Nerve supply • Primarily from sympathetic portion of autonomic NS • Sympathetic stimulation causes vasoconstriction of renal vessels, temporarily decreasing urine formation • Controls blood flow thru glomerular capillaries but is not essential for kidney to function; e.g. transplanted kidney Urine Volume Regulation • Urine volume is determined by amount of water contained in tubular filtrate when it reaches the renal pelvis • 2 hormones, ADH from posterior pituitary gland, and aldosterone secreted by adrenal cortex are responsible for majority of this regulation • ADH most important in regulating urine volume o Acts on DCT and collecting ducts to promote water reabsorption o If absent, water will not be reabsorbed and lost in urine, resulting in increased urine volume= polyuria • Aldosterone increases reabsorption of sodium into bloodstream in DCT and collecting duct o Causes osmotic imbalance that encourages water to follow Na+ out of tubular filtrate and into blood o But, water cannot move out of DCT and collecting ducts unless sufficient ADH is present • Glomerular filtrate moves thru tubules and eventually into renal pelvis bc of difference in pressure that exists btwn fluid in Bowma n’s capsule and fluid in renal pelvis o Bowman’s capsule pressure is higher than almost non -existent pressure in renal pelvis o This forces fluid to move along thru the tubules of nephrons Regulation of BP • Kidneys help maintain homeostasis by regulating BP • When BP falls, the renin-angiotensin-aldosterone system responds to bring it back to normal • Specialized juxtaglomerular cells in AGA constantly monitor BP within arterioles • Densely packed cells called macula densa in ascending loop of Henle monitor NaCl conc of tubular filtrate • If juxtaglomerular cells detect decrease in BP or if macula densa come in contact w less NaCl (lower amount of slower movement) juxtaglomerular cells release renin • Renin: enzyme that facilitates splitting of angiotensin 1 from angiotensin, which is then converted to angiotensin 2 by ACE (angiotensin converting enzyme) • Angiotensin 2 causes arteriole constriction and stimulates release of aldosterone from adrenal glands • Increasing sodium and water reabsorption into bloodstream increases blood volume, which better fills vascular space and increases BP
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- Winter '12
- peritubular capillaries, renal pelvis, glomerular filtrate, glomerular capillaries