45 - The gastrointestinal system – functions. Digestion in the mouth: mastication, secretion, enzymatic breakdown and absorption. Swallowing – phases and regulation

gi system and fucntions

The GI system generally refers to the gastrointestinal tract (the continuous tube: mouth, pharynx, esophagus, stomach, small & large intestines, rectum, anus).

Functions:

1. provides our body with a permanent supply of water, electrolytes, nutrients and vitamins.

2. Motility -peristalsis movement of food through the alimentary tract

3. Secretion- saliva, gastric juice, pancreatic juice- digestive enzymes, bile

4. absorption of water, electrolytes and vitamins, alcohol- stomach

5. excretion- done by colon, K+ waste—faeces

6. protection- HCL, leukocytes in intestinal juices

these functions are controlled locally by the Hormonal and nervous system

SAME PP (ACRONUM)

GIT is external to the body

Digestion in the mouth

Mastication:

• teeth are responsible for --cutting and chewing action.

• Jaws used

• Tongue moves the food around

Secretion:

• Saliva secreted in mouth which is responsible for digestion. It contains a serous and a mucous

secretion form.

• Secreted from parotid (serous), submandibular and sublingual (serous&mucous) and many

buccal glands.

• mucous secretion contains mucin, mainly responsible for lubrication and surface protection.

Salivary enzymes:

1. salivary a- amylase: starts to break carbohydrates

2. lingual lipase: starts to break down lipids

saliva ph- 7-7.5 in 24 hrs 1-1.5 litres- has water and minerals

Phases of Swallowing

Phases of Swallowing

1. Oral Phase (Voluntary):

   • Food is chewed and formed into a bolus.

   • The tongue pushes the bolus voluntarily into the pharynx.

2. Pharyngeal Phase (Involuntary):

   • Bolus stimulates swallowing receptors in the pharynx.

   • Soft palate elevates to block nasal passage.

   • Palatopharyngeal folds narrow the passage.

   • Vocal cords close tightly.

   • Larynx elevates and epiglottis covers the laryngeal opening to prevent aspiration.

   • Pharyngeal muscles contract in a downward wave to push food towards esophagus.

   • Larynx elevation also opens the upper esophageal sphincter.

3. Esophageal Phase (Involuntary):

   • Primary peristalsis: continuation of the swallowing wave from pharynx down esophagus to stomach; gravity helps.

   • Secondary peristalsis: triggered by esophageal distension to clear remaining food until esophagus is empty.

• Parasympathetic branch of ANS-

So, acetylcholine → M3 muscarinic receptors → increased saliva secretion.

and GI motility.

symp inhibits