6C The Kidneys

Question 1

Function of the kidneys

Answer 1

To excrete waste products and regulate the water potential of the blood

Question 2

Describe ultrafiltration of the kidney

Answer 2

As blood passes through the capillaries in the cortex of the kidneys substances are filtered out of the blood and into long tubules that surround the capillaries

Useful substances are then reabsorbed

Question 3

Define selective reabsorption

Answer 3

Useful substances are reabsorbed into the blood

Question 4

Explain how blood is filtered at the start of the nephrons

Answer 4

Blood from the renal enters smaller arterioles in the cortex of the kidneys
Each arteriole splits into a glomerulus a bundle of capillaries looped inside the Bowman’s capsule

This is where ultrafiltration takes place

The afferent arteriole takes blood into each glomerulus

The efferent arteriole takes blood away from the glomerulus and is smaller in diameter so blood is under high pressure

The liquid and small molecules pass through three layers to get into the Bowman’s capsule and enter the nephron tubules the capillary wall a membrane and the epithelium of the bowman’s capsule

Larger molecules stay in the blood
The substances that enter the bowman’s capsule are known as the glomerular filtrate

Question 5

What happens to the glomerular filtrate

Answer 5

It passes along the rest of the nephron and useful substances are reabsorbed

Then the filtrate flows then the collecting duct and passes out the kidney along the ureter

Question 6

When does selective reabsorption take place

Answer 6

As the glomerular filtrate flows along the proximal convoluted tubule (DVT)

Useful substances leave the tubules of the nephrons and enter the capillary network that’s wrapped around them

The epithelium of the wall of the PCT has microvilli to provide a large surface area for the reabsorption from the glomerular filtrate into the blood

Useful substances like glucose are reabsorbed along the PCT via active transport and facilitated diffusion

Water enters the blood by osmosis as the water potential of the blood is lower than the filtrate

Water is reabsorbed from the PCT loop of Henle DCT and the collecting duct

The filtrate that remains is urine which passes out the bladder along the uterer

Question 7

What does urine contain

Answer 7

Water and dissolved salts
Urea
Hormones and excess vitamins

Question 8

What does urine usually not contain

Answer 8

Proteins and blood cells
Glucose