Page 289 - Biology_F5

Biology for Advanced Level Secondary Schools

Cuboidal epithelium easily; it catalyses the hydrolysis of starch
This tissue is made up of cells which are into maltose using the enzyme called salivary
cube-like in shape with a central nucleus. α-amylase. It maintains the pH of the mouth
They usually form a lining of the salivary between 6.5 and 7.5. This level is optimum
glands where they perform secretory for the action of salivary amylase to function
functions (Figure 5.13). In some cases which is accomplished by its constituent
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the cell surface of this tissue is ciliated or mineral salts (example NaHCO ).
flagellated. 3

Chemically, the digestion of food in the
Cells mouth involves converting starch into
Nucleus maltose by salivary α-amylase. The tongue
which is located at the back of the buccal

Basement cavity rolls the food into a ball-like structure
membrane called bolus and forces it against the soft

Figure 5.13: Cuboidal epithelium palate during swallowing, thereby closing
the nasal cavity. The opening in the larynx
Digestion in the mouth (voice box) called glottis, is also closed by
a flap like structure called epiglottis. Then,
Task 5.11 the bolus enters the oesophagus.
Search from internet sources the
simulations/videos showing the The oesophagus
process of digestion in the human
being. Note what you have observed. In the oesophagus the bolus is moved by a
series of wave-like movements caused by

Mechanical and chemical digestion of food involuntary contraction and relaxation of its
starts in the mouth. Mechanical digestion circular and longitudinal smooth muscles.
is achieved by teeth through mastication This process is described as peristalsis.
The contraction of circular muscles (inner
(chewing). During mastication, the food muscles) causes the oesophagus to become

is mixed with saliva, a watery mixture of narrow and long. The contraction of
mucus and amylase secreted by the salivary longitudinal muscles (outer muscles) causes
glands in response to thought, smell, taste the oesophagus to become wide and short.
or sight of food. Saliva is a neutral or very These contractions and relaxations of circular
weak alkali with the pH ranging between 6.5 and longitudinal muscles push the bolus
and 7.5. Saliva has the following functions down the alimentary canal. Additionally
,
with regard to digestion: it lubricates food the peristalsis waves of contractions assist
so that it can move through the oesophagus in mechanical digestion (Figure 5.14).

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