kidneys

Question 1

3 stages

Answer 1

ultrafiltration
selective reabsorption
osmoregulation

Question 2

what happens during ultrafiltration

Answer 2

(substances move from blood to nephron)
-blood enters glomerulus from the afferent arteriole and leaves by efferent arteriole
-as the diameter of the efferent is smaller than the afferent arteriole there is a high hydrostatic pressure
-this forces smaller molecules eg glucose and ions through fenestrations of glomerulus and into lumen of Bowmans capsule =glomerular filtrate
-large proteins are too big to pass through fenestrations in capillary so remain in blood.

Question 3

what happens during selective reabsorption

Answer 3

(substances move from nephron (PCT, loop of Henle, DCT) into blood ie the return of useful substances into blood)

-in PCT(proximal convoluted tubule) - glucose is actively transported into the cell then moves into blood by facilitated diffusion.
-in PCT- Na+ moves by facilitated diffusion into cell then into blood by active transport via Na+/K+/ATPase pump
-water is reabsorbed by osmosis down water gradient (as blood has more negative water gradient than nephron due to reabrpobuton of glucose)
-the remaining filtrate in the nephron= urine

Question 4

adaptations of kidneys

Answer 4

-lots of mitochondria for active transport
-microvilli on cells inc SA for absorption
-lots of channel/carrier proteins for facilitated diffusion and active transport

Question 5

osmoregulation A

Answer 5

-water moves from loop of Henle down the water gradient by osmosis into medulla then blood
-at the top of ascending limb, Na+ and Cl- are actively transported into medulla
-the ascending limb is impermeable to water so the water which cannot leave therefore gradient of medulla becomes negative

-now the water potential gradient of medulla is more negative than ascending limb therefore water moves out into medulla by osmosis then reabsorbed into blood
(glomerular filtrate becomes more concentrated)
-at the bottom of the ascending limb Na+ and Cl- move out by facilitated diffusion further lowering water potential of medulla
-the longer the loop of henle the more negative the water potential in medulla therefore steeper water gradient
-water also leaves DCT by osmosis down grading and is reabsorbed by blood

Question 6

osmoreguklatiom b (dehydration)

Answer 6

not enough water in blood so need to absorb more water from filtrate