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Flashcards in Digestion and Absorption Deck (43):
1

Define digestion

The chemical breakdown of food by enzymes secreted by glandular cells in the mouth, chief cells in the stomach and the exocrine cells of the pancreas, or enzymes bound to the apical membranes of enterocytes.
Although some digestion of carbohydrates, proteins and fats occurs in the stomach, most occurs in the small intestine

2

What are cavital enzymes?

Enzymes secreted from the salivary glands, stomach and pancreas, have signifiant chemical degradation of food.

3

What are hydrolytic enzymes?

Enzymes associated with the small intestinal brush border. Hydrolysis by these enzymes is termed contact or membrane digestion

4

Where in the GIT does most digestion occur?

Small intestine

5

Define absorption

The movement of material from the intestinal lumen to the blood. Secretion implies movement in the opposite direction. The brush border is the barrier of movement

6

What is the glycocalyx layer?

Layer of glycoproteins on the outside of the microvilli

7

What is the unstirred layer?

Layer of intestinal secretions that sit on top of the microvilli, the first barrier

8

What is an enterocyte?

Cell of the intestinal lining

9

What percentage of calories digested are carbohydrates?

50%

10

Composition of carbohydrates

50% starch
30% sucrose
6% lactose
1-2% maltose
trehalose, glucose, fructose, cellulose, sorbitol, hemicellulose and pectins make up the remainder

11

What does the starch compound consist of?

Two polysaccharides, amylose and amylopectin

12

What is amylose?

Straight chain polymer of glucose linked by a-1,4-glycolytic bonds. The repeating disaccharide unit is maltose

13

What is amylopectin?

Plant starch, major form of carbohydrate in the diet and is similar to amylose; however, in addition to the 1,4-glycosidic bonds, there is a 1,6-linkage for every 20-30 glucose units

14

What is glycogen?

High-molecular weight polysaccharide similar to amylopectin in molecular structure but with considerably more 1,6-linkages

15

How many glucose residues does the average alpha-limit dextrin contain?

5-10

16

Percentages of membrane enzymes that break down alpha-1,6 bonds in alpha-dextrin

95% isomaltase
5% glucoamylase

17

Percentages of membrane enzymes that break down alpha-1,4 bonds in alpha-dextrin

60% glucoamylase
20% sucrase
20% isomaltase

18

Percentages of membrane enzymes that break down maltotriose

50% isomaltase
25% sucrase
25% glucoamylase

19

Percentages of membrane enzymes that break down maltose

50% isomaltase
25% sucrase
25% glucoamylase

20

What is the enzyme that breaks down lactose into glucose and galactose?

Lactase

21

What is the enzyme that breaks down sucrose into glucose and fructose?

Sucrase

22

What is the enzyme that breaks down trehalose into glucose?

Trehalase

23

Is digestion or absorption the rate limiting step of carbohydrate digestion?

Absorption

24

What are the transporters involved in carbohydrate absorption?

GLUT2, GLUT5 and SGLT1

25

What does GLUT5 allow to enter the cell?

Fructose

26

What does GLUT2 allow to leave the cell?

Fructose, glucose and galactose

27

What does SGLT1 allow to enter the cell?

Glucose and galactose, is Na+ dependent, Na+ has to move out of the basolateral membrane via a Na+/K+ ATPase to maintain concentration gradient

28

Where is pepsinogen secreted from?

Chief cells of the crypt pits of the stomach

29

How is pepsinogen converted to pepsin?

Converted in the presence of H+, HCl secreted from the parietal cells in the stomach

30

What percentage of protein digestion occurs in the stomach?

Around 15%

31

What is the function of pepsin?

Breaks down proteins into smaller peptide fragments - optimum pH 1-3

32

At what pH does pepsin stop working?

pH 5

33

Where is the main site of protein digestion?

Duodenum

34

What does an endopeptidase do?

Splits proteins into smaller fragments by breaking bonds

35

What does an exopeptidase do?

Cleaves single amino acids off the end of proteins

36

What size peptides can be absorbed in the small intestine?

Small peptides - di and tripeptides
Single amino acids

37

What transporters are involved in the absorption of proteins?

PepT1, 3Na+/2K+ ATPase and NaH exchanger

38

What are most fats in the diet in the form of?

Triglycerides - 3FAs linked with glycerol

39

What is TAG hydrolysed by in the digestive tract?

Pancreatic lipase

40

What do bile acids to do to fats?

Solubilises larger fat molecule, increasing surface area for the action of lipase enzyme

41

What are micelles?

Monoglycerides and fatty acids associate with bile salts and phopholipids to form micelles. Cannot be absorbed

42

What types of fat can be absorbed?

Free fatty acids or monoglycerides pass through the cell membrane via diffusion

43

What happened to free fatty acids when they are in the cell?

Meet the smooth endoplasmic reticulum, which turns them back into triglycerides in order to maintain a concentration