Critical Care Nursing
Critical Care Nursing, The University of Iowa
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II. Anatomy - Structure and Function
Kidneys - 2 bean shaped structures which lie in the retroperitoneal space between 12 thoracic and 3rd lumbar vertebrae.
Left kidney sits behind the spleen. Right kidney sits behind the liver and is slightly lower than the left. Each kidney is enclosed in a tough fibrous capsule and is supported and protected by fat tissue.
Hilus - fissure in the central concave portion of the kidney where blood vessels enter and leave.
Ureters - enter at the hilus, connect the kidney to the bladder.
Cortex - outer third of the kidney which has a brownish-red hue.
Medulla - contains light-colored, cone-shaped masses, the renal pyramids. The free ends of the pyramids form a papilla, which opens into the renal pelvis. The renal pelvis is made up of calyces, which drain the upper and lower haves of the kidney. The calyces unite with the renal pelvis at the upper end of the ureter.
Each kidney is composed of approximately 1.2 million nephrons, which are the functional units of the kidney.
Each nephron contains a glomerulus and a tubule.
The glomerulus consists of a network of capillaries encased in a thin-walled sac, a Bowman's capsule. Fluid and particles from the blood are filtered through the membrane of the glomerulus into the Bowman's capsule. The Bowman's capsule extends to form the tubules of the nephron. Water, nutrients, electrolytes, and other substances are reabsorbed from the glomerular filtrate as it passes through the tubules. Fluid from the tubules flows into the collecting duct, which collects fluid from several nephrons. The collecting duct empties into the renal pelvis.
The nephron is supplied by two capillary beds, a glomerulus, and a peritubular network. The glomerulus is a unique, high pressure capillary filtration system that is located between two arterioles, the afferent and efferent arterioles. The low-pressure reabsorptive system of the peritubular capillary network arises from the efferent arteriole.