The digestive tract: mouth to oesophagus

A long tube with helpers

The digestive system is a long tube, the alimentary canal, from the mouth to the anus. Helper organs, the salivary glands, liver and pancreas, send their juices into it.

In the oral cavity, teeth cut and grind food: mechanical digestion. Three pairs of salivary glands add saliva: water, mucus and salivary amylase. Amylase breaks starch into maltose.

The chewed mass is the bolus. The tongue pushes it to the back of the mouth and into the pharynx. The oesophagus, about 25 cm long, carries it to the stomach by peristalsis.

Peristalsis is a wave of muscle contraction behind the food. It pushes the bolus along, so food reaches the stomach even if you lie down.

Key terms

Alimentary canal

The long tube through which food passes and is digested.

Salivary amylase

Breaks starch into maltose in the oral cavity.

Epiglottis

Closes the glottis during swallowing so food does not enter the lungs.

Peristalsis

Muscle waves that move food along the oesophagus and gut.

Short questions with model answers

1. Q1. State the role of salivary glands in digestion. (Short Answer 1)

   • What they make.
   • What each part does.

   Three pairs of glands moisten food and start the chemical digestion of starch.

2. Q2. What do swallowing and peristalsis mean? (Short Answer 2)

   • Swallowing.
   • Peristalsis.

   Swallowing moves the bolus into the pharynx; peristalsis carries it down to the stomach.

Common mistakes

• ✗ Food just falls down the oesophagus by gravity.

  ✓ Peristalsis pushes it; muscle waves move food along.

• ✗ The mouth only chews; chemical digestion starts in the stomach.

  ✓ Salivary amylase starts digesting starch in the oral cavity.

• ✗ The epiglottis closes the nose during swallowing.

  ✓ The palate closes the nasal cavity; the epiglottis closes the glottis (windpipe).

MCQs

1. 1. The wavelike movement of muscles that pushes food through the digestive system is called:

   1. (a) Chemical digestion
   2. (b) Mechanical digestion
   3. (c) Peristalsis
   4. (d) Absorption
   Show answer

   (c) Exercise MCQ 2 (p. 10).

2. 2. Which group of enzymes breaks up starches?

   1. (a) Amylases
   2. (b) Lipases
   3. (c) Proteases
   4. (d) Pepsin
   Show answer

   (a) Exercise MCQ 4 (p. 10): salivary amylase is one.

3. 3. What closes the opening of the trachea during swallowing?

   1. (a) The palate
   2. (b) The tongue
   3. (c) The cardiac sphincter
   4. (d) The epiglottis
   Show answer

   (d) p. 3: the top of the trachea is pushed up against the epiglottis.

4. 4. Salivary amylase changes starch into:

   1. (a) Glucose
   2. (b) Maltose
   3. (c) Amino acids
   4. (d) Fatty acids
   Show answer

   (b) p. 3. Maltose is a disaccharide of two glucose units.

5. 5. About how long is the oesophagus?

   1. (a) 2.5 cm
   2. (b) 25 cm
   3. (c) 2.5 m
   4. (d) 7 m
   Show answer

   (b) p. 4.

Quick revision

• The alimentary canal runs from mouth to anus; salivary glands, liver and pancreas help.
• The mouth grinds food and salivary amylase turns starch into maltose.
• The epiglottis guards the windpipe; peristalsis moves the bolus to the stomach.