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.

READ:   9 Ways to Prevent Kidney Stones

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.

READ:   Urinary Tract Infection: Symptoms, Diagnosis, and Treatment

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

Pyelonephritis (Acute) ICD-9: 590.10 Description Pyelonephritis, also called infective tubulointerstitial nephritis or kidney infection, is inflammation of the kidney and renal pelvis due to infection. One or both kidneys may be affected. The infection can result in the destruction or scarring of renal tissue, impairing kidney function. It is the most common type of kidney disease and is more common in women than in men due in part to the anatomic difference between men and women. Etiology Pyelonephritis is most commonly due to infection by the bacteria Escherichia coli. E. coli is a normal intestinal bacteria that grows rapidly. It is found in fecal matter. Proteus, Pseudomonas, Staphylococcus, and Enterococcus bacteria are less frequent agents of the infection. The bacteria typically ascend to the kidneys from the lower urinary tract, but they also may enter the kidneys through the blood or lymph. Women, particularly those who are pregnant or who practice poor genital hygiene, are at risk. In m...
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...
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...
8 Signs and Symptoms of Kidney Stones What are kidney stones? Kidney stones are hard collections of salt and minerals often made up of calcium or uric acid. They form inside the kidney and can travel to other parts of the urinary tract. Stones vary in size. Some are as small as the period at the end of this sentence — a fraction of an inch. Others can grow to a few inches across. Some kidney stones can become so large they take up the entire kidney. A kidney stone forms when too much of certain minerals in your body accumulate in your urine. When you aren’t well hydrated, your urine becomes more concentrated with higher levels of certain minerals. When mineral levels are higher, it’s more likely that a kidney stone will form. About 1 out of every 11 people in the United States will get a kidney stone. Stones are more common in men, people who are obese, and those who have diabetes Smaller kidney stones that remain in the kidney often don’t cause any symptoms. You might not notice anything is amiss until the ...
Polycystic Kidney disease ICD-9: 753.12 Description Polycystic kidney disease is a developmental defect of the collecting tubules in the cortex of the kidneys. Groups of tubules that fail to empty properly into the renal pelvis slowly swell into multiple, grapelike, fluid-filled sacs or cysts. The pressure from the expanding cysts slowly destroys adjacent normal tissue, progressively impairing kidney function. Both kidneys are usually affected and are grossly enlarged. Polycystic kidney disease is one of the most common hereditary diseases in the United States, affecting more than 600,000 people. It is the cause of nearly 10% of end-stage renal disease and affects men, women, and all races equally. Etiology There are two forms of the disease, each due to a genetic defect. The more common adult form, usually manifested during midlife, is an autosomal dominant defect. The much less common infant and childhood forms, manifested at birth or during childhood, are autosomal recessive defects. The followin...