digestion and absorption

Question 1

fats

Answer 1

saturated: meat fat, butter, cheese, cream
unsaturated: olive, rape seed, nuts
cholesterol: plants and animals, dairy products, palm oil

Too much…..
Atherosclerosis (MI, stroke)
Obesity

Question 2

protein

Answer 2

Polymers of 20 amino acids
Essential (9): phenylalanine, valine,
tryptophan, threonine, isoleucine,
methionine, histidine, leucine,
& lysine

Question 3

digestion

Answer 3

Digestionis the process by which food is broken down into components simple enough to be absorbed in the intestine.

Carried out by enzymes secreted by
-glandular cells in the mouth
-chief cells in the stomach
-exocrine cells of the pancreas
-enzymes bound to the apical membrane
of enterocytes.

Question 4

salivary secretion

Answer 4

Production: parotid, submandibular and sublingual salivary glands

Moistens food
Starts the digestion of
carbohydrates a-amylase

Starts the digestion of lipids (minor: lingual lipase)

Question 5

stomach

Answer 5

Start of protein digestion

Chief cells: secrete pepsinogen

Parietal cells: hydrochloric acid secretion
denatures proteins activates pepsin
= endopeptidase

Question 6

zymogens

Answer 6

Many enzymes are synthesised as inactive precursors that are subsequently activated by cleavage of one/a few specific peptide bonds. The inactive precursor is called azymogen(orproenzyme).

Pepsinogen inactive ——> pepsin active

Question 8

proteolytic enzymes, PANCREATIC SECRETIONS

Answer 8

Trypsin- proteins
Chymotrypsin- proteins
Carboxypeptidase- proteins
Elastase- proteins (elastin)
- released as zymogens

Question 9

non-proteolytic enzyme, pancreatic secretions

Answer 9

Phospholipase - phospholipids
Amylase- starch
Lipase- triglycerides
Ribonuclease- RNA
Deoxyribonuclease- DNA
- released in active forms

Question 10

liver

Answer 10

Production and secretion of bile

Stored in gallbladder and released into
the duodenum after a meal

Emulsification of fat particles

Aids absorption of fats by forming
complexes called micelles

Question 11

bile

Answer 11

bile salts:
synthesised from cholesterol——> colic acid, chenodeoxycholic acid

Conjugated to amino acid (glycine or taurine)
Amphipathic

Functions:
1.Emulsification of lipid aggregates
2.Solubilisation & transport of lipids in aqueous environment

Question 12

small intestine

Answer 12

Duodenum:
Mixing secretions from pancreas, liver and duodenum with food
Neutralisation of acid
Further digestion
Absorption

Jejunum:
Completing breakdown
Nutrient absorption

Ileum:
Nutrient absorption

Question 13

small intestine

Answer 13

Brush border enzymes:
Integral part of the
membrane
(not free in lumen)

Peptidases
Lactase
Sucrase
Maltase

Question 14

mouth

Answer 14

Mastication

Bolus

Carbohydrates:
Starch broken down by
a-amylase to maltotriose,
maltose and a-limit dextrin

Proteins: nothing

Lipids: lingual lipase present
but minor contribution

Question 15

stomach

Answer 15

Churning

Chyme

Carbohydrates: nothing

Proteins: HCl denatures proteins & activates pepsin
(endopeptidase that cleaves proteins to
smaller peptides)

Lipids: gastric lipase present
but minor contribution

Question 16

duodenum, chyme and carbs

Answer 16

Chyme mixes with pancreatic juice and bile
Slightly alkaline

Carbohydrates: a-amylase further digests starch
Brush border disaccharidases (maltase, sucrase, lactase)
Result in monosaccharides

Question 17

duodenum, proteins and lipids

Answer 17

Proteins: cleaved by trypsin, chymotrypsin, elastase,
carboxypeptidases to produce increasingly
smaller peptides/dipeptides
Brush border peptidases produce dipeptides/amino acids

Lipids: pancreatic lipase digests lipids to
monoglycerides and fatty acids. Phospholipase
digests phospholipids to lysolecithin & fatty acids

Question 18

absorption

Answer 18

Passive absorption – diffusion
slow
needs concentration gradient or charge gradient

Facilitated transport
slightly faster
involves membrane carrier
controllable

Active transport
uses energy
fast
uses membrane carrier
controllable

Question 19

absorption of lipids- formation of micelles

Answer 19

polar head group
non polar hydrocarbon chain
hydrophobic lipid core (insoluble long chain fatty acids)

Question 20

chylomicron formation

Answer 20

If fatty acids are less than
12 carbons long they go
straight to the portal blood

If larger,
triglyceride reformed into
protein/lipid structure called
a chylomicron.

Chylomicrons 76-100nm
diameter secreted into
lymphatics via lacteals.