renalphysiologyf2009out - Renal Physiology Renal • Major...

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Unformatted text preview: Renal Physiology Renal • Major functions of the kidney – regulate blood volume and blood pressure • water loss, erythropoietin, renin – regulate ion concentrations in plasma • control amount of ions lost – stabilize pH – conserve nutrients/excrete waste products – assist liver in detoxification of waste/metabolites Kidney structure - cortex - medulla - renal pelvis - ureter Fig. 24-4a, Martini Renal Circulation • Nephron location in kidney cortical area • _______ arterioles • Efferent arterioles Fig. 24-5b, Martini Nephron: the functional unit of the kidney the • Structures – afferent arteriole – efferent arteriole – renal corpuscle • contains glomerulus – renal tubule Nephron (overview) Fig. 24-6, Martini Fig. – Proximal convoluted tubule • reabsorption of organic nutrients – Loop of Henle (descending and ascending limbs) water, Na , and Cl reabsorption Fig. 24-6, Martini • urine formation: diuresis urine diuresis – ________________ into nephron tubules tubules • occurs at renal corpuscle – non-selective process – _________________ of solutes/fluid into ECF into • occurs throughout nephron tubules – selective process – ___________ of solutes/fluid into nephron tubule ___________ into lumen lumen • occurs throughout nephron tubules Urine formation: filtration filtration – filtration occurs at renal corpuscle only • glomerular filtration – movement of fluid across the filtration membrane movement filtration • ‘_______________’ capillary (slits and pores present) • movement of fluid caused by net filtration pressure movement net – ~10 mmHg – glomerular hydrostatic pressure (GHP) • higher than capillary pressures • afferent arteriole is larger in diameter than efferent afferent arteriole-causes higher pressure arteriole-causes – ___________ mm Hg Glomerular structure Fig. 24-8b, Martini • glomerular filtration – capsular hydrostatic pressure (CsHP) • force working against glomerular filtration pressure – averages about 15 mm Hg – net hydrostatic pressure (NHP): net • GFP – CsHP = NHP GFP • (45 to 55)-15 = 30 to 40 mm Hg – blood colloidal osmotic pressure (BCOP) blood • force that opposes hydrostatic pressure force opposes • ________ mm Hg • glomerular filtration – net filtration pressure (FP) • • • FP = NHP – BCOP FP = ____ mm Hg – ___ mm Hg = ____ mm Hg force acting to move filtrate out of plasma – glomerular filtration rate (GFR) • ~125 ml/min • ~180 liters/day (__________) – 70 times plasma volume in body • 99 % is reabsorbed – this is the main function of the kidney!!! Fig. 24-10b, Martini Urine formation Urine reabsorption (secretion) • utilizes trans-epithelial transport • a step-wise movement of solutes across cells 1) from tubule lumen to tubule cell • apical end of tubule cell apical end 2) from tubule cell to peritubular fluid (ECF) • basolateral_ surface of tubule cell basolateral_ surface • then entry into blood stream can occur – water, ions, organic compounds » osmosis and diffusion proximal convoluted tubule (Fig. 24-12) • reabsorption of organic nutrients – facilitated transport and co-transport mechanisms – from tubular fluid, co-transport with Na+ in fluid • glucose transporter • reabsorption of ions – co-transporters, channels, exchange transporters at co-transporters, apical surface apical • Na+, HCO3, Cl• Na+ reabsorption increased by angiotensin II – Na+/K+ exchange pumps, co-transporters transport material into peritubular space (ECF) material proximal convoluted tubule (Fig. 24-12) • water reabsorption – as osmolarity of tubule fluid decreases, water as flows into tubule cell flows – 108 liters/day (of the 180 liters filtrate/day) here • passive reabsorption of ions – assuming the ions are permeable, they diffuse assuming down their concentration gradient down • secretion – at this point, H+ secreted • aids in Na+ reabsorption Fig. 24-12, Martini proximal convoluted tubule (PCT) reabsorption mechanisms organic compounds ions CO2 secretion mechanisms H+ Loop of Henle: Descending Limb Loop (Fig. 24-13b) – PERMEABLE to water • reabsorption of H2O • ~45 liters reabsorbed/day ~45 – IMPERMEABLE to solutes • deeper into medulla, peritubular osmolarity increases • as filtrate moves downward, more water is removed – Why does the peritubular osmolarity increase? Fig. 24-13b, Martini Martini Loop of Henle Loop processes: processes: descending limb ascending limb Loop of Henle: Ascending Limb Loop Ascending (Fig. 24-13a, b) – IMPERMEABLE_ to water – transport of Na+ and Cl- into peritubular space • Na+, K+/2Cl- carrier at apical surface • K+-Cl cotransport and Na+-K+ exchange pump at basolateral surface basolateral • removes 2/3 of all Na+ and Cl- from filtrate • Primary transport – no net loss of K+ from lumen – more ions removed at beginning of ascending limb • cause of osmotic gradient in medulla • contributes ~750 mOsm/liter to the medullary osmotic contributes gradient gradient Ascending Limb, Loop of Henle: Ascending processes for reabsorption (Na+, Cl-) processes Fig. 24-13a, Martini • What else contributes to the osmolarity increase in What the renal medulla? the – papillary duct is permeable to urea – urea contributes ~450 mOsm/liter to the medullary osmotic gradient osmotic – Fig. 24-13c • What keeps the osmotic gradient constant? – removal of water and ions by the _vasa recta_ • transport solutes/ water from peritubular fluid to blood transport vessel vessel • removal of solutes/ water from kidney via circulatory removal system system – Fig. 24-16 Fig. 24-13c, Martini Martini Permeability of nephron to urea and water Role of papillary duct in maintenance of renal medullary osmotic values Fig. 24-16, Martini role of Vasa Recta in maintaining osmotic gradient in renal medulla movement of H2O and solutes into circulatory system distal convoluted tubule distal • Reabsorption processes – Na and Cl • Na+: Na+-K+ exchange pump • enhanced by presence of aldosterone – steroid hormone: typically slow-acting – increases number of Na+ channels and Na+/K+ pumps pumps – reduces the amount of Na+ ions lost in urine – Ca • primary site for Ca++ reabsorption • reabsorption stimulated by parathyroid hormone, reabsorption stimulating calcitriol synthesis by kidneys stimulating Fig. 24-14a, Martini Distal convoluted tubule, proximal region Na+,Cl- reabsorption Ca++ reabsorption K+ secretion distal convoluted tubule distal region aldosterone sensitive Na+ absorption K+ secretion with prolonged aldosterone release, excess K+ is lost, causing condition of too low [K+] Fig. 24-14b, Martini distal convoluted tubule • secretion – creatinine, drugs, toxins • performed using carrier-mediated transport – hydrogen ions • Na+-H+ exchange pump (H+) • HCO3--Cl- exchange pump (HCO3-) – HCO3- produced from carbonic anhydrase activity – transported from tubule cells – absorbed into blood (buffer) • Overall effect: Na+ absorbed for each H+ secreted distal convoluted tubule distal • secretion – K ions • Na+-K+ exchange pump removes K+ from peritubular fluid peritubular – at the basolateral surface of tubule cell • K+ lost through channels on apical surface Fig. 24-14c, Martini • collecting tubule – “collecting duct” • reabsorption – Na+, H2O, HCO3- • secretion – H+, Cl-, NH4+ collecting tubule collecting (“collecting duct”) • reabsorption – – – aldosterone sensitive Na+-K+ exchange pump bicarbonate reabsorption urea • passive reabsorption in papillary duct – water • secretion – H+, Cl-, NH4+ • water reabsorption/secretion (Fig. 24-15, 16) – _obligatory_ water reabsorption • • • proximal tubule, descending loop of Henle 85% water reabsorbed (~_153 liters/day) cannot adjust this level of reabsorption – driven by osmosis only driven osmosis Fig. 24-15a, Martini Obligatory water reabsorption • water reabsorption/secretion (Fig. 24-15, 16) – Faculative water reabsorption Faculative water • • • ~_27 liters can be reabsorbed/day distal convoluted tubule and collecting tubule regulated by antidiuretic hormone (ADH) – induces expression of aquaporin-2 (water induces channels), which makes the nephron tubules more water permeable more Fig. 24-15b, Fig. Martini Martini ________________ water reabsorption • method of ADH induction of aquaporin-2 – receptor-mediated hormonal signaling (ADH) Silverthorn, Fig. 19-6 • How are ADH levels and reabsorption levels How controlled? controlled? – renin-angiotensin pathway (Na & H O) renin-angiotensin (Na • stimulated by decreases in blood pressure – juxtaglomerular cells respond – aldosterone pathway (Na ) aldosterone (Na • steroid hormone • released by adrenal glands when: – stimulated by high [K+] » depolarizes cells, causes release – angiotensin II present Renin acts to convert angiotensinogen to angiotensin I (Silverthorn, Fig. 19-13) Regulation of GFR Regulation 1) autoregulation – – stabilizes GFR when BP changes abruptly ____________ in BP causes: ____________ • • • – dilation of afferent arteriole dilation of glomerular capillaries constriction of efferent arteriole ___________ in BP causes opposite effect: • constriction of afferent arteriole – these changes keep GFR constant Regulation of GFR Regulation 1) hormonal regulation a) renin-angiotensin system renin-angiotensin • • renin released from juxtaglomerular apparatus due to: – low blood flow – osmotic concentration of distal tubule fluid too low stimulation of renin-angiotensin pathway then causes : – general vasoconstriction of arterioles secretion of aldosterone: causes ↑ Na reabsorption secretion Fig. 24-11, Martini Regulation of GFR Regulation 1) hormonal regulation a) atrial natriuretic peptide • • • • increase blood volume/pressure causes production – produced in response to chronic stretching of the produced right atrium right ______________ of afferent arteriole constriction of efferent arteriole – ______ GFR, ↑ urine production ______ overall effect is to ___________ GFR and reduce overall GFR blood volume blood ...
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