L23 - GI Digestion And Absorption Flashcards
What is digestion? (2)
Sequence by which food is broken down and chemically converted
- to be absorbed by cells of an organism
- used to maintain vital bodily functions
What are the cells involved in the secretion in the salivary glands? (4)
- myoepithelial cells
- serous cells
- duct cells
- mucous cells
What do serous cells secrete? (2)
- amylase
- lingual lipase
What does amylase do? (2)
- breakdown of carbohydrates
- brief, inactivated in acidic conditions
What does lingua lipase do? (4)
- breakdown of trigkycerides (fat)
- optimal at pH 4-5
- continues throughout GI tract
- important in newborns
What are the types of cells in the stomach that secrete? (4)
- parietal cell
- chief cell
- mucous cell
- G cell
What do parietal cells do? (2)
secretes HCl
- denatures protein
- pepsinogen to pepsin
What do chief cells do? (2)
Secrete pepsinogen
- converted to pepsin
- protein digestion
What do mucous cells do? (2)
- protection
- lubrication
What do G cells do?
Produce gastrin
- controls HCl, motility, pepsin, muscous
What is the gastric acid secretion? (2)
HCl (~2.5L/day)
- stomach pH 2-3
- optimal for pepsin
What is gastric acid secretion stimulated by? (3)
- histamine
- gastrin
- ACh
What is contained within the storage vesicles? (3)
- trypsinogen
- chymotrypsinogen
- procarboxypeptidases
What happens to the - trypsinogen, chymotrypsinogen, procarboxypeptidases released?
Broken down by eneteropeptidases on the brush border
= activates them
What else is secreted in the pancreatic secretion? (4)
- amylase - starch - active
- lipase - fat - active
- RNAase
- DNAase
What is secreted from the gall bladder?
Bile
Where is bile formed in, stored and concentrated, and released into? (3)
- liver from cholesterol in diet
- gallbladder
- into SI
What controls the digestive process? (3)
- 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
What routes of absorption are there? (2)
- Lipids - to lymph lacteal
- Sugars and a/a - to portal blood supply
What are the mechanisms of absorption? (2)
- active transport
- carrier-mediated (facilitated) transport
What is protein digestion?
Proteases catalyse hydrolysis of a/a
What are the main proteases? (3)
- pepsin in stomach
- trypsin, chymotrypsin from pancreas
- peptidases in intestinal brush border
Where does protein absorption occur?
In the SI
(Active transport of tripeptides, dipeptides and a/a)
What is carbohydrate digestion? (3)
- Mouth - begins, salivary amylase
- Stomach - denatures amylase
- SI - pancreatic amylase - digested by intestinal brush border enzymes
What happens in carbohydrate absorption? (3)
- 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
What is the main site of fat digestion?
Small intestine
What is fat digestion critically dependent on? (3)
- secretions from the liver and pancreas
- emulsification required
- bile and lipase involved from gallbladder and pancrease
What are the sequence of steps in fat absorption? (5)
- 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
What occurs at the stomach for oral drug absorption?
Disintegration and dissolution
- by acid environment and mechanical churning
How is the drug absorbed in oral drug absorption? (3)
- passive diffusion
- facilitated diffusion
- active transport
What is oral drug absorption determined by? (3)
- physiochemical properties
- formulation
- route of administration
What is oral drug absorption affected by? (5)
- luminal pH
- SA
- perfusion
- bile
- mucus
What is oral drug absorption influenced by?
Intestinal transit time
What does enteric coating do? (2)
- prevents formulation from gastric fluid in stomach
- release drug component in intestinal region
What is the enteric coating prepared from?
Gastric resistant polymers
- insoluble at low pH
What is drug releaae controlled by?
pH
How does enteric coating help? (4)
- prevents gastric distress/nausea due to irritation
- protect acid-labile drugs
- delivers drugs intended for local action at intestine
- provide delayed release compounds
