Osmoregulation

Step 1 ultrafiltrartion

• blood enters via afferent arteriole and splits into lots of smaller capillaries making up the glomerulus filtrate

• water and small molecules like glucose and mineral ions forced out of capillaries and for the glomerulus filtrate

• large proteins and blood cells too big

step 1- how does the filtration happen in the capillaries

• the capillary endothelium have tiny gaps between them

• podocytes surrounding capillaries have tiny gaps

step 2- selective reabsorbtion

1) concentration of Na+ in pct decreased as they are actively transported out of pct into blood in capillaries

2) due to concentration gradient, sodium ions diffuse down the gradient from lumen of pct into the pct epithelial cells

• example of co transport- proteins which transport sodium ions carry glucose with it into epithlial cells

3) glucose diffuses into blood from the epithelial cells

• all glucose reabsorbed

adaptations of PCT epithelial

• microvilli provide large surface area

• have lots of mitochondria to provide energy for active transport

Osmoregukation step 3- structure of loop of henle

Made from 2 limbs

• ascending limb

• descending limb

step 3 loop of henle

• mitochondria in walls of acsending limb of loop of henle- actively transport sodium ions out of loop of henle descending limb

• accumulation of Na+ in medulla and interstitial space, lowering water potential

• water diffuses out of descending limb by osmosis

• reabsorbed into blood

• at base of ascending limb, some sodium ions are transported out by diffusion

step 4- reabsorbtion of water at dct and collecting duct

• due to sodium ions being actively transported out of loop of henle, when filtrate reaches DCT it is dilute

• filtrate moves into DCT and collecting duct where the medulla is very concentrated

• so even more water diffuses out of DCT and collecting duct

• the remaining fluid is urine

desert animals have longer loop of henle to increase surface area for sodium ion transport to lower water potential further to allow more water ro be re absorbed

What is negative feedback

Mechanisms to restore any deviations from normal in a system back to original state

What is hypertonic blood

too low water potential

• too much water keave cells and move into blood by osmosis

what is hypotonic blood

• blood with too high water potential

  • too much water moves from blood to cells cells will lyse

What is the hypothalamus

• produces adh

• changes in water potential of blood detected by osmoreceptors in hypothalamus

• if water potential is too low water leaves osmoreceptors by osmosis so they shrivel and stimulates hypothalamus to produce

• water potential is too high- water enters osmoreceptors by osmosis so the hypothalamus produces less ADH

What is the role of ADH

• makes walls of DCT and collection duct more permeable to water- so more water is re absorbed into the blood. more concentrated urine with less volume

How dows adh actually work

• adh binds to receptors on cell membrane of DCT and collecting duct complementary to adh

• when bound it activates phosphorylase enzyme in cells

• causes vesicles containing aquaporins to fuse with cell membrane- aquaporins embedded

What happens when blood water potential is too high?

• osmoreceptor cells swell and burst

• causes hypothalamus to release less adh

• DCT and CD become less permeable to water

• less water re absorbed into blood and more is lost in urine

What happens when blood water is too low?

• osmoregulator cells in hypothalamus shrivel

• hypothalamus produces ADH which is released into blood by posterior pituitary gland

• DCT and collection duct made more permeable with more aquaporins

• more water re absorbed into blood and urine becomes more concentrated and has less volume

• blood water returns to normal