Absorption

Question 1

Where does absorption take place?

Answer 1

in mammals the products of digestion are absorbed across cells lining the ileum (final section of the small intestine)

Question 2

How is the small intestine adapted for absorption?

Answer 2

• thin epithelium (one cell thick)
  → short diffusion distance
• very long and folded
  → large surface area for efficient absorption
• villi (thin walls + surrounded by network of capillaries) and epithelial cells have microvilli
  → good blood supply, short diffusion distance, large SA, maintains conc gradient

Question 3

How are monosaccharides and amino acids absorbed?

Answer 3

1.) sodium ion and monosaccharide/aa bind to carrier protein and move into the cell via co-transport
2.) the sodium ion moves into the blood via active transport which requires ATP
3.) monosaccharide/aa moves out of the cell via facilitated diffusion as the concentration is lower in the blood

Question 4

Why is active/co-transport required in absorbing monosaccharides/amino acids?

Answer 4

to absorb monosaccharides/aa from the lumen to the gut there must be a higher conc in the lumen that epithelial cells but its usually higher in the epithelial cells

Question 5

Why must the conc of sodium ions be higher in the lumen?

Answer 5

to maintain a concentration gradient so equilibrium is not reached so monosaccharides and amino acids can still move by co-transport.

Question 6

How are lipids absorbed?

Answer 6

• due to non polar nature of the fatty acids and monoglycerides they simply diffuse across the cell membrane into the epithelial cell.
• once inside they will be modified back into triglycerides which are then packaged with phospholipids, protein and cholesterol to form chylomicrons (in endoplasmic reticulum + golgi body)
• these are transferred by exocytosis (as they are large) to the lacteal running through the center of a villus