Some of the internal organs are prone to the accumulation of toxins, residues and the accumulation of organic waste; it is particularly the case of the liver, the kidneys, the gall bladder and the spleen.
The largest internal organ in humans, the liver is also one of the most important. It has many functions, among them the synthesis of proteins, immune and clotting factors, and oxygen and fat-carrying substances. Its chief digestive function is the secretion of bile, a solution critical to fat emulsion and absorption. The liver also removes excess glucose from circulation and stores it until it is needed. It converts excess amino acids into useful forms and filters drugs and poisons from the bloodstream, neutralizing them and excreting them in bile. The liver has two main lobes, located just under the diaphragm on the right side of the body. It can lose 75 percent of its tissue (to disease or surgery) without ceasing to function.
One of the most common liver diseases is hepatitis, an inflammation of the liver. Hepatitis may be caused by exposure to certain chemicals, by autoimmune diseases, or by bacterial infections. But hepatitis is most often caused by one of several viruses. The hepatitis A virus (HAV) can produce flu like symptoms and jaundice, but many people who contract it have no symptoms. The disease tends to resolve on its own. Because HAV lives in feces in the intestinal tract, hepatitis A is prevalent in areas where drinking water is contaminated with raw sewage. Good hygiene practices and a hepatitis A vaccination are effective measures of prevention.
Hepatitis B is a more serious ailment. Unlike HAV, hepatitis B virus (HBV) may remain active in the body for many years after the time of infection, sometimes permanently damaging the liver. HBV is found in blood and other body fluids—tears, saliva, and semen—and is spread through unprotected sexual intercourse and the sharing of infected needles or other sharp objects that puncture the skin.
In developed countries, alcohol-induced liver diseases far outnumber hepatitis and all other liver disorders. Heavy alcohol use causes fat deposits to build up in the liver, possibly leading to chronic hepatitis, which causes scarring and destruction of liver cells. Over many years, scarring in the liver can progress to cirrhosis, a disease characterized by diminished blood flow through this important organ. When this occurs, toxins are not adequately removed from the blood, blood pressure increases in the hepatic portal vein, and substances produced by the liver, such as blood proteins, are not adequately regulated. Cirrhosis cannot be reversed, but liver function can significantly improve in people who stop consuming alcohol during the early stages of this condition. Beyond abstinence from alcohol, treatments for cirrhosis may include drug therapy or surgery to redirect blood flow.
Kidney, paired organ whose functions include removing waste products from the blood and regulating the amount of fluid in the body. The basic units of the kidneys are microscopically thin structures called nephrons, which filter the blood and cause wastes to be removed in the form of urine. Together with the bladder, two ureters, and the single urethra, the kidneys make up the body’s urinary system. Human beings, as well as members of all other vertebrate species, typically have two kidneys.
Like kidney beans, the body’s kidneys are dark red in colour and have a shape in which one side is convex, or rounded, and the other is concave, or indented. The kidneys of adult humans are about 10 to 13 cm (4 to 5 in) long and about 5 to 7.5 cm (2 to 3 in) wide—about the size of a computer mouse.
The kidneys lie against the rear wall of the abdomen, on either side of the spine. They are situated below the middle of the back, beneath the liver on the right and the spleen on the left. Each kidney is encased in a transparent, fibrous membrane called a renal capsule, which helps protect it against trauma and infection. The concave part of the kidney attaches to two of the body’s crucial blood vessels—the renal artery and the renal vein—and the ureter, a tube like structure that carries urine to the bladder.
A primary function of kidneys is the removal of poisonous wastes from the blood. Chief among these wastes are the nitrogen-containing compounds urea and uric acid, which result from the breakdown of proteins and nucleic acids. Life-threatening illnesses occur when too many of these waste products accumulate in the bloodstream. Fortunately, a healthy kidney can easily rid the body of these substances.
Approximately one million nephrons (right) compose each bean-shaped kidney (left). The filtration unit of the nephron, called the glomerulus, regulates the concentration within the body of important substances such as potassium, calcium, and hydrogen, and removes substances not produced by the body such as drugs and food additives. The filtrate, urine, leaves the nephron through a long tubule and collecting duct. Chemical signals triggered by the body’s need for water and salt cause the walls of the tubule to become more or less permeable to these substances, which are reabsorbed accordingly from the urine.
The Gall Bladder
The gallbladder, muscular organ that serves as a reservoir for bile, present in most vertebrates. In humans, it is a pear-shaped membranous sac on the undersurface of the right lobe of the liver just below the lower ribs. It is generally about 7.5 cm long and 2.5 cm in diameter at its thickest part; it has a capacity varying from 30 to 50ml. Structurally, the gallbladder consists of an outer peritoneal coat (tunica serosa); a middle coat of fibrous tissue and unstriped muscle (tunica muscularis); and an inner mucous membrane coat (tunica mucosa).
The function of the gallbladder is to store bile, secreted by the liver and transmitted from that organ via the cystic and hepatic ducts, until it is needed in the digestive process. The gallbladder, when functioning normally, empties through the biliary ducts into the duodenum to aid digestion by promoting peristalsis and absorption, preventing putrefaction, and emulsifying fat.
The major disorder associated with the gallbladder is the presence of gallstones, varying in shape and size from a pea to a small pear. Accreted from the constituent salts in the bile, they are most common in diabetic patients, in blacks, and in women; their presence increases with age. Two of the reasons for the growth of gallstones are believed to be the presence of excessive amounts of substances such as calcium and cholesterol in the bile and the retention of bile in the gallbladder for a long period of time.
Another common disorder of the gallbladder is cholecystitis, or inflammation of the organ, which is believed to be a result of the presence of highly concentrated bile. Chronic cholecystitis is sometimes aggravated by bacterial infection, leading to perforation and peritonitis. Less common is the growth of malignant tumours, which are associated with gallstones and constitute about 3 percent of all cancer in humans.
The spleen is a flattened, oblong organ that removes disease-producing organisms and worn-out red blood cells from the bloodstream. Situated in the upper left abdominal cavity, in contact with the pancreas, the diaphragm, and the left kidney. It is supported by bands of fibres that are attached to the peritoneum (the membrane lining the abdominal cavity). The spleen varies in size but, in adult humans, it is about 13 cm long, up to 10 cm wide and 3.8 cm thick, and weighs about 200g.The spleen is fed by the splenic artery, and venous blood from the spleen enters the liver.
The spleen removes iron from the hemoglobin of red blood cells for use in the body. It also removes such waste materials as bile pigments for excretion as bile by the liver. The spleen produces antibodies against various disease orga isms and manufactures a variety of blood cells.
Many diseases affect the spleen. In splenomegaly, the spleen enlarges. This condition is usually an indication of bacterial, parasitic, and viral infections, such as infectious mononucleosis, tuberculosis, malaria, rheumatoid arthritis, and histoplasmosis. Splenomegaly may also be caused by cirrhosis of the liver. In hypersplenism, a malfunctioning or hyperactive spleen may so increase its normal rate of destroying red blood cells as to cause a variety of hemolytic anemias. Hemorrhage of an enlarged spleen may magnify anemia and also cause an iron deficiency. Small splenic abscesses may run a benign course without detection. Large splenic abscesses, however, may rupture into the bowel cavity to cause peritonitis (inflammation of the abdominal wall lining), and the infection may invade the bloodstream and be carried to the liver, where it may form additional abscesses. Splenic cysts are rare, and the spleen is seldom the site of a carcinoma, or cancer.
A hyperactive spleen may sometimes be treated with radiation or corticosteroids (steroids that are extracted from the adrenal cortex). Abscesses are treated with broad-spectrum antibiotics or surgical drainage. Surgical removal of the spleen is required if the spleen or the splenic artery ruptures.
The spleen is a fist-sized, spongy organ located behind the stomach, just under the diaphragm. Part of the lymphatic system, the spleen is composed of two types of tissue. White pulp produces lymphocytes, which release antibodies into the bloodstream to combat infection. More prominent is the red pulp, in which macrophages filter broken cells, parasites, bile pigments, and other useless substances from the blood. Iron from broken red blood cells is stored in the spleen for later use.
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