The GI Tract
• The GI tract contains food from the time it is eaten until is digested & absorbed or eliminated from the body.
• Pharynx (back of the mouth at top of throat)
• Small intestine.
• Large intestine.
The 6 Processes of the Digestive System
3. Mixing & propulsion
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
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)
- 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
• 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
• 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)