(LEC 22) Vertebrate Excretory System- Kidneys

Vertebrates need to remove N and have different forms of nitrogenous waste

sunfish - excrete ammonia through their gills

Mudpuppy

Spadefoot toad- boback talks about wiping his nose after touching, sneezing, trouble seeing

Spotted turtle- uric acid

Herring gull- actively giving off uric acid

Kidney 

1. Main kidney excretory organ in vertebrates

2. Functional unit of the kidney is the nephron (do the work). More than 200k of these in one kidney

   1. Blood vessel component

   2. Tubule component

Filtration— reabsorption and secretion— absorption

Kidney-filters all of the blood and put into urine and retain what we do want

Formation of Urine

1. Filtration

   1. occurs in the glomerulus (dense ball of capillaries)

   2. blood pressure drives H2O and some solutes out of glomerulus and into bowmans capsule (the tubule)

2. Tubular Reabsorption'

   1. filtrate (as soon as liquid blood enters tubule it is called filtrate) from glomerulus enters renal tubule

      1. cells lining these tubule reabsorb ions, nutrients, water and return these to blood system

   2. when do we need active transport? when we are going from low to high concentration

   3. excess ions and urea are left in tubule

3. Tubular Secretion

   1. additional substances are actively secretes into tubule for removal

Dissection of a Nephron

• 180 liters of blood is filtered by glomeruli per day. Possible because glomerular capillaries:

  • have high blood pressure

  • are highly permeable to water

• Proximal Convoluted Tubule

  • reabsorbs 75% of fluid entering nephron. How?

    • high surface area- high # of microvilli line walls

    • high # mitochondria for active transport

      • Na+

      • Glucose

      • Amino Acids

    • not all molecules can go across easily into bowman’s capsule

• urine is 4x more concentrated than blood

• Loop of Henle- massilevely important in concentrating the urine

  • part of the countercurrent multiplier

  • thin descending limb

    • not permeable to Na+ and Cl-

    • highly permeable to H2O

  • thick ascending limb

    • actively reabsorb Na+ and Cl-

    • impermeable to H2O

This creates high [Na+] and [Cl-] in medullary interstitium which pulls water osmotically from descending limb

• Vasa recta (pertibular capillaries)

  • quickly removed H2O that has been reabsorbed via osmosis

  • walls of capillaries are highly permeable to H2O, Na+, Cl-

  • the parallel and opposing directions of these capillaries and collecting duct creates a countercurrent multiplier

• distal concoluted tubule and collecting duct

  • highly permeable to H2O

How do we get that filtration?

• liquid comes out of fenestra, go through liquid membrane and into Bowman’s capsule

• some capillaries have a lot of fenestra some dont, but the ones in the .. have a lot

• epitheleal potocytes- cells of bowmans capsule

• filtration slits- where liquid goes through from capillary lumen towards bowman’s capsule

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