Digestion Absorption + Metabolism Flashcards
What does the small intestine do?
Digestion of food, absorption of water, nutrients and electrolytes
What is peristalsis?
Where adjacent segments of the GI tract contract in sequence resulting in the propulsion of food along the GI tract
What are some functions of the stomach?
- stores large quantities of food until it can be accommodated in the intestine
- mixing of food with gastric sections to form chyme
- regulates emptying chyme into duodenum
- secretion of intrinsic factor (for B12 absorption)
- secretion of HCL and proteases
What does HCL do within the stomach?
Activates pepsin (pepsinogen-pepsin)
Kills pathogenic organisms
Denatures and breaks down food proteins
Increases absorption of iron/calcium
How does the small intestine fulfill its roll of increasing surface area
Does this by the folds of kerckring, villi and microvilli (3,10,20X) SA increase
Describe the structure of villi?
Large SA for absorption due to fold in the mucosal layer, microvilli and the brush border membrane of mucosal epithelial cells
What does the large colony of bacteria in the large intestine do?
It can metabolize fiber to short chain fatty acids which is then absorbed by passive diffusion.
These bacteria also produce vitamin K
How is starch broken down in they GI tract and what enzymes are used?
Starch goes to dextrins and maltose via salivary amylase
Then this goes to maltose via pancreatic amylase
Finally maltose to glucose via maltase
How are glucose and galactose absorbed?
They get into the epithelial cell via a sodium-dependent glut transporter (SGLT-1)
Glut 2 helps facilitate them out the cell (actively transported out via Na+/k+
Pump)
How is fructose transported out of cell into blood?
Glut2 transporter
In terms of protein digestion in GI tract, explain the full process
Starting at stomach, HCL activates pepsin which breaks down proteins to large peptides
Then specific pancreatic enzymes break down larger peptides into smaller peptides
Then at BB more enzymes break down the small peptides to di-peptides or amino acids
How is pepsinogen converted to Pepsin in the stomach?
HCL is released from the parietal cells which will convert inactive pepsinogen to active pepsin
How are the pancreatic proteases in the duodenum activated?
They remain inactive until food arrives at small intestine to active mate membrane-bound enterokinase which will in turn convert trypsinogen-trypsin, chymotrypsinogen-chymotrypsin and procarboxypeptidase to carboxypeptidase
How is protein absorbed in the small intestine? (Not di-peptides)
Active transporters will take Na+ and amino acids across the brush border and into the capillary
How are di-peptides absorbed in the small intestine?
They can get into the intestinal membrane through active transport using a hydrogen co-transporter
Cytoplasmic peptidases then split di-peptide into amino acids to allow them to go into the hepatic portal vein
Where do the amino acids go after absorption
They Go to the liver, can be used to make pyruvate or can go to muscles to stimulate protein synthesis
Where does lipid digestion originate?
In the mouth (saliva contains small amounts of lipase)
In the stomach the acid-stable lipase will continue to hydrolyse triglycerides (slow process as TG not water soluble)
What does pancreatic lipase do?
It is secreted into the duodenum and will further continue hydrolysing the triglycerides
Describe the process of lipid digestion in GI tract
Bile salts from the gall bladder will break down large lipid droplets to emulsion droplets, then panc. Lipase breaks the emulsion droplets to FFA’s and monoglycerides, these then go to micelles
What are micelles and what is their structure
Tiny lipid that is free to move in a water medium
Consists of a hydrophobic core (monoglycerides and FFAs) and bile salts on the outside (hydrophilic side outwards)
How are medium chain FFA absorbed in the small intestine?
They travel from the lumen to the capillary via passive diffusion and carrier mediated transport and are water soluble (albumin coated with FFA in capillary)
Triglycerides are synthesized in the endoplasmic reticulum, how does this occur?
TG synthesis occurs from FFA (typically long chain) and monoglycerides crossing the brush border
How are chylomicrons formed?
Following TG synthesis in ER, chylomicrons are formed from TG, phospholipid, protein and cholesterol and are essentially the carrier lipoprotein for getting dietary TG in the body. They are water soluble and get transported to the lymphatic system
Where does vitamin absorption typically occur?
In the jejunum and ileum (via passive diffusion)
How are the fat soluble vitamins (ADEK) absorbed?
They are absorbed along with FFA (particularly LCFA, eg. Chylomicrons - lymphatic system)
Where are the water soluble vitamins absorbed?
C - distal part of small intestine
B6 - mainly in jejunum
B12 - mainly in ileum
What happens to water-soluble vitamins at high concentrations?
They will diffuse into epithelial cells of small intestine
What happens to the water soluble vitamins at low concentrations?
Active processes are now involved in absorbing water soluble vitamins in small intestine
What type of active process is required for absorption of vitamin B1 and vitamin C?
An Na+ dependent active process
How is vitamin B12 absorbed?
It requires the formation of a complex with an intrinsic factor (released by parietal cells).
B12 is then absorbed in the ileum by binding a B12 intrinsic-factor complex to a receptor to then be engulfed by epithelial cells
What happens if there is a deficiency of a vitamin?
Active transport will occur (apart from vitamin D)
Water soluble rarely become deficient
Where does absorption of minerals occur?
In the small intestine, in general they aren’t absorbed very well
How is sodium absorbed?
Via an active transport process, produces a osmotic gradient which then allows water to enter cell and be absorbed by osmosis
What things are required in an energy drink?
Carbohydrate (energy)
Sodium - 40mg/100ml as this increases water and carb absorption
