Page 48 - Biology Form Two

Biology for Secondary Schools

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Mouth Oral cavity

Tongue Pharynx
Epiglottis

Oesophagus

Trachea

Figure 2.3: Structure of oral cavity

The oesophagus is a muscular tube
connecting the pharynx with the upper Longitudinal muscles
part of the stomach. The food passes Circular muscles

through the oesophagus by a series of
wave-like muscular contractions and Circular muscles contract
relaxations of the oesophagus walls. Longitudinal muscles relax
Such series of muscular contractions Food bolus

is called peristalsis. Peristalsis Circular muscles relax
facilitates the movement of food from Lumen
the mouth to the pharynx as shown
in Figure 2.4. The oesophagus walls Figure 2.4: Peristaltic movement of food

have two types of muscles known as The peristaltic movement of food along
circular and longitudinal muscles that the oesophagus continues until it reaches
work antagonistically. As the food the stomach. At the junction between the
is swallowed, the circular muscles oesophagus and the stomach, there is a

above the food bolus contract and ring of muscles called cardiac sphincter.
longitudinal muscles relax making When the food reaches this point, the
the lumen smaller and squeezing food muscles automatically relax and allow
bolus downwards. the food to enter the stomach. Once
the food is in the stomach, the cardiac
sphincter muscles contract and close the
entrance into the stomach. This prevents

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