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The Urinary System

The Urinary System. Chapter 12. Extracellular Fluid. Interstitial fluid lies between cells and other tissue components Blood transports substances by way of the circulatory system Interstitial fluid + blood = extracellular fluid. Maintaining Extracellular Fluid.

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The Urinary System

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  1. The Urinary System Chapter 12

  2. Extracellular Fluid • Interstitial fluid lies between cells and other tissue components • Blood transports substances by way of the circulatory system • Interstitial fluid + blood = extracellular fluid

  3. Maintaining Extracellular Fluid • Urinary system keeps volume and composition of extracellular fluid within tolerable ranges • It interacts with the digestive, respiratory, and circulatory systems to fulfill this task

  4. Urinary System Interactions food, water intake oxygen intake elimination of carbon dioxide DIGESTIVE SYSTEM RESPIRATORY SYSTEM nutrients, water, salts carbon dioxide oxygen CIRCULATORY SYSTEM URINARY SYSTEM water, solutes elimination of food residues rapid transport to and from all living cells elimination of excess water, salts, wastes

  5. Water Gains and Losses Water Losses • Urination • Cell secretions • Sweating • Water in feces Water Gains • Absorption from gut • Metabolism

  6. Solute Gains and Losses Solute Gains • Absorption from gut • Cell secretions • Respiration • Metabolism Solute Losses • Urinary excretion • Respiration • Sweating

  7. Controlling Water Gain & Loss • Urinary excretion provides the most control over water loss • Concentration of urine can be varied

  8. Components of Urinary System • Pair of kidneys • Pair of ureters • Urinary bladder • Urethra

  9. Function of Kidneys • Filter water, mineral ions, wastes from the blood • Adjust filtrate concentration and return most to blood • Remaining water and solutes in filtrate constitute urine

  10. Structure of Kidney • Renal capsule surrounds kidney • Two regions • Outer renal cortex • Inner renal medulla • Renal pelvis collects urine and funnels it to ureter

  11. Urinary Excretion • Urine flows from each kidney to a ureter • Ureters deliver urine to bladder • Contraction of the smooth muscle of the bladder forces urine out of the body into the urethra • Skeletal muscle surrounds urethra; allows voluntary control of urination

  12. Nephron • Functional unit of the kidney • Each consists of a renal tubule and associated capillaries Bowman’s capsule (red) collecting duct distal tubule proximal tubule loop of Henle

  13. Urine Formation • Urine forms in nephrons by three processes Glomerular filtration Tubular reabsorption Tubular secretion

  14. Glomerular Filtration • Glomerular capillaries have large pores • Each day about 180 liters of fluid leak from glomerular capillaries into kidney tubules

  15. Filtration Rate Varies • Increased blood pressure increases glomerular filtration • Flow volume to kidneys changes in response to neural, endocrine, and local changes

  16. Reabsorption • Each day, about 180 liters of filtrate flows into tubules • 1 to 2 liters excreted • Most filtrate is reabsorbed peritubular capillaries

  17. Tubular Reabsorption • Takes place along tubular parts of nephron • Most of filtrate’s water and solutes move out of nephron across tubule wall • They then move into neighboring peritubular capillaries

  18. Tubular Secretion • The opposite of reabsorption • Molecules are transported out of the peritubular capillaries, through tubule cells, and into the filtrate • Eliminates H+ ions, metabolites, and toxins

  19. Tubular Reabsorption filtrate in tubule interstitial fluid Na+ Na+ Na+ Cl- Na+ Na+ Na+ H2O peritubular capillary sodium pump

  20. In the Proximal Tubule • Most water and sodium are reabsorbed in proximal tubule • Sodium ions are pumped out, other ions and water follow • Water and solutes move into peritubular capillaries • Volume of fluid in tubule is reduced, solute concentration is little changed

  21. In Loop of Henle • Descending loop is permeable to water • Ascending loop is impermeable • Sodium is actively transported across wall of ascending loop • Water moves out of descending loop by osmosis and is reabsorbed by peritubular capillaries

  22. Antidiuretic Hormone (ADH) • ADH acts on collecting ducts; makes walls more permeable to water • Hypothalamus detects an increase in blood solute levels (sign of dehydration) • Signals posterior pituitary to release ADH • ADH makes urine more concentrated and dilutes blood

  23. Aldosterone • Stimulates reabsorption of sodium • Sensory receptors in heart and blood vessels detect a drop in blood sodium • The receptors call for the secretion of renin by cells in the glomerular wall

  24. Aldosterone • Reactions produce angiotensin II • Angiotensin II stimulates aldosterone secretion by the adrenal cortex • Aldosterone acts on cells of distal tubules and collecting ducts; increases sodium reabsorption

  25. Thirst • Osmoreceptors detect decrease in blood volume, increase in blood solute levels • Signals activate both the thirst center in hypothalamus and ADH-secreting cells • Angiotensin II also acts on brain to promote thirst and ADH secretion

  26. Kidney Disorders • Polycystic kidney disease • Nephritis • Glomerulonephritis • Kidney stones

  27. Renal Failure • Both kidneys are damaged to the point where they are nonfunctional • Fatal if not treated • Dialysis is used to restore normal solute balances temporarily • Transplant is only way to fully restore function

  28. Acid-Base Balance • Kidneys work in concert with buffering systems to keep pH in normal range • Normal range is 7.37 to 7.43 • Normal metabolism produces an excess of H+

  29. Buffer Systems • Weak acid and weak base that can reversibly bind and release ions • Bicarbonate-carbon dioxide buffer system can neutralize excess H+

  30. Regulating Blood pH (1) • Involves secretion of H+ and reabsorption of HCO3- (bicarbonate) • HCO3- in filtrate combines with H+ to form carbonic acid (H2CO3) • H2CO3 becomes CO2 and H2O, which are reabsorbed into blood from filtrate

  31. Regulating Blood pH (2) • In blood, HCO3 dissociates to form HCO3- and H+ • The H+ can be secreted into proximal tubule, while the HCO3- remains in blood, thus increasing blood pH • H+ also can combine with K + or ammonia and leave body in urine

  32. Core Temperature • Internal temperature of an animal’s body • Must be maintained within a narrow range for normal enzyme function • Heat gains and losses must be kept in balance

  33. Heat Gains and Losses • Metabolic reactions generate heat • Radiation, conduction, and convection can move heat to or from body to surroundings • Evaporation causes cooling

  34. Maintaining Temperature • Peripheral thermoreceptors in skin • Thermoreceptors deeper in body • Feed input to hypothalamus • Hypothalamus sends messages to effectors by way of nervous system

  35. Response to Cold • Peripheral vasoconstriction • Pilomotor response • Shivering response • Nonshivering heat response • Hypothermia

  36. Response to Heat Stress • Peripheral vasodilation • Sweating • Hyperthermia • Heat stroke

  37. Fever • Part of response to tissue damage • Hypothalamus resets body thermostat at higher temperature • Moderate fever can promote healing and need not be suppressed

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