Gastrointestinal Physiology: Digestion Flashcards
What are the 3 main nutrients that undergo chemical digetion?
Carbohydrates, lipids and proteins
These are made up of long chains of glucose joined by alpha 1-4 glycosidic bonds.
Starch and glycogen
What are the 3 disaccharides?
Sucrose, lactose and maltose
Why are lipids not essential to our bodies?
Because we can produce them endogenously so no need for them to be in our diet
What are some of the properties of lipids in our body? (3)
- slow gastric emptying
- source of energy
- fat soluble vitamins A, D, E and K
What is the main component of lipids?
Triglycerides
This reduces the size of nutrients to allow them to be absorbed.
Chemical digestion
Where does chemical digestion occur? And what does it use to break down the food particles?
Chemical digestion occurs at the surface of food particles.
It uses digestive enzymes secreted by SI and pancreas to break the food down
This breaks up food and increases surface area available for chemical digestion. Usually occurs at the mouth.
Mechanical digestion
These are highly specific extracellular organic catalysts that are responsible for breaking down food particles during chemical digestion.
Digestive enzymes
What is the optimal pH for each of these enzymes:
a) salivary enzymes
b) gastric enzymes
c) small intestinal enzymes
a) alkaline
b) acidic
c) alkaline
What does it mean by digestive enzymes being highly specific?
Different enzymes bind to different substrates
- amylase => starch
- proteases => proteins
- lipase => lipids
What are the 2 stages of chemical digestion?
Luminal digestion and contact digestion
This is the initial digestion which involves enzymes secreted into the lumen.
Additional question: this can occur at 3 different organs in the GI tract, what are those 3 and what enzymes specifically carryout this type of digestion?
Luminal digestion
Luminal digestion occurs in the stomach, the small intestine and the mouth. The enzymes in the stomach are usually pepsin, small intestine: pancreatic enzymes (pancreatic amylase, trypsin, chymotrypsin etc., and in the mouth: salivary amylase
This is the type of digestion which occurs in the small intestine. It involves enzymes produced by enterocytes which are attached to the brush border of the enterocytes.
Contact digestion (via microvilli brush border enzymes)
Remember: these enzymes are produced by the epithelial cells (enterocytes) of the small intestine. Segmentation helps contact digestion occur.