6.10 - Absorption of the products of digestion

Question 1

What are the villi

Answer 1

The fold of the ileum in the small intestine that increase SA for faster absorption of soluble food

Question 2

Describe how villi increase the efficiency of absorption

Answer 2

• increase the SA for diffusion
• very thin —> short diffusion pathway
• contain muscle = so can move = helps to maintain diffusion gradients by mixing contents of the ileum (ensures that as the products of digestion are absorbed, it is then taken away, so that a conc. gradient is always maintained)
• well supplied with blood vessels so that blood can carry away absorbed molecules and hence maintain a diffusion gradients
• contains microvilli which are on the CSM —> further increases SA

Question 3

Describe the process for absorption of glucose/amino acids

Answer 3

• Na+ ions actively transported out of the ileum epithelial cells —> the lumen of the ileum (by the sodium-potassium pump). Creating concentration gradient — higher conc. Na+ ions in lumen of the ileum, than inside the epithelial cell
• this causes Na+ ions to diffuse from the lumen of the ileum —> epithelial cell, down their concentration gradient. They do this via the sodium-glucose co-transporter proteins
• the co-transporter carriers glucose into the cell with the sodium. As a result the concentration of glucose inside the cell increases
• glucose diffuses out of the cell, into the blood, down its concentration gradient through a protein channel, by facilitated diffusion

Question 4

Describe the process of lipid absorption

Answer 4

• micelles (bile salts attached to the fatty acids + monoglycerides) come into contact with the epithelial cells of the villi that line the lumen
• the micelles break down and because the fatty acids and monoglycerides are lipid-soluble, they diffuse straight into the epithelial cells
• Once inside the cell, monoglycerides and fatty acids are transported to the endoplasmic reticulum
• they are recombined into triglycerides then moved to Golgi apparatus
• chylomicrons form (made by triglycerides associating with cholesterol and lipoproteins)
• These are special particles adapted for transport of lipids
• they move out of the epithelial cell by exocytosis and into lymphatic capillaries called lacteals
• chylomicrons pass (via lymphatic vessels) into the blood stream where the triglycerides in the chylomicrons are hydrolysed by an enzyme in the endothelial cells of blood capillaries.