Alimentary - digestion and absorption Flashcards
What is digestion?
The mechanical, chemical and microbial breakdown of large, insoluble food molecules into simple absorbable compounds
e.g. starches to sugars
What is absorption?
The process of simple compounds taken across the intestinal membranes into the blood stream.
This occurs mainly in the small intestines (omnivores/carnivores) and large intestines (hindgut fermentors)
What are alpha amylases?
Hydrolysis of startch to sugars, attaching alpha-1-4-glycosidic links only
Present in saliva, and deactivated in stomach
What are enterocytes?
Absorptive functional unit of the digestive tract. Need an energy supply.
Joined by tight junctions, and have villi on the top to increase surface area.
How are carbohydrates absorbed?
Glucose, fructose, and galactose
Fructose - carrier mediated diffusion down concentration gradient
Glucose and galactose - active transport
- requires SGLT-1 to get into cell
-moved to blood via carrier mediated diffusion
What are proteases?
Enzymes that breakdown proteins and peptides by cleaving the peptide bonds within proteins by hydrolysis
Whats a zymogen?
An inactive precursor, such as pepsinogen, and are activated immediately before use
What are the two groups of proteases?
Endopeptidases - attack middle of the amino acid. From stomach and pancreas
Exopeptidases - attack end of the amino acid- From pancreas and small intestines
How do gastric endopeptidases work?
Pepsins function at low pH and attack all proteins.
try - aa
leu-aa
What are the three pancreatic endopeptidases?
3 from pancreas:
- Trypsinogen -> Trypsin (lys-aa)
- Chymotrypsinogen -> Chymotrypsin (tyr - aa)
- Pro-elastase -> Elastase (ala-aa)
How do pancreatic exopeptidases work?
Attach the ends
Carboxypeptidases - split the carboxy terminal
How do SI exopeptidases work?
Aminopeptidases - split the N terminal
What do lipases do?
They breakdown triacyglycerols
Where are there lipases?
Lingual lipases in mouth and stomach
Pancreatic lipases in SI (require phospholipids and bile acids for activation)
How are fats digested?
- Chyme is sprayed into SI
- Bile salts stabilise liquid droplets (emulsiying them)
- Bile salts and phospholipids from bile breakdown the lipid droplets to micelles to increase SA
- Micelles are taken to brush border for absorption
- In the cell they are joined with proteins and form chylomicrons to transport in the lymph
- In tissues, chylomicrons are broken down and remnants are then taken up by liver and further metabolised to HDL, LDL and VLDL.
