Digestion and Absorption

Question 1

Define digestion and absorption

Answer 1

Digestion - Breakdown of nutrients into absorbable molecules.

Absorption - Movement of nutrients, water and electrolytes from the gut lumen into the internal environment

Question 2

Describe the structure or the small intestinal mucosa

Answer 2

Surface of the small intestine is arranged in circular folds of Keckring. villi project from the folds and are covered in enterocytes and goblet cells. Microvilli cover the apical surface of cells creating a brush boarder

Question 3

Name the dietary requirements

Answer 3

Carbahydrates, lipids, proteins, vitamins (fat and water soluble) and minerals (trace metals)

Question 4

Describe the digestion of carbohydrates

Answer 4

Mouth - Salivary alpha amylase being digestion.

Stomach - Amylase on the inside of the bolus continue to act whereas the amylase on the surface is denatured.

Duodenum - Pancreatic amylase as well as the brush boarder enzymes start acting on disaccharides.

Question 5

Name the digestible and indigestible carbohydrates

Answer 5

Digestable - Starch (plants) and glycogen (animals) they are digestible as the alpha 1-4 glycoside bonds are broken by amylase.

Indigestible - Cellulose (plants) this is because chains are linked by beta 1-4 glycoside bonds and we have no enzymes to break this down

Question 6

Describe what is produced when amylase breaks down Polysaccharides

Answer 6

Produces maltotriose, maltose and alpha-limit dextrin

Question 7

Describe how the products of amylase are now digested?

Answer 7

They are digested by oligosaccharidases; alpha-glucosidase cleaves alpha 1-4 glycosidic bonds to remove single glucose units.
Isomaltase cleaves alpha 1-6 glycosidic bonds in the alpha limit dextrin oligosaccharides

Question 8

Describe the digestion of the products of amylase and oligosaccharidases

Answer 8

Hydolysis by disaccharidases,

Maltose - digested by maltase to produce glucose.

Sucrose - digested by sucrase to produce glucose and fructose.

Lactose - digested by lactase to produce galactose and glucose. These are the final products of carb digestion

Question 9

Describe the absorption of glucose and galactose

Answer 9

Secondary active transport - Use of the sodium dependent glucose transporter 1. These are located on the apical membrane.

Question 10

Describe the absorption of fructose

Answer 10

Facilitated diffusion via the glucose transporter 5. On apical membrane

Question 11

Describe how endopeptidase and exopeptidase function

Answer 11

Endopeptidase - Hydrolyse the interior peptide bond of proteins.

Exo - Hydrolyse one amino acid at a time from one end or the other.

Question 12

Name examples of endopeptidases

Answer 12

Pepsin, Trypsin, Chymotrypsin and elastase

Question 13

Name two examples of exopeptidase

Answer 13

Carboxypeptidase and aminopeptidase

Question 14

Summerise protein digestion

Answer 14

Gastric phase - Proteins denatures by hydrocholric acid and pepsin.

Pancreatic phase - broken down into amino acids and oligopeptides by trypsin, chymotrypsin or carboxypeptidase.

Mucosal phase - Oligopeptides further broken down into amino acids or dipeptides/tripeptides by aligopeptidase or aminopeptidase

Question 15

Describe the complications of digesting lipids

Answer 15

Dietary lipids are hydrophobic so they must be solubilised before digestion and absorption occurs. Digestion beings in the stomach with the action of lingual and gastric lipases and is completed in the SI with the action of pancreatic enzymes

Question 16

Name the 4 main types of lipids and the 3 main types of enzymes

Answer 16

1) Fats/oils,
2) Phospholipids,
3) Cholesterol and cholesterol esters,
4) Fatty Acids.

Enzymes - Lipases, phospholipases and cholesterol esterases.

Question 17

Describe the digestion of triacylglycerols by lipases

Answer 17

• In mouth and stomach a small amount are digested via salivary and gastric lipases. Heat and movements in the stomach mix food with lipases but hydrolysis is slow due to large aqueous/lipid interface. As hydrolysis proceeds the rate increases due to fatty acids acting as surfactants breaking down lipid globules.
  Duodenum - Pancreatic lipases aided by bile salts. Where majority of digestion occurs

Question 18

What is the role of bile salts in emulsions?

Answer 18

Bile salts coat lipids to make emulsions

Question 19

What occurs to produces of lipid digestion?

Answer 19

They are solubilised in mixed micelled and stored in the core. The surface of micelles are coated in bile salts. The monoglycerides and fatty acids are then removed from micelles and enter cells via diffusion

Question 20

What occurs when lipid products dissuse into a call?

Answer 20

The absorbed fats combine with cholesterol and proteins to from chylomicrons which are then released into the lymphatic system as they are too big to enter vascular capillaries

Question 21

Describe why recycling of bile salts is so important

Answer 21

Because we do not have enough to deal with the average meal so after use most are reabsorbed from the terminal ileum into the liver via the enterohepatic circulation (via hepatic portal vein)

Question 22

Describe the absorption of water in the large intestines

Answer 22

Na actively absorbed in exchange for K, K reabsorbed in exchange for H+, Cl absorbed in exchange for bicarbonate ions and so water follows due to osmosis. This is controlled by enteric nerve plexi and hormonal control