The Alimentary Canal: The Mouth and the Oesophagus (Leaving Cert Biology): Revision Notes

The Alimentary Canal: The Mouth and the Oesophagus

1. Mouth
2. Oesophagus
3. Stomach
4. Small intestine
5. Liver
6. Pancreas
7. Large intestine

1. Mouth

Mechanical (physical) and chemical digestion occur in the mouth.

Mechanical Digestion (Teeth)

• Teeth break food into smaller pieces.
• This increases the surface area for enzyme action and speeding up the digestion of food.
• It is a form of mechanical/physical digestion.
• There are four types of teeth: | 1. Incisors | Cutting and slicing food. | |---|---| | 2. Canines | Gripping and tearing food. | | 3. Pre-molars | Chewing and grinding food. | | 4. Molars | Chewing and grinding food. |

Adult Dental Formula:

$$2 \left(\frac{2}{2} I\ \frac{1}{1} C\ \frac{2}{2} P\ \frac{3}{3} M\right)= 32$$

I = incisor

C = canine

P = pre-molar

M = molar

Mouth: Chemical Digestion

• Chemical digestion is carried out in the mouth by the enzyme amylase.
• Amylase is found in saliva which is produced by the salivary glands. These glands are located under the tongue, at the back of the jaws and in the cheeks.
  • Saliva contains water, salts, mucous, amylase, and lysozyme.
  • Amylase converts starch (polysaccharide) to maltose (a disaccharide).
  • Ideal pH in the mouth: 7-8.

• Food is formed into a bolus and pushed into the pharynx.
• A flap of tissue called the epiglottis covers the trachea (windpipe) to ensure that the bolus enters the oesophagus.

2. Oesophagus

• The oesophagus, like the rest of the alimentary canal, is made of involuntary muscle.
• This muscle contracts to push food along the alimentary canal.
• This process is called peristalsis.
• Fibre (cellulose) in the diet stimulates peristalsis.