L23 - GI Digestion And Absorption

Question 1

What is digestion?

Answer 1

Sequence by which food is broken down and chemically converted
- to be absorbed by cells of an organism
- used to maintain vital bodily functions

Question 2

What are the cells involved in the seretion in the salivary glands?

Answer 2

• myoepithelial cells
• serous cells
• duct cells
• mucous cells

Question 3

What do serous cells secrete?

Answer 3

• amylase
• lingual lipase

Question 4

What does amylase do?

Answer 4

• breakdown of carbohydrates
• brief, inactivated in acidic conditions

Question 5

What does lingua lipase do?

Answer 5

• breakdown of trigkycerides (fat)
• optimal at pH 4-5
• continues throughout GI tract
• important in newborns

Question 6

What are the types of cells in the stomach that secrete?

Answer 6

• parietal cell
• chief cell
• mucous cell
• G cell

Question 7

What do parietal cells do?

Answer 7

secretes HCl
- denatures protein
- pepsinogen to pepsin

Question 8

What do chief cells do?

Answer 8

Secrete pepsinogen
- converted to pepsin
- protein digestion

Question 9

What do mucous cells do?

Answer 9

• protection
• lubrication

Question 10

What do G cells do?

Answer 10

Produce gastrin
- controls HCl, motility, pepsin, muscous

Question 11

What is the gastric acid secretion?

Answer 11

HCl (~2.5L/day)
- stomach pH 2-3
- optimal for pepsin

Question 12

What is gastric acid secretion stimulated by?

Answer 12

• histamine
• gastrin
• ACh

Question 13

What is contained within the storage vesicles?

Answer 13

• trypsinogen
• chymotrypsinogen
• procarboxypeptidases

Question 14

What happens to the - trypsinogen, chymotrypsinogen, procarboxypeptidases released?

Answer 14

Broken down by eneteropeptidases on the brush border
= activates them

Question 15

What else is secreted in the pancreatic secretion?

Answer 15

• amylase - starch - active
• lipase - fat - active
• RNAase
• DNAase

Question 16

What is secreted from the gall bladder?

Answer 16

Bile

Question 17

Where is bile formed in, stored and concentrated, and released into?

Answer 17

• liver from cholesterol in diet
• gallbladder
• into SI

Question 18

What controls the digestive process?

Answer 18

Stretch receptors - send signals to brain, triggers secretion of digestive juices
Stomach - gastrin, promotes production of stomach acids
Intestine - releases secretin and cholecystokinin, stimulates secretion of pancreatic juice and bile

Question 19

What routes of absorption are there?

Answer 19

Lipids - to lymph lacleal
Sugars and a/a - to portal blood supply

Question 20

What are the mechanisms of absorption?

Answer 20

• active transport
• carrier-mediated (facilitated) transport

Question 21

What is protein digestion?

Answer 21

Proteases catalyse hydrolysis of a/a

Question 22

What are the main proteases?

Answer 22

• pepsin in stomach
• trypsin, chymotrypsin from pancreas
• peptidases in intestinal brush border

Question 23

Where does protein absorption occur?

Answer 23

In the SI
(Active transport of tripeptides, dipeptides and a/a)

Question 24

What is carbohydrate digestion?

Answer 24

Mouth - begins, salivary amylase
Stomach - denatures amylase
SI - pancreatic amylase
- digested by intestinal brush border enzymes

Question 25

What happens in carbohydrate absorption?

Answer 25

• enzymes on luminal surface of SI epithelial cells digest disaccharides into monosaccharides
• absorbed by facilitated diffusion or active transport with Na+
• leave epithelial cells by facilitated diffusion, enter blood, distributed throughout body

Question 26

What is the main site of fat digestion?

Answer 26

Small intestine

Question 27

What is fat digestion critically dependent on?

Answer 27

• secretions from the liver and pancreas
• emulsification required
• bile and lipase involved from gallbladder and pancrease

Question 28

What are the sequence of steps in fat absorption?

Answer 28

• FA & monoglycerides pass through epithelial cell layer
• converted to triglycerides
• combine with cholesterol, phospholipids, protein = chylomicron
• water soluble, enters lacteal
• transported from lacteal to bloodstream

Question 29

What occurs at the stomach for oral drug absorption?

Answer 29

Disintegration and dissolution
- by acid environment and mechanical churning

Question 30

How is the drug absorbed in oral drug absorption?

Answer 30

• passive diffusion
• facilitated diffusion
• active transport

Question 31

What is oral drug absorption determined by?

Answer 31

• physiochemical properties
• formulation
• route of administration

Question 32

What is oral drug absorption affected by?

Answer 32

• luminal pH
• SA
• perfusion
• bile
• mucus

Question 33

What is oral drug absorption influenced by?

Answer 33

Intestinal transit time

Question 34

What does enteric coating do?

Answer 34

• prevents formulation from gastric fluid in stomach
• release drug component in intestinal region

Question 35

What is the enteric coating prepared from?

Answer 35

Gastric resistant polymers
- insoluble at low pH

Question 36

What is drug releaae controlled by?

Answer 36

pH

Question 37

How does enteric coating help?

Answer 37

• prevents gastric distress/nausea due to irritation
• protect acid-labile drugs
• delivers drugs intended for local action at intestine
• provide delayed release compounds