4.5 Co-transport and absorption of glucose in the ileum

Question 1

What part do villi and microvilli in the ileum play in absorption?

Answer 1

increase surface area upon which diffusion, facilitated diffusion and active transport may occur

Question 2

What characteristics can membranes have to increase absorption?

Answer 2

-possess microvilli (~0.6μm long) to increase surface area
-increased density of transmembrane proteins on membrane

Question 3

What is the role of diffusion in absorption?

Answer 3

glucose and amino acids move from the ileum into the blood via facilitated diffusion; the blood’s constant circulation helps maintain a suitable concentration gradient

Question 4

What is the role of active transport in absorption?

Answer 4

the glucose and amino acids that couldn’t be absorbed through diffusion is moved into the epithelial cells through a process called co-transport

Question 5

Describe the process of co-transport.

Answer 5

1- sodium ions are actively transported out of the epithelial cells through the sodium-potassium pump (carrier protein), into the blood. this results in a higher concentration of Na+ in the lumen than the epithelial cells.
2- sodium ions diffuse into the epithelial cells through a different carrier protein (co-transport protein) and bring the amino acids or glucose with them (the aa and glucose are polar molecules with areas of δ- charge, which is attracted to the Na+)
3- the amino acids and glucose pass into the blood plasma by facilitated diffusion through another carrier protein

Question 6

Why does co-transport count as indirect active transport, rather than direct active transport?

Answer 6

the sodium ions diffusing into the cell is what transports the glucose and amino acids, rather than ATP directly