Human Digestive System

• The human digestive system is a single tube that extends from the mouth to the anus.

• According to the function performed, its structure changes at different places.

• Glands such as the salivary glands, liver and pancreas supply enzymes and other substances (bile) to different parts of the digestive tract.

Main Functions

• Digestion of food

• Absorption of digested end products

• Removal of undigested materials from the body

Parts of the Digestive System

• Buccal cavity (Mouth)

• Salivary glands

• Oesophagus

• Stomach

• Liver

• Gall bladder

• Pancreas

• Small intestine

• Large intestine

• Caecum

• Appendix

• Rectum

• Anus

Buccal Cavity

• Digestion begins in the mouth.

• Teeth cut, tear and grind food into small pieces.

• The tongue mixes food with saliva and helps in swallowing.

Saliva

• moistens food and contains salivary amylase.

• which starts the digestion of starch.

  
  

Oesophagus

• Food is swallowed and passes through the oesophagus.

• Food is moved to the stomach by peristaltic movements.

Stomach

• Food is mixed by muscular movements.

• Gastric glands secrete gastric juice.

• Gastric juice contains :

  
  

  Hydrochloric acid (HCl)

  Pepsin

  Mucus

  
  

• Protein digestion begins in the stomach.

• Mucus protects the stomach wall from the action of acid.

Small Intestine

• Digestion is completed in the small intestine.

• Bile from the liver helps in fat digestion.

• Pancreatic juice and intestinal juice complete the digestion of carbohydrates, proteins and fats.

• The inner wall has numerous villi.

• Villi increase the surface area for absorption.

• Digested nutrients are absorbed into blood capillaries and lacteals in the villi.

Large Intestine

• Water and mineral salts are absorbed.

• Undigested food is converted into faeces.

• Faeces are temporarily stored in the rectum.

• Faeces are expelled through the anus.

Digestive Juices and Their Functions