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Kidney Function

Kidney Function. Filtration, re-absorption and excretion Filtration: dissolved fluids move inot urinary system Re-absorption: substances move from urin into blood secretion/excretion: substances move from blood into urine. Nephron.

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Kidney Function

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  1. Kidney Function • Filtration, re-absorption and excretion • Filtration: dissolved fluids move inot urinary system • Re-absorption: substances move from urin into blood • secretion/excretion: substances move from blood into urine

  2. Nephron • Each kidney is composed of over 1 million filters all working at the same time to filter the blood (each filter is called a nephron) • Each nephron is in both the renal cortex AND the medulla of the kidney

  3. Nephron function 1: filtration • Afferentarteriole goes into bowman's capsule and becomes the glomerulus • Blood is initially filtered between the glomerulus and the bowman's capsule • Filtration occurs at 4x the pressure than in a normal capillary!

  4. Dissolved substances move from areas of high pressure to low • Water, nitrogenous wastes, nutrients and ions are therefore pushed from the glomerulus into the bowman's capsule • The components of blood that do not leave the capillary are carried away through an efferentarteriole (such as blood cells and proteins, which are too big to fit through the “filter”)

  5. Brain break!!!! How many evolutionists does it take to change a light bulb?

  6. Only one, but it takes 8 million years!!!

  7. Nephron function 2: re-absorption • The efferent arteriole then forms a true capillary network around the rest of the nephron (called peritubular capillary network) • As filtrate flows through nephron, many substances are re-absorbed both actively and passively into the peritubular capillary network

  8. Proximal convoluted tubule (PCT) • Glucose, aa's and Na+ are actively reabsorbed at PCT • CL- is passively reabsorbed by following Na+ back into the blood (through Cl- channels) • Water is passively reabsorbed by diffusion • Some urea reabsorbed due to osmotic pressure

  9. Loop of Henle • Water leaves the descending limb, but cannot be reabsorbed by the ascending limb because it is impermeable to water. • NaCl moves out of the thickest part of the ascending limb. • As the fluid moves up the loop, there is less NaCl available to move out, therefore the outer medulla has a lower OP than the inner medulla

  10. Loop of Henle (cont'd) • Urea which leaks out of the lower part of the collecting duct, also increases the OP of the inner medulla • The establishment of this osmotic gradient ensures that water continues to move out of the entire length of both the descending loop and the collecting duct

  11. Nephron function 3: Secretion/tubular excretion • Active transport of molecules from the blood to the nephron • Occurs in the distal convoluted tubule • Uric acid, ammonia and H+ (as HCO3) is secreted • Penicillin and histamine also secreted

  12. Excretion cont'd... • The substances that make up urine are the substances which are filtered, secreted and not absorbed • A small amount of water • Nitrogenous wastes • Bicarbonate, sulphates and phosphates • Excess ions

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