HUMAN DIGESTIVE SYSTEM

CHEMICAL DIGESTING AND ABSORPTION

Enzymes for digestion of macromolecules

Carbohydrates: carbohydrases- Polysaccharides – disaccharides - monosaccharides

Proteins: proteases-Proteins – polypeptides – peptides – amino acids

Lipids: lipases- Lipids – glycerol and fatty acids

Nucleic Acid: nucleases- Nucleic Acids – nucleotides – sugars, phosphates, nitrogenous bases

CHEMICAL DIGESTING AND ABSORPTION

1. MOUTH

Carbohydrates: Salivary Amylase

CHEMICAL DIGESTING AND ABSORPTION

2. STOMACH

Proteins: Pepsin

CHEMICAL DIGESTING AND ABSORPTION

3. SMALL INTESTINE

Carbohydrates: pancreatic amylasesucrasemaltaselactase

Proteins: TrypsinChymotrypsinPeptidases

CHEMICAL DIGESTING AND ABSORPTION

3. SMALL INTESTINE

Lipids: BileLipases

Nucleic Acids: NucleasesNucleosidases

FACTORS AFFECTING ENZYME ACTION

Factors affecting enzyme action include:1. Temperature2. pH

FACTORS AFFECTING ENZYME ACTION

Factors affecting enzyme action include:1. Temperature

- Increase temperature- Increase enzyme activity- Chemical bonds within enzymes

weaken- Enzyme denatures (change in

molecular shape and structure)** Each enzyme can work within a

narrow range of temperatures

FACTORS AFFECTING ENZYME ACTION

Factors affecting enzyme action include:2. pH

- Change in pH- Enzyme denatures (change in

molecular shape and structure)** Each enzyme can work within a

narrow range of pH

ABSORPTION IN THE SMALL INTESTINE

1. CARBOHYDRATES- Carbohydrates are digested- Monosaccharides are absorbed by the lining of the small intestine- Monosaccharides are delivered to the liver and converted to glucose- Glucose is delivered to all parts of the body- Excess glucose is stored in the liver as glycogen (minimal amounts stored in muscles)

ABSORPTION IN THE SMALL INTESTINE

2. PROTEINS- Proteins are digested- Amino acids are absorbed by the lining of the small intestine- Monosaccharides are delivered to the liver and

processed- Converted to sugars- Used in energy-releasing chemical reactions- Converted into urea which is later filtered and excreted in urine- Amino acids are carried by circulatory

system to cells of body

ABSORPTION IN THE SMALL INTESTINE

2. LIPIDS- Lipids are digested- Glycerol and fatty acids are absorbed by the

lining of the small intestine then reassembled into triglycerides

- Triglycerides are coated with proteins to become water-soluble

- Protein-coated triglycerides are transferred to the bloodstream

- Protein coating is removed and triglycerides are broken down by lipase enzymes back to glycerol

and fatty acids- Used for energy

LARGE INTESTINE

Main functions:- Hold remaining material not absorbed in small

intestine- Reabsorb water (~90%) back into the blood

and extra-cellular fluid- Anaerobic bacteria break down undigested

matter further- Some produce important vitamins (Ex. Folic acid, B

vitamins, vitamin K) which are absorbed back into blood- Also produce fecal odour

- Feces formation- Brown colour due to break down of bilirubin (from

hemoglobin)