Urinary system anatomy and physiology review

The urinary system is responsible for the production and elimination of urine when a type of waste called urea is removed from the blood. Urea is produced when protein-containing foods are broken down in the body. Urea is carried in the bloodstream to the two kidneys, where urine is formed. The two ureters, the urinary bladder, and the urethra, are responsible for the elimination of urine. Figure illustrates the urinary system in relationship to the body, and Figure illustrates the interior and exterior features of the urinary system organs.

The urinary system

FIGURE. The urinary system

Frontal section of the right kidney showing internal structures and blood vessels

FIGURE. (A) Frontal section of the right kidney showing internal structures and blood vessels. (B) Magnified section of the kidney shows several nephrons. (From Scanlon, VC, and Sanders, T: Essentials of Anatomy and Physiology, ed 5. FA Davis, Philadelphia, 2007, p 422, with permission.)

The kidneys, each about the size of a fist, help to regulate the water, electrolyte (ionized salt), and acid-base content of the blood, and they selectively filter the waste products of metabolism.

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They also play an important role in regulating blood pressure. Each kidney contains more than 1 million nephrons, which are the principal filtering units of the kidney. Each nephron houses a ball of tiny blood capillaries called the glomerulus and a renal tubule. It is here that the three-part process of selective filtration of wastes, reabsorption of vital minerals and fluid, and secretion of waste products and other substances takes place. As urine is formed, it passes through the nephrons into the renal tubules of the kidneys.

Nephron with associated blood vessels

FIGURE. Nephron with associated blood vessels

From the kidneys, urine travels into the ureters, thin tubes about 8 to 10 inches in length, on its way to the urinary bladder. Small amounts of urine drip into the urinary bladder about every 12 seconds. The urinary bladder is a balloon-shaped muscular organ that stores urine until it is emptied. It can hold about 16 ounces of urine for 2 to 5 hours. Nerves in the urinary bladder indicate when it should be emptied. Sphincter muscles keep urine from leaking into the urethra too soon and relax when it is time to urinate.

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It is worth emphasizing the reabsorption process of the kidneys’ nephrons. Were it not for this process, the body would rapidly be depleted of its fluid. Typically, only 1% of the fluid passing through a nephron is excreted as urine.

A routine diagnostic test for suspected urinary disease is a urinalysis, which includes testing the specific gravity; pH; and presence of protein, blood, sugar, and ketones. It includes a microscopic examination for the presence of white blood cells (WBCs) and red blood cells (RBCs), casts, bacteria, and crystals. Normal urine is amber in color with a slightly acid reaction, has a peculiar odor, and frequently deposits a precipitate of phosphates when fresh. The specific gravity varies from 1.005 to 1.030. The greater the rate of urine excretion, the lower is the specific gravity. Refer to Table, Significance of Changes in Urine, throughout the chapter, noting possible abnormalities and their significance to the disease in question.

Table. Significance of Changes in Urine

Significance of Changes in Urine

Renal cell carcinoma or Kidney cancer ICD-9: 189.x Description Renal cell carcinoma (RCC), also known as renal cell adenocarcinoma, is by far the most common type of kidney cancer, accounting for 90% of kidney cancers. RCC usually grows as a single mass within the kidney but can be found in more than one part of the kidney or in both kidneys. It occurs most often in individuals over age 40. Etiology The cause is essentially unknown; however, risk factors include smoking, obesity, hypertension, long-term dialysis, and exposure to chemicals and irritants, such as asbestos or cadmium in the workplace. Signs and Symptoms Symptoms may include hematuria, flank or side pain that does not go away, a lump or mass palpated in the side or abdomen, weight loss, and fever. Some clients report feeling listless and not well. Diagnostic Procedures A complete physical examination may reveal an enlarged mass. BUN and creatinine levels are checked. A CT scan using contrast media is often used in diagnosis, as is the i...
Nephrotic syndrome ICD-9: 581.9 Description Nephrotic syndrome is a condition or a complex of signs and symptoms (syndrome) of the basement membrane of the glomerulus. (The basement membrane surrounds each of the many tiny capillaries comprising a glomerulus.) The disease is characterized by severe proteinuria, often to the extent that the body cannot keep up with the protein loss, which is known as hypoalbuminemia. The disease is further characterized by hyperlipemia (excessive levels of fatlike substances called lipids in the blood), lipiduria (lipids in the urine), and generalized edema. Etiology Nephrotic syndrome may result from a variety of disease processes having the capacity to damage the basement membrane of the glomerulus. Between 70% and 75% of the cases of nephrotic syndrome result from some form of glomerulonephritis. The syndrome also may arise as a consequence of diabetes mellitus, systemic lupus erythematosus, neoplasms, or reactions to drugs or toxins. The disease is occasio...
Hydronephrosis ICD-9: 591 Description Hydronephrosis is the distention of the renal pelvis and calyces of a kidney due to pressure from accumulating urine. The pressure impairs, and may eventually interrupt, kidney function. One or both kidneys may be affected. Etiology Hydronephrosis is caused by a urinary tract obstruction. The ureters and renal pelvis dilate proximal to, or behind, the obstruction. This swelling causes the hydronephrosis with resultant destruction of functional tissue. In children, the obstruction is usually the result of some congenital defect in urinary tract structure. In adults, the obstruction is more often acquired, resulting from blockage by neoplasms or uroliths, commonly called kidney stones or renal calculi. Urinary tract obstruction in men may be produced by benign or malignant enlargement of the prostate. Women may experience urinary tract obstruction as a complication of pregnancy. Underlying disorders such as neurogenic bladder also may allow urine to acc...
End-stage renal disease ICD-9: 585.6 Description End-stage renal disease (ESRD), usually the result of chronic renal failure, is the gradual, progressive deterioration of kidney function to the point that the kidneys cannot sustain their necessary dayto-day life activity. As the kidney tissue is progressively destroyed, the kidney loses its ability to excrete the nitrogenous end products of metabolism, such as urea and creatinine, which accumulate in the blood and eventually reach toxic levels. As kidney function diminishes, every organ in the body is affected, and dialysis or kidney transplantation is eventually needed for survival. Etiology Causes of ESRD include diabetes mellitus (leading cause), hypertension, chronic glomerulonephritis, pyelonephritis, obstruction of the urinary tract, congenital anomalies such as polycystic kidneys, vascular disorders, infections, medications, and toxic agents. Signs and Symptoms The early signs and symptoms are oliguria and azotemia, or the presence of n...
Anatomy of the Urinary System How do the kidneys and urinary system work? The body takes nutrients from food and converts them to energy. After the body has taken the food components that it needs, waste products are left behind in the bowel and in the blood. Illustration of the anatomy of the urinary system, front view The kidney and urinary systems help the body to eliminate liquid waste called urea, and to keep chemicals, such as potassium and sodium, and water in balance. Urea is produced when foods containing protein, such as meat, poultry, and certain vegetables, are broken down in the body. Urea is carried in the bloodstream to the kidneys, where it is removed along with water and other wastes in the form of urine. Other important functions of the kidneys include blood pressure regulation and the production of erythropoietin, which controls red blood cell production in the bone marrow. Kidneys also regulate the acid-base balance and conserve fluids. Illustration of the anatomy of the kidney K...