BIOL 320 1st Edition Lecture 21 Outline of Last Lecture I Metabolic Hormones II Insulin Effects III Nutrient Timing IV Developmental Aspects I Urinary System Outline of Current Lecture V Juxtaglomerular Apparatus VI Blood Pressure Renal Circulation VII Filtration Membrane VIII Mechanisms of Urine Formation IX Glomerular Filtration X Glomerular Filtration Rate XI Intrinsic Controls of GFR XII Extrinsic Controls of GFR XIII Other Factor Affecting GFR XIV Tubular Reabsorption XV Sympathetic Nervous System XVI Tubular Secretion XVII Ureters XVIII Urinary Bladder Current Lecture Juxtaglomerular Apparatus Three Types of Cells o JG cells granular cells within granules is renin act as mechanoreceptors o Macula densa act as chemoreceptors respond to sodium chloride levels o Mesangial cells interconnected with gap junctions may pass signals between macula densa JG cells granular cells Blood Pressure Renal Circulation Blood pressure decline along renal circulation Relatively high in glomerulus Strong outward force pushing fluid out of capillaries in glomerulus Filtration Membrane porous membrane between blood filtrate Filter between blood interior glomerular capsule 1 Glomerular capillaries have fenestrated epithelium too small for RBCs 2 Visceral membrane of capsule has foot processes podocytes with slits 3 Gel like basement membrane repels negatively charged particles Mechanisms of Urine Formation The kidneys filter the body s entire plasma volume 60 x day The filtrate contains all plasma components except proteins and RBCs To become urine the filtrate loses keepers water nutrients essential ions Urine contains metabolized waste unneeded substances Urine formation blood composition adjustment 1 Glomerular filtration 2 Tubular reabsorption keepers removed from filtrate 3 Tubular secretion waste filtrate Glomerular Filtration Glomerular filtration is very efficient because of 1 Fenestrations in the capillary wall permeable membrane large surface area 2 Glomerular blood pressure is high relatively 3 High net filtration pressure Net Filtration Pressure NFP pressure responsible for filtrate formation NFP HP g OP g HP c o HP g glomerular hydrostatic pressure o OP g osmotic pressure of glomerular blood o HP c capsular hydrostatic pressure Glomerular Filtration Rate GFR Definition mL min of filtrate formed two types of controls intrinsic extrinsic Factors governing GFR related to glomerular BP 1 Total surface area of filter 2 Filter membrane permeability 3 Net filtration pressure If GFR is too high needed substances can t be reabsorbed are lost into urine If GFR is too low all is reabsorbed including wastes Three regulatory mechanisms 1 Renal autoregulation intrinsic 2 Neural controls extrinsic 3 Hormonal mechanism renin angiotensin mechanism Intrinsic Controls of GFR Under normal conditions renal autoregulation maintains a nearly constant GFR when MAP is 80 180mmHg Two types of control 1 Myogenic control o If elevated blood pressure afferent arteriole constricts maintains normal GFR protects glomeruli from high systemic blood pressure o If low blood pressure afferent arteriole vasodilate maintains normal GFR 2 Flow dependent tubuloglomerular feedback directed by macula densa cells o If GFR increased filtrate concentration of sodium chloride is high because no time for reabsorption macula densa cells respond to increased sodium by releasing vasoactive chemicals vasoconstriction of afferent arteriole o If GFR decreased opposite happens Extrinsic Controls of GFR Under resting conditions 1 Renal blood vessels maximally dilated 2 Intrinsic controls in charge Under extreme stress epinephrine norepinephrine by S ANS constrict afferent arteriole inhibits filtration triggers renin angiotensin mechanism Other Factors Affecting GFR Prostaglandins vasodilators counteract vasoconstriction by norepinephrine prevent renal damage when increase in systemic resistance Intrarenal angiotensin II reinforces angiotensin II Adenosine vasoconstrictor Tubular Reabsorption Definition process of selectively reclaiming desirable substances Details we produce 180 L day of filtrate but only 1 5 L of urine Main site PCT Transported substances move through three membranes Substances reabsorbed o Ions o All organic nutrients o Water Water ion reabsorption is hormonally regulated Reabsorption o Sodium reabsorption is always active sodium transport drive reabsorption of other solutes water Sympathetic Nervous System During extreme stress epinephrine norepinephrine activates vasoconstriction of afferent arteriole Diverts blood away from kidney temporarily Also activates the renin angiotensin system Tubular Secretion substances move from peritubular capillaries into tubules Important for eliminating undesirable substances ridding body of excess potassium ions controlling pH of blood dispose of substances bound to big proteins didn t go through to filtrate getting rid of substances not already in filtrate Ureters Entry to bladder base of bladder through posterior wall As bladder pressure increases distal ends close preventing back flow Tri layered wall 1 Transitional epithelium 2 Smooth muscle 3 Fibrous connective tissue Propulsion active responds to stretch by contracting Urinary Bladder Normally holds about 500mL Retroperitoneal Three openings one for each ureter for the urethra Trigone between three areas site of most infections Layers o Mucosa transitional epithelium o Muscularis longitudinal circular detrusor oblique muscle compresses o Adventitia