The Digestive System 1 Lab # 8

Digestion has two facets:

1- Mechanical digestion

2- Chemical digestion

It is the physical breakdown of food into smaller particlesMechanical digestion exposes more food surface to the action of digestive enzymes and is achieved by:- Cutting and grinding action of the teeth - Churning action of stomach and small intestines

It is a series of hydrolysis reactions that breaks dietary macromole-cules into their monomers:

Chemical digestion is carried out by digestive enzymes produced by salivary glands, stomach, pancreas and small intestine.

Polysaccharides monosaccharidesProteins amino acidsFats monoglycerides and fatty acidsNucleic acids nucleotides

Starch is the most digestible carbohydrateCellulose and chitin are indigestible Polysaccharides

Monosaccharides

Digestion

1- Carbohydrates

Oligosaccharides

Disaccharides

MonosaccharidesThey are absorbed immediately

Amylases Amylases Amylases

Starch is the most digestible carbohydrate

2- Proteins

Protein

Polypeptides

Aminoacids

Proteases Peptidases

They are absorbed immediately

Ex: Pepsin

Monoglycerides

+

Fatty acids

3- Lipids

Triglycerides

+

Glycerol Fatty acids

Lipases

Lipases

Starch

+ Amylase

+ Benedict’s reagent

Greenish-brownish precipitate

+ Lugol’s reagent

Dark blue color

Monosaccharides

HCl

Pepsinogen (zymogen)

Pepsin (active enzyme)

Removed peptide

Partially digested proteins

Test Protein Digestion

Parietal cells

Chief cells

+ Biuret reagent

Lavender-pink color

Hydrophobic quality of lipids makes their digestion and absorption more complicated that carbohydrates and proteinsEnzymes that digest lipids (fats) are called lipasesThe lingual lipase secreted by the intrinsic salivary glands of the tongue is active in mouth, but more active in stomach along with gastric lipase. 10-15% of lipids digested before reaches duodenumPancreatic lipase in the small intestine digest most of the fats

1- EmulsificationComponents of the bile

Emulsificationdroplets

Fat globule is broken up and coated by lecithin and bile acids.

Test Lipid Digestion

2- Fat HydrolysisPancreatic lipase acts on triglycerides. It removes the first and third fatty acids from glycerol backbone and leaves the middle oneThe product of lipase action are two free fatty acids (FFAs) and a monoglyceride

Pancreatic lipase Emulsification droplets are acted upon by pancreatic lipase, which hydrolyzes the first and third fatty acids from triglycerides usually leaving the middle fatty acid.

Free fatty acid

pH