Absorption of Nutrients

Question 1

What happens when chemical digestion is complete?

Answer 1

• Complex carbohydrates will have broken down into simple sugars. Proteins into amino acids. Fats into fatty acids and glycerol.
• These products along with substances such as vitamins, minerals and water, are then absorbed through the wall of the small intestine into to the blood.

Question 2

How are fatty acids and glycerol absorbed?

Answer 2

Fatty Acids and Glycerol are absorbed by simple diffusion. In the cells of the villi the fatty acids and glycerol recombine to form fats. The tiny fat droplets enter the lacteals.

Question 3

How are amino acids absorbed?

Answer 3

Amino Acids are absorbed by active transport into the blood capillaries

Question 4

How are simple sugars absorbed?

Answer 4

Simple sugars (glucose) are absorbed by active transport. They pass through the cells on the outside of the villi and into the blood capillaries.

Question 5

How are water/water-soluble vitamins absorbed?

Answer 5

Water and water-soluble Vitamins are absorbed into the blood capillaries by diffusion.

Question 6

Where are nutrients absorbed?

Answer 6

Nutrients are absorbed through the internal surface of the small intestine, so efficient absorption requires a large surface area.

Question 7

How is a large surface area in the SI achieved?

Answer 7

• The SI is very long – about 6-7m.
• The inner lining (mucosa) has folds that extend from the folded surface.
• The cells covering the outside of the villi have tiny, microscopic projections from their external surface (microvilli).

Question 8

Describe the structure of the villi?

Answer 8

Each villus is about 1mm long and covered by a single layer of cells. Inside the villus is a lymph capillary (lacteal) which is surrounded by a network of blood capillaries.

Question 9

How is absorption helped in the villi?

Answer 9

By muscular movements of the intestinal wall that keep the villi moving and bring the villi into contact with different parts of the intestinal contents that are constantly changing.

Question 10

What is simple diffusion in the SI?

Answer 10

There is a higher concentration of nutrient materials in the interior of the small intestine than in the cells lining the villi.

Question 11

What is active transport in the SI?

Answer 11

Involves the cells of the villi using energy to take in nutrients against a concentration gradient (from lower to higher concentration).

Question 12

How are nutrients transported into the lymphatic system?

Answer 12

1. From the walls of the villi, simple sugars, amino acids, water and water-soluble vitamins are absorbed into the blood capillaries.
2. Fatty acids and glycerol recombine in cells of the villi to form fats and, along with the fat-soluble vitamins, enter the lacteals.
3. Substances that are absorbed into the lacteals are transported in the lymph system, which eventually empties into the blood through veins the upper part of the chest.

Question 13

How are nutrients transported into the blood?

Answer 13

1. The substances that are absorbed into the blood capillaries are carried by the hepatic portal vein to the liver.
2. Here they may be removed for further processing, or they may remain in the blood to be carried to other body cells.

Question 14

What is the role of the large intestine in water absorption?

Answer 14

1. There are no villi in the large intestine, and no digestive juices are secreted, although the lining does secrete a large amount of mucus.
2. Movement of material through the large intestine is slow, taking 18-24 hours for material to pass through.
3. During this time, most of the remaining water is absorbed so the contents become more solid.

Question 15

What is the role of the large intestine in vitamin absorption?

Answer 15

1. Bacteria in the large intestine break down much of the remaining organic compounds.
2. Some bacteria produce vitamins, which are then absorbed through the wall into the blood. Mineral nutrients are absorbed.