Digestion

Question 1

Amylase

Answer 1

• optimum pH: 7
• starch -> maltose
• produced in the salivary glands, released into the mouth
• produced in the pancreas, released into the duodenum

Question 2

Pepsin

Answer 2

• optimum pH: 1.5
• protein -> polypeptide
• produced by the gastric glands, released into the stomach

Question 3

Describe the pH of the stomach

Answer 3

• provided by HCl

* mucus lining provides protection

Question 4

Maltase

Answer 4

• optimum pH: 7
• maltose -> glucose
• produced in the pancreases, released into the duodenum

Question 5

Lipase

Answer 5

• optimum pH: 7
• lipid -> lipid components
• produced in the stomach and pancreas, released into duodenum

Question 6

Trypsin

Answer 6

• optimum pH: 7

* polypeptides -> amino acids

Question 7

Bile function

Answer 7

• neutralises pH
• sodium hydrogencarbonate (hydrogencarbonate ions -> alkaline)
• secreted by the pancreas and by Brunner’s glands in the duodenum

Question 8

Brunner’s glands

Answer 8

• lead to crypts of Lieberkuhn

Question 9

Crypts of Lieberkuhn

Answer 9

• tubular invaginations of glandular epithelia at the base of vili
• close to the base, there are actively dividing stem cells
• Paneth cells

Question 10

Paneth cells

Answer 10

secrete microbial agents to protect stem cells in crypts of Lieberkuhn from infection

Question 11

Bile

Answer 11

• produced by the liver
• stored in the gall bladder
• released via the bile duct
• neutralises HCl
• bile salts emulsify fats

Question 12

Emulsification of fats

Answer 12

Break fat globules into tiny droplets, increasing SA

Question 13

Ileum function

Answer 13

Absorption

Question 14

Ileum adaptations

Answer 14

• many folds, convolutions and twists to increase SA
• thin walls
• high capillary density -> carries sugars, AAs, minerals, vitamins (A, C and E) and water-soluble substances
• villi

Question 15

Villi adaptations

Answer 15

• épithélial cells with lots of mitochondria

* microvilli project themselves into the lumen of the small intestine -> forms a brush border

Question 16

Absorption

Answer 16

Takes place via diffusion and active transport

Question 17

Why is absorption of lipids hard?

Answer 17

• large and hydrophobic long-chain fatty acids are not easily suspended in the watery intensional chyme
• bile salts and lecithin enclose them in a micelle

Question 18

Micelle

Answer 18

• tiny polar sphere with hydrophilic ends facing the watery environment and hydrophobic tails turned into the interior
• creates a receptive environment for long-chain fatty acids
• can easily squeeze between microvilli and get v. Close to the luminal cell surface

Question 19

Why are micelles necessary?

Answer 19

lipids would sit on the surface of the chyme and never come into contact with the absorptive surfaces of the epithelial cells

Question 20

Leaving the micelle

Answer 20

Having reached the cell surface, lipid substances exit the micelle and are absorbed by simple diffusion

Question 21

The process of lipid exocytosis from epithelial cells

Answer 21

1) fatty acids and monoglycerides leave micelle and enter epithelial cells
2) fatty acids link to form triglycerides
3) fatty globules combine with proteins to form chylomicrons, inside the Golgi
4) chylomicrons are extruded from the epithelial cells and enter a lacteal
5) lymph in the lacteals transports chylomicrons away from intestine; exocytosis

Question 22

Describe the stomach

Answer 22

• dotted with pits leading to tubular gastric glands

* gastric glands secrete gastric juices

Question 23

Gastric juices

Answer 23

• mainly water
• mucus
• HCl
• pepsinogen

Question 24

Mucus

Answer 24

• from goblet cells

* protection and lubrication

Question 25

HCl

Answer 25

* from oxyntic cells | * aka pariétal cells

Question 26

Pepsinogen

Answer 26

* from chief cells * aka. peptic, zymogen cells * a precursor; inactive form of an enzyme that is converted by HCl to pepsin (active enzyme)

Question 27

Pepsin

Answer 27

* large polypeptides -> small polypeptides | * endopeptidase

Question 28

Endopeptidases

Answer 28

* breaks the peptide links within a polypeptide chain; does not break the terminal peptide links * produces almost no individual AAs * creates more ends on which exopeptidases can work, with increased SA * e.g. pepsin, trypsin

Question 29

Trypsin

Answer 29

Derived from trypsinogen

Question 30

Mechanical digestion

Answer 30

Muscles in the stomach wall churn contents, covering them in enzymes

Question 31

Acid chyme

Answer 31

* uniform creamy paste | * creates by combining chemical and mechanical digestion

Question 32

Exopeptidases

Answer 32

* break the terminal peptide bonds * e.g. aminopeptidase * e.g. carboxypeptidase

Question 33

Aminopeptidase

Answer 33

Acts on terminal peptide bonds at the amino end of the polypeptide chain

Question 34

Carboxypeptidase

Answer 34

Acts on terminal peptide bonds at the carboxyl end of the polypeptide chain

Question 35

Dipeptidases

Answer 35

* secreted by enterocytes into the small intestines * hydrolyse dipeptides * membrane-bound

Question 36

Enterocytes

Answer 36

Intestinal lining cell

Question 37

Nucléase

Answer 37

Nucleic acids -> nucleotides

Question 38

Chymotrypsin

Answer 38

Proteins -> small polypeptides

Question 39

Entérokinase

Answer 39

Trypsinogen -> trypsin

Question 40

Sucrase

Answer 40

Sucrose -> α-fructose + α-glucose

Question 41

Lactase

Answer 41

Lactose -> α-glucose + β-galactose

Question 42

Peptidases

Answer 42

Peptides -> amino acids

Question 43

Proteases

Answer 43

Proteins -> polypeptide chains

Question 44

Nucleotidases

Answer 44

Nucleotides -> bases, sugars and phosphates

Question 45

Water in digestion

Answer 45

* essential for hydrolytic breakdown of food | * transport medium for secretions