paper 2 - kidneys and osmoregulation Flashcards
what does the kidney do
- receives blood from each renal artery and blood returns to circulation via the renal vein
- in the kidney excretory products like urea are removed from the blood and the water and ion conc are regulated to produce urine
what is the basic functional unit of the kidney
- the nephron
- there are many nephrons in each kidney
- their upper part lies in the cortex and the loop of henle and collecting duct extended into the medulla.
what happens in the nephron
1) ultrafiltration - in bowmens capsule
2) selective reabsorption in the proximal convultuted tube
how does blood enter the nephron and leave
- enters through afferent arteriole which branches off the renal artery
- this branches into a mass of capillaries called glomerulus, enclosed by the cup shaped structure of the bowmans capsule
- blood leaves the glomerulus via the afferent arteriole and moves through the capillaries associated with other regions of the nephron before leaving the kidney via the renal vein
how does ultrafiltration in the bowmans capsule occur
- the afferent arteriole is wider than the efferent arteriole, creating high hydrosatic pressure in capilaries of glomerulus
- capillaries are one cell thick and closely associated with basement membrane
- small molecules such as glucose, amino acids and urea are forced across permeable capillary wall, through pores in the basement membrane and between the feet of podocytes
- large molecules such as plasma protiens and cells are too large to pass and so remain in the blood plasma
what is the bowmans capsule reffered to as
the molecular sieve
what are the blood products small enough to pass through bowmans
- water
- na
- cl
- glucose
- amino acids
how does selective re absorption in the proximal convuluted tube occur
- all glucose and amino acids are reabsorbed by co transport via co transport carrier protiens in the epithelial membrane
- as solutes move back into the blood plasma the water potential of the plasma decreases and 80% of the water from the filtrate is reabsorbed by osmosis
- larger molecules such as protiens with a small molecular mass are absorbed by endocytosis
how is the proximal convuluted tube cells adapted to carry out selective reabsorption
- many microvilli - to increase sa for faster re absorption as more transport protiens can be embedded within the membrane
- many mitochondria - to produce ATP required for active transport for substances
- close association with many capillaries, large sa for exchange
how is water re absorbed in the loop of henle
- counter current multiplier system within medulla which produces osmotic gradient for re-uptake of water
what is the process occuring in the loop of henle
1) na and cl actively transported out of the top of the ascending limb into the tissue fluid of medulla
2) lowers water potential of meddula
3) but the ascending limb is impermeable to water so water cant move out
4) descending limb is permeable to water so as the water potential is lower in the medulla water leaves the filtrate in the descending limb by osmosis and into tissue fluid and blood down wp gradient
5) descending limb impermeable to ions
6) causes filtrate ion conc to increase as move down descending limb as it loses water but ions cant move out, becomes more concentrated
7) at the apex conc is highest
8) na and cl diffuse out of ascending limb down a steep conc gradient
9) lowers wp in medulla and water follows by osmosis but only from descending limb
how does the counter current multiplier at the loop of henle result in max water reabsorption
- descending limb is permeable to water but not ions
- ascending limb is permeable to ions but not water
- active transport of ions out at the top of the ascending limb ( when ion conc in filtrate is dropping ) ensures water always moving out to the descending limb
- maintains a water potential gradient along the whole of the descending limb
what does it mean if the loop of henle is longer
- greater the difference is conc between A and D limbs
- drives re absorption of more water
what is re absorption in the distal convoluted tubule
- cells of distal convoluted tubule also have many microvilli and many mitochondria as they are adapted for active transport of na and k
- permeability of these cell membranes are affected by hormones, allowing osmoregulation
- distal convoluted tubule adjusts the filtrate conc by actively transporting na and k into or out of the tubule.
what is reabsorption in the collecting duct
- there is a wp for the movement of water out of the collecting duct, however the permeabiltiy of the walls collecting duct are also affected by hormones
- if the walls are more water permeable, water leaves the duct into the medulla ( high solute conc) and the urine is more concentrated and lower volume
- if the walls are less water permeable, less water leaves the duct into the medulla and the urine is less concentrated with a higher volume
- the collectig duct walls receptors for ADH allowing osmoregulation
what is osmoregulation
control of water potential of the blood
how does osmoregulation occur
1) osmoreceptors in hypothalamus detect decrease in wp as they lose water
2) causes ADH from posterior pituatory gland into the blood
3) ADH travels to kidneys in blood and ADH receptors on the surface of the collecting duct and the distal convuluted tubule causing them to become more water permeable
4) by causing a series of enzyme catalysed reactions resulting in vesicles containing aquaporins fusing the cell membrane
5) permeability of membrane to water is increased so more water moves from CD to DCT down a wp gradient ( due to high ion conc in medulla ) out of filtrate back into blood
osmoregulation condensed
- ADH detected by cell surface receptors
- enzyme controlled reactions
- vesicles containing water permeable channels ( aquaporins ) fuse to membrane
- more water can be reabsorbed
