Major Functions of the Kidneys and the Urinary SystemSlide 2Slide 3The Male UrethraNephron- The Functional Unit of the KidneysThe Anatomy of a NephronUrine Drainage through the Kidney and bodyBlood flow through the KidneyBasic Functions of a NephronSlide 10The Glomerular Filtration MembraneFiltration Pressures and Glomerular Filtration RateFactors affecting filtration rate in the kidneyRegulation of Glomerular Filtration Rate Renal Auto-regulation (see page 1008)Regulation of Glomerular Filtration Rate Neural Regulation (see page 1008)Slide 16Regulation of Glomerular Filtration Rate Hormonal Regulation (see page 1014-1015)Regulation of Glomerular Filtration Rate Hormonal Regulation (see page 1014 )Angiotensin II PathwayRenin – Angiotensin - Aldosterone SystemSlide 21Urine Concentration via Countercurrent MultiplicationSlide 23Slide 24Roles of the Different Nephron Regions in Urine FormationSlide 26Slide 27Slide 28Summary of the roles of the different nephron regions in urine formationMajor Functions of the Kidneys and the Urinary System1. Regulation of blood ionic composition2. Maintenance of blood osmolarity3. Regulation of blood volume4. Regulation of blood pressure5. Regulation of blood pHMajor Functions of the Kidneys and the Urinary System6. Release of hormonescalcitriol – active formof Vitamin D, helps control calcium homeostasis.erythropoietin – stimulates RBC production7. Regulation of blood glucose levels viagluconeogenesisMajor Functions of the Kidneys and the Urinary System8. Excretion of wastes and foreign substancesThe Male UrethraSpecializations of the male urethra:1. Prostatic urethra2. Membranous urethra3. Penile urethraNephron- The Functional Unit of the Kidneys•Cortical Nephrons:80 to 85% of nephrons. Have short Loops of Henle that lay mainly in the cortex•Juxtamedullary Nephrons:15 to 20% of nephrons. Have long Loops of Henle that extend into the deepest regions of the medulla. Produce the most concentrated urine.The Anatomy of a Nephron•Subdivision of a Nephron:1. Renal Corpuscle2. Proximal Convoluted tubule3. Descending Loop of Henle4. Ascending Loop of Henle5. Distal Convoluted tubule6. Collecting duct7. Papillary ductUrine Drainage through the Kidney and body•From papillary duct•Minor Calyx•Major Calyx•Ureter•Urinary Bladder•Urethra:prostaticmembranouspenileBlood flow through the KidneyBasic Functions of a NephronThe Glomerular Filtration MembraneFiltration Pressures and Glomerular Filtration Rate•Filtration Pressure is the force that drives the fluid and its dissolved substances through the glomerular filterNet Filtration pressure NPF (or Net Hydrostatic Pressure NHP) is the difference between three pressures:1. Glomerular (blood) hydrostatic pressure GHP or GBHP2. Capsular Hydrostatic Pressure (CHP)3. (Blood) Colloid Osmotic Pressure (BCOP)The relationship can be expressed byNPF = GBHP – (CHP + BCOP)Glomerular Filtration Rate: amount of filtrate the kidneys produce each minute. (about 125 ml per minute)Determined by a creatinine clearance testFactors affecting filtration rate in the kidneyRegulation of Glomerular Filtration RateRenal Auto-regulation (see page 1008)Regulation Major StimulusMechanism Effect on GFRMyogenic Stretching of afferent arteriole walls due to increased systematic BPContraction of smooth muscles in afferent arteriole wallDecrease GFR by constricting the lumenDecline in glomerular blood pressureDilation of AA and G. capillariesConstriction ofEAIncreases GFRRegulation of Glomerular Filtration RateNeural Regulation (see page 1008)Regulation Major Stimulus Mechanism Effect on GFRTubuloglomerular feedbackRapid increase in Na+ and Cl-In lumen at the macula densa due to increased BPDecreased release of Nitric Oxide by JGA causing AA constrictionDecrease GFR and filtrate volumeRegulation of Glomerular Filtration RateNeural Regulation (see page 1008)Regulation Major Stimulus Mechanism Effect on GFRSympathetic Nerves(Autonomic)Acute fall in systematic blood pressure. Release of norepinephrineConstriction of afferent arteriolesDecrease GFR and filtrate volume to maintain blood volumeRegulation of Glomerular Filtration Rate Hormonal Regulation (see page 1014-1015)Regulation Major Stimulus Mechanism Effect on GFRAngiotensin II Decreased blood volume or decreased blood pressureConstriction of both afferent and efferent arteriolesDecreases GFRAtrial natriuretic peptideStretching of the arterial walls due to increased blood volumeRelaxation of the mesangial cells increasing filtration surfaceIncreases GFRRegulation of Glomerular Filtration Rate Hormonal Regulation (see page 1014 )Regulation Major Stimulus Mechanism Effect on GFRAntidiuretic hormone ADHIncreased Angiotensin II or decreased volume of extracellular fluidStimulate insertion of aquaporin-2 (water channels)In apical membrane or principal cellsIncreases blood volume to return GFR to normalAldosterone Secreted from adrenal cortex because of increased Angiotensin II levelsIncreases reabsorption of Na+ and water by principal cells of the DCT collecting ductIncreases blood volume to return GFR to normalAngiotensin II Pathway1. Renin is released to the blood by JGA cells due to decreased renal blood flow or perfusion.2. Renin converts a plasma protein (angiotensinogen) into angiotensin I3. Angiotensin-Converting Enzyme (ACE) in the lungs convertes Angiotensin I into Angiotensin IIRenin – Angiotensin - Aldosterone SystemD e c r e a s e d R e n a l P e r f u s i o nA n g i o t e n s i n o g e nR e n i nA n g i o t e n s i n IA C EA l d o s t e r o n eA n g i o t e n s i n I IV a s o c o n s t r i c t i o nR e n i n r e l e a s e b y J u x t a g l o m e r u l a r C e l l sS y m p a t h e t i c N e r v e I m p u l s e sUrine Concentration via Countercurrent Multiplication•Thin descending limb of Henle is permeable to water but notsolutes•Thick ascending limb of Henle is impermeable to water and solutes. Contains active transport mechanisms for sodium and chloride.Urine Concentration via Countercurrent Multiplication•Sodium and Chloride are reabsorbed by thick ascending limb into the peritubular fluid•These ions elevate the medulla osmotic pressure•This increases osmotic flow of water out of the thin descending limb•Increased osmotic potential of tubular filtrate increases active transport in the TALUrine Concentration via Countercurrent MultiplicationRoles of the Different Nephron Regions in Urine FormationProximal Convoluted