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Chapter 15: The Urinary System Urinary System: general functions • excretion – kidneys produce urine • elimination – ureters, bladder, urethra • regulation of blood volume and solute concentration Urinary System Kidney Coverings • renal capsule • adipose capsule – important to hold in position Kidneys have the following regions • cortex – site of urine production • medulla • renal pelvis Kidney Anatomy How is urine made? • A filtrate of the blood…… • So we need to look at blood flow through the kidney Flow of blood through kidneys Map of Blood Flow EC Updates • House definitions – should have ~ 30 per show • Reports: – 1-2 pages, double spaced. – 300-500 words. – Please type. Functional unit of kidney is the nephron • Structures which form urine • About 1.25 million in each kidney • Consists of glomerulus and renal tubule Nephron Nephron Parts of the Nephron • • • • • glomerulus proximal convoluted tubule loop of Henle distal convoluted tubule collecting duct Glomerulus • knot of capillaries • Bowman’s capsule surrounds glomerulus • filtration Glomerulus • podocytes form porous membrane Renal Tubule • proximal convoluted tube (PCT) • loop of Henle • distal convoluted tube (DCT) Renal Tubule • lumen (cells exposed to filtrate) covered with microvilli • reabsorption • secretion Collecting Ducts • transports urine from nephrons to renal pelvis • give medullary pyramids striped appearance Two capillary beds • glomerulus • peritubular Glomerulus • site of filtration • afferent arteriole • efferent arteriole • high blood pressure in this capillary bed Peritubular Capillaries • from efferent arteriole • low pressure, porous vessels • adapted for absorption What is the goal of urine production? • Maintain homeostasis by regulating – volume of blood – composition of blood How can this happen at the kidneys? • blood needs to be filtered • compounds that are accidentally filtered need to be reabsorbed • need to have the option to adjust the filtrate at the last minute, secretion Urine Formation • a) filtration • b) tubular reabsorption • c) tubular secretion Filtration • Where does this occur? – glomerulus • What promotes filtration? – hydrostatic pressure – forces solutes and water out of capillary & into capsule • nonselective, passive process • filtrate is essentially blood plasma - proteins Reabsorption • Where? – most in PCT, some in DCT and collecting ducts • Why? – filtrate contains many useful substances • glucose, amino acids, ions, water • How? – water = passive – most substances = active transport • What is left behind? – nitrogenous waste products remain in filtrate • urea, uric acid, creatinine Secretion • move substances from blood of peritubular capillaries to tubular cells, then into filtrate • H+, K+, creatinine, certain drugs • PCT, DCT Urine • In 24 hours: kidneys filter 150-180 L plasma produce 1.0-1.8 L of urine • urine = water + solutes – specific gravity (how heavy vs. water) – 1.001-1.035 Urine • normal solutes: Na+, K+ ions, urea, uric acid, creatinine, ammonia, HCO3- ions • abnormal solutes: glucose, blood proteins, RBCs, hemoglobin, WBCs, bile Lab • Activities: 1, 7, 9 – slides • Digestive lab
