the potential hazard of any given venomous snake to humans, including their distribution and behavior. For example, while the inland taipan is regarded as the world's most venomous snake based on LD50 tests on mice, it is a shy species and strikes, has not caused any known human fatalities.
On the other hand, India's Big Four, while less venomous than the inland taipan, are found in closer proximity to human settlements and are more confrontational, thus leading to more deaths from snakebite. In addition, some species, such as the black mamba and coastal taipan show some aggression when alarmed or in self-defence, may deliver fatal doses of venom, resulting in high human mortality rates. Snakebite Snake venom Venomoid Big Four List of venomous animals Venomous fish Venomous mammals Poisonous amphibians Toxic birds Venomous snakes and outdoor workers Bite-prevention and treatment information for outdoor workers
Lymphatic vessel
The lymphatic vessels are thin-walled vessels structured like blood vessels, that carry lymph. As part of the lymphatic system, lymph vessels are complementary to the cardiovascular system. Lymph vessels are lined by endothelial cells, have a thin layer of smooth muscle, adventitia that bind the lymph vessels to the surrounding tissue. Lymph vessels are devoted to the propulsion of the lymph from the lymph capillaries, which are concerned with absorption of interstitial fluid from the tissues. Lymph capillaries are larger than their counterpart capillaries of the vascular system. Lymph vessels that carry lymph to a lymph node are called afferent lymph vessels, those that carry it from a lymph node are called efferent lymph vessels, from where the lymph may travel to another lymph node, may be returned to a vein, or may travel to a larger lymph duct. Lymph ducts drain the lymph into one of the subclavian veins and thus return it to general circulation. Lymph flows away from the tissues to lymph nodes and to either the right lymphatic duct or the largest lymph vessel in the body, the thoracic duct.
These vessels left subclavian veins respectively. The general structure of lymphatics is based on that of blood vessels. There is an inner lining of single flattened epithelial cells composed of a type of epithelium, called endothelium, the cells are called endothelial cells; this layer functions to mechanically transport fluid and since the basement membrane on which it rests is discontinuous. The next layer is that of smooth muscles that are arranged in a circular fashion around the endothelium, which by shortening or relaxing alter the diameter of the lumen; the outermost layer is the adventitia. The general structure described here is seen only in larger lymphatics; the smallest vessels lack both the outer adventitia. As they proceed forward and in their course are joined by other capillaries, they grow larger and first take on an adventitia, smooth muscles; the lymphatic conducting system broadly consists of two types of channels—the initial lymphatics, the prelymphatics or lymph capillaries that specialize in collection of the lymph from the ISF, the larger lymph vessels that propel the lymph forward.
Unlike the cardiovascular system, the lymphatic system has no central pump. Lymph movement occurs despite low pressure due to peristalsis and compression during contraction of adjacent skeletal muscle and arterial pulsation; the lymphatic circulation begins with blind ending permeable superficial lymph capillaries, formed by endothelial cells with button-like junctions between them that allow fluid to pass through them when the interstitial pressure is sufficiently high. These button-like junctions consist of protein filaments like platelet endothelial cell adhesion molecule-1, or PECAM-1. A valve system in place here prevents the absorbed lymph from leaking back into the ISF. There is another system of semilunar valves that prevents back-flow of lymph along the lumen of the vessel. Lymph capillaries have many interconnections between them and form a fine network. Rhythmic contraction of the vessel walls through movements may help draw fluid into the smallest lymphatic vessels, capillaries. If tissue fluid builds up the tissue will swell.
As the circular path through the body's system continues, the fluid is transported to progressively larger lymphatic vessels culminating in the right lymphatic duct and the thoracic duct. The system collaborates with white blood cells in lymph nodes to protect the body from being infected by cancer cells, viruses or bacteria; this is known as a secondary circulatory system. The lymph capillaries drain the lymph to larger contractile lymphatics, which have valves as well as smooth muscle walls; these are called the collecting lymphatics. As the collecting lymph vessel accumulates lymph from more and more lymph capillaries in its course, it becomes larger and is called the afferent lymph vessel as it enters a lymph node. Here the lymph is removed by the efferent lymph vessel. An efferent lymph vessel may directly drain into one of the lymph ducts, or may empty into another lymph node as its afferent lymph vessel. Both the lymph ducts return the lymph to the blood stream by emptying into the subclavian veins The functional unit of a lymph vessel is known as a lymphangion, the segment between two valves.
Since it is contractile, depending upon the ratio of its length to its radius, it can act either like a contractile chamber propelling the fluid ahead, or as a resistance vessel tending to stop the lymph in its place. Lymph vessels act as reservoirs for plasma and other substances including cells that have leaked from the vascular system and transport lymph fluid back from the tissues to the circulatory system. Without functioning lymph vessels, lymph cannot be drained and edema results; the afferent lymph vessels enter at all parts of the periphery of the lymph node, after branching and forming a dense plexus in the substance of the capsule, open into the lymph sinuses of the cortical part. It carries unfiltered lymph into the node. In doing this th
Cervical lymphadenopathy
Cervical lymphadenopathy refers to lymphadenopathy of the cervical lymph nodes. The term lymphadenopathy speaking refers to disease of the lymph nodes, though it is used to describe the enlargement of the lymph nodes; the term lymphadenitis refers to inflammation of a lymph node, but it is used as a synonym of lymphadenopathy. Cervical lymphadenopathy is a symptom, not a diagnosis; the causes are varied, may be inflammatory, degenerative, or neoplastic. In adults, healthy lymph nodes can be palpable, in the axilla and groin. In children up to the age of 12 cervical nodes up to 1 cm in size may be palpable and this may not signify any disease. If nodes heal by resolution or scarring after being inflamed, they may remain palpable thereafter. In children, most palpable cervical lymphadenopathy is infective. In individuals over the age of 50, metastatic enlargement from cancers of the aerodigestive tract should be considered. Cervical lymphadenopathy can be thought of as local where only the cervical lymph nodes are affected, or general where all the lymph nodes of the body are affected.
Pericoronitis Staphylococcal lymphadenitis Mycobacterial lymphadenitis Rubella Cat scratch fever Infectious mononucleosis Streptococcal pharyngitis Viral respiratory infection Toxoplasmosis Tuberculosis Brucellosis Primary herpes simplex infection Syphilis Cytomegalovirus Human immunodeficiency virus Histoplasmosis Chicken pox Lymph nodes may become enlarged in malignant disease. This cervical lymphadenopathy may be metastatic. Alternatively, enlarged lymph nodes may represent a primary malignancy of the lymphatic system itself, such as lymphoma, lymphocytic leukemia,Metastatic lymph nodes are enlarged because tumor cells have detached from the primary tumor and started growing in the lymph node. Since cancer occurs more in older people, this kind of lymphadenopathy is more common in older persons. Metastatic lymph nodes tend to feel hard and may be fixed to underlying tissues and may or may not be tender; the lymph nodes that directly drain the area of the cancer are affected by the spread.
In such cases, this discovery leads to a search for the primary malignancy, firstly in the nearby area with endoscopy, "blind" biopsies, tonsillectomy on the side of the lymphadenopathy. If no tumor is found the rest of the body is examined, looking for lung cancer or other possible sites. If still no primary tumor is detected, the term "occult primary" is used. In lymphoma there are multiple enlarged nodes which feel rubbery to palpation. Rhabdomyosarcoma Neuroblastoma Surgical trauma, e.g. following a biopsy in the mouth Kawasaki disease, Kikuchi-Fujimoto disease Rosai-Dorfman disease Castleman disease sarcoidosis Lupus erythematosus Cyclic neutropenia Orofacial granulomatosis In possible malignancy, it is routine to perform a throat examination including mirror and/or endoscopy. On ultrasound, B-mode imaging depicts lymph node morphology, whilst power Doppler can assess the vascular pattern. B-mode imaging features that can distinguish metastasis and lymphoma include size, calcification, loss of hilar architecture, as well as intranodal necrosis.
Soft tissue edema and nodal matting on B-mode imaging suggests tuberculous cervical lymphadenitis or previous radiation therapy. Serial monitoring of nodal size and vascularity are useful in assessing treatment response. Fine needle aspiration cytology has a sensitivity and specificity percentages of 81% and 100% in the histopathology of malignant cervical lymphadenopathy. PET-CT has proven to be helpful in identifying occult primary carcinomas of the head and neck when applied as a guiding tool prior to panendoscopy, may induce treatment related clinical decisions in up to 60% of cases
Pit viper
The Crotalinae known as pit vipers, crotaline snakes, or pit adders, are a subfamily of venomous vipers found in Eurasia and the Americas. They are distinguished by the presence of a heat-sensing pit organ located between the eye and the nostril on both sides of the head. 18 genera and 151 species are recognized: seven genera and 54 species in the Old World, against a greater diversity of 11 genera and 97 species in the New World. These are the only viperids found in the Americas; the groups of snakes represented here include rattlesnakes and Asian pit vipers. The type genus for this subfamily is Crotalus, of which the type species is the timber rattlesnake, C. horridus. These snakes range in size from the diminutive hump-nosed viper, Hypnale hypnale, that grows to an average total length of only 30–45 cm, to the bushmaster, Lachesis muta, a species known to reach a maximum total length of 3.65 m in length. What makes this subfamily unique is that all member species share a common characteristic: a deep pit, or fossa, in the loreal area between the eye and the nostril on either side of the head.
These loreal pits are the external openings to a pair of sensitive infrared-detecting organs, which in effect give the snakes a sixth sense to help them find and even judge the size of the small, warm-blooded prey on which they feed. Osine triphosphate, monoamine oxidase, generalized esterases and acetylcholine esterase have been found in it; when prey comes into range, infrared radiation falling onto the membrane allows the snake to determine its direction. Experiments have shown, when deprived of their senses of sight and smell, these snakes can strike at moving objects less than 0.2 °C warmer than the background. The paired pit organs provide the snake with thermal rangefinder capabilities; these organs are of great value to a predator that hunts at night, as well as for avoiding the snake’s own predators. Among vipers, these snakes are unique in that they have a specialized muscle, called the muscularis pterigoidius glandulae, between the venom gland and the head of the ectopterygoid. Contraction of this muscle, together with that of the m. compressor glandulae, forces venom out of the gland.
The subfamily Crotalinae is found in the Old World from eastern Europe eastward through Asia to Japan, Indonesia, peninsular India and Sri Lanka. In the Americas, they range from southern Canada southward to Central America to southern South America. Crotalines are a versatile subfamily, with members found in habitats ranging from parched desert to rainforests, they may be either arboreal or terrestrial, one species is semiaquatic: the cottonmouth, Agkistrodon piscivorus. The altitude record is held jointly by Crotalus triseriatus in Mexico and Gloydius strauchi in China, both of which have been found above the treeline at over 4,000 m elevation. Although a few species of crotalines are active by day, such as Trimeresurus trigonocephalus, a bright green pit viper endemic to Sri Lanka, most are nocturnal, preferring to avoid high daytime temperatures and to hunt when their favored prey are active; the snakes' heat-sensitive pits are thought to aid in locating cooler areas in which to rest. As ambush predators, crotalines wait patiently somewhere for unsuspecting prey to wander by.
At least one species, the arboreal Gloydius shedaoensis of China, is known to select a specific ambush site and return to it every year in time for the spring migration of birds. Studies have indicated. Many temperate species of pit vipers congregate in sheltered areas or "dens" to overwinter, the snakes benefiting from the combined heat. In cool temperatures and while pregnant, pit vipers bask on sunny ledges; some species do not mass together in this way, for example the copperhead, Agkistrodon contortrix, or the Mojave rattlesnake, Crotalus scutulatus. Like most snakes, crotalines strike only if cornered or threatened. Smaller snakes are less to stand their ground than larger specimens. Pollution and the destruction of rainforests have caused many pit viper populations to decline. Humans threaten pit vipers, as many are hunted for their skins or killed by cars when they wander onto roads. With few exceptions, crotalines are ovoviviparous. Among the oviparous pit vipers are Lachesis and some Trimeresurus species.
All egg-laying crotalines are believed to guard their eggs. Brood sizes range from two for small species, to as many as 86 for the fer-de-lance, Bothrops atrox, a species among the most prolific of all live-bearing snakes. Many young crotalines have brightly coloured tails that contrast with the rest of their bodies. Used in a behavior known as caudal luring, the young snakes make worm-like movements with their tails to lure unsuspecting prey within striking distance. In the past, the pit vipers were classed as a separate family: the Crotalidae. Today, the monophyly of the viperines and the crotalines as a whole is undisputed, why they are treated here as a subfamily of the Viperidae. *) Not including the nominate subspecies. T) Type genus. List of crotaline species and subspecies Crotalinae by common name Crotalinae by taxonomic synonyms Pit organs at Life is Short, but Snakes are Long
Bacteria
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
Supraclavicular lymph nodes
Supraclavicular lymph nodes are lymph nodes found superior to the clavicle, palpable in the supraclavicular fossa. The supraclavicular lymph nodes on the left side are called Virchow's nodes. A Virchow's node is a left-sided supraclavicular lymph node. Virchow's nodes take their supply from lymph vessels in the abdominal cavity, are therefore sentinel lymph nodes of cancer in the abdomen gastric cancer, ovarian cancer, testicular cancer and kidney cancer, that has spread through the lymph vessels; such spread results in Troisier's sign, the finding of an enlarged, hard Virchow's node. Virchow's nodes are named after Rudolf Virchow, the German pathologist who first described the nodes and their association with gastric cancer in 1848; the French pathologist Charles Emile Troisier noted in 1889 that other abdominal cancers, could spread to the nodes. Malignancies of the internal organs can reach an advanced stage before giving symptoms. Stomach cancer, for example, can remain asymptomatic while metastasizing.
One of the first visible spots where these tumors metastasize is one of the left supraclavicular lymph node. The left supraclavicular nodes are the classical Virchow's node because they receive lymphatic drainage of most of the body enters the venous circulation via the left subclavian vein; the metastasis may block the thoracic duct leading to regurgitation into the surrounding Virchow's nodes. Another concept is that one of the supraclavicular nodes corresponds to the end node along the thoracic duct and hence the enlargement. Differential diagnosis of an enlarged Virchow's node includes lymphoma, various intra-abdominal malignancies, breast cancer, infection. An enlarged right supraclavicular lymph node tends to drain thoracic malignancies such as lung and esophageal cancer, as well as Hodgkin's lymphoma; this article incorporates text in the public domain from page 697 of the 20th edition of Gray's Anatomy Cervin, J. R.. "Virchow's node revisited. Analysis with clinicopathologic correlation of 152 fine-needle aspiration biopsies of supraclavicular lymph nodes".
Archives of Pathology & Laboratory Medicine. 119: 727–30. PMID 7646330. Negus, D.. B.. "Filling of cervical and mediastinal nodes from the thoracic duct and the physiology of virchow's node—studies by lymphography". British Journal of Surgery. 57: 267–71. Doi:10.1002/bjs.1800570407. PMID 5437920. Mizutani, Masaomi. "Anatomy and histology of Virchow's node". Anatomical Science International. 80: 193–8. Doi:10.1111/j.1447-073X.2005.00114.x. PMID 16333915. Synd/1222 at Who Named It? Image at umich.edu - must rollover https://web.archive.org/web/20080216031919/http://www.med.mun.ca/anatomyts/head/hnl3a.htm http://www.aafp.org/afp/20021201/2103.html
