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16. The Urinary System


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16. The Urinary System

  1. 1. The Urinary System
  2. 2. Learning Objectives <ul><li>List and describe the functions of the kidneys. </li></ul><ul><li>Describe the gross and microscopic anatomy of the kidneys. </li></ul><ul><li>List the main blood vessels associated with the kidneys. </li></ul><ul><li>Define the terms glomerular filtration , renal threshold , polyuria , polydypsia , urolithiasis , and uremia . </li></ul><ul><li>Describe the production of urine. </li></ul><ul><li>Describe the mechanisms that affect urine volume. </li></ul><ul><li>Describe the structures and functions of the ureters and urinary bladder. </li></ul><ul><li>Describe the processes involved in micturition. </li></ul><ul><li>Describe the structure and functions of the urethra. </li></ul>
  3. 3. The Urinary System <ul><li>Parts of urinary system: </li></ul><ul><li>Two kidneys </li></ul><ul><li>Two ureters </li></ul><ul><li>Urinary bladder </li></ul><ul><li>Urethra </li></ul>
  4. 4. Kidney Functions <ul><li>Maintain homeostasis through: </li></ul><ul><ul><li>Filtration, reabsorption, secretion </li></ul></ul><ul><ul><li>Fluid balance regulation </li></ul></ul><ul><ul><li>Acid-base balance regulation </li></ul></ul><ul><ul><li>Production of hormones </li></ul></ul>
  5. 5. Kidneys <ul><li>Located in dorsal abdominal area ventral to and on either side of the first few lumbar vertebrae </li></ul><ul><li>Retroperitoneal to abdominal cavity; between peritoneum and dorsal abdominal muscles </li></ul><ul><li>In most domestic animals, right kidney is more cranial than the left </li></ul><ul><li>Thick layer of perirenal fat usually surrounds kidneys to help protect them from pressure exerted by surrounding organs </li></ul>
  6. 6. Gross Anatomy of Kidneys <ul><li>Fibrous connective tissue capsule </li></ul><ul><li>Hilus: indented area on medial side of the kidney </li></ul><ul><ul><li>Ureters, nerves, blood and lymph vessels enter and leave kidney </li></ul></ul><ul><li>Renal Pelvis: funnel-shaped area inside hilus </li></ul><ul><ul><li>Forms beginning of the ureter </li></ul></ul><ul><ul><li>Lined with transitional epithelium </li></ul></ul>
  7. 7. Gross Anatomy of Kidneys <ul><li>Renal cortex: outer portion of the kidney </li></ul><ul><li>Renal medulla: inner portion around the renal pelvis </li></ul><ul><li>Calyx: cuplike extension of the renal pelvis into which the medullary pyramids fit </li></ul><ul><ul><li>Calyces act as funnels to direct fluid into renal pelvis </li></ul></ul>
  8. 8. Microscopic Anatomy of Kidneys <ul><li>Nephron: basic functional unit of kidneys </li></ul><ul><li>Number of nephrons per kidney varies </li></ul><ul><li>Each nephron consists of a renal corpuscle, proximal convoluted tubule, loop of Henle and distal convoluted tubule </li></ul>
  9. 9. Renal Corpuscle <ul><li>Located in renal cortex </li></ul><ul><li>Function: filters blood in first stage of urine production </li></ul><ul><li>Composed of glomerulus surrounded by Bowman’s capsule </li></ul><ul><ul><li>Glomerulus: “tuft” of capillaries </li></ul></ul><ul><li>Fluid filtered out of blood is called glomerular filtrate </li></ul>
  10. 10. Proximal Convoluted Tubule (PCT) <ul><li>Continuation of capsular space of Bowman’s capsule </li></ul><ul><li>Lined with cuboidal epithelial cells with a brush border on lumen side </li></ul><ul><li>Twisting path through the cortex </li></ul><ul><li>Glomerular filtrate now called the tubular filtrate </li></ul>
  11. 11. Loop of Henle <ul><li>Descends from PCT into medulla, turns, heads upward into cortex </li></ul><ul><li>Descending loop has epithelial cells similar to those of PCT </li></ul><ul><li>At bottom of loop, epithelial cells flatten to simple squamous epithelial cells and lose their brush border </li></ul><ul><li>Ascending loop wall becomes thicker again </li></ul>
  12. 12. Distal Convoluted Tubule (DCT) <ul><li>Continuation of ascending loop of Henle </li></ul><ul><li>DCT from all nephrons in the kidney empty into collecting ducts </li></ul><ul><ul><li>Carry tubular filtrate through medulla </li></ul></ul><ul><ul><li>Empty into renal pelvis </li></ul></ul><ul><ul><li>Primary site of action of ADH and regulation of potassium and acid-base balance </li></ul></ul>
  13. 13. Blood Supply <ul><li>Renal artery enters the kidney at the hilus </li></ul><ul><ul><li>Divides into smaller arteries and arterioles </li></ul></ul>
  14. 14. Blood Supply <ul><li>Afferent glomerular arterioles carry blood into the glomerular capillaries of renal corpuscle </li></ul><ul><li>Glomerular capillaries filter some of the plasma out of blood and put it in the capsular space of Bowman’s capsule </li></ul>
  15. 15. Blood Supply <ul><li>Efferent glomerular arterioles receive blood form glomerular capillaries </li></ul>
  16. 16. Blood Supply <ul><li>Efferent glomerular arterioles divide to form the peritubular capillaries </li></ul><ul><ul><li>Surrounds the rest of the nephron </li></ul></ul><ul><ul><li>Oxygen transfer to the cells of the nephron takes place here </li></ul></ul><ul><ul><li>Tubular reabsorption and secretion also occurs here </li></ul></ul>
  17. 17. Blood Supply <ul><li>Peritubular capillaries converge to form venules, then larger veins, and finally the renal vein. </li></ul><ul><li>The renal vein leaves the kidney at the hilus and joins the abdominal portion of the caudal vena cava. </li></ul>
  18. 18. Filtration of Blood <ul><li>Glomerular capillaries contain many large fenestrations in capillary endothelium </li></ul><ul><ul><li>Fenestrations not large enough to allow blood cells or large proteins to pass through </li></ul></ul><ul><li>High blood pressure in the glomerular capillaries forces some plasma out of the capillaries and into the capsular space of Bowman’s capsule </li></ul><ul><li>Glomerular filtration rate (GFR): how fast plasma is filtered through glomerulus </li></ul>
  19. 19. Reabsorption <ul><li>Substances to be reabsorbed pass out of the tubular lumen through or between tubular epithelial cells </li></ul><ul><li>Substances to be reabsorbed then enter interstitial fluid and pass through endothelium into peritubular capillaries </li></ul>
  20. 20. Sodium Reabsorption <ul><li>Sodium in tubular filtrate attaches to carrier protein that moves it into the cytoplasm of the PCT epithelial cell </li></ul><ul><ul><li>Glucose and amino acids attach to same carrier protein and follow sodium into the cell by passive transport (sodium cotransport) </li></ul></ul>
  21. 21. Sodium Reabsorption <ul><li>Sodium is actively pumped out of cell into interstitial fluid, where it moves into peritubular capillaries </li></ul><ul><ul><li>Glucose and amino acids move from the PCT cell into interstitial fluid and then into the peritubular capillaries by passive diffusion </li></ul></ul>
  22. 22. Reabsorption <ul><li>Sodium ions are also reabsorbed in ascending loop of Henle and DCT </li></ul><ul><ul><li>Usually exchanged for hydrogen, ammonium, or potassium ions </li></ul></ul><ul><li>Potassium and calcium reabsorption take place in the PCT, ascending loop of Henle and DCT </li></ul><ul><ul><li>Calcium moves from the filtrate under the influence of Vitamin D, parathyroid hormone (PTH), and calcitonin </li></ul></ul><ul><li>Magnesium is reabsorbed from the PCT, ascending loop of Henle, and the collecting duct </li></ul><ul><ul><li>PTH release increases the reabsorption of magnesium </li></ul></ul>
  23. 23. Reabsorption <ul><li>Chloride (Cl – ) diffuses from tubular filtrate into the epithelial cells and interstitial space in response to electrical imbalance created by (Na + ) removal </li></ul><ul><li>Some of the water in the filtrate moves into the interstitial space and peritubular capillaries by osmosis once sodium, glucose, amino acids, and chloride have left the tubular filtrate </li></ul>
  24. 24. Secretion <ul><li>Primarily occurs in the DCT </li></ul><ul><li>Hydrogen, potassium, and ammonia are eliminated by secretion </li></ul><ul><li>Some medications are also eliminated from the body by secretion </li></ul>
  25. 25. Urine Volume Regulation <ul><li>Determined by amount of water contained in the tubular filtrate when it reaches renal pelvis </li></ul><ul><li>Controlled by actions of ADH and aldosterone </li></ul><ul><li>ADH acts on the DCT and collecting ducts to promote water reabsorption </li></ul><ul><li>Aldosterone increases reabsorption of sodium </li></ul><ul><ul><li>Causes osmotic imbalance that encourages water to follow sodium out of the tubular filtrate and into blood </li></ul></ul>
  26. 26. Ureters <ul><li>Leave kidney at the hilus </li></ul><ul><li>Outer fibrous layer, middle smooth muscle layer, and inner layer lined with transitional epithelium </li></ul><ul><ul><li>Transitional epithelium allows ureters to stretch as urine passes through them on its way to urinary bladder </li></ul></ul><ul><ul><li>Smooth muscle layer propels urine through ureter by peristaltic contractions </li></ul></ul>
  27. 27. Ureters <ul><li>Ureters enter urinary bladder at an oblique angle </li></ul><ul><li>When the bladder is full, it collapses the opening of the ureter, preventing urine from backing up into ureter </li></ul>
  28. 28. Urinary Bladder <ul><li>Lined with transitional epithelium that stretches as the bladder becomes filled with urine </li></ul><ul><li>Wall of the urinary bladder contains smooth muscle bundles </li></ul><ul><li>Neck of the bladder extends caudally from the sac into the pelvic canal and joins the urethra </li></ul><ul><li>Around the neck of the urinary bladder are circular muscles composed of skeletal muscle fibers </li></ul>
  29. 29. Control of Urination <ul><li>Micturition or uresis: expulsion of urine from the urinary bladder into the urethra </li></ul><ul><li>Urine accumulates until pressure of the filling bladder activates stretch receptors in bladder wall </li></ul>
  30. 30. Control of Urination <ul><li>A spinal reflex returns a motor impulse to bladder muscles causing them to contract </li></ul><ul><ul><li>Contraction gives the sensation of having to urinate </li></ul></ul><ul><li>Voluntary control of the muscular sphincter around the neck of the bladder results in temporary control of urination </li></ul>
  31. 31. Urethra <ul><li>Continuation of the neck of the urinary bladder </li></ul><ul><li>Carries urine from the urinary bladder to the external environment </li></ul><ul><li>Lined with transitional epithelium which allows it to expand </li></ul>
  32. 32. Urethra <ul><li>The female urethra is shorter and straighter than the long, curved male urethra. </li></ul><ul><ul><li>In the female the urethra opens on the ventral portion of the vestibule of the vulva. </li></ul></ul><ul><ul><li>In the male the urethra runs down the center of the penis and also functions in the reproductive system. </li></ul></ul>