Blood Water Potential Control

Question 1

Ultra filtration

Answer 1

In glomerulus and bowman’s capsule

Ultra filtration is filtration under high hydrostatic pressure created in the glomerulus due to a difference in diameter of the arterioles: afferent wider than efferent arteriolar so high blood pressure in the renal artery greater than water potential of blood

Capillary endothelial cell has walls

Pores in basement membrane forms a filter between the blood and the nephron

Podocytes create filtration slots on epithelial layer of the capsule

Acts as a molecular sieve :blood cells and large proteins stay in the blood as they are too large

Much of the blood plasma (including dissolved small glucose and urea) passes through into the bowman’s capsule as filtrate

Question 2

How is proximal convoluted tube adapted to reabsorption

Answer 2

Large surface area many micro Villi

Lots of mitochondria to synthesise arp for active transport

Close to blood capillaries

Question 3

How does loop of Henley provide osmotic gradient in the medulla for reabsorption of water

Answer 3

Loop of henle creates a high concentration of salts with a low water potential in the medulla for reabsorption of water by osmosis from descending limb and collecting duct by osmosis, reducing the volume of the filtrate

Ascending limb is impermeable to water and cells actively transport na+ into the tissue fluid of the medulla

Descending limb cells are permeable to water so water moves out of the filtrate by osmosis down water potential gradient

Question 4

Adaptations of loop of henle

Answer 4

The loop of henle reduces the water potential of the medulla by losing ions at the bottom of the loop and by active transport

A longer loop would lose more ions and create a lower water potential in the medulla than other organisms

A shorter loop would lose less ions and create a higher water potential in the medulla than other organisms

Question 5

How is sodium ion gradient maintained in the loop of henle

Answer 5

Mitochondria in the walls of the cells provide energy to actively transport sodium ions out of the ascending limb of the loop of henle

The accumulation of sodium ions in outside of the nephron in the medulla lowers the water potential

Therefore water diffuses out by osmosis into the interstitial space and then the blood capillaries water is then reabsorbed into the blood

At the base of the ascending limb some sodium ions are transported about by diffusion as there is now a very dilute solution due to all the water that has moved out