Physiology - Digestion + Absorption Flashcards
Assimilation
Overall process of digestion and absorption
Lumina ldigestion is mediated by x
pancreatic enzymes
secreted into the duodenum
Membrane digestion is mediated by x
enzymes situated at the brush border of epithelial cells
enzyme for carb digestion + location
a-Amylase
- salivary
- pancreatic
a- amylase creates
a) monoaccharide glucose
b) oligosaccharide
B
bc it can only break intra-bonds
absorption of GLUCOSE + GALACTOSE (lactose) in the duodenum + jejunum is through xx transport, mediated by xxx transporter
xx secondary active trasnport
xxx SGLT1 (sodium Glucose co-trasnporter)
Exit for all monosaccharides is mediated by
facilitated diffusion by GLUT2
Fructose absorbed through
facilitated diffusion by GLUT5
Protein digestion occurs in
- stomach (not essential for protein digestion)
- duodenum
Gastric peptidases
- HCl denaturing proteins
- PEPSIN - endopeptidase
Pancreatic proteases
secreted as proeznymes from the acinar cells in the pancreas (exocrine pancreas) + converted to active form in the duodenum
Trypsin –> oligo
Chymotrypsin –> oligo
Elastase –> oligo
Carboxypeptidase A + B –> single aa
oligo 70%
free aa 30%
aa absorption at the Brush border - moa
+ disease associated
2
Na+-dependent co-transporters mediating ‘uphill’ movement
(secondary active transport)
dysfunction results in Hartnup disease
- system B0AT1
Na+independent
mediates uptake of
cationic amino acids (dysfunction results in cystinuria)
aa absorption at BASOLATERAL MEMBRANE
for INFLUX - e Na+
-dependent
supplying the enterocyte’s nutritional requirements along with absorbed amino acids
for EFFLUX - Na+
-independent
absorpiton of Di-, tri-, and tetra-peptides occurs
1. at x
2. via x mechanism
at brush border (cotransport)
via H+ -dependent mechanism (PepT1
emulsification of ingested lipids occurs by 1,2,3
emulsion = small oil droplets suspended in water
- mouth - chewing
- stomach - gastric churning and squirting through the narrow pylorus. Content mixed with digestive enzymes from mouth and stomach
- small intestine – segmentation and peristalsis mix the luminal content with pancreatic and biliary secretions
which lipids are insoluble in water
cholesterol esters,
TAGs
role of stomach in lipid digestion
gastric lipase
secreted from chief cells
hydrolyses TAGs
- inactive in the duodneum due to digestion by pancreatic protease and unfavourable pH
role of pancreas in lipid digestion
Pancreatic lipase
secreted from acinar cells
in response to CCK
Full activity requires
* colipase co-factor
* alkaline pH
* Ca2+
* bile salts
* fatty acids
Additional lipases include
* carboxyl ester hydrolase
* phospholipase A2
Roles of CCK
- STIMULATES BILE FLOW (Bile salts released into the duodenum in bile from the gall bladder)
- stimulase acinar cells in the pancreas to secerete pancreatice lipase
role of bile salt
+ dysfunction consequences
act as detergents to help emulsify large lipid dropletsto small droplets
increase surface area for attack by pancreatic lipase, but
block access of the enzyme to the TAGs
➢ Problem solved by colipase, an amphipathic polypeptide secreted with
lipase by the pancreas
*Failure to secrete bile salts results in:
*o** lipid malabsorption** - steatorrhoea (fat in faeces)
o secondary vitamin deficiency due to failure to absorb fat soluble vitamins
(A,D, E and K)
Bile salts released into the duodenum in bile from the gall bladder in
response to CCK
Why is BILE important
Without bile, fat digestion and absorption would be very inefficient, leading to:
❌ Fat malabsorption – Fats would pass through the intestines undigested, causing steatorrhea (fatty stools).
❌ Deficiency in Fat-Soluble Vitamins – Without bile, the body would struggle to absorb vitamins A, D, E, and K, leading to health issues like vision problems, weak bones, and blood clotting issues.
❌ Buildup of Waste Products – Bilirubin and cholesterol wouldn’t be properly excreted, increasing the risk of gallstones or jaundice.
Gallstones: Hardened bile components can form stones, blocking bile flow and causing pain.
Liver Disease: Conditions like cirrhosis reduce bile production, leading to poor fat digestion.
**Bile Duct Obstruction: **If bile can’t reach the intestine (due to a tumor, gallstones, or inflammation), fat digestion is impaired.
Roles of bile
✅ Emulsifies Fats – Bile breaks large fat droplets into tiny micelles, making it easier for enzymes (lipases) to digest them.
✅ Aids in Fat Absorption – Micelles help transport fatty acids and fat-soluble vitamins (A, D, E, K) to intestinal cells for absorption.
✅ Eliminates Waste – Bile helps excrete bilirubin (from red blood cell breakdown) and excess cholesterol through feces.
✅ Neutralizes Stomach Acid – Bile contains bicarbonate, which helps neutralize stomach acid when food enters the small intestine.
✅ Antimicrobial Properties – Some bile salts prevent harmful bacteria from growing in the intestines.
what is a micelle + what is its purpose
Hydrophobic
core containing
TAGs and
esterified
cholesterol
hydrophilic shell
PURPOSE:
how is a micelle formed
formed by bile salts
