6.4.3 Controll Of Bloow Water

Question 1

Describe the structure of a nephron

Answer 1

Has a good network of capillaries

In Cortex:
-Renal(bowman’s) capsule
-proximal convoluted tube (PCT)
-Distal convoluted tube (DCT)

Medulla:
-descending and ascending limb (loop of henle)
-collecting duct

Question 2

Role in diffrent parts of nephron

Answer 2

Bowman’s capsule - formation of glomerular filtrate (ultrafiltration)

PCT-reabsorption of water and glucose (selective absorption)

Loops of henle- maintenance of gradient of Na ions in medulla

DCT and collecting duct - reabsorption of water

Question 3

Formation of glomerular filtrate

Answer 3

High hydrostatic pressure in golmerulus:
-as diameter of afferent ateriole(in) i wider than efferent ateriole (out)

Small substances (water, glucose, ions, urea) forces into golmerular filtrate by:
-pores between capillary endothelial cells
- capillary basement membrane
-podocytes

Large proteins remain in blood

Question 4

Reabsorption of glucose in PCT

Answer 4

Na actively transported out of epithelia cells to capillary

Na moves by facilitated diffusion into epithelial cells down a conc gradient, brining glucose against its conc gradient

Glucose moves into capillary by facilitated diffusion

Question 5

PCT and water reabsorption

Answer 5

Glucose lowers water potential in capillaries

Water moves via osmosis down water potential gradient

Question 6

Features of PCT allow rapid absorption

Answer 6

Microvilli- large SA
Many channel proteins - facilities diffusion/co transport
Many carrier proteins for active transport
Many mitochondria for ATP (active transport)
Many ribosomes to produce channel proteins

Question 7

Why is glucose found in the urine of an untested diabetic person

Answer 7

Blood conc is to high so not all glucose is reabsorbed into PCT

As glucoses carrier proteins are saturated and working at a max rate

Question 8

Importance of maintaining Na gradient in medulla

Answer 8

So water potential can decrease down the medulla

So water potential gradient is maintenance between collecting duct and medulla

To maximise reabsorption of water via osmosis

Question 9

Role of loop of henle

Answer 9

Ascending:
-Na is actively transported out
-water remains as limb is impermeable to water
- increases the conc of Na in medulla, lowering water potential

Descending:
-water moves out via osmosis then reabsorbed by capillaries
-Na diffuses back in

Question 10

Reabsorption of water in DCT

Answer 10

Water moves out of DCT and collecting duct by osmosis down a water potential gradient

Controlled by ADH which increases their permeability

Question 11

Role of hypothalamus in water regulation

Answer 11

Contains osmoreceptors which detached a change in blood water potential

Produce more ADH when water is low and less when water is high

Question 12

Why do animals
Needing to conserve water have longer loops of henle

Answer 12

More Na moved out so gradient is maintained for longer in medulla

So water potential gradient is maintained for longer

More water reabsorbed from collecting duct.

Question 13

Role of posterior pituitary gland

Answer 13

Secretes more or less ADH

Question 14

Role of ADH

Answer 14

Attaches to receptors on collecting duct and DCT

Stimulates addition of Channel proteins into cell surface membranes

Increases permeability of cells in collecting duct and DCT Stimulates addition

So increases water reabsorption by osmosis

Decreases volumes and increase conc of urine