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The urinary system removes wastes and toxins from the body. It also regulates the amount of water in the body and the amount and kinds of electrolytes that it contains. Urinary system malfunctions can occur at any time throughout the lifespan, but their likelihood increases with age because of decreased general muscle tone and the kidneys' reduced capacity to function.
The urinary system is composed of the kidneys, urinary bladder, ureters, and urethra.
Kidneys Vital organs have layers, a thin covering called the renal capsule encloses and gives shape to the kidney. A thicker layer of fatty tissue, called the perirenal fat, surrounds the renal capsule. Finally, a thin layer of connective tissue, called the renal fascia, forms each kidney's protective outer covering. The hilum is a narrowest part of the kidney, where blood vessels and nerves enter.
The kidneys produce urine, which is water that contains other substances in solution. In producing urine, the kidneys remove two natural products of metabolism, urea and uric acid, along with other waste products from the blood. The kidneys also filter, reabsorb, and secrete non-waste products back into the system. • The kidneys contain about 2.5 million nephrons which are tiny structures where the urine-making process begins. The capillary network found inside each nephron is called a glomerulus, which assists in filtration.
Ureters Two tubes, one extending from each kidney to either side of the urinary bladder. After urine is produced and processed in the kidneys, it is transported by them. Peristalsis, or involuntary muscle contractions moves the urine through the ureters and into the urinary bladder.
Urinary Bladder It collects urine so that it can be expelled in significant quantities at intervals. The process of urine expulsion, called urination or micturition, begins when a circular muscle called the internal sphincter relaxes, thus permitting urine to enter the opening of the urethra. This first section of the urethra extends only a few inches and is met at the other end by another circular muscle called the external urethral sphincter.
Urethra The urethra, the tube that carries urine out of the body, is connected to the bottom of the bladder. The micturition reflex sends a signal that it is time to open the external urethral sphincter and permit the urine to enter the urethra proper so that it can be expelled.
