Osmoregulation Flashcards
What are the 5 stages of osmoregulation?
1.Ultrafiltration
2.Selective reabsorption (proximal convoluted tubule)
3.Loop of Henle
4. Distal convoluted tubule
5. collecting duct
What is ultrafiltration in osmoregulation?
It happens in the renal capsule.
The efferent arteriole is narrower than the afferent arteriole increasing the pressure in the glomerulus.
The basement membrane acts as a filter which along with endothelial cells of the capillary, and the podocytes of the renal capsule, keep water and the large proteins in the capillary.
Meanwhile most water, all of the glucose, amino acids and urea, plus most ions are filtered out.This forms the filtrate.
What happens in the second stage of osmoregulation- selective reabsorption?
This occurs in the proximal convoluted tubule.
Here all of the glucose and amino acids are reabsorbed into the blood by active transport. This allows all of it to be reabsorbed.
Some ions are reabsorbed, and most of the water is reabsorbed by osmosis.
What happens in the Loop of Henle?
In the descending limb water moves by osmosis into the medulla, and it then reabsorbed into the blood.
The further into the medulla the loop travels the more negative the water potential, this ensures a water potential gradient throughout.
The ascending limb is impermeable to water, however ions are actively transported out into the medulla to maintain the water potential- counter current.
What happens in the distal convoluted tubule and collecting duct?
This is where the body has a final opportunity to recover ions and water before it is excreted as urine. ions would be recovered by active transport, water by osmosis.
What is the main role of the distal convoluted tubule?
The cells that make up the walls of the distal convoluted tubule have microvilli and mitochondria that allow them to reabsorb material rapidly from the filtrate, by active transport.
The main role of the distal convoluted tubule is to make final adjustments to the water and salts that are bing reabsorbed and to control the pH of the blood by selecting which ions to reabsorb .
What happens if we are dehydrated?
The osmoreceptors in the hypothalamus detect this and release ADH (antidiuretic hormone).
This binds to the cells of the collecting duct, causing aquaporisn to be added to the cell membranes, speeding up the recovery of water.
The result is smaller volume of more concentrated urine.
