6.9 - Absorption

Question 1

Absorption of triglycerides

Answer 1

1. Micelles are broken down to release fatty acids and monoglycerides.
2. As they are both non-polar, fatty acids and monoglycerides can diffuse into the epithelial cells that line the ileum.
3. Triglycerides reform inside the cells’ endoplasmic reticulum.
4. Triglycerides are packaged into chylomicrons for transport.
5. Chylomicrons are released from the epithelial cells by exocytosis into lacteals, which are lymphatic vessels in the villi.
6. Chylomicrons are transported via lymph vessels in the lymphatic system to the blood.

Question 2

Absorption of amino acids and monosaccharides

Answer 2

1. Sodium ions are actively transported out of ileum epithelial cells.
2. This sets up a sodium ion concentration gradient between the ileum lumen and the epithelial cells.
3. Sodium ions are co-transported with amino acids or monosaccharides from the lumen into the epithelial cells.
4. Amino acids and monosaccharides move by facilitated diffusion from epithelial cells into the blood.

Question 3

Adaptations of the ileum for absorption (5):

Answer 3

• The walls are folded into finger-like villi to increase surface area.
• Epithelial cells have microvilli to further increase surface area.
• It has thin walls reduce diffusion distance.
• It has an extensive capillary network and a good blood supply to maintain steep diffusion gradients.
• Muscles in the ileum wall contract to mix content and bring new material into contact with villi.