The Digestive System

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The GI Tract

• The GI tract contains food from the time it is eaten until is digested & absorbed or eliminated from the body. 

Organs include: 

• Mouth 

• Pharynx (back of the mouth at top of throat)

• Oesophagus. 

• Stomach 

• Small intestine. 

• Large intestine.

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The 6 Processes of the Digestive System

1. Ingestion

2. Secretion

3. Mixing & propulsion

4. Digestion 

5. Absorption

6. Defeacation

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Ingestion and Secretion


• taking foods & liquids into the mouth (eating). 


  • cells within the walls of the GI tract & accessory organs secrete a total of about 7 litres of water, acid, buffers, & enzymes into the lumen of the tract to help digestion
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Mixing and Propulsion

  • Contraction and relaxation of smooth muscle in the walls of the GI (Peristalsis) tract mix food and secretions and move them towards the anus

• The ability of the GI tract to mix and move material is called ` motility’. 

• Following C. section – Paralytic Ileus (paralysis of the intestine)

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  • Mechanical and chemical processes break down ingested food into small molecules. 
  • mechanical digestion - teeth cut and grind food before itis swallowed, 
  • smooth muscles of the stomach and small intestine churn the food
  • Food molecules are dissolved and mixed with digestive enzymes. 
  • Chemical digestion - the large carbohydrate, lipid, protein, and nucleic acid molecules in food are broken down into smaller molecules by digestive enzyme
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• The entrance of the products of digestion (ingested and secreted fluids, ions, and small molecules) into the epithelial cells lining the lumen of the GI tract

• The absorbed substances pass into interstitial fluid and then into blood or lymph and circulate to cells throughout the body

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• Wastes, indigestible substances, bacteria, cells shed from the lining of the GI tract, and digested materials that were not absorbed leave the body through the anus = defecation. 

 • The eliminated material is termed faeces (stool)

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