Kidney Anatomy Study Guide

I. Kidney Anatomy A. Every day the kidneys filter nearly 200 liters of fluid from the bloodstream, allowing toxins, metabolic wastes, and excess ions to leave the body in urine while returning needed substances to the blood; of this, only 1-2 L of urine is actually formed daily B. Location and External Anatomy 1. Kidneys - bean-shaped organs that lie retroperitoneal in the superior lumbar region. 2. The medial surface is concave and has a renal hilus that leads into a renal sinus, where the blood vessels, nerves, and lymphatics lie. 3. The adrenal glands lie on top of the kidneys; a fatty encasement cushions the kidneys and holds them in place, preventing ptosis – dropping of
The filtration membrane lies between the blood and the interior of the glomerular capsule, and allows free passage of water and solutes – fenestrated, or porous II. Kidney Physiology: Mechanisms of Urine Formation A. Step 1: Glomerular Filtration 1. Glomerular filtration is a passive, nonselective process in which hydrostatic pressure forces fluids through the glomerular membrane. a. Filtrate and is the raw material that the renal tubules process to form urine; essentially plasma minus blood cells and large plasma proteins 2. Filtration membrane has a large surface area and is thousands of times more permeable to water and solutes 3. Maintenance of relatively constant glomerular filtration rate is important b/c reabsorption of water & solutes depends on how quickly filtrate flows thru tubules. 4. Glomerular filtration rate – volume of filtrate formed each minute by the combined activity of all 2 million glomeruli of the kidneys. Factors that govern the GFR are: a. Total surface area available for filtration b. Filtration memrane permeability c. Net filtration pressure 5. Anuria – abnormally low urinary output (less than
The wall of the bladder has three layers: an outer adventitia, a middle layer of detrusor muscle, and an inner mucosa that is highly folded to allow distention of the bladder without a large increase in internal pressure VI. Urethra A. The urethra is a muscular tube that drains urine from the body; it is 3–4 cm long in females, but closer to 20 cm in males B. 2 sphincter muscles in the urethra: the internal urethral sphincter, which is involuntary and formed from detrusor muscle; and the external urethral sphincter, which is voluntary and formed by the skeletal muscle at the urogenital diaphragm C. The external urethral orifice lies between the clitoris and vaginal opening in females, or occurs at the tip of the penis in males VII. Micturition A. Micturition, or urination, is the act of emptying the bladder 1. As urine accumulates, distention of the bladder activates stretch receptors, which trigger spinal reflexes, resulting in storage of urine. 2. Voluntary initiation of voiding reflexes results in activation of the micturition center of the pons, which signals parasympathetic motor neurons that stimulate contraction of the detrusor muscle and relaxation of the urinary