The Digestive System

Gross Structure

  • Mouth - Salivary Gland - secrete saliva containing mucus, salts and amylase. Breaks down starch and lubricates food so it's easier to swallow
  • Oesophagus - Muscular tube. Contractions move food from mouth to stomach. Mucus secreted from goblet cells to lubricate food
  • Stomach - Small sac with folds to allow expansion. Walls produce gastric juice consisting of hydrochloricacid, mucus and pepsin. Pepsin hydrolyses proteins + mucus protects stomach being digested
  • Pancreas - releases pancreatic juice into small instestine. Contains amylase and lipase. Also neutralises the hydrochloric acid from stomach with bile
  • Small Intestine - Long, folded muscular tube. Inner wall folds to form villi, epithelial cells have micro villi on. Produces enzymes from walls
  • Large Intestine - Absorbs water so food becomes faeces
  • Rectum - Faeces stored here before being removed via anus - process called egestion
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  • Physical Breakdown - physical digestion through use of structures like teeth and the muscular action of churning in the stomach. Allows ingestion and large SA for chemical digestion
  • Chemical Digestion - Breaking down of large insoluble molecules into smaller soluble ones through hydrolysis

Digestion - the breaking down of larger molecules into smaller molecules

Hydrolysis - Splitting up of molecules by adding water to chemical bonds holding them together

Absorption - uptake of soluble molcules into the body

Assimilation - Incorporating absorbed molecules into body tissue

Many foods are polymers (carbohydrates, proteins) and to be absorbed must be broken down into monomers (monosaccharides, amino acids). Enzymes catalyse hydrolysis to do this

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Proteins - Amino Acids

Polypeptide - More than two amino acids joined together

Proteins are made up of one or more polypeptides


  • All have general structure of               R

                                               H2N  --  C --  COOH


COOH = carboxyl group  NH2 = amino group  R = variable group

In glycine (smallest amino acid) the R group is just a Hydrogen


Amino acids are joined via condensation reactions to form a peptide bond

OH + H combine to form water which is a product of the reaction

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