Role of the nephron in osmoregulation Flashcards
What are the 4 stages in the nephrons role in osmoregulation?
Ultrafiltration
Selective reabsorption
Loop of henle
DCT and Collecting duct
How is glomerular filtrate formed?
Blood enters kidney via renal artery at high pressure
Blood travels to the afferent arteriole and then the glomerulus
This creates a high hydro static pressure, forcing water glucose and mineral ions out of the capillaries
Blood cells and Proteins are too large so cannot be forced out through endothelial cells
What resists the movement of the filtrate out of the glomerulus?
Capillary endothelial cells
Epithelial cells of the renal capsule
Hydro static pressure of the fluid in renal capsule space
Low water potential of blood in glomerulus
What modifications aided in the movement of the filtrate out of the capillaries?
Renal capsule inner layer contains podocyte cells that have spaces between them to allow fluid to move
Glomerular capillaries endothelial cells has gaps between its cells to allow filtrate to pass
How are the epithelial cells in the proximal convoluted tubule adapted?
Microvilli to increase surface area for absorption
Infoldings at their bases for large surface area to transfer substances into blood capillaries
High mitochondria density for ATP for active transport
How is glucose and water reabsorbed by the proximal convoluted tubule?
Na+ actively transported from epithelial cells lining PCT into blood capillaries
Na+ diffuses down conc gradient from lumen of PCT into epithelial lining cells through co transport protein via facilitated diffusion
Co transport proteins also allow transport of glucose along with the Na+
Molecules that are co transported into the epithelial cells diffuse into the blood capillaries
What are the 2 regions of the loop of henle?
Ascending limb
Descending limb
What are the characteristics of the ascending limb?
Wider
Thicker walls
Impermeable to water
What are the characteristics of the descending limb?
Narrower
Thinner walls
Highly permeable to water
What is the process for the maintenance of sodium ions in the loop of Henle and absorbtion into collecting duct?
Na+ is actively transported out of the ascending limb into the interstitial fluid
This creates a low water potential in the interstitial region
Walls of ascending limb are impermeable to water but the walls of the descending limb are permeable
Water moves out of the descending limb into the interstitial space via osmosis and enters capillaries to be taken away
Filtrate progressively loses water as it moves down the descending limb with water potential being the lowest at the hair pin
Na+ diffuses out of the filtrate into the interstitial space as it moves up the ascending limb and is actively transported out further up
In the interstitial space between the collecting duct and ascending limb, the fluid has a high water potential near the cortex which decreases the deeper into the medulla it goes
Collecting duct is permeable to water so moves out by osmosis down a concentration gradient and into capillaries
Gradient is maintained down the whole length of the collecting duct
Explain the role of the distal convoluted tubule and collecting duct in reabsorbing water
DCT has microvilli on its epithelial cells and many mitochondria, increasing reabsorption from the filtrate by active transport.
DCT makes final adjustments to water and salts that are reabsorbed and controls blood pH by selecting which ions to reabsorb
Water moved by osmosis from the collecting duct into the interstitial fluid and then into the blood
How does the loop of Henle act as a counter current multiplier?
The water potential in the filtrate of the loop of Henle and collecting duct reduces as it moves down, meeting interstitial fluid with an even lower water potential so a constant gradient is maintained
