Digestion and absorption

Question 1

Function of Intestines

Answer 1

Site of exchange of digested nutrients in mammals

Question 2

What is Digestion?

Answer 2

Breakdown of Large Insoluble Molecules into Small Soluble Molecules (so they can move into the blood and then into the body cells)

Starch/Glycogen (Carbohydrates) into Glucose by Amylase (Salivary in mouth, Pancreatic in small intestine) and Maltase/Lactase/Sucrase (on lining of small intestine)

Proteins into Amino Acids by Endopeptidase/Exopeptidase/Dipeptidase (Endopeptidase in stomach, Exopeptidase in small intestine, Dipeptidase on lining of small intestine)

Lipids into Monoglyceride and 2 Fatty Acids by Lipase (in small intestine)

Question 3

What do the intestines Absorb?

Answer 3

Small Intestine absorbs small soluble nutrients (glucose, amino acids, monoglyceride and fatty acid, vitamins and minerals)

Large Intestine absorbs water

Question 4

Enzymes of Carbohydrate

Answer 4

Starch/Glycogen (Salivary Amylase in Mouth, Pancreatic Amylase in Small Intestine) into Maltose

Maltose (Maltase on lining of Small Intestine) into Glucose

Lactose (Lactase on lining of Small Intestine) into Glucose and Galactose

Sucrose (Sucrase on lining of Small Intestine) into Glucose and Fructose

Question 5

Enzymes of Protein Digestion

Answer 5

Endopeptidase (in stomach), hydrolyses peptide bonds in middle of polypeptide chain into many smaller chains

Exopeptidase (in small intestine), hydrolyses peptide bonds at end of chains to leave dipeptides

Deipeptidase (on lining of small intestine), hydrolyse dipeptides into amino acids

Question 6

Enzymes of Lipid Digestion?

Answer 6

Lipase in Small Intestine leaves Monoglyceride and 2 Fatty Acids

Question 7

Adaptations of SI for Absorption?

Answer 7

folded to form Villus (large surface area)

cells lining SI have Microvilli (large surface area)

wall of SI is thin (short diffusion distance)

rich blood supply (maintains concentration gradient)

cells lining SI have transport proteins, enzymes (maltase, lactase, sucrase, didpeptidase) and many mitochondria

Question 8

Absorption of Glucose and Amino Acids in SI?

Answer 8

sodium ions are actively transported from the cells lining the SI into the blood

lowers the sodium ion concentration in the cell

therefore sodium ions move from the lumen of the SI into the cell

this pulls in glucose and amino acids via a cotransport protein

therefore glucose and amino acids builds up in the cell and moves into the blood by diffusion

Question 9

Absorption of Monoglyceride and Fatty Acids?

Answer 9

Lipids initially emulsified by Bile into Micelles (smaller droplets)

Micelles digested by Lipase into Monoglyceride and 2 Fatty Acids

Monoglyceride and Fatty Acids absorbed by Cells lining SI by simple diffusion

Form a Chylomicron (lipid + cholesterol + lipoprotein)

Enters Lymph as Lacteal, then enters Blood

Question 10

What is Lactose Intolerance

Answer 10

Person does not make Lactase Enzyme

Lactose remains Undigested

Leads to Diarrhoea and Flatulence

Undigested Lactose in Lumen of Intestine lowers it’s water potential, so water enters the lumen by osmosis leading to water faeces (Diarrhoea)

Undigested Lactose brokendown by micro-organisms in Large Intestine, giving off gas (Flatulence)