Nursing Preparation Study Guide

Nursing Preparation Study Guide More blood flows into the kidneys than necessary for the provision of oxygen and nutrients to the kidney. This blood supply nourishes the kidney, and a portion of blood is filtered by the kidney for processing. When stress is placed on the body due to hemorrhage, the blood flow to the kidneys is reduced, resulting in a decrease in urine production. Blood enters the kidneys through the renal arteries, from the abdominal aorta. Around 1200 mL of blood can enter the kidneys per minute. The renal artery that enters each kidney branches into segmental arteries, which branch into interlobar arteries. Eventually, the blood vessels become arterioles that supply the glomeruli. The glomerulus is a ball-shaped tangled network of capillaries, and is part of a nephron (the main structural and functional unit of the kidney). There are two main sections in the kidney, the renal cortex and renal medulla. Nephrons are located throughout the kidney, with the first part of the nephron in the cortex. This part of the nephron, the renal corpuscle, filters urine. Nephrons have a thin wall that allows fluid to pass from the glomeruli into them. Blood gradually drains from the nephrons and into peritubular capillaries; these become venules and veins until the filtered blood leaves the kidney via the renal vein. A clearance value shows the degree to which a substance is removed from the blood by excretion in the voided urine. Glomerular filtrate and plasma are similar; however, glomerular filtrate contains little protein. While 125 mL of glomerular filtrate is produced per minute, most of it is reabsorbed by the renal tubules. Since none of the creatinine in the glomerular filtrate is reabsorbed, the plasma clearance of creatinine is 125 mL per minute. To measure the rate of glomerular filtration, clearance tests are utilized. A test substance is used that passes easily into the glomerular filtrate, but is neither reabsorbed nor secreted by renal tubular cells. The concentration of material in the glomerular filtrate is approximately the same as the concentration of the material inthe plasma. The rate of excretion and the plasma concentration are the only factors necessary to compute the rate of glomerular filtration. Urine filtered from the blood through the nephrons passes through the renal tubule and through various tubes and processes. It eventually reaches minor calyces and then major calyces. Next, the urine enters the renal pelvis that becomes the ureter. The ureter passes urine to the bladder. The body makes about a liter of urine a day, which is stored in the bladder until emptying. Urine exits the body through the urethra. The kidneys are highly vulnerable to damage by toxins, as one-fifth of the body’s blood supply passes through them at any given time. 8.3.1 Functions The functions of the urinary system are to help maintain homeostasis by: • Producing urine • Storing urine • Eliminating urine

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