Mechanism of Action:

Substrate: compound to be acted on by the enzyme

Active Site: lactation on the enzyme where it attaches to the substrate

Product: the released result of the reaction

Maltose acted on by maltase to form 2 glucose

Amylose acted on by amylase to form X glucose

Protein acted on by pepsin to form oligopeptides

Fact acted on by lipase to form fatty acids

Hormones and Digestion
• Gastrin
o Secreted by the G-cells in the antrum of the stomach
o Stimulates parietal cells to secrete HCl
• Secretin – released because of acid in duodenum
o Stimulates pancreas to secrete fluid and bicarbonate into the gut
• Cholecystokinin (CCK) - Fats and(or) proteins entering the SI stimulate the release of CCK
o Causes pancreas to secrete digestive enzymes
o Stimulates gall bladder to release bile salts
• Leptin
o Insulin causes secretion
o Secreted from adipocytes
o Acts on hypothalamic leptin receptors to inhibit feed intake
o Increases energy expenditure

 

GI Tract Secretions

Source

Secretion

Species

Substrate(Function)

Mouth

S. Amylase

Pig, man

Glycogen, starch, dextrin

Mucin

All

Lubrication

Pregast. esterase

Young Ruminant

Fat - milk fat

Stomach

Pepsin

All

Protein

HCl

All

Activate pepsin (protein)

Lipase

All

Fats

Mucin

All

Protection & lubrication

Rennin

Young Ruminant

Milk protein (casein)

Intrinsic factor

All

Vit. B12 absorption

Mucin (pyloric)

All

Protection & lubrication

Pancreas

Amylase

All

Starch

Sucrase

All

Sucrose

Trypsin

All

Protein, peptides

Chymotripsin

All

Protein, peptides

Carboxypeptidase

All

Protein, peptides

Lipase

All

Fats

Liver

Bile

All

Fat emulsification

S.I.

Enterokinase

All

Trypsinogen activation

Aminopeptidase

All

Protein

Dipeptidase

All

Dipeptides

Nucleotidase

All

Nucleotides

Nucleosidase

All

Nucleosides

Alkaline Phosphatase

All

Organic phosphates

Lipase

All

Fat

Maltase

All

Maltase

Lactase

All (Avian)

Lactose

Sucrase

All

Sucrose

L.I.

Mucin

All

Protection & lubrication

Bioenergetics

Bioenergetics =energy associated with biological systems. Release, storage, and use of this energy.

75% of diet DM used for energy. Energy is not a nutrient, derived from organic compounds (protein, CHO, fat) in the diet

Energy derived = complete or partial oxidation of organic compounds. These organic compounds absorbed in the GI tract. Energy is in chemical form (stored in bonds - covalent bonds). If animals can break these bonds - they can use this energy released from the breaking of these bonds. Energy may escape!

Trapping energy = Requires systematic breaking of bonds & trapping electrons. Electrons are actually where energy comes from.

e- ® O2® H2O and results in energy available for work

Systemic breaking of bonds = required to produce energy - examples: glycolosis, Krebs.

Chemical energy originally from the sun!!

CO2 + H2O + ATP ® glucose (protein, fats, CHO's) All are forms of chemical energy.

So reverse the action to release energy.

Heat = most common form of energy in biochemical reactions because most chemical energy will be converted to heat (INEFFICIENT!!!)

Inefficient metabolism = Body is not 100% efficient, not all ATP energy will be used for work. Heat will escape (given off) = allows for optimum body temperature maintenance

Calorie = the unit of heat measured.

Definition = the amount of heat required to raise the temperature of 1g of H2O 1oC from 14.5 oC to 15.5 oC at 1 atmospheric pressure.

Kilocalorie = 1000 calories

Gross Energy (or caloric density) = Total energy in a compound. Measure with bomb calorimeter

Bomb calorimeter = Pure O2 environment, combust (ignite) = blows up. All chemical energy is converted to heat - measure heat produced and that is caloric density or Gross Energy!

Glucose = 3.75 kcal/g

CHO = 4 kcal/g

Protein = 4 kcal/g

Fat = 9 kcal/g

Alcohol = 7 kcal/g