absorption in the small intestine

Question 1

state and describe the three parts of the small intestine.

Answer 1

duodenum - the shortest part of the small intestine and is where most digestion using enzymes take place.
jejunum - absorbs carbohydrates and proteins and the inner surface is covered in villi and microvilli.
ileum - mainly absorbs vitamin B12, bile salts and any products of digestion not absorbed by jejunum.

Question 2

describe the structure of the ileum in the small intestine.

Answer 2

• the wall is made up of folds which has many villi on the surface.
• has a large surface area for absorption of enzyme molecules and products of digestion.

Question 3

describe some adaptations of the cells lining the small intestine that help with efficient absorption.

Answer 3

lots of microvilli - large surface area for more absorption.
many mitochondria - respiration to produce ATP via active transport.
many proteins in the membrane e.g channel and carrier for facilitated diffusion and active transport - allows co-transport of sodium and glucose.
- membrane bound enzymes digest disaccharides

Question 4

describe the absorption in the small intestine (co-transport).

Answer 4

• actively transport sodium out of epithelial cells into the blood using sodium-potassium pump (potassium ions move into epithelial cell).
• this creates a conc gradient of higher sodium concentration in the ileum than in the epithelial cell.
• sodium ions move from ileum into epithelial cell, along with glucose through co-transport protein.
• glucose moves from epithelial cell to blood via facilitated diffusion (down conc gradient).

Question 5

suggest why membrane bound enzymes are important in digestion.

Answer 5

they are located on the cell membranes of epithelial cells lining ileum and they maintain concentration gradient for absorption (by hydrolysing molecules).