Page 30 - E-Biology Sec.2 2024-2025 U1_Handy

3- Oesophagus A muscular tube passes through the neck and into the chest cavity,

and parallel to the vertebral column with 25 cm long.
It is lined with glands to secrete mucus.
It transfers the food from pharynx to stomach by series
of rhythmical muscular contractions and relaxations “Peristalsis”
continues along the alimentary canal to churn & mix the food + dig. juices.

B) Gastric digestion

Muscles

4- Stomach A dilated muscular sac.

It starts with a circular muscle controls the cardiac sphincter.

It ends with a circular muscle controls the pyloric sphincter.

It secretes gastric juice (colorless acidic liquid) consists of:

1- Water (90%).
2- HCl: creates an acidic medium (PH= 1.5 – 2.5) for:

Killing any Stopping the Activation of
harmful bacteria action of ptyalin pepsinogen.

3- Pepsin: is secreted in inactive form “pepsinogen” then it is activated by HCl.

Protein + water Gastric (pepsin) polypeptides (semi-liquid) (partially digested)

HCl

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First Term