BSC2086 A P II Final Exam Study Guide Lesson 20 Lesson 20 The Urinary System Part II Renal Physiology Goal of urine production maintain homeostasis Regulates volume composition of blood o Concentrates filtrate produced by glomerular filtration Failure fatal dehydration lose too much H2O o Absorbs retains valuable materials for use by other tissues Ex glucose amino acids etc o Excretes metabolic waste products Organic wastes dissolved in blood Ex Urea creatinine uric acid Kidneys usually produce concentrated urine o 1 200 1 400 mOsm L 4x plasma concentration o Ways of Expressing Osmotic Concentration Osmolarity Total number of solute particles per liter Expressed in osmoles per liter Osm L milliosmoles per liter mOsm L Body fluids have osmotic concentration of 300 mOsm L Concentrations of large organic molecules Grams or milligrams per unit of volume of solution Aldosterone and ADH o mg dL o g dL Urine osmolarity can be increased by the secretion of aldosterone ADH Aldosterone Increases number of Na K exchange pumps at DCT collecting duct to absorb Na in exchange for K o H2O is reabsorbed by osmosis follows Na ADH increases water channels aquaporins in apical cell membranes of DCT collecting duct o Concentrates 100 mOsm L tubular fluid arriving at DCT to 1 200 mOsm L when it reaches the minor calyx Without ADH o Water is NOT reabsorbed all fluid reaching DCT is lost in urine o Produces large amounts of dilute urine 30 400 mOsm L 24L day seen in diabetes insipidus o Posterior pituitary normally is continuously secreting low levels of ADH DCT collecting system are always permeable to water Collecting system reabsorbs 16 8 L day 9 3 of filtrate Produces 1 200 mL per day 0 6 of filtrate of urine 800 1 000 mOsm L 1 BSC2086 A P II Final Exam Study Guide Lesson 20 Glomerular Filtration Filtration Pressures glomerular filtration is governed by the balance between o Hydrostatic pressure fluid pressure o Colloid osmotic pressure of materials in solution on either side of Hydrostatic Pressure Glomerular hydrostatic pressure is blood pressure in capillary walls glomerular capillaries o Tends to push water solute molecules out of plasma and into filtrate o Is significantly higher than capillary pressures in systemic circuit Higher pressure due to arrangement of vessels at glomerulus 2 BSC2086 A P II Final Exam Study Guide Lesson 20 Blood leaving glomerular capillaries flows into an efferent arteriole with a diameter smaller than afferent arteriole Efferent arteriole produces resistance o Requires relatively high pressures to force blood into it Capsular Hydrostatic Pressure CsHP Opposes glomerular hydrostatic pressure o Pushes water solutes out of filtrate and into plasma o Results from resistance to flow along nephron conducting system o Averages 15 mmHg Net Hydrostatic Pressure NHP The difference between glomerular hydrostatic pressure and capsular hydrostatic pressure Colloid Osmotic Pressure Osmotic pressure resulting from the presence of suspended proteins o Blood Colloid Osmotic Pressure BCOP Tends to draw water out of filtrate and into plasma Opposes filtration Averages 25 mmHg Net Filtration Pressure NFP Average pressure forcing water and dissolved materials out of glomerular capillaries and into capsular space o At the glomerulus it is the difference between Hydrostatic pressure blood colloid osmotic pressure across glomerular capillaries NFP GHP CsHP BCOP Should NEVER be negative Negative means kidneys are absorbing water from filtrate If zero no filtration is occurring Glomerular Filtration Rate GFR Amount of filtrate kidneys produce each minute o 10 of fluid delivered to kidneys 3 BSC2086 A P II Final Exam Study Guide Lesson 20 Leaves bloodstream enters capsular spaces Averages 125 mL min at each kidney o Glomeruli generate about 180 liters 48 gallons of filtrate per day 99 is reabsorbed in renal tubules o Control of the GFR three 3 interacting levels of control Autoregulation local level Maintains GFR despite changes in local blood pressure blood flow Changes diameters of afferent arterioles efferent arterioles glomerular capillaries Reduced blood flow glomerular blood pressure triggers o Dilation of glomerular capillaries afferent arteriole o Constriction of efferent arterioles Rise in renal blood pressure o Stretches walls of afferent arterioles o Causes smooth muscle cells to contract o Causes constriction of afferent arterioles keeps GFR at normal rate o Rise in renal blood pressure stretches walls of afferent arterioles contraction of smooth muscle cells constriction of afferent arterioles Hormonal Regulation initiated by kidneys Renin Angiotensin System o Constricts efferent arteriole increasing GFP o Stimulates Aldosterone adrenal cortex ADH posterior pituitary secretion Na H2O reabsorption Increases thirst Increase sympathetic motor tone cardiac output o o o Vasoconstriction of arterioles precapillary sphincters 4 BSC2086 A P II Final Exam Study Guide Lesson 20 Natriuretic Peptides ANP BNP o Dilate afferent arteriole constricts efferent arteriole o to increase GFP GFR Increase urine production to lower blood volume pressure Autonomic Regulation by sympathetic division of ANS Mostly consists of sympathetic postganglionic fibers Sympathetic activation o Constricts afferent arterioles o Decreases GFR slows filtrate production Changes in blood flow to kidneys due to sympathetic stimulation o May be opposed by autoregulation at local level Reabsorption and Secretion Control of blood pH important to homeostasis o By H removal bicarbonate production at kidneys Acidosis Abnormally low acidic blood pH o Lactic Acidosis Develops after exhaustive muscle activity o Ketoacidosis Develops in starvation from breakdown of lipids or amino acids or diabetes mellitus Alkalosis Abnormally high basic blood pH o Can be caused by prolonged aldosterone stimulation Stimulates secretion of H and loss of H in urine 5 BSC2086 A P II Final Exam Study Guide Lesson 20 The Vasa Recta o Formed from peritubular capillaries of juxtamedullary nephrons o Functions to Return solutes water reabsorbed in medulla to general circulation without disrupting the concentration gradient Some solutes absorbed in descending portion do not diffuse out in ascending portion More water moves into ascending portion than is moved out of descending portion Carries both H2O solute out of medulla Urine Transport Storage and Elimination Take place in the urinary tract o Ureters o Urinary bladder o Urethra Transitional Epithelium
View Full Document
Unlocking...