the Kidney Flashcards
What is osmoregulation
Controlling the water potential of blood
Structure of the nephron
Where the kidney filters blood and useful substances are absorbed
Parts of the nephron
- Glomerulus
- Bowman’s capsule
- Proximal convoluted tubule
- Descending loop of Henle
- Ascending loop of henle
6.Distal convoluted tubule - Collecting duct
Function of the glomerulus and bowman’s capsule
Glomerulus: filters small solutes from the blood
Bowman’s capsule: the start of the proximal convoluted tubule
Function of the proximal and distal convoluted tubule
Proximal: reabsorbs ions, water and nutrients
Distal: selectively reabsorb ions to maintain pH
Function of the ascending and descending loop of henle
Ascending: reabsorbs Na+ and Cl- from the filtrate
Descending: allows water to pass from the filtrate into the interstitial fluid
What are the steps of osmoregulation and where they occur
- Formation of the glomerular filtrate (glomerulus)
- Reabsorption of glucose and water (proximal convoluted tubule)
- Maintenance of Na+ gradient in the medulla (loop of henle)
- Reabsorption of water (distal convoluted tubule)
Formation of the glomerular filtrate
The efferent arteriolar is smaller in diameter than the afferent arteriole. This causes an increase in hydrostatic pressure. Water and ions are pushed through the pores of the basement membrane into bowman’s capsule. Proteins are too large to pass through.
Selective Reabsorption
Na+ actively transport out of the epithelial cell into the blood, lowering conc of Na+ in the cell.
Na+ diffuse down the conc gradient to the proximal convoluted tubule via carrier proteins.
Molecules are co transported into the epithelial cell of the PCT and then diffuse into the blood. Glucose and water are reabsorbed.
Modifications of the bowman’s capsule to reduce resistive barrier
Thin layer of the capsule made from podocytes, which have spaces between to allow substances to pass through the gaps.
Microvili, to increase surface area
Infoldings, increase surface area
Mitochondria, to provide ATP for active transport
Loop of henle
Involved in Reabsorption
Hair pin shaped and found in the renal medulla
Present in a salty environment
Uses the counter current multiplier to ensure a water potential gradient
Structure of the descending and ascending limb
Descending, permeable to water and has narrow and thin walls.
Ascending, impermeable to water, permeable to Na+ and Cl- and have wider and thicker walls
stage 1 of water reabsorption (movement of ions)
Na+ and Cl- are actively transported using ATP from the ascending limb to the interstitial space
stage 2 of water reabsorption (ascending limb)
as there is more NA+ in the interstitial space this lowers the water potential of the medulla, but the ascending limb is impermeable to water, so there is no movement of water
stage 3 of water reabsorption( the descending limb)
the descending limb is permeable to water, so water leaves the filtrate to the interstitial space via osmosis, due to water potential gradient
stage 4 of water reabsorption (water potential in the medulla)
the filtrate loses water as it moves down the descending limb, reaching its lowest water potential at the tip in the medulla.
stage 5 of water reabsorption (loss of water)
water that is lost from the collecting duct, is reabsorbed into the blood by osmosis and is carried away by the capillaries.
stage 6 of water reabsorption (final water potentials)
there is a water potential gradient in the interstitial space, the highest water potential in the cortex, getting lower as you go deeper in the medulla, so water continues to move out of the collecting duct and into the interstitial space. the counter current multiplier maintains the water potential to ensure water continues to leave the tubule via osmosis
features of ADH
Anti-diuretic hormone, produced in the hypothalamus, stored in the posterior pituitary gland, targets cells lining the distal convoluted tubule and collecting duct
what happens when you are dehydrated
- osmoreceptors lose water due to a low water potential causing them to shrink, detecting the decrease in water potential.
- this stimulates nerve cells in the hypothalamus triggering an action potential.
- increased ADH production by the posterior pituitary gland.
- ADH is carried in the blood to the collecting duct.
function of aquaporins
aquaporins are protein channels which are complementary in shape to water. the aquaporins reabsorb water via osmosis.
