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PHGY 210
K.Andrew White

Renal Physiology Kidney Functions By making urine, the kidneys are achieving a number of things. 1. Regulation a. Water b. Inorganic ion balance c. Acid-base balance 2. Removal of metabolic waste products a. From blood b. Excretion in urine c. Without this, blood would be dirty in a couple of days i. Cant survive longer than 2 weeks 3. Removal of foreign chemicals a. From blood i. Urine discolored when you take antibiotics b. Excretion in urine 4. Production of hormones & enzymes a. Erythropoietin i. Hormone that controls erythrocyte production b. Renin i. Enzyme that controls formation of angiotensin ii. Influences blood pressure + iii. Influences Na balance c. 1,25-dihydroxy vitamin D i. Active vitamin ii. Influences Ca balance Kidney Anatomy Weight Population Location Urine Size 150 g 0.1% of the Behind the Made by Fist Figure 14.01 population peritoneum both the is born cortex & with only 1 On either medulla kidney but side of the live normal vertebral Eliminated lives column into the pelvis Against the posterior Flows abdominal through wall. the ureter to the bladder 2 Afferent arteriole Renal cortex Renal medulla Interlobar artery Arcuate Renal pelvis artery Renal artery Ureter Interlobular artery Urine Blood Flow After blood flows around, it is collected back in the venous system & backtracks the way it came. Arteries and veins run side by side. Nephron Each kidney contains ~1 million subunits called nephrons 3 Urine Formation Glomerular Filtration The glomerular capillary wall is the beginning of how urine is made. 1. Blood/plasma goes through fenestra of endothelial cells 2. Through mesh of GBM Glomerular capillary wall 3. Through filtration slit 4. Into Bowmans space (filtration barrier) a. Contains most substances in plasma i. Water ii. Low-molecular weight substances iii. Large molecules cant pass Visceral 1. Cells glomerular a. Like RBC epithelial cells b. Reason why blood in (podocytes) urine is a bad sign 2. Proteins GBM a. Albumin Endothelial cells b. Globulin 3. Protein-bound substances a. of Ca2+ b. Fatty acids iv. Same [ ] as in plasma Forces Involved in Filtration No proteins in the Bowman space fluid = no oncotic pressure o Power to pull water back in is because of the [proteins] Forces involved in Figure 14.08 filtration (oncotic pressure) 4 Glomerular Filtration Rate GFR: the volume of fluid filtered from the glomeruli into Bowmans space per unit time. Normal GFR for a 70kg person is 180L/day o Normal plasma volume is ~3.5L plasma is filtered 51 times per day at glomeruli. Filtered load: the total amount of any freely filtered substance. GFR is regulated by: Net filtration pressure o Only physiologically-significant method o Decreased GFR Capillary blood pressure goes down Dilate efferent or constrict afferent arteriole Measure of kidney failure o Increased GFR Capillary blood pressure goes up Constrict efferent or dilate afferent arteriole Membrane permeability and surface area available for filtration o Only relevant in pathological conditions Tubular Secretion Peritubular capillaries tubules o Filtered load < amount excreted in urine o Most important examples: H and K + o Usually coupled to reabsorption of Na +
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