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Chapter 16: Urinary System and Excretion

Chapter 16: Urinary System and Excretion. THE NEPHRON. Each kidney contains about one million microscopic filtering tubules called NEPHRONS. Anatomy of a Nephron. Each nephron has its own blood supply.

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Chapter 16: Urinary System and Excretion

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  1. Chapter 16: Urinary System and Excretion

  2. THE NEPHRON • Each kidney contains about one million microscopic filtering tubules called NEPHRONS

  3. Anatomy of a Nephron • Each nephron has its own blood supply. • An afferent arteriole approaches the glomerular capsule and divides to become the glomerulus, a knot of capillaries. • The efferent arteriole leaves the capsule and branches into the peritubular capillary network. • Afferent = Going Toward, Arriving. • Efferent = Leaving, Exiting • Peritubular = Around the Tubule

  4. Nephron anatomy

  5. Parts of a Nephron • The closed end of the nephron is a cuplike Glomerular/Bowman’s capsule. • Spaces between podocytes of the glomerular capsule allow small molecules to enter the lumen from the glomerulus via glomerular/pressure filtration.

  6. Proximal convoluted tubule • The cuboidal epithelial cells of the proximal convoluted tubule have many mitochondria and microvilli to carry out active transport (following passive transport) from the tubule to blood.

  7. The descending loop of the nephron (Loop of Henle)allows water to leave and the ascending portion extrudes salt. Active transport is used in the upper portion of the ascending limb to drive out Sodium ions, Chloride ions passively follow.

  8. The cuboidal epithelial cells of the distal convoluted tubule have numerous mitochondria but lack microvilli. • They carry out active transport from the blood to the tubule or tubular secretion. • Collecting ducts gather in the renal medulla and form the renal pyramids.

  9. DRAW A NEPHRON And do it RIGHT NOW !!

  10. Urine Formation • 1. Glomerular Filtration • During glomerular filtration, small molecules including water, wastes, and nutrients are forced from the blood inside the glomerulus to the inside of the glomerular capsule. • Blood cells, platelets, and large proteins do not move across. • About 180 liters of water are filtered daily.

  11. Reabsorption from Nephrons

  12. 2. Tubular Reabsorption • During tubular reabsorption, certain nutrients, water and some urea moves from the proximal convoluted tubule into the blood of the peritubular capillary network. • Tubular reabsorption is a selective process because only molecules recognized by carrier molecules are actively reabsorbed. • The rate of this process is limited by the number of carriers.

  13. 3. Tubular Secretion • During tubular secretion, specific substances such as hydrogen ions, creatinine, and drugs such as penicillin move from the blood into the distal convoluted tubule. • In the end, urine contains substances that have undergone glomerular filtration but have not been reabsorbed, and substances that have undergone tubular secretion.

  14. 4. Water Reabsorption • Water is reabsorbed all along the Nephron, as tubular reabsorption of salts, glucose, amino acids occurs at the proximal convoluted tubule, water will passively follow. • As filtrate moves down the Descending Limb of Henle, salt and urea molecules suck water out of the filtrate. • As filtrate moves down the Collecting Ducts, cells are permeable to water, this allows the salts and urea outside the collecting duct to suck water into the tissue fluid.

  15. 5. Excretion of Urine

  16. Steps in urine formation

  17. Practice Quiz 2 1 • M

  18. Nephron Structure KEY • Glomerulus • Efferent Arteriole • Afferent Arteriole • Proximal Convoluted Tubule • Loop of Henle • Descending Limb of LOH • Ascedning Limb of LOH • Peritubular Capillary Bed (Network) • Distal Convoluted Tubule • Renal Venule ( leading to Renal Vein) • Renal Arteriole (from Renal Artery) • Collecting Duct

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