the kidneys

Question 1

glomerelus

Answer 1

osmoregulation occurs in the glomerelus in the kidneys
glomerulus are long tubes surrounded by capilleries
there are around 1M glomerelus in each kidney

Question 2

4 stages

Answer 2

ultrafiltration occurs due to high hydrostatic pressure
water and other dissolved substances forced out of glomerulus capilleries and into renal artery.
selective reabsorption occurs in the proximal convulted tubule/PCT
loop of henle maintains sodium ion concentration so water can be reabsorbed.
water moves out of the distale convulted tubule and collecting duct so it returns to the blood
collecting duct carries remaining liquid to ureter where it forms urine

Question 3

ultrafiltration

Answer 3

blood enters through the afferent arteriole
this branches into many capilleries called the glomerelus which creates a high hydrostatic pressure
water and other dissolved minerals pass into glomerulus filtrate

proteins and blood cells are too large to pass through gaps in endothilial cells so stay in the blood and the blood leaves via the efferent arteriole.

Question 4

selective re absorption

Answer 4

occurs in PCT
85% of glomerulus filtrate is reabsorbed back into the blood
excess mineral ions and urea left behind

sodium ions are actively transported from the cell lining the PCT into the blood in the capilleries
creates a concentration gradient for sodium ions
sodium ions and glucose move from the lumen of the PCT to the cell lining the PCT via co transport, using ATP and a carrier protein
glucose can then diffuse from the cell lining the PCT into the blood in the capilleries
so all glucose has been re absorbed.

Question 5

adaptations of cells lining PCT for reabsorption

Answer 5

microvilli- increase surface area for absorption
mitochondria- provide ATP for active transport.

Question 6

loop of henle

Answer 6

helps to maintain sodium ion concentration gradient so all water is reabsorbed.
descending limb
thinner walls
permeable to water

ascending limb
thicker walls
impermeable to water

sodium ions and chloride ions actively transported out of ascending limb into medulla
accumulation of sodium ions in medulla lowers the water potential, causing water to move from the ascending limb into the intestitial space and then the blood
so all water gets reabsorbed into the blood.

at the base of the ascending limb, some sodium ions can move around via diffusion as very dilute solution due to all water that has moved out.

Question 7

DCT and collecting duct

Answer 7

due to sodium ions being actively transported out of loop of henle, when filtrate reaches DCT and collecting duct it is very dilute.
filtrate moves into DCT and collecting duct
this part is even more concentrated
even more water diffuses out of the DCT
remaining forms urine

Question 8

how is the loop of henle of a desert animal different for a human?

Answer 8

longer loop of henle for desert animal
more sodium ions actively transported out of ascending loop on henle
lower water potential
more water reabsorbed into the blood
urine is more concentrated