Page 290 - Biology_F5

Nutrition

Oesophagial sphincter The stomach
contracted The stomach is a highly elastic muscular
Relaxed muscles organ. It has two valve-like rings of
Contracted muscles smooth muscles called sphincters that can
open and close. One sphincter is called
Relaxed muscles
Sphincter relaxed cardiac sphincter. It is located between the
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oesophagus and the stomach. The second
sphincter is called pyloric sphincter. It is
Stomach positioned between the small intestine and
the stomach. The stomach wall consists of
a layer of mucous membrane called gastric
Figure 5.14: Wave of peristalsis in the oesophagus mucosa that is highly folded and is equipped
with small pits (gastric pits), leading to
gastric glands (Figure 5.15) in which gastric
juice is secreted.
Gastric pits

Surface Pepsinogen
epithelium HCl Pepsin

Mucous
cell neck

Parietal cells
Gastric glands

Chief cells

Figure 5.15: Structure of the gastric mucosa

Gastric juice has the following components: and pepsin respectively. It also kills any

bacteria that might have entered the
Water: This is a solvent involved in
hydrolysis by which food substances are stomach through food.
broken down.
Mucus: This protects the stomach from
Hydrochloric acid (HCl): This is an acid its own digestive enzymes and lubricates
produced by parietal cells of the gastric the wall for easy passage of food to the
mucosa. Hydrochloric acid activates small intestine.
prorennin and pepsinogen into rennin

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