Anatomy lecture notes 4

Anatomy lecture notes 4 - Organs of the urinary system s: 2...

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Organs of the urinary systems: 2 kidneys NEED INFO!! Nephron ( fig 25.4 25.5) - Functional unit of kidney - 1 million per kidney - 2 parts: renal component vascular 3 major processes in urine formation 1.)glomerular filtration 2.) tubular reabsorption 3.)Tubular secretion I. Glomerular filtration: - passive, non-selective, based on pressure differences on either side of filtration membrane ( basis = size) - junction of glomerular capillaries walls and visceral layer of capsule - blood pressure in glomerular capillaries is higher than in ordinary capillaries - Glomerular capillaries are also about 1000x more permeable to H2) and solutes Blood enters glomerules bp forces it through filtration membrane what gets through: filtrate Filtrate: blood plasma minus formed elements and most proteins; - Water, glucose, vitamins, amino acuds, very small proteins, N2 wastes, ions Glomercular filtration rate (GFR) – amount filtered from the blood per capsule / per minute - Main force responsible: glomerular hydrostatic - (B.P.) pressure ( 55 mm Hg) – pushes fluid out of blood into capsule Opposing forces: (pulls fluid into capillaries) Glomerular osmotic pressure (-30mmHg) capsular hydrostatic pressure 15mm Hg) 55 mm Hg – (30 + 15 mmHg) = *10 mm Hg *****net filtration pressure Seems small, but adequate due to high permeability of glomerular capillaries However, a 15% drop in blood pressure stops filtration
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Increased blood pressure = increase GFR Dehydration = increased glom erular osomotic pressure = decreased GFR II.) Tubular a bsorption: begins as soon as filtrate enters the proximal convoluted tubule ( PCT) - (Recover about 60% of volume) - Reclamation of nutrients, water , ions - (both active and passive means) Na + , glucose, a.a, vitamins, K + , Mg ++ , Ca ++ - active transport Cl - , HCO 3 - , urea (some ) – passive transport (solvent drag) Water – osmosis Less absorbed – urea (50%) creatinine uric acid III.) Tubular secretion: materials added to filtrate from blood for removal - Dispose of substances not already part of filtrate (eg. Drugs) - Eliminate undesirable reabsorbed substances - Eliminate excessive K + **********controls blood Ph - (secrete more H+ into filtrate when blood pH is low) and r eabsorb more HCO 3 - - Secrete more HCO 3 - into filtrate if blood pH increases - Retain Cl - to balance less of (-) ions Control = renal autoregulation ( Kidneys control its own blood flow) - GFR – could increase 30% without compromising function - If to low inadequate filtration - Problem: most H 2 O reabsorbed (including wastes and toxins) Mechanisms: 1.) Myogenic mechanism ( smooth muscle contracts when stretched) a. Increased blood pressure (systemic) = increased constriction of afferent arterioles ( restricts blood flow to nephron) b. Decreased blood pressure – dilation of afferent arteriole, glomerules gets more blood 2.) Tubuloglomerular feedback a. *****juxtaglomerular apparatus (JGA)
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b. ***** Place where walls of afferent arterioles contact the wall
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This note was uploaded on 06/17/2011 for the course BIOLOGY 2401 taught by Professor Shannon during the Spring '10 term at Lone Star College.

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Anatomy lecture notes 4 - Organs of the urinary system s: 2...

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