water control

Question 1

what are the 4 stages of osmoregulation in the nephron

Answer 1

formation of glomerular filtrate by ultrafiltration
reabsorption of glucose and water by proximal convoluted tubule
maintenance of gradient of sodium ions in the medulla by the loop of henle
reabsorption of water by the distal convoluted tubule and collecting ducts

Question 2

describe the formation of the glomerular filtrate

Answer 2

process of ultrafiltration in the glomerulus
afferent arteriole wider than efferent causes build up of hydrostatic pressure in glomerulus. water glucose and mineral ions squeezed out to form filtrate

Question 3

what is the movement of the filtrate out of the glomerulus resisted by

Answer 3

capillary epithelial cells
connective tissue and epithelial cells of blood capillary
ep cells of renal capsule
lower water potential of blood in the glomerulus

Question 4

what overcomes the things that resist the glomerular filtrate forming

Answer 4

podocytes specialised cells- lower pressure in bowmans capsule and allows filtrate to pass through the gaps in them. bigger conc gradient from glomerulus to bowmans capsule

Question 5

describe the process of the reabsorption of glucose and water

Answer 5

happens in the proximal convoluted tubule
Na ions actively transported from cells lining the PCT to capillaries, give conc gradient from lumen of PCT to the ep cells of PCT
Na moves down conc gradient via protein carriers and facilitated diffusion but actually paired up with glucose so co transport
molecules transported into ep cells then diffuse into blood
85% of filtrate reabsorbed here

Question 6

describe the process of the maintenance of the sodium conc gradient

Answer 6

in loop of henle
Na ions actively transported out of ascending limb by ATP
creates lower water potential in medulla between limbs walls of descending limb permeable water moves out by osmosis into medulla then into blood
ascending limb impermeable so water doesn’t move out there
h2o moves out and reaches lowest water potential at bottom of loop of henle
Na ions diffuse out then are actively transported out at the ascending limb bringing water potential back up

Question 7

describe what happens at the distal convoluted tubule and collecting duct

Answer 7

high water potential in cortex and high w.p of filtrate in DCT
low wp in medulla lots of ions
collecting duct permeable to water as filtrate moves down into medulla water moves out by osmosis and into the blood
counter current multiplier means as the water potential of the filtrate decreases it also decreases in the medulla so water moves out by osmosis down entire length of collecting duct

Question 8

how does the body respond to a drop in water levels in the blood

Answer 8

osmoreceptors in hypothalamus detect fall in water pot
pituitary gland produces antidiuretic hormone (ADH)
ADH secreted into capillaries
ADH sent to kidney via blood
ADH activates phosphorylase which increases the permeability of the collecting duct and the DCT to water
also increases diffusion of urea into medulla increasing difference of water pot more water moves out of filtrate by osmosis and into the blood returning water potential of blood to normal levels
urine is more concentrated
also thirst centre stimulated so drink more

Question 9

how does the body respond to too high water potential in the blood

Answer 9

osmoreceptors in hypothalamus detect rise in water potential and reduces impulses to pituitary gland which releases less ADH
walls of DCT and collecting duct less permeable to water and urea
more dilute urine produced
more water leaves body
water potential of blood returns to normal