The Medial Umbilical Ligament
The urethra is a tube that conveys urine from the urinary bladder to the outside of the body. Its wall is lined with mucous membranes and contains a relatively thick layer of smooth muscle tissue. It also contains numerous mucous glands, called "urethral glands," that secrete mucus into the urethral canal. In females the urethra is about 4 cm long. It passes forward from the bladder, descends below the symphysis pubis, and empties into the labia minor. Its opening is located above the vaginal opening and about 2.5 cm below the clitoris. In males, the urethra, which functions both as a urinary canal and a passageway for cells and secretions from various reproductive organs, can be divided into three sections: the prostatic urethra, the membranous urethra, and the penile urethra.
The outside surface of each kidney is convex, while the side toward the center is deeply concave. The resulting middle depression leads into a hollow chamber called the "renal sinus." The entrance to this sinus is termed the "hilum," and through it pass various blood vessels, nerves, lymphatic vessels, and the ureter. The superior end of the ureter is expanded to form a funnel-shaped sac called the "renal pelvis," which is located inside the renal sinus. The pelvis is divided into two or three tubes, called the "major calyces" (the singular is calyx), and they are divided into several (eight to fourteen) "minor calyces."
About one-quarter (750-1,000 pints daily) of the blood which is output by the heart is sent to the body's "filter treatment plant", where it is purified by the kidneys and circulated on to the rest of the body. One to two thousandths (1/1000-2/1000) of the blood flow becomes fluid waste and is sent into the bladder for storage until it can be conveniently expelled. This toxic waste is called urine. The kidneys are located about two inches above the body's midline just below and behind the liver in the upper abdomen and behind the lower ribs. They receive about 120 pints of blood per hour, even if other body systems are shorted. They are the balancers of internal fluids, so if we overeat or overdrink one day and diet the next, or if we have an active, "sweaty" day, the kidneys will compensate and see that these fluctuations in fluid, salt and glucose are leveled out. It is important to drink plenty of fluids each day to keep the kidneys in good working order. The "kidney" bean is so named because of its resemblance to the shape and color of the kidneys. Many people believe the kidneys lie down in the flanks and are surprised when pain from kidney disorder comes from the upper middle back area.
The Medial Umbilical Ligament
After birth, when circulation in the placenta stops, only the pelvic portion of the umbilical artery remains patent, becoming the internal iliac and the first part of the superior vesicle artery in adulthood. The remainder of this vessel is converted into a solid fibrous cord, called the "medial umbilical ligament," which extends from the pelvis to the umbilicus, or navel, the depression in the abdomen that marks the point where the umbilical cord was attached to the fetus.
A kidney contains about one million nephrons, the functional units of the kidney, and each of these consist of a renal corpuscle and a renal tubule. A "renal corpuscle" is composed of tangled clusters of blood capillaries called a "glomerulus," and a thin-walled, saclike structure, called the "Bowman's capsule," which surrounds the glomerulus. The Bowman's capsule is an expansion at the closed end of a renal tubule. It is composed of two layers of cells: an inner layer that closely covers the glomerulus, and an outer layer that is continuous with the inner layer and with the wall of the renal tubule. The renal tubule leads away from the Bowman's capsule and becomes highly coiled. The coiled portion is named the "proximal convoluted tubule." Several of the distal convoluted tubules merge into the renal cortex to form a collecting duct, which in turn passes into the renal medulla, becoming larger and larger as it joins other collecting ducts, the resulting tube is called the papillary duct.
The substance of the kidney is divided into two distinct regions: an inner medulla and an outer cortex. The "renal medulla" is composed of conical masses of tissue called "renal pyramids," whose bases are directed toward the convex surface of the kidney, and which apex to form the renal papillae. The "renal cortex" forms a shell around the medulla. Its tissues dip into the medulla between adjacent renal pyramids to form "renal columns." The granular appearance of the cortex is due to the random arrangement of tiny tubules associated with "nephrons," the functional units of the kidney.
There are two uterine tubes that carry urine from the kidneys to the bladder. Each ureter is about ten to twelve inches long. Urine flows down partly by gravity, but mainly by waves of contractions which pass several times per minute through the muscle layers of the urethral walls. Each ureter enters the bladder through a tunnel in the bladder wall, which is angled to prevent the urine from running back into the ureter when the bladder contracts.
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