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Charlotte Youngson

25 -The Urinary System Pre-lecture questions 1. Draw a nephron, label each part and briefly describe the function of each part. ******* 2. How does antidiuretic hormone (ADH) regulate blood volume? Urinary System Organs • Kidneys are major excretory organs • Urinary bladder is the temporary storage reservoir for urine • Ureters transport urine from the kidneys to the bladder • Urethra transports urine out of the body *NOTES • This renal artery will feed those million glomeruli • Ureter carry urine. Kidney Functions • Removal of toxins, metabolic wastes, and excess ions from the blood • Regulation of blood volume, chemical composition, and Ph *NOTES • Renin is released when bp is low. Blood volume is adjusted by kideys. Ph level of 7.4. Nephrons Structural and functional units that form urine ~1 million per kidney • Two main parts 1. Glomerulus: a tuft of capillaries 2. Renal tubule: begins as cup-shaped glomerular (Bowman’s) capsule surrounding the glomerulus • Renal corpuscle • Glomerulus + its glomerular capsule • Fenestrated glomerular endothelium • Allows filtrate to pass from plasma into the glomerular capsule *NOTES • Everything that is placed back in blood or nor filtered, goes back to upper artery of glomerulus. 65% of 180litres is rabsorbed in PCT. 20% is at loop of henry. 15% reabsorbed depends Renal Tubule • Glomerular capsule • Parietal layer: simple squamous epithelium • Visceral layer: branching epithelial podocytes • Extensions terminate in foot processes that cling to basement membrane • Filtration slits allow filtrate to pass into the capsular space *NOTES • Filtration barriers –holes in glomerulus and There is foot processes as well (podocytes). • Diseases: • Blood in urine-if its too permissive, blood will get in urine. • Or big proteins. Filtration Membrane Porous membrane between the blood and the capsular space Consists of 1. Fenestrated endothelium of the glomerular capillaries 2. Visceral membrane of the glomerular capsule (podocytes with foot processes and filtration slits) 3. Gel-like basement membrane (fused basal laminae of the two other layers) • Allows passage of water and solutes smaller than most plasma proteins • Fenestrations prevent filtration of blood cells • Negatively charged basement membrane repels large anions such as plasma proteins • Slit diaphragms also help to repel macromolecules Nephrons: two types 1. Cortical nephrons—85% of nephrons; almost entirely in the cortex 2. Juxtamedullary nephrons • Long loops of Henle deeply invade the medulla • Extensive thin segments • Important in the production of concentrated urine Nephron Capillary Beds 1. Glomerulus • Afferent arteriole  glomerulus  efferent arteriole • Specialized for filtration • Blood pressure is high because • Efferent arterioles are smaller in diameter than afferent arterioles • Arterioles are high-resistance vessels 2. Peritubular capillaries • Low-pressure, porous capillaries adapted for absorption • Arise from efferent arterioles • Cling to adjacent renal tubules in cortex • Empty into venules 3. Vasa recta • Long vessels parallel to long loops of Henle • Arise from efferent arterioles of juxtamedullary nephrons • Function information of concentrated urine *NOTES • For constantly dehydrated organisms, they have more of long nephrons. Kidney Physiology: Mechanisms of Urine Formation • The kidneys filter the body’s entire plasma volume 60 times each day • Filtrate • Blood plasma minus proteins • Urine • <1% of total filtrate • Contains metabolic wastes(amine group) and unneeded substances Mechanisms of Urine Formation 1. Glomerular filtration (in glomerulus) 2. Tubular reabsorption (out of tubule) • Returns all glucose and amino acids, 99% of water, salt, and other components to the blood 3. Tubular secretion (from vasa rectum into tubule) • Reverse of reabsoprtion: selective addition to urine *NOTES • Arrow in tubule –secretion • Arrow out of tubule- reabsorbtion 1. Filtration - Net Filtration Pressure (NFP) The pressure responsible for filtrate formation (10 mm Hg) Glomerular Filtration Rate (GFR) • Volume of filtrate formed per minute by the kidneys (120–125 ml/min) • Governed by (and directly proportional to) • Tot
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