BSC 2086 01 Anatomy and Physiology II Spring 2013 20 The Urinary System Part 2 2012 Pearson Education Inc An Introduction to the Urinary System Learning Outcomes 26 3 Describe the basic processes responsible for urine formation 26 4 Describe the factors that influence glomerular filtration pressure and the rate of filtrate formation 26 5 Identify the types and functions of transport mechanisms found along each segment nephron and describe hormonal the volume and concentration of of the influence on urine 2012 Pearson Education Inc An Introduction to the Urinary System Learning Outcomes 26 6 Describe the structures and functions of the ureters urinary bladder and urethra discuss the voluntary and involuntary regulation of urination and describe the micturition reflex 26 7 Describe the effects of aging on the urinary system 2012 Pearson Education Inc 26 3 Renal Physiology The Goal of Urine Production Maintain homeostasis By regulating volume and composition of blood Concentrates filtrate produced by glomerular filtration Failure leads to fatal dehydration lose too much H2O Absorbs and retains valuable materials for use by other tissues Ex glucose amino acids etc Including excretion of metabolic waste products Organic wastes such as urea creatinine uric acid that are dissolved in blood 2012 Pearson Education Inc 26 3 Renal Physiology The Kidneys Usually produce concentrated urine 1200 1400 mOsm L four times plasma concentration Ways of Expressing Osmotic Concentration Osmolarity Total number of solute particles per liter Expressed in osmoles per liter Osm L or milliosmoles per liter mOsm L mOsm L Body fluids have osmotic concentration of about 300 Concentrations of large organic molecules Grams or milligrams per unit volume of solution mg dL 2012 Pearson Education Inc or g dL 26 5 Aldosterone and ADH Urine osmolarity can be increased by the secretion of aldosterone and ADH 1 Aldosterone increases number of Na K exchange pump at DCT and collecting duct to reabsorb Na in exchange for K H2O is reabsorbed by osmosis 2 ADH increases water channels aquaporins in apical cell membranes of DCT and collecting duct 1 Concentrates 100 mOsm L tubular fluid arriving at DCT to be concentrated to 1200 mOsm L when it reaches the minor calyx 2012 Pearson Education Inc 26 5 Reabsorption and Secretion Without ADH urine Water is not reabsorbed all fluid reaching DCT is lost in Produces large amounts of dilute 30 400 mOsm L urine 24 L day seen in diabetes insipidus Note post pit normally is continuously secreting low levels of ADH DCT and collecting system are always permeable to water Collecting system reabsorbs 16 8 L day 9 3 of filtrate produces 1200 mL per day 0 6 of filtrate of urine 800 1000 mOsm L 2012 Pearson Education Inc Figure 26 15a The Effects of ADH on the DCT and Collecting Duct Renal cortex PCT DCT Glomerulus KEY Na Cl transport Antidiuretic hormone Water reabsorption Variable water reabsorption Solutes Collecting duct Large volume of dilute urine Renal medulla Tubule permeabilities and the osmotic concentration of urine in the absence of ADH 2012 Pearson Education Inc Figure 26 15b The Effects of ADH on the DCT and Collecting Duct Renal cortex KEY Na Cl transport Antidiuretic hormone Water reabsorption Variable water reabsorption Renal medulla Tubule permeabilities and the osmotic concentration of urine in the presence of ADH 2012 Pearson Education Inc Small volume of concentrated urine Table 26 3 Tubular Reabsorption and Secretion 2012 Pearson Education Inc Table 26 4 Renal Structures and Their Function 2012 Pearson Education Inc Table 26 4 Renal Structures and Their Function 2012 Pearson Education Inc 26 4 Glomerular Filtration Filtration Pressures Glomerular filtration is governed by the balance between Hydrostatic pressure fluid pressure Colloid osmotic pressure of materials in solution on either side of capillary walls Remember the lesson on filtration at a capillary 2012 Pearson Education Inc 26 4 Glomerular Filtration Hydrostatic Pressure Glomerular hydrostatic pressure is blood pressure in glomerular capillaries Tends to push water and solute molecules Out of plasma and into the filtrate Is significantly higher than capillary pressures in systemic circuit Due to arrangement of vessels at glomerulus Blood leaving glomerular capillaries flows into an efferent arteriole with a diameter smaller than afferent arteriole Efferent arteriole produces resistance requires relatively high pressures to force blood into it 2012 Pearson Education Inc 26 4 Glomerular Filtration Capsular Hydrostatic Pressure CsHP Opposes glomerular hydrostatic pressure Pushes water and solutes Out of filtrate Into plasma Results from resistance to flow along nephron and conducting system Averages about 15 mm Hg 2012 Pearson Education Inc 26 4 Glomerular Filtration Net Hydrostatic Pressure NHP Is the difference between glomerular hydrostatic pressure and capsular hydrostatic pressure Colloid Osmotic Pressure Is the osmotic pressure resulting from the presence of suspended proteins Blood colloid osmotic pressure BCOP Tends to draw water out of filtrate and into plasma Opposes filtration Averages 25 mm Hg 2012 Pearson Education Inc 26 4 Glomerular Filtration Net Filtration Pressure NFP average pressure forcing water and dissolved materials Out of glomerular capillaries Into capsular space At the glomerulus it is the difference between Hydrostatic pressure and blood colloid osmotic pressure across glomerular capillaries NFP GHP CsHP BCOP should never be negative but if zero then no filtration occurring If negative that would mean urine was being pumped back into the capillaries 2012 Pearson Education Inc Figure 26 10b Glomerular Filtration Factors Controlling Glomerular Filtration Glomerular hydrostatic pressure GHP Filtrate in capsular space Plasma proteins Solutes Blood colloid osmotic pressure BCOP 50 25 15 10 mm Hg Net filtration pressure NFP Capsular hydrostatic pressure CsHP Capsular colloid osmotic pressure Net filtration pressure 2012 Pearson Education Inc 26 4 Glomerular Filtration The Glomerular Filtration Rate GFR amount of filtrate kidneys produce each minute About 10 of fluid delivered to kidneys Leaves bloodstream Enters capsular spaces Averages 125 mL min at each kidney Glomeruli generate about 180 liters 48 gallons of filtrate per day 99 is reabsorbed in renal tubules 2012 Pearson Education Inc 26 4 Glomerular Filtration Control of the GFR Three interacting levels of control 1 Autoregulation local
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