How does blood enter the kidney?
Renal artery
What is the function of the kidney?
Filter out urea and excess water/ions from the blood
What is osmoregulation?
The regulation of the water potential of the blood
What is ultrafiltration?
The filtering of substances out of the blood
What is selective reabsorption?
The reabsoprtion of useful substances and the right volume of water into the blood
What is a nephron?
Long tubules with bundles of capillaries where the blood is filtered
What happens during ultrafiltration?
- Blood enters from the renal artery into smaller arterioles
- The afferent arteriole takes blood to the glomerulus
- High pressure forces out liquid and small molecules into the Bowman’s capsule
- The efferent arteriole transports the blood away which now contains only large proteins/blood cells
Why is there a high pressure in the glomerulus?
The efferent arteriole is smaller in diameter than the afferent arteriole
What is the glomerular filtrate?
The substances from the blood that enter the Bowman’s capsule
Which substances are not filtered out of the blood and why?
Blood cells
Proteins
Too large to pass through capillary endothelium
What cells makes up the epithelium of the Bowman’s capsule?
Podocytes
What happens during reabsorption in the proximal convoluted tubule?
- Glucose and solutes are reabsorbed into the blood by active transport
- Water moves into the blood by osmosis down the water potential gradient
How are the cells in the proximal convoluted tubule adapted for reabsorption?
Microvilli provide large surface area
Where is the loop of Henle?
The medulla (inner layer of the kidneys)
What are the two parts of the loop of Henle?
Descending limb
Ascending limb
Explain how the loop of Henle works
- At the top of the ascending limb, Na+ ions are actively transported into the medulla
- The water potential of the medulla is lowered
- Water moves out of the descending limb, into the medulla by osmosis
- The glomerular filtrate is more concentrated
- At the bottom of the ascending limb, Na+ ions diffuse into the medulla
- The water potential in the medulla is lowered
Why is it important that the ascending limb is impermeable to water?
So that water does not move out of the ascending limb and into the medulla and increase the water potential
What is the whole point of the loop of Henle?
To make the water potential of the medulla very low
So water moves out of the DESCENDING LIMB
How are the distal convoluted tubule, medulla, loop of Henle and collecting duct linked ?
The loop of henle lowers the water potential of the medulla
Water moves out of the DCT and collecting duct into the medulla
How is the water that enters the medulla reabsorbed into the blood?
Through the capillary network
Why is the countercurrent of the loop of Henle important?
Maintains a concentration gradient in the medulla across the whole length of the loop
More water can move into the medulla
How is the volume of water which is reabsorbed into the capillaries controlled?
Changing the water permeability of the DCT and collecting duct
What happens when the water potential of the blood is too low?
- Osmoreceptors in the hypothalamus detect the decrease in water potential
- Posterior pituitary gland releases ADH
- ADH binds to receptors on cell membranes of DCT and collecting duct cells
- Aquaporins move to and fuse with cell membrane
- More water can pass out and into the medulla so more water is reabsorbed
What happens to the urine when the water potential of the blood is too low?
Very concentrated and little volume
as more water has been reabsorbed
