digestion and absorption

Question 1

what is digestion?

Answer 1

large, insoluble molecules hydrolysed into smaller molecules that can be absorbed across cell membranes and into bloodstream

Question 2

how are carbohydrates digested?

Answer 2

. require more than one enzyme to hydrolyse them into monosaccharides; amylases and membrane bound disaccharides
. amylase produced in pancreas and salivary glands. Hydrolyses polysaccharides into disaccharide maltose by hydrolysing glycosidic bonds
. sucrase and lactase are membrane bound enzymes that hydrolyse sucrose and lactose ( sucrose- fructose and glucose, lactose- galactose and glucose)

Question 3

How are proteins digested?

Answer 3

. Proteins are large polymer molecules that can be hydrolysed by 3 enzymes:
- endopeptidases; hydrolyse peptide bonds between amino acids in middle of a polymer chain
-Exopeptidases; hydrolyse peptide bonds between amino acids at end of polymer chain
-Membrane bound dipeptides; hydrolyse peptide bonds between 2 amino acids

Question 4

How are lipids digested?

Answer 4

. Digested by lipase ( chemical) and action of bile salts ( physical)
. Lipase produced in pancreas and can hydrolyse ester bond in triglycerides to form monoglycerides and fatty acids
. Bile salts produced in liver and emulsify lipids to form tiny droplets called micelles. Increases SA for lipase to act on ( happens before lipase action)

Question 5

How are micelles formed?

Answer 5

. They’re water soluble vesicles formed of fatty acids, glycerol, monoglyceride and bile salts
. They deliver fatty acids,monoglycerides and glycerol to epithelial cells of ileum for absorption

Question 6

Absorption in mammals?

Answer 6

. Products of digestion are absorbed across cells lining to ileum wall covered in villi- thin walls surrounded by network of capillaries and epithelial cells have even smaller microvilli
. These features maximise absorption by inc SA, decreasing diffusion distance and maintaining a concentration gradient

Question 7

How are monosaccharides and amino acids absorbed?

Answer 7

. Glucose and amino acids absorbed from lumen to gut
. Must be a higher conc in lumen compared to epithelial cell for facilitated diffusion
.BUT
. there’s usually more in epithelial cells so active transport and co transport required

Question 8

How are lipids absorbed?

Answer 8

. Micelles encounter ileum epithelial cells, due to nature of fatty acids and monoglycerides, they can simply diffuse across cell surface membrane to enter cells of epithelial cells
. Once in cell, modified back into triglycerides inside of endoplasmic reticulum and Golgi body
. Triglycerides/ fatty globules combine with proteins to form chylomicron inside of Golgi apparatus
. Chylomicron released from Golgi and Golgi vesicle move towards other end of epithelial cell and released by exocytosis
. Absorbed into rest of body through lacteal lymph vessel and chylomicron absorbed inside lacteal and transported around lymph and drains into capillary system