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Urinary System

Urinary System. Chapter 15. Functions. Filter blood Dispose of wastes and excess ions Regulate blood volume and blood pressure Maintain chemical make up (solute balance) of blood Regulate acid/base balance of blood Stimulate formation of erythrocytes Reservoir for urine . Anatomy Review.

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Urinary System

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  1. Urinary System Chapter 15

  2. Functions Filter blood Dispose of wastes and excess ions Regulate blood volume and blood pressure Maintain chemical make up (solute balance) of blood Regulate acid/base balance of blood Stimulate formation of erythrocytes Reservoir for urine

  3. Anatomy Review • Blood filtered within nephron • Flow of blood: • Filtrate travels from nephron to collecting ducts and from collecting ducts to minor calyx, major calyx, and into ureters

  4. Nephron Functional unit of the kidney Filters blood, forming filtrate which eventually becomes urine Two types: cortical nephron (cortex), juxtamedullary nephron (extends into medulla

  5. Nephron Glomerulus –capillary knot Maintains Bowman’s Capsule –collects filtrate Renal tubules: proximal convoluted tubule, loop of Henle, distal convoluted tubule Distal convoluted tubule of the nephron empties into the collecting duct

  6. Urine Formation • Three main processes • Glomerular filtration • Tubular reabsorption • Tubular secretion • As filtrate moves through the nephron water and solutes are exchanged between the tubules of the nephron and capillary beds

  7. Glomerular Filtration • Dependent upon blood pressure • Too high and blood loses solutes and large proteins (albumin) • Too low and blood is not adequately filtered • Podocytes wrap around glomerular capillaries forming filtration slits

  8. Tubular Reabsorption • Cells lining tubules take up (reabsorb) solutes and water from filtrate, returning them to blood • Urea, uric acid, creatinine, are poorly reabsorbed • PCT: NaCl, HCO3-, H2O, Glucose, Amino Acids • Loop of Henle: H2O, NaCl • DCT: NaCl • See Red and Blue Arrows

  9. Tubular Secretion • Cells lining tubules secrete (remove from blood) solutes, drugs, poisons, ion, and place them into filtrate • PCT: drugs, poisons, H+ • Loop of Henle: none • DCT: K+ and drugs • Renin-Angiotension cause secretion of aldosterone from the adrenal medulla • Aldosterone causes the reabsorption of Na+ which causes reabsorption of H2O • See green arrows

  10. Collecting Ducts • Depending on presence or absence of hormones • Reabsorb water and Urea • Secrete water and potassium • Antidiuretic Hormone (ADH) secreted from posterior pituitary causes aquaporins to be inserted in the collecting duct to facillitate reabsorption of water

  11. Fluid, Electrolyte, and Acid Base Balance • Water is on of the most important molecules: • transport solutes in blood • Universal solvent • Proper protein folding • Water is found in the cytosol, extracellular fluid, blood • Solute concentrations of each affect flow or accumulation of water…..water follows its best friend sodium

  12. Water Regulation • Thirst mechanism –driving force for water intake • Response to rising solute levels in blood • Solute levels are detected by osmoreceptors found in the hypothalamus • High solute content of blood activates the thirst center in the hypothalamus triggering the desire to drink water • ADH causes insertion of aquaporins in collecting duct to reabsorb water • Alcohol inhibits ADH

  13. Electrolyte Balance • The movement of water is coupled to electrolytes • Aldosterone is released from the adrenal gland in response to low Na+ levels in blood • Na+ is reabsorbed in the presence of aldosterone • Reabsorption of Na+ causes the secretion of other ions • Water follows its best friend sodium, aldosterone indirectly regulates water balance of blood and thus blood volume and pressure

  14. Electrolyte Balance Aldosterone release is controlled by the Juxtaglomerular cells (JG cells) within the kidney JG cells secrete renin in response to low blood pressure…they are baroreceptors! Renin converts to angiotension II and triggers the adrenal cortex to secrete aldosterone

  15. Electrolyte Balance

  16. Acid-Base Balance • Respiratory, cardiovascular and urinary systems all work in conjunction of maintain the acid-base balance of blood • Respiratory off loads CO2 from tissues preventing acid buildup within extracellular fluid • Cardiovascular system binds H+ ions to hemeglobin and converts CO2 to bicarbonate (HCO3-) to prevent acid buildup within blood • Kidneys remove HCO3- from blood by secreting it in urine or reabsorbing and recycling HCO3- when needed

  17. Homeostatic Imbalances Hydronephrosis –kidney damage due to improper drainage of urine through ureters Renal calculi –uric acid or salt crystrals from highly concentrated urine Urethritis – inflamed urethra Cystitis –inflamed bladder Pyelitis –inflamed kidney Incontenence –loss of voluntary control of bladder sphincters Diabetes insipidus –inability of kidneys to conserve water Polyuria –excretion of large amounts of water Glomerulonephritis –build up of antibody-antigen complexes within the glomerulus

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