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Gastrointestinal System
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Lecture notes on the gastrointestinal system
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Polina LobachevaImportance of the GI system:
- Energy sources (macronutrients)
- Essential organic and inorganic nutrients (vitamins and
minerals) for physiology functions
- Organic compounds (amino acids) required for growth and
repair
- Inorganic compounds (water)
Organisation of the GI system
- 5.5meters long in a living human; it’s longer in a dead person
as the smooth muscles relax and are able to stretch
7L of fluid is secreted by the gastric tract, which includes:
- 2L from the stomach (gastric)
- 1.5L from the intestine
- 1.5L from the pancreas
- 0.5L from the liver
Organ Secretion Functions
, Polina Lobacheva
Mouth and pharynx Salt and water - moisten food Chewing (mastication), swallowing
Salivary glands Mucus - lubrication
Amylase - polysaccharide digestive enzyme
Oesophagus Mucus (lubrication) Move food to stomach (peristaltic waves)
Stomach HCl - solubilisation of particles, kill microbes, activation of Store, mix, dissolve, continue digestion, regulate rele
pepsinogen to pepsin into intestine
Pepsin - protein digestive enzyme
Mucus - lubricate and protect epithelial surface
Pancreas Enzymes - digest CHO, fats and proteins Secretion of enzymes and bicarbonate (neutralises
Bicarbonate - Neutralise HCl entering small intestine acidity from the stomach), non-digestive endocrine
functions
Liver Bile salts - Solubilise water-insoluble fats Secretion of bile and other non-digestive functions
Bicarbonate - neutralise HCl entering small intestine
Organic waste products and trace metals - elimination in faeces
Gallbladder Stores and concentrates bile between meals
Small intestine Enzymes - food digestion Digestion and absorption of most substances
Salt and water - maintain fluidity of luminal contents
Mucus - lubrication
Large intestine Mucus (lubrication) Storage and concentration of undigested matter,
absorption of salt and water, defecation
Structure of the GI tract wall, the 4 major tissue layers (listed from the inside out):
1. Mucosa (inner lining)
a. Epithelial cells which are moistened by secretion
b. Gland cells that secrete digestive juices
c. Endocrine gland cells that secrete GI hormones
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