Digestive system

The alimentary canal consists of the mouth, oesophagus, stomach, small intestine (duodenum and ileum), large intestine (colon, rectum), and anus. Food passes directly through these organs during digestion and egestion.

The accessory organs include the salivary glands, pancreas, liver, and gall bladder. These organs aid digestion by secreting enzymes or other substances into the alimentary canal; food doesn't pass directly through them.

The mouth is where ingestion and mechanical digestion (chewing) begin, and chemical digestion of carbohydrates starts with salivary amylase enzyme breaking down starch into maltose.

The oesophagus transports food from the mouth to the stomach via peristalsis, which are wave-like muscle contractions that push the bolus down. No digestion or absorption occurs here.

The stomach stores and mixes food with gastric juice, which contains hydrochloric acid (kills bacteria, optimum pH for enzymes) and pepsin (enzyme that starts protein digestion). Mechanical digestion also occurs through churning.

The duodenum is the first part of the small intestine where digestive enzymes from the pancreas and bile from the liver mix with the chyme. It continues the digestion of carbohydrates, proteins, and lipids.

The ileum is the last part of the small intestine where the absorption of digested food molecules occurs into the bloodstream. It has villi and microvilli to increase the surface area for absorption.

The colon absorbs water and salts from undigested food, while the rectum stores faeces until egestion. The large intestine does not produce digestive enzymes.