16.6 nephron

Question 1

4 roles of nephron in osmoregulation

Answer 1

1. formation of glomerular filtrate by ultrafiltration
2. reabsorption of glucose and water by proximal convoluted tube
3. maintenance of gradient of sodium ions in medulla by loop of Henle
4. reabsorption of water by distal convoluted tubule and collecting ducts

Question 2

Glomerular filtrate

Answer 2

diameter of afferent arteriole is greater than efferent arteriole

creates hydrostatic pressure in glomoreulus

water, glucose and mineral ions are squeezed out of pores between endothelial cells

Question 3

Why blood cells and large proteins can’t pass into renal capsule

Answer 3

too large

Question 4

resistance in glomerulus filtrate

Answer 4

capillary endothelial cells
connective tissue of blood capillary
epithelial cells of renal capsule
hydrostatic pressure of fluid in renal capsule space
low wpt of blood in glomerulus

Question 5

Modifications to reduce resistance

Answer 5

• podocytes of renal capsule inner layer have spaces between them, allowing filtrate to pass beneath them and through grasp between their branches
• endothelium of glomoreular capillaries have very small spaces between the cells that fluid can pass through

Question 6

reabsorption of glucose and water by proximal convoluted tube

Answer 6

• sodium ions actively transported out of cells lining proximal convoluted tubule into blood capillaries which carry them away(Na+ conc of cells is lowered)
• Na+ diffuse down conc gradient from lumen out of proximal convoluted tubule into epithelial lining cells through special carrier proteins (facilitated diffusion)

-carrier proteins co transport with Na+ ions(e.g. glucose, amino acid, Cl-)

• molecules which have been co-transported diffuse into blood, so are reabsorbed as well as water

Question 7

Proximal convoluted tube adaptations

Answer 7

• microvilli to provide large SA to reabsorb from filtrate
• infoldings at bases for large SA to transfer reabsorbed substance into blood capillaries
• high density mitochondria to provide ATP for active transport

Question 8

2 regions of loop of Henle

Answer 8

1. descending narrow limb with thin walls that highly permeable to water
2. ascending wider limb with thick walls that are impermeable to water

Question 9

loop of Henle reabsorbing water from collecting duct

Answer 9

1. Na+ ions actively transported out of ascending limb of loop of Henle using ATP
2. Creates low water potential in interstitial spaceThick ascending walls allow no osmosis
3. Walls of descending limbs are permeable so water passes out the filtrate by osmosis into interstitial space
4. filtrate progressively loses water as it moves down descending limb, lowering its water potential
5. at base, Na+ ions diffuse out filtrate. As they move up ascending limb, ions are actively transported out and filtrate develops progressively higher wpt
6. interstitial space between ascending limb and collecting duct has gradient of wpt with highest in cortex and lower in medulla
7. water passes out of filtrate by osmosis into permeable collecting duct, being carried away by blood vessels within
8. wpt of filtrate is lowered but so is wpt interstitial space, so water continues moving out via osmosis

Question 10

region between loop of henle limbs

Answer 10

interstitial space

Question 11

ADH

Answer 11

controls the number of channel proteins specific to water in collecting duct, that controls water loss

Question 12

distal convoluted tube

Answer 12

reabsorbs material from filtrate by active transport
controls PH of blood by selecting ions, water and salts to be reabsorbed

permeability is affected by hormones

Question 13

counter-current multiplier

Answer 13

loop of Henle has counter-current flow that means filtrate in collecting duct with low wpt meets interstitial fluid with lower wpt

wpt gradient exists between entire collecting duct