Digestive System

The Digestive System is essential for human growth and sustainability. Digestion is an often complicated system or process that allows for the breakdown of different types of chemicals or molecules.

This allows a large molecules to be broken down into consumable and usable nutrients that can be absorbed more readily.

Absorption is done through cells and into the blood stream

Ingestion – introduces food to the digestive process

Categories of Human digestion

1.)  Cephalic phase

–  Saliva from mouth begins breakdown.
–  Mastication or chewing of food helps with breakdown
–  Taste and smells stimulate release gastric secretion
–  Starches are broken down here

2.)  Gastric phase

–  Stimulated by expansion of stomach with food particles
–  pH may change
–  Gastric juices are released

3.)  Intestinal phase

–  Movement of food particles through intestines
–  Will end in Defecation
–  Some absorption occurs
–  Active transport and enzymes are essential

Mechanical breakdown:

–  Force from teeth and tongue to breakdown food into smaller particles. [Mastication]
–  Swallowing
–  Peristalsis – smooth muscle movement

Chemical breakdown:

–  The reactive force to breakdown molecules into simple structures
–  Enzymes
–  Saliva
–  Acids
–  Bile
–  Water

Additional Aspects of Digestion:

–  Peptides become Amino Acids – Breakdown begins in the stomach but is further broken down in the Small Intestines.
–  Enzymes from the Pancreas can cut protein into smaller peptides
–  Lipids (Fats) become Fatty acids and Glycerol.
–  Pancreatic lipase with the help of bile, together they cause the breakdown of Triglycerides into the free fatty acids.
–  Carbohydrates become sugars such as glucose.
–  Pancreatic amylase breaks carbohydrates into complex sugars. Then the enzymes in the small intestines break the complex sugars into simple sugars.

4 main hormones involved in regulation of the Digestive System

1.)  Gastrin

–  Found in stomach and stimulates gastric glands to secrete “pepsinogen” and “hydrochloric acid“.

2.)  Secretin

–  Found in the duodenum and signals release of “sodium bicarbonate” in pancreas which causes the release of “bile” from the liver

3.)  Cholecystokinin (CCK)

–  Found in duodenum and stimulates release of digestive enzymes in pancreas and causes release of “bile” from gallbladder.

4.)  Gastric inhibitory peptide (GIP)

–  Found in duodenum and causes decrease activity of stomach.
–  Also stimulates the release of insulin from pancreas


–  Addition of nutrients to cells and blood stream
–  Diffusion
–  Osmosis
–  Active Transport


–  The removal of waste and undigested material
–  Done through Defecation

Organs involved:

1.)  Oral Cavity

2.)  Esophagus

3.)  Stomach

4.)  Small Intestines

5.)  Large Intestines