Post on 24-Dec-2015
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)