General description and location
Several classification systems have existed for lymphoma, which use histological and other findings to divide lymphoma into different categories. Perfect for days when you can't be outdoors. Please try again later. May use after dinner, before bedtime, to relax and de-stress the body. Lymphedema may be inherited primary or caused by injury to the lymphatic vessels secondary.
Human Body Systems
Intestinal Roundworms Ascariasis, Ascaris Infection. Isospora Infection see Cystoisospora Infection. Kala-azar Leishmaniasis, Leishmania Infection. Leishmaniasis Kala-azar, Leishmania Infection. Liver Flukes Clonorchiasis, Opisthorchiasis, Fascioliasis.
Loiasis Loa loa Infection. Lymphatic filariasis Filariasis, Elephantiasis. Pediculosis Head or Body Lice Infestation. Pthiriasis Pubic Lice Infestation. Pseudoterranova Infection Anisakiasis, Anisakis Infection. Taeniasis Taenia Infection, Tapeworm Infection.
Tapeworm Infection Taeniasis, Taenia Infection. Trichuriasis Whipworm Infection, Trichuris Infection. Trypanosomiasis, American Chagas Disease. In the male it is about 20 centimetres long and carries not only the urine but also the semen and the secretions of the prostate, bulbourethral, and urethral glands.
During urination and ejaculation it opens up, and its diameter then varies from 0. The male urethra has three distinguishable parts, the prostatic, the membranous, and the spongy, each part being named from the structures through which it passes rather than from any inherent characteristics.
The prostatic section of the male urethra commences at the internal urethral orifice and descends almost vertically through the prostate, from the base of the gland to the apex, describing a slight curve with its concavity forward. It is about 2. The membranous part of the male urethra is in the area between the two layers of a membrane called the urogenital diaphragm.
The urethra is narrower in this area than at any other point except at its external opening and is encircled by a muscle, the sphincter urethrae. The two small bulbourethral glands are on either side of it. The membranous urethra is not firmly attached to the layers of the urogenital diaphragm. The spongy part of the male urethra is that part of the urethra that traverses the penis. It passes through the corpus spongiosum of the penis.
The ducts of the bulbourethral glands enter the spongy urethra about 2. The female urethra is much shorter 3 to 4. It begins at the internal opening of the urethra into the bladder and curves gently downward and forward through the urogenital diaphragm, where it is surrounded, as in the male, by the sphincter urethrae. It lies behind and below the symphysis pubis.
Except for its uppermost part, the urethra is embedded in the anterior wall of the vagina. The external urethral orifice is immediately in front of the vaginal opening, about 2. The urethra of the male is a tube of mucous membrane supported on a submucous layer and an incomplete muscular coat.
The membrane forms longitudinal folds when the tube is empty; these folds are more prominent in the membranous and spongy parts. There are many glands in the mucous membrane, and they are more common in the posterior wall of the spongy part. The submucous layer is composed of fibroelastic connective tissue containing numerous small blood vessels, including more venules than arterioles. The thin muscular coat consists of smooth involuntary and striated voluntary muscle fibres.
The smooth muscular layer, longitudinally disposed, is continuous above with the detrusor muscle of the bladder and extends distally as far as the membranous urethra, where it is replaced and partly surrounded by striated muscle of the external sphincter.
The somatic nerves to the external sphincter are the efferent and afferent components of the pudendal nerve, arising from the second, third, and fourth sacral segments of the spinal cord.
The female urethra has mucous, submucous, and muscular coats. As in the male, the lining of the empty channel is raised into longitudinal folds. It also shows mucous glands, mentioned in the preceding paragraphs as existing in the male urethra.
The submucous coat resembles that in the male, except that the venules are even more prominent. In both sexes, but especially in females, this layer appears to be a variety of erectile tissue. The muscular coat extends along the entire length of the female urethra and is continuous above with the musculature of the bladder.
It consists of inner longitudinal and outer circular layers, and fibres from the latter intermix with those in the anterior wall of the vagina, in which the urethra is embedded. We welcome suggested improvements to any of our articles. You can make it easier for us to review and, hopefully, publish your contribution by keeping a few points in mind.
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Next page Human excretion. Learn More in these related Britannica articles: Changes that take place in the bladder and the urethra during pregnancy are attributable to relaxation of the muscles supporting these structures, to change in position, and to pressure. A rarer type of ostomy, such as the esophagostomy or the tracheostomy, is performed to introduce substances into the body or to aid breathing.
Human body , the physical substance of the human organism, composed of living cells and extracellular materials and organized into tissues, organs, and systems. Human anatomy and physiology are treated in many different articles. Kidney , in vertebrates and some invertebrates, organ that maintains water balance and expels metabolic wastes. Primitive and embryonic kidneys consist of two series of specialized tubules that empty into two collecting ducts, the Wolffian ducts see Wolffian duct.
The more advanced kidney metanephros of adult reptiles, birds, and mammals is…. More About Renal system 3 references found in Britannica articles Assorted References role of autonomic nervous system In human nervous system: The urinary system effects of ostomy surgery In ostomy pregnancy In pregnancy: LiveScience - Urinary System: Articles from Britannica Encyclopedias for elementary and high school students.
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This enables them to protect against inhaled and swallowed foreign bodies. The tonsils are the tissues affected by tonsillitis. The spleen is not connected to the lymphatic system in the same way as lymph nodes, but it is lymphoid tissue.
This means it plays a role in the production of white blood cells that form part of the immune system. Its other major role is to filter the blood to remove microbes and old and damaged red blood cells and platelets. The thymus gland is a lymphatic organ and an endocrine gland that is found just behind the sternum.
It secretes hormones and is crucial in the production, maturation, and differentiation of immune T cells. Bone marrow is not lymphatic tissue, but it can be considered part of the lymphatic system because it is here that the B cell lymphocytes of the immune system mature. During gestation, the liver of a fetus is regarded as part of the lymphatic system as it plays a role in lymphocyte development.
Explore the model using your mouse pad or touchscreen to understand more about the lymphatic system. The lymph system has three main functions. The lymphatic system helps maintain fluid balance. It returns excess fluid and proteins from the tissues that cannot be returned through the blood vessels.
The fluid is found in tissue spaces and cavities, in the tiny spaces surrounding cells, known as the interstitial spaces. These are reached by the smallest blood and lymph capillaries. Around 90 percent of the plasma that reaches tissues from the arterial blood capillaries is returned by the venous capillaries and back along veins. The remaining 10 percent is drained back by the lymphatics. Each day, around liters is returned. This fluid includes proteins that are too large to be transported via the blood vessels.
Loss of the lymphatic system would be fatal within a day. Without the lymphatic system draining excess fluid, our tissues would swell, blood volume would be lost and pressure would increase. Most of the fats absorbed from the gastrointestinal tract are taken up in a part of the gut membrane in the small intestine that is specially adapted by the lymphatic system.
The lymphatic system has tiny lacteals in this part of the intestine that form part of the villi. These finger-like protruding structures are produced by the tiny folds in the absorptive surface of the gut.
Lacteals absorb fats and fat-soluble vitamins to form a milky white fluid called chyle. This fluid contains lymph and emulsified fats, or free fatty acids. It delivers nutrients indirectly when it reaches the venous blood circulation. Blood capillaries take up other nutrients directly. The third function is to defend the body against unwanted organisms.
Without it, we would die very soon from an infection. Our bodies are constantly exposed to potentially hazardous micro-organisms, such as infections.
However, pathogens often do succeed in entering the body despite these defenses. In this case, the lymphatic system enables our immune system to respond appropriately. If the immune system is not able to fight off these micro-organisms, or pathogens, they can be harmful and even fatal.
A number of different immune cells and special molecules work together to fight off the unwanted pathogens. The lymphatic system produces white blood cells, known as lymphocytes. There are two types of lymphocyte, T cells and B cells.
They both travel through the lymphatic system. As they reach the lymph nodes, they are filtered and become activated by contact with viruses, bacteria, foreign particles, and so on in the lymph fluid.
From this stage, the pathogens, or invaders, are known as antigens. As the lymphocytes become activated, they form antibodies and start to defend the body. They can also produce antibodies from memory if they have already encountered the specific pathogen in the past. Collections of lymph nodes are concentrated in the neck, armpits, and groin. We become aware of these on one or both sides of the neck when we develop so-called "swollen glands" in response to an illness.
It is in the lymph nodes that the lymphocytes first encounter the pathogens, communicate with each other, and set off their defensive response. Activated lymphocytes then pass further up the lymphatic system so that they can reach the bloodstream. Now, they are equipped to spread the immune response throughout the body, through the blood circulation. The lymphatic system and the action of lymphocytes, of which the body has trillions, form part of what immunologists call the "adaptive immune response.
The lymphatic system can stop working properly if nodes, ducts, vessels, or lymph tissues become blocked, infected, inflamed, or cancerous.
Cancer that starts in the lymphatic system is known as lymphoma. It is the most serious lymphatic disease. Hodgkin lymphoma affects a specific type of white blood cell known as Reed-Sternberg cells. Non-Hodgkin lymphoma refers to types that do not involve these cells. Cancer that affects the lymphatic system is usually a secondary cancer. This means it has spread from a primary tumor , such as the breast, to nearby or regional lymph nodes.