3.1 Structure and function of the digestive system

The Digestive System

A coordinated group of organs designed to mechanically and chemically break down food, absorb nutrients and eliminate waste.

Main organs of the digestive system

• Buccal cavity

• Salivary glands

• Oesophagus

• Stomach

• Small intestines

• Large intestines (colon/bowel)

• Rectum

• Anus

• Pancreas

• Pancreatic duct

• Liver

• Gallbladder

• Bile Duct

Buccal cavity

The first segment of the digestive system that contains the teeth, tongue and salivary glands.

Functions of the buccal cavity

• Ingest food

• Initiate physical and chemical digestion

• Facilitate swallowing

• Support speech and breathing

Another name for the buccal cavity

Mouth

Function of the teeth

It is used for mechanical breakdown.

Function of the tongue

It is used to mix food

Function of the salivary glands

It releases saliva containing amylase, which is an enzyme that starts the chemical digestion of starch.

Bolus

A small, rounded, moistened mass of chewed food formed in the mouth during digestion.

Oesophagus

A long, muscular tube lined with mucus-secreting cells.

Function of the oesophagus

It uses peristaltic contractions to move food toward the stomach.

Peristalsis

Wave-like muscle contractions that move food through the alimentary canal.

Stomach

A J-shaped muscular organ with glands in its lining that secretes hydrochloric acid and pepsinogen.

Function of the stomach

It’s thick muscular walls stores and churns food, mixing it with gastric juices to form chyme.

Pepsin

What pepsinogen is converted to in acidic conditions

Chyme

The semi-liquid mixture of partially digested food and gastric juices in the stomach.

Small intestine

Long, folded tube containing villi, that is made up of the duodenum, jejunum and ileum.

Function of the small intestine

The site for final digestion and nutrient absorption.

The organ that is often referred to as the ‘small bowel’

Small intestine

Duodenum

The first and shortest part of the small intestine, where the bile and pancreatic enzymes break down food.

Where the duodenum receives the bile and pancreatic enzymes from

It receives bile from the gallbladder and pancreatic juice from the pancreas.

Liver

A large organ above stomach.

Functions of the liver

It processes nutrients, produces bile and detoxifies harmful substances.

Bile

Emulsifies fats into smaller droplets, increasing the surface area for enzyme action.

Bile duct

Located in the upper right part of the abdomen, connecting the liver and gallbladder to the small intestine.

Function of the bile duct

Transports bile from the liver to the gallbladder.

Gallbladder

A small sac under the liver.

Functions of the gallbladder

Stores and concentrates bile produced by the liver, releasing it into the duodenum.

Pancreas

It is located behind the stomach.

Functions of the pancreas

Produces digestive enzymes and bicarbonate to neutralise stomach acid.

Pancreatic duct

A small tube that runs horizontally through the centre of the pancreas.

Function of the Pancreatic duct

Carries pancreatic juice to the duodenum.

Pancreatic juice

Contains enzymes that complete the chemical breakdown of carbohydrates, fats and proteins.

Jejenum

The middle part of the small intestine

ileum

The final and longest part of the small intestine, where nutrients are absorbed into the bloodstream.

Large intestine

Short, wide tube, that is made up of the cecum, colon, rectum and anus.

Functions of the large intestine

It absorbs water and forms faeces.

The organ that is often referred to as the ‘large bowel’

Large intestine

Colon

Absorbs water and electrolytes from undigested food, forming faeces.

Rectum

Temporarily stores faeces.

Anus

It is controlled by two sphincter muscles and regulates the release of faeces.

The two organs located at the end of the large intestine

Rectum and anus

Faeces

Waste material formed in the colon, consisting of undigested food, bacteria and water.