Process in Digestive System

• Digestion


  process of breaking down food into smaller molecules to be absorbed by the body
• Digestions' sequence of events


  ingestion, propulsion, digestion, absorption, assimilation, and excretion
• Ingestion


  -taking in food into the mouth and gastrointestinal tract.

  -It also involves salivary action and physical breakdown of food through mastication.
• Amylase


  -is the enzyme in saliva that is responsible for digestion of starch

  (sugars in plants) and glycogen (sugars in animals).
• Chemical breakdown of food has already begun in the mouth.
• Mastication


  grinding of food by the teeth
• Propulsion


  is the movement of food down the gastrointestinal tract.
• Swallowing


  is a voluntary type of propulsion where tongue pushes the food down to the esophagus.
• Peristalsis


  involuntary type of propulsion, wherein muscles of the digestive

  tract involuntarily contract and relax alternately to create rippling movements.
• Mechanical Digestion


  breaks down food molecules without chemical reactions.

  ○ Mastication: oral cavity

  ○ Churning: stomach

  ○ Segmentation: small

  intestine
• Chemical Digestion


  -breaks down food molecules by using chemical reactions.(enzymes and acids)

  -Gastrin triggers the stomach to produce pepsinogen, mucus, and hydrochloric
• Most of the digestion takes place in the small intestine.
• Saliva


  fluid in the mouth that helps digest food
• Absorption


  -involves transport of the digested food into the bloodstream via intestinal capillaries and lacteals.

  -The small intestine also absorbs some of the water, minerals, and alcohol.

  -The large intestine absorbs most of the water and some vitamins.
• Assimilation


  -involves building up of complex substances after absorption. This process is the opposite of absorption.
• ○ Fatty acids are used to form fats.

  ○ Amino acids are used to form proteins.

  ○ Monosaccharides are used to form polysaccharides

  (glycogen for animals).

  ○ Essential compounds such as hormones and enzymes

  are also synthesized.
• Vili


  finger like projections which cover the walls of the intestine. Absorbs nutrients from food so the body has energy. Presence of this increases the surface area for absorption.
• Microvilli


  when villi are further divided into smaller projections
• Excretion


  -elimination of the undigested food.
• Feces


  -indigestible materials like cellulosic fiber, small amounts of water, mucus, and bacteria.

  -Peristalsis and mass movements in the large intestine move the feces into the rectum.
• Mass movements


  slow and long contractions within the large areas of the large intestine.
• Defecation Reflex


  when feces fills rectum, it signals excretion