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

sections

digestive system

digestion in mouth

swallowing

regulation of swallowing

digestive system

• The digestive system is composed of a long tube called the gastrointestinal tract. Digestive system- of the pharynx, oral cavity, stomach, gall bladder, liver, small/large intestine- duodenum colon, anal canal and rectum.

• Accessory organs include- tongue, teeth, salivary glands, pancreas, liver and gall bladder

• 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

     +GIT is external to the body

digestion in 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

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

swallowing

• Swallowing: has 3 stages—oral, pharyngeal and oesopha1geal

  • oral → the food is voluntarily taken into the pharynx by using the tongue

  • pharyngeal → bolus of food stimulates epithelial swallowing receptor areas.

  1. the soft palate is pulled upward to prevent reflux of food into nasal cavities.

  2. The palatopharyngeal folds are pulled together to form a slit through which the food can pass

  3. the vocal cords of the larynx are strongly approximated and the larynx

  4. is pulled upward → the epiglottis is pulled back to cover the opening of the larynx.

  5. Upward movement of the larynx enlarges the opening of the esophagus

  6. the entire muscular wall of the pharynx contract and this contraction wave is spreading downwards.

• oesophageal stage

  • primary peristalsis: is the continuation of the peristaltic wave from the pharynx → esophagus into the stomach → enhanced also by gravity

  • secondary peristalsis :is the distention of the esophagus and it continues until all the food is emptied into the stomach

regulation of swallowing

• Parasympathetic branch of ANS

• Acetycholine- muscarinic receptors-- stimulates secretion of saliva with the digestive enzymes

• Sympathetic inhibits saliva production