1224_Day22_Lecture - The Urinary System Functions of the...

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Unformatted text preview: The Urinary System Functions of the Kidneys Homeostasis – Volume and composition Processes: – Filtering blood plasma – Blood volume, BP, and osmotic concentration regulation – Secreting renin – Secreting erythropoietin – Synthesizing calcitrol – Excretion Anatomy of Kidney Nephron Functional unit Renal corpuscle Glomerulus Glomerular capsule Renal tubule PCT Nephron loop DCT Collecting duct Types – Cortical vs. Juxtamedullary Steps of Urine Formation Glomerular Filtration – Makes “filtrate” Tubular Reabsorption Tubular Secretion Water Conservation Glomerular Filtration Hydrostatic pressure Filtration membrane – Capillary endothelium Fenestrated – Basement membrane Negatively charged gel Filtration Slits – Podocytes Foot processes – Negatively charged Filtration Pressure NFP = BHP - (COP + CP) Glomerular Hydrostatic Pressure Capsular Hydrostatic Pressure Colloid Osmotic Pressure – Proteins within blood Capsular Osmotic Pressure – Essentially is 0 mmHg Unless kidney disease Glomerular Filtration Rate Glomerular filtration rate (GFR) – Amount of filtrate per minute by kidneys Males: 125 mL/min (180 L/day) Females: 105 mL/min (151 L/day) – Only 1-2 liters per day of urine output Regulation of GFR If – – – – If GFR too high: Fluid too rapid Urine output rises Dehydration Electrolyte depletion GFR too low: – Fluid too slow – Reabsorb wastes Homeostatic Mechanisms Blood flow adjusted by changes in glomerular BP Mechanisms – Renal autoregulation Kidneys alter GFR despite high arterial BP – Sympathetic Control SNS – Renin-angiotensin mechanism Renal Autoregulation Regulation arterioles of afferent/efferent – Myogenic Mechanism Pressure ∆ in renal blood vessels Smooth muscle contracts when stretched ↑ BP stretches AA Constricts AA ↓ blood flow Renal Autoregulation Tubuloglomerular Feedback Juxtaglomerular Apparatus (JGA) Juxtaglomerular (JG) cells – Macula Densa cells – Mesangial Cells Juxtaglomerular Apparatus Macula Densa – Flow or fluid composition – Secrete messenger to stimulate JGC JG cells – Constrict or dilate afferent arteriole – Secrete renin Mesangial cells – Chemo/mechanorecepto r – Communication between MD and JGC Sympathetic Control Sympathetic NS – Constrict afferent arterioles Adrenal epinephrine – Constrict afferent arterioles Strenuous exercise or circulatory shock – Shunts blood away from kidneys – Indirectly triggers renin-angiotensin mechanism Stimulating the macula densa cells – SNS directly stimulates JG cells to release renin Renin-Angiotensin Mechanism Systemic BP and ECF volume Renin released – Angiotensin I made Converted to Angiotensin II Angiotensin Converting Enzyme (ACE) Angiotensin II vasoconstricts – – – – Increases MAP Constricts AA and EA Stimulates aldosterone Stimulates ADH ...
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  • Spring '17
  • Kidney anatomy, Nephron, macula densa, macula densa cells

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