KIDNEY

Question 1

What is the role of the kidney?

Answer 1

Part of the urinary system, that excretes waste products. It has 3 main roles:
1. Removal of urea, which is produced from the liver by excess amino acids
2. Adjusting salt levels in the blood
3. Adjusting water levels in the blood

This is done by filtering the high-pressure blood, and reabsorbing useful substances, while urine is left to be excreted

Question 2

What is ultrafiltration?

Answer 2

In the kidney, are thousands of nephrons, which are the site of this and reabsorption.
1. Blood from the renal artery flows through the glomerulus - a bundle of capillaries at the nephron’s beginning
2. Water, urea, salts and glucose are squeezed into the Bowman’s capsule under high pressure
3. The membranes between these blood vessels filter out proteins and blood cells as they are too big, and stay in the blood
4. What is left in the Bowman’s capsule is called the glomerular filtrate

Question 3

What is reabsorption?

Answer 3

After ultrafiltration, the glomerular filtrate flows along the nephron and substances begin to be reabsorbed back into the blood:
1. Glucose is reabsorbed at the proximal convoluted tubule (needed for respiration) by active transport, since it is working against the concentration gradient
2. Useful salts are reabsorbed
3. Sufficient water is reabsorbed from the collecting duct to the blood by osmosis
4. What is left (water, salts, urea) form urine, down the ureter, into the bladder and out of the nephron

Question 4

What is osmoregulation?

Answer 4

Water is lost by sweating, breathing and urinating, and osmoregulation is the body’s balance of water coming in and out of the body

Question 5

How is water level controlled in the kidney?

Answer 5

Anti-diuretic hormone increases the permeability of the nephron’s collecting ducts, so more water is reabsorbed into the blood, and this is released from the pituitary gland
This process is controlled by negative feedback - if the body’s levels are out of order, mechanisms are triggered to return to normal

If the body has too little water and the brain recognises this, more ADH is released, and the kidney absorbs more water (opposite if there is too much water)

Question 6

What are the components of the nephron?

Answer 6

Proximal convoluted tubule - reabsorb glucose, some salts and some water from the filtrate
Bowman’s capsule - collects filtrate from glomerulus
Collecting duct - absorbs more water from the filtrate, before urine is sent to the ureter
Loop of Henle - goes down into the medulla, and reabsorbs water from the filtrate

Question 7

How do concentrations of substances change down the nephron?

Answer 7

As the blood enters the glomerulus, all substances are at 100% concentration
With the glomerular filtrate, glucose, urea and salts are present in full, and water concentrations, but protein was too big and stayed in the blood
After the proximal convoluted tubule, glucose and most water is also reabsorbed back into the blood, but the conc. of salts doesn’t change, while the conc. of urea increases
At the collecting duct, the conc. of urea has increased massively and the conc. of salts increases, and most water has been reabsorbed.