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Urinary System

Urinary System. Urine Formation. Nephrons. Structural and functional unit of the kidney ~ 1 million per kidney Form urine. Nephron Functions. Filtration – blood to lumen Reabsorption – lumen to blood Secretion - blood to lumen Excretion – lumen to exterior environment.

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Urinary System

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  1. Urinary System Urine Formation

  2. Nephrons • Structural and functional unit of the kidney • ~ 1 million per kidney • Form urine

  3. Nephron Functions • Filtration – blood to lumen • Reabsorption – lumen to blood • Secretion - blood to lumen • Excretion – lumen to exterior environment

  4. Nephron Structure 1. Bowmans Capsule • Double-walled structure that surrounds the glomerulus • Parietal wall – simple squamous epithelium • Viseral wall – composed of podocytes; cling to the glomerulus and form filtration slits

  5. High BP • Size difference between afferent and efferent arterioles; more comes in than goes out Check out the size difference AA EA G

  6. Site of Filtration • Nonselective, passive process • Any product smaller than proteins are forced through the walls of the glomerular capillaries and into the renal tubules: • Water • Glucose • Salts • nitrogen wastes

  7. 2. Proximal Convoluted Tubule (PCT) • Receives the filtered fluid, or filtrate, from Bowman’s capsule • Simple cuboidal epithelium • Lots of microvilli and mitochondria • Why would these structures be important?

  8. Site of Reabsorption • Peritubular capillaries surrounding the PCT reabsorb several materials from the filtrate: • Water, glucose, a.a., ions (especially Na+) • most reabsorption uses active transport

  9. Site of Secretion • Some materials move from the peritubular capillaries into the renal tubules • H+, K+ • Creatinine • Poisons

  10. 3. Loop of Henle • Receives filtrate from PCT • 2 regions • Descending • Permeable to water • Ascending • Impermeable to water • Primary role is concentration of urine

  11. Concentrating the Urine • The Loop of Henle creates a concentration gradient in the ISF • As the filtrate moves down the loop, H20 diffuses out • As the filtrate moves up the loop, salts move out • As the urine moves through the Collecting Duct, water moves out to follow the [solute]

  12. 4. Distal Convoluted Tubule (DCT) • Receives filtrate from Loop of Henle • Also participates in secretion and reabsorption of the same products as in the PCT

  13. 5. Collecting Ducts • Receives urine from several DCT’s • Extends through the renal medulla and empty into minor calyces from the renal papillae. • Reabsorption of water

  14. Factors that Influence Urine Production: • Reabsorption of water and electrolytes is regulated by 2 hormones: • Antidiuretic Hormone (ADH) • Aldosterone

  15. ADH • Increases permeability of the Collecting Duct to water • Concentrates urine • Increases reabsorption of water • Secretion of ADH is regulated by a negative feedback loop • Osmoreceptors of hypothalamus monitor solute concentration levels of blood plasma • When high [solute], stimulates pituitary gland to secrete ADH

  16. If you’ve been drinking a lot of fluids, and blood plasma has a low [solute] (high water), the secretion of ADH is inhibited • More water is secreted in urine • Ethanol inhibits the secretion of ADH • You secrete lots of water • Become dehydrated

  17. Aldosterone • Produced by the cortex of the adrenal • Produced when: • Plasma Na+ is too low • Low BV and BP • Increases Na+ reabsorption from the DCT

  18. Diuretics • Any substance that slows the reabsorption of water • Excrete more water in urine • Can cause dehydration • Ex – alcohol – inhibits ADH release • Ex -Caffeine – inhibits renal sodium reabsorption

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