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Flashcards in Digestion & Absorption Deck (32):
1

What polysaccharides are digested by humans?

glucose polymers

2

What disaccharides are digested by humans?

lactose and sucrose

3

What monosaccharides are absorbed by humans?

glucose and fructose

4

What digests carbohydrates in the mouth?

Salivary alpha-amylase - hydrolyses 1:4alpha linkages between glucose molecules

5

What digests carbohydrates in the duodenum/jejenum?

pancreatic alpha-amylase in the lumen and isomaltase, sucrase and maltase at the brush border

6

What triggers release of pancreatic alpha-amylase?

CCK

7

What linkage are amylases ineffective at?

1:6 alpha linkages

8

What does isomaltase do?

Break up 1:6 alpha linkages

9

What does sucrase do?

Breaks up sucrose into fructose and glucose

10

How are maltase and sucrase activated?

By pancreatic proteases

11

Where are glucose and fructose predominantly absorbed?

At the tips of the villi

12

How is glucose transported?

Via SGLT1 transporter with sodium against its concentration gradient

13

What is the function of sweet taste receptors on the villi?

When activated they activate the SGLT1 transported to enhance glucose uptake

14

How is fructose transported?

Via GLUT5 transporter down its concentration gradient into epithelial cells and via GLUT2 into the interstitium

15

What digests proteins in the stomach?

Pepsin

16

Where does pepsin come from?

Pepsinogen (the inactive form) is secreted by chief cells and is then activated by acid to pepsin

17

What is the action of pepsin?

Hydrolyses bonds between an aromatic amino acid and a second amino acid

18

What enzymes digest proteins in the duodenum and jejunum?

mostly trypsin and chymotrypsin but also elastase and carboxypeptidase A and B

19

Where does trypsin come from?

It is secreted by the pancreas as trypsinogen and is activated by enterokinase at the brush border membrane

20

Where does chymotrypsin come from?

It it secreted by the pancreas as chymotrypsinogen and is activated by trypsin

21

What is the action of trypsin, chymotrypsin and elastase?

act at interior bonds of peptides to produce short polypeptides

22

What is the action of carboxypeptidases?

act at the carboxy terminals of peptides to produce free amino acids

23

What happens to the short polypeptides at the brush border membrane?

They are broken down by aminopeptidases, carboxypeptidases, endopeptidases and dipeptidases

24

How are free amino acids absorbed?

Via 7 or or more different transporter mechanisms - 5 of which require sodium and 2 of which require chloride

25

How is fat digested in the mouth?

With a lingual lipase - but only with minor effect

26

How is fat digested in the stomach?

With a gastric lipase - but only with minor effect

27

How is fat digested in the duodenum?

By lipase and cholesterol esterase

28

How is lipase activated in the duodenum?

by colipase which is activated by trypsin

29

How is cholesterol esterase activated?

By bile

30

How is fat emulsified?

By bile salts and lecithin and contractile mixing - forms micelles

31

How is fat absorbed?

The bile salts on the edge of the micelles dissolve partly in the membrane allowing the lipids to dissolve across the membrane and enter the cell where they reform triglycerides and form chylomicrons which are secreted by exocytosis into the lymphatics

32

What are the main three short chain fatty acids produced by fermentation of dietary fibre?

acetate, proprionate and butyrate