Co-transport and absorption of glucose in the ileum (Small intestine)

Question 1

How do the epithelial cells in the small intestine help to increase the rate of diffusion?

Answer 1

• They have microvilli - finger-like projections (about 0.6um).
• The microvilli provide more SA for insertion (putting) of carrier proteins through where diffusion, FD and AT can take place.
• To increase transport across membranes, you can also increase the number of protein channels and carrier proteins in any given area - increase their density.

Question 2

How can cells increase the rate of transportation?

Answer 2

• Increase in SA.

- Increase the number of protein channels and carrier molecules in their membrane.

Question 3

What is the diffusion which goes on inside of the small intestine?

Answer 3

• As carbohydrates and proteins are constantly digested, they are normally more glucose and amino acids in the ileum than the blood. (carbohydrates are broken down into glucose and proteins into amino acids).
• Blood is constantly circulated by the heart, so the glucose which has been absorbed would be constantly removed by the cells as they get used up during respiration.
• This helps to maintain the concentration gradient between inside the ileum and blood.
• So the rate of diffusion across epithelial cell-surface membranes is increased.

Question 4

Why is diffusion not the best way of transportation for absorption?

Answer 4

Because diffusion only helps the concentration on either side of the intestinal epithelium to become equal so it does achieve the idea to absorb all the available glucose and amino acid.
So instead of diffusion, glucose and amino acids are absorbed through active transport.

Question 5

What is the mechanism by which the glucose and amino acids are absorbed from the small intestine?

Answer 5

Co-transport.
Because both glucose or amino acids are drawn into the cell along with sodium ions that have been actively transported out by the sodium-potassium pump.

Question 6

Explain what happens in the sodium-potassium pump with the co-transport of glucose?

Answer 6

1) Sodium is actively needed in the blood capillary and potassium is needed to be pumped in from the blood into the epithelial cell, so Na+ is transported from the epithelial cell by the sodium-potassium pump into the blood. It takes place at a carrier protein molecule that is found in the cell surface membrane of the epithelial cell.
(This is a form of active transport because it goes against the gradient)
2) This allows a greater concentration of Na+ in the lumen than inside of the epithelial cell.
3) Because there’s a low conc. of Na+ in the epithelial cell, Na+ is then needed to be pumped from the lumen into the epithelial cell down the conc. gradient through a different type of carrier protein (co-transport protein) in the CSM. As sodium pumps through this protein, it takes a molecule of glucose or amino acid with them.
4) The glucose/amino acid is passed into the blood plasma by facilitated diffusion using another type of carrier.

Question 7

What is diarrhoea?

Answer 7

An intestinal disorder where watery feaces are produced frequently.

• It causes damage to the epithelial cells lining the intestine.
• Loss of microvilli due to toxins.
• Excessive secretion of water due to toxins.

Question 8

How can diarrhoea be treated?

Answer 8

Oral rehydration therapy.

Question 9

Why dehydration while with diarrhoea can be fatal?

Answer 9

Insufficient fluid is taken in and excessive fluid is lost from the body.

Question 10

Why just by drinking water is ineffective for diarrhoea?

Answer 10

• Water is not been absorbed from the intestine e.g. cholera, water is being lost from cells.
• Drinking water does not replace the ions that have been lost from the cells.

Question 11

What does a rehydration solution contain?

Answer 11

• Water - to rehydrate the tissues.
• Sodium ions - to replace the lost sodium ions from the epithelium of the intestine and can allow alternative sodium-glucose carrier proteins to be used. (Because there are other types of carrier proteins in the plasma membrane. As sodium ions are absorbed, the water potential of the cell falls and water enters by osmosis).
• Glucose - Stimulate the uptake of sodium ions from the intestine and to provide energy.
• Potassium ions - replace lost potassium ions and to stimulate appetite.
• other electrolytes - e.g. chloride ions to prevent electrolyte imbalance and a condition called metabolic acidosis.

Question 12

How can oral rehydration help with diarrhoea?

Answer 12

It does not cure diarrhoea by it allows the patient to stay hydrated until they are been cured.