BIOL 320 1st Edition Lecture 21Outline of Last Lecture I. Metabolic HormonesII. Insulin EffectsIII. Nutrient TimingIV. Developmental AspectsI. Urinary SystemOutline of Current Lecture V. Juxtaglomerular ApparatusVI. Blood Pressure & Renal CirculationVII. Filtration MembraneVIII. Mechanisms of Urine FormationIX. Glomerular FiltrationX. Glomerular Filtration RateXI. Intrinsic Controls of GFRXII. Extrinsic Controls of GFRXIII. Other Factor Affecting GFRXIV. Tubular ReabsorptionXV. Sympathetic Nervous SystemXVI. Tubular SecretionXVII. UretersXVIII. Urinary BladderCurrent LectureJuxtaglomerular Apparatus- Three Types of Cells:o -JG cells: granular cells; within granules is renin; act as mechanoreceptorso -Macula densa: act as chemoreceptors; respond to sodium chloride levelso -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 glomerulusFiltration 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 slits3. 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 filtration2. 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 area2. 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 pressureo --OP[g] = osmotic pressure of glomerular bloodo --HP[c] = capsular hydrostatic pressureGlomerular 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 filter2. Filter membrane permeability3. 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 cellso --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 arterioleo --If GFR decreased, opposite happensExtrinsic Controls of GFR- -Under resting conditions:1. Renal blood vessels maximally dilated2. Intrinsic controls in charge- -Under extreme stress: epinephrine & norepinephrine by S-ANS --> constrict afferent arteriole --> inhibits filtration --> triggers renin-angiotensin mechanismOther Factors Affecting GFR:- -Prostaglandins: vasodilators; counteract vasoconstriction by norepinephrine; prevent renal damage when increase in systemic resistance- -Intrarenal angiotensin II: reinforces angiotensin II- -Adenosine: vasoconstrictorTubular 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 --Ionso --All organic nutrientso --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 systemTubular 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 filtrateUreters- -Entry to bladder: base of bladder through posterior wall- -As bladder pressure increases: distal ends close, preventing back flow- -Tri-layered wall1. Transitional epithelium2. Smooth muscle3. Fibrous connective tissue- -Propulsion: active, responds to stretch by contractingUrinary Bladder- -Normally holds about 500mL- -Retroperitoneal- -Three openings: one for each ureter & for the urethra- -Trigone: between three areas (site of most infections)- -Layerso --Mucosa: transitional epitheliumo --Muscularis: longitudinal; circular; detrusor (oblique muscle…compresses)o