Lecture 26: Chemical digestion in GIT Flashcards
What is the main reason for chemical digestion?
Digest food and break it up into small enough pieces to be absorbed
How many amino acids can be made by the human body?
▪ 12 amino acids can be made by the body in adults
▪ Essential amino acids cannot be made by the body:
- 8 in adults
Are lipids essential for humans?
▪ Most lipids are not essential
BUT
▪ Omega -3 and -6 fatty acids
▪ Fat soluble vitamins; A, D, E & K (KADE)
What are humans source(s) of protein?
▪ 50% diet: plant and animal protein
▪ 50% Endogenous (body) proteins
- Secreted into intestine
- Enzymes
- Immunoglobulins
What is the main role of amino acids in the body?
Source of amino acids to make body proteins (main job)
Not a major source of energy under normal conditions
What is the main structure of lipids that we eat?
Mostly triglycerides (TAGs):
▪ Glycerol backbone
▪ 3 fatty acids
What are the relative sizes of short, medium and long chain fatty acids?
Short chain fatty acids:
▪ < 6 carbons
Medium chain fatty acids:
▪ 6 - 12 carbons
Long chain fatty acids:
▪ 13 - 24 carbons
In what form can carbohydrates be absorbed into the GIT?
monosaccharides
In what form can proteins be absorbed into the GIT?
amino acids, small peptides (2 - 3 amino acids)
In what form can lipids be absorbed into the GIT?
free fatty acids, monoglycerides (glycerol + 1 fatty acid)
What are digestive enzymes?
Digestive enzymes are extracellular, organic catalysts
Can cellulose (fiber) be broken down and digested in humans?
Cellulose can’t be digested by the body:
▪ amylase can’t break β-bonds between glucose molecules
What is the optimal pH for salivary and pancreatic enzymes?
slightly alkaline pH
What is the optimal pH for gastric (stomach) enzymes?
acidic pH
Which of the following statements is CORRECT?
1. Polysaccharides are made up of many amino acids.
2. Proteins are an important source of energy in the diet.
3. Mechanical digestion increases the surface area of food
particles.
4. Fiber cannot be digested by humans because amylase is unable to break ⍺-bonds between glucose molecules.
3
Chippy chips
What are the two stages of chemical digestion?
- Luminal digestion: Starts chemical digestion
- Chemical digestion by acid and enzymes which have been secreted into the lumen of the GIT and mixed through the food/chyme - Contact digestion: Finishes chemical digestion
- Chemical digestion by enzymes made by and attached to the brush border of enterocytes (small intestine epithelial cells)
What can be digested in the luminal digestion phase?
Carbohydrate, Protein and Lipids/Fat
What can be digested in the contact digestion phase?
Further break down Carbohydrate and Protein via Brush border disaccharidases and Brush border peptidases
What is the digestion process for carbohydrates?
- Luminal digestion
Starch (polysaccharide)
▪ Initiated in the mouth by salivary amylase
▪ Continued in the small intestine by pancreatic amylase - Contact digestion
▪ In the small intestine disaccharidases are bound to the brush border
▪ Different enzymes for different disaccharides:
▪ sucrase for sucrose, lactase for lactose, maltase for maltose
What is the digestion process for proteins?
- Luminal digestion
▪ Initiated in the stomach by HCl acid (hydrochloric acid) and pepsin (protease)
▪ Continued in the small intestine by pancreatic proteases:
- Trypsin
- Chymotrypsin
- Carboxypeptidase - Contact digestion
▪ In the small intestine peptidases are bound to the brush border
▪ Different enzymes for different peptide bonds
Short peptides are broken down into __________ as
result of contact digestion by ___________on the
brush border of the intestinal cells.
1. amino acids : peptidases
2. triglycerides : peptidases
3. amino acids : disaccharides
4. monosaccharides : lipases
1
Are digestive enzymes water or fat soluble?
Digestive enzymes are water soluble and dissolved in
the fluid within the lumen of the GIT
Does fat (lipids) undergo contact digestion?
NO
Fats only undergo luminal digestion (no contact digestion), which occurs in the stomach and small intestine
What percentage of fats are digested in the stomach and what enzymes are responsible?
Lingual and gastric lipase digest ≈ 30% of TAGs in the stomach