5.2 Kidneys

Question 1

Describe the process of ultrafiltration.

Answer 1

• Blood is under high pressure in the glomerulus.
• Water and other small molecules are forced through.
• This forms the glomerular filtrate in the bowman’s capsule.
• Proteins and cells are too large to pass through, so stay in blood.

Question 2

During ultrafiltration, what layers do molecules pass through?

Answer 2

• Pores in the capillary endothelium
• Basement membrane
• Pores in the bowman’s capsule endothelium which is lined with podocytes.

Question 3

Why can’t mitosis happen in podocytes?

Answer 3

• Due to podocytes having an irregular shape.

Question 4

What part of the kidney absorbs 85% of the useful substances?

Answer 4

• Proximal convoluted tubule.

Question 5

Describe selective reabsorption.

Answer 5

• Water is absorbed by osmosis.
• Useful substances absorbed by the proximal convoluted tubule into the blood.
• Glucose is reabsorbed by co-transport/facilitated diffusion with sodium ions.

Question 6

How is glucose re-absorbed by co-transport?

Answer 6

• Sodium ions actively transported out of the epithelial cells of the PCT and into the blood.
• Lower concentration of sodium ions in the cell than in the PCT, which has established a concentration gradient.
• Sodium ions and glucose transported from the lumen of the PCT into the epithelial cells by co-transport, using a carrier protein.
• Glucose moves into blood by facilitated diffusion using a channel protein.