Chapter 19 The Kidneys

Chapter 19 The Kidneys - Ch 19: The Kidneys Ch Homeostatic...

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Unformatted text preview: Ch 19: The Kidneys Ch Homeostatic regulation of ECF volume and BP Osmolarity 290 mOsm Ion balance Na+ and K+, etc. pH (acid-base balance (acid-base Excretion of wastes & foreign substances Hormone production EPO Renin Functional unit of kidneys: ?? Five Processes of Urinary System Five 1. 2. 2. 3. 3. 4. 4. 5. Filtration, Filtration, Reabsorption, Reabsorption, Secretion, Secretion, Excretion Micturition Related by equation: E=F-R+S 180 L / day filtered, >99% 180 reabsorbed, 1.5 L/day excreted 1.5 Figs 19-2/3 1) Filtration 1) = Movement of fluid from blood Movement to lumen of nephron (rel. nonspecific process) nonspecific Once in lumen – consider it Once outside body outside Composition of filtrate? Fig 19-4 1) Filtration, cont’d: Passage across 3 Barriers Barriers 1. Capillary endothelium Capillary is fenestrated is 2. Basal lamina Basal 1. 1. 3. Filters proteins Bowman’s capsule Bowman’s epithelium (visceral layer), including podocytes including Some small molecules Some (Ca2+, low m.w. fatty acids) (Ca low bind to plasma proteins ⇒ ? Fig 19-4 Cause of Filtration Cause Fig 19-6 Three types of pressures are at work: Hydrostatic pressure in capillaries Hydrostatic (see exchange in tissues) (see Osm. Pcapillaries > Osm. P Bowman’s capillaries capsule capsule Hydrostatic fluid P from presence Hydrostatic of fluid in Bowman’s capsule of Net (?) driving pressure: ~ 10 mmHg Net driving GFR = Glomerular Filtration Rate GFR Glomerular Describes filtration efficiency: Amount Describes of fluid filtered per unit of time of Fig 19-5 Average GFR ~ 180 L/day! Filtration Coefficient is influenced by Net filtration pressure Available surface area of glomerular Available capillaries capillaries GFR is closely regulated to remain GFR constant over range of BPs (80 - 180 mm Hg) (80 Goal is to control blood flow though Goal both afferent and efferent arterioles efferent – via ? via Regulation of GFR Regulation Several mechanisms provide Several close control of GFR; Filtration Pressure (BP) Hydrostatic, colloid Resistance in afferent vs. Resistance efferent arterioles efferent Tubuloglomerular feedback JG Apparatus Hormones and ANS Angiotensin II Angiotensin (vasoconstrictor) (vasoconstrictor) Prostaglandins (vasodilator) Regulation of GFR via Tubuloglomerular Feedback Tubuloglomerular As GFR ↑, flow through DCT ↑ flow Macula densa cells: Macula release paracrines release juxtaglomerular cells (smooth muscle fibers from afferent arteriole): contract afferent Thus GFR ↓ Thus Fig 19-10 2) Tubular Reabsorption (99% of filtrate) (99% 2) Highly selective and variable and Amount of filtrate / day? Amount Urine production / day? Urine % reabsorbed? Mostly transepithelial transport Mostly (examples: Sodium and glucose) (examples: Reabsorption may be active (Na+, glucose) or passive (urea) glucose) Figs 19-12/13 Fig 19-5 2) Tubular Reabsorption (99% of filtrate) (99% May be active Na+ transport Recall Antiports and Symports Symports or Passive (think concentration or and osmotic gradients) and Paracellular Paracellular E.g., urea Transcytosis Proteins Fig 19-11 Na+ Reabsorption in Na PCT: Transepithelial PCT: Transport Transport Apical: Leak Apical channels for Na+. Movement down conc. gradient. Fig 19-12 Basolateral: Na+/K+ ATPase. Na+ Linked Glucose Reabsorption Reabsorption Apical: Na+-glucose cotransport Fig 19-13 Basolateral: Glucose diffusion down conc. gradient Passive Urea Reabsorption Na+ actively reabsorbed H2O follows passively ↑ [urea] ⇒ passive reabsorption (diffusion into blood) Saturation of Renal Transport Saturation Saturation = Maximum rate of transport (tm) Same 3 characteristics as Same discussed in mediated mediated transport transport Transport maximum determined by by Saturation → Renal Threshold Threshold Specificity Competition Competition (Fig 19-15d) 3) Secretion 3) 2nd route of entry (from ECF) into tubules for selected molecules selected Mostly transepithelial transport (analogous to Mostly reabsorption). Depends mostly on active membrane reabsorption). transport systems Provides mechanism for rapid removal of substances (most important for H+, K+, foreign organic ions (most foreign and drugs such as penicillin etc.) and 4) Excretion = Urine Output 4) Excretion of excess ions, H2O, toxins, “foreign O, molecules” “nitrogenous waste” (NH4+ , urea) molecules” urea) Depends on Filtration, Reabsorption, Secretion E=F–R+S Direct measurement of F, R, S impossible infer from comparison of blood & urinalysis infer For any substance: (Renal) Clearance = (Renal) plasma volume completely cleared of that substance per minute Typically expressed as ml/min Clinical Importance of GFR and Clearance Clearance GFR is indicator for overall kidney function Clearance → non-invasive way to measure GFR Inulin (research use) Neither secreted nor reabsorbed Creatinine (clinically useful) If a substance is filtered and reabsorbed but not If secreted ⇒ clearance rate < GFR If a substance is filtered and secreted but not reabsorbed ⇒ clearance rate > GFR 5. Micturition Spinal cord integration: 2 Spinal simultaneous efferent signals simultaneous In infant just simple spinal reflex Later: learned reflex under conscious Later: control from higher brain centers control Various subconscious factors affect Various reflex reflex Fig 19-18 Renal Failure & Artificial Kidney Renal Symptoms when < 25% Symptoms functional nephrons functional due to: 1. Kidney infections 2. Chemical poisoning (lead, paintthinner) etc. Hemodialysis: 3/week 4-8h/session Alternative: CAPD Alternative: Continuous Ambulatory Peritoneal Dialysis Manneken Pis in Brussels ...
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This note was uploaded on 12/24/2011 for the course STEP 1 taught by Professor Dr.aslam during the Fall '11 term at Montgomery College.

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