Book 4 - Self Instructional Manual for Cancer Registrars - SEER ...

The function of the kidney is to remove metabolic waste products from the blood and to maintainthe electrolyte 1 balance. This is accomplished by the production of urine.The formation of urine and the regulation of the internal environment of the body by the kidneysare a composite of four processes:• Filtration of the blood through the capillaries of the glomerulus into Bowman's capsule• Selective reabsorption by the renal tubules of materials required to maintain the internalenvironment of the body, i.e., the fluid and electrolyte balance• Secretion of certain substances produced in the distal and collecting tubules causingpotassium, hydrogen ions, and other substances to be taken from the blood and added tothe tubular filtrate• Maintenance of acid-base balance (pH 2 7.4) by regulating the amount of acid or basewhich the kidneys eliminate in the urine.The Production of UrineThe aorta brings waste-filled blood from the heart to the kidneys by way of the renal arteries. Herein the kidneys the waste products of metabolism and toxic substances are eliminated. Blood entersthe glomerulus through the afferent arteriole which divides into capillaries. These will later unite toform the efferent arteriole that drains blood from the glomerulus. As the blood passes through theglomerulus, water, glucose, salts, and nitrogenous wastes are filtered into Bowman's capsule whichis the beginning of the renal tubule. The contents of the distal portion of the tubule pass to branchesof the collecting tubule which empties into the calyces of the renal pelvis. These contents are thentransported through the ureters from the renal pelvis to the bladder. Certain substances required tomaintain fluid and electrolyte balance are reabsorbed by the peritubular capillaries 3 (e.g., sodium,glucose, water) and returned to the blood. Secretions produced in the distal and collecting tubulescause other substances to be added to the tubular filtrate from the blood (e.g., potassium, hydrogenions, and ammonia).Some abnormal constituents found in the urine are albumin, blood, calculi, melanin, and malignantcells.Through the capillaries of the glomeruli, approximately 120 milliliters (ml) of water and salts arefiltered from the blood each minute. Most of the water is reabsorbed as are other essentialsubstances unless their concentration in the body happens to be too high. The urine passes outthrough the collecting tubules at a rate of approximately 1.0 milliliter per minute, so that a healthyperson will excrete about 1 to 1 and 1/2 liters per day.Xelectrolytes--mainly, ions such as sodium, potassium, ammonium chloride, bicarbonate,phosphate, and sulfate. Levels vary with diet and other factors.2pH--refers to the hydrogen ion concentration expressing both acidity and alkalinity on a scale whosevalues run from 0 to 14 with 7 representing neutrality, numbers less than 7 increasing acidity, andnumbers greater than 7 increasing alkalinity.3peritubular capillaries--capillary beds that surround the renal tubules.249