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Unformatted text preview: URINARY SYSTEM
Filtration Reabsorption Secretion Excretion Fluid & Electrolyte Balance - Kidneys produce urine - Flows out of kidneys through the ureters - Urine is stored in the bladder - Urine is excreted from the body through the urethra (Micturition)
Figure 19-1a Blood Flow: 25% CO Wow! -Renal arteries from aorta -Renal veins to inferior vena cava Figure 19-1b Outer cortex Inner medulla Nephrons cortical (80%) + juxtamedullary (20%) Figure 19-1c Figure 19-1i Nephron (Fig. 19.1j) Tubule components
Bowman's capsule Proximal convoluted tubule Loop of Henle (descending limb ascending limb) Distal convoluted tubule Collecting duct urine collects in renal pelvis Vascular components
Afferent arteriole Glomerulus Efferent arteriole Peritubular capillaries (Vasa recta if they dip down into medulla) venules to veins Figure 19-1j Figure 19-1g Figure 19-1h Renal corpuscle Glomerulus + Bowman's capsule Juxtaglomerular apparatus Distal tubule (macula densa)+ arterioles (juxtaglomerular cells) Urine Formation Filtration Reabsorption Secretion Diffusion, active transport, hormonal regulation Figure 19-2 Filtration Renal corpuscle: Glomerulus Bowman's capsule Filtrate is isosmotic to plasma (300 mOsM) Reabsorption Tubule lumen Peritubular capillaries 70% of filtrate (isosmotic fluid) in PCT Loop of Henle more solute is reabsorbed than water (100 mOsM) DCT + collecting duct variable reabsorption based on hormones (50-1200 mOsM) Secretion Peritubular capillaries Tubule lumen Selective transport Table 19-1 Figure 19-5 Filtration Fenestrated capillaries Podocytes surround capillaries - form slits for filtrate to enter B's capsule Hydrostatic pressure = 55 mm Hg Compared to 30-35 mmHg in others) Net filtration along entire length of glomerulus Figure 19-4a Figure 19-4d Figure 19-6 GFR (Glomerular Filtration Rate) Fluid volume filtrated/time (125 mL/min) (180 L/day, plasma volume of 3 L) 2 factors: Net filtration pressure
Renal blood flow Blood pressure Filtration coefficient
Surface area Capillary/B's capsule permeability Figure 19-7 GFR Regulation Maintain constant GFR by controlling BF through arterioles (Fig. 19-8) Myogenic response Tubuloglomerular feedback Neural control Renin-Angiotensin system Figure 19-8 - Overview Myogenic Response Afferent arterioles Stretch of smooth muscle in arteriole wall results in a reflex contraction Vasoconstriction when BP increases (+ GFR) Decreases flow to glomerulus to GFR Tubuloglomerular Feedback Changes in solute concentration past the macula densa influence the release of a paracrine that causes vasoconstriction of the afferent arteriole GFR will solute (NaCl) flow past macula densa. This will release of vasoconstrictor chemical (paracrine) and vasoconstriction of afferent arteriole and GFR (Fig. 19-10) Figure 19-10 - Overview Neural Control Sympathetic stimulation of -receptors on vascular smooth muscle causes vasoconstriction to GFR Protective function when BP falls dramatically ( GFR to conserve volume) Renin-Angiotensin System Renin is released from JG cells of afferent arteriole when BP Sympathetic neurons also stimulate release of renin Macula densa (low solute flow) signals JG cells to release renin Figure 20-15 Figure 19-9 - Overview Renin (enzyme) converts angiotensinogen (inactive plasma protein made by the liver) to Angiotensin I Angiotensin I is converted to Angiotensin II by ACE (angiotensin converting enzyme) Angiotensin II potent vasoconstrictor Increases BP to restore GFR Reabsorption Active (primary or secondary) or passive Transepithelial transport + paracellular pathway Na+ - dependent transport is common Figure 19-11 - Overview Figure 19-12 - Overview Figure 19-13 - Overview Transport Maximum (Tm) Saturation occurs when all available transporters are occupied Transport is maximized Renal threshold plasma concentration where saturation occurs Presence in urine as indicator Figure 19-14 Figure 19-15a Figure 19-15b Figure 19-15d Secretion Enhances excretion Active process (secondary active transport is common) Secretion of H+ and K+ - important to regulate their concentrations H+ Secretion Controls pH Increased H+ in blood results in increase H+ secretion Decreased H+ in blood results in decrease H+ secretion K+ Secretion Influenced by hormone Aldosterone Angiotensin II stimulates the release of aldosterone from the adrenal gland (steroid hormone produced in the cortex) Stimulates principal cells in the DCT* and CD to increase K+ secretion K+ secretion is coupled to Na+ reabsorption Water wants to follows Na+ reabsorption Requires another hormone to increase water permeability Hormone = Antidiuretic hormone (ADH) (Vasopressin) ADH Angiotensin II stimulates the hypothalamus to release ADH from the posterior pituitary gland Increases permeability of the CD's to water to increase water reabsorption and decrease urine output Figure 20-14 ADH major mechanism for controlling water content in blood by regulating permeability of CD to water Absence diluted urine, increased urine volume Presence concentrated urine, decreased urine volume ...
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- Fall '08