FOOD20003 Lecture Notes - Lecture 4: Pepsin, Dipeptide, Monoglyceride
28 Jun 2018
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WEEK 2 – DIGESTION AND ABSORPTION
Introduction:
• Cells require a constant supply of nutrients
o Supplied via the blood
• Digestive system:
o Digestion à mechanical (chewing) and chemical breakdown of food, extraction of nutrients, and
breakdown of macro-nutrients
o Absorption à transfer of nutrients from the lumen of the small intestine to blood/lymphatic
capillaries
o Excretion: elimination of wastes inside the body
§ food is not excreted b/c it’s from outside the body
Overview of Digestion
• The GI tract is the flexible muscular tube from mouth to anus.
• The mouth is the beginning of the digestive system.
• Digestion in the mouth involves mastication (chewing), the stimulation of taste buds and swallowing.
• After swallowing, the food is called a bolus.
• The oesophagus is the tube that leads the bolus to the stomach.
• The stomach adds juices and grinds the bolus into chyme (semi liquid).
• The pyloric sphincter regulates the flow of chyme into the small intestine.
• The small intestine receives digestive juices from the gallbladder and the pancreas
• The three segments of the small intestine are the duodenum, the jejunum and the ileum.
• The large intestine (colon) begins at the ileocaecal valve and ends at the rectum and anus.
PART 1. THE GASTROINTESTINAL (GI) TRACT
Principle organs & functions
• Mouth: Chews and mixes food with saliva
• Oesophagus: Passes food from the mouth to the stomach
• Stomach: Adds acid, enzymes and fluid. Churns and mixes to a liquid mass
• Small intestine: Secretes enzymes that digest all energy-yielding nutrients to smaller molecules
o Cells of wall absorb nutrients into the blood and lymph
• Large intestine: Reabsorbs water and minerals. Passes waste (Fibre, bacteria and unabsorbed nutrients)
along with water to the rectum
• Rectum: Stores waste prior to elimination
• Anus: Holds rectum closed and opens to allow elimination
o Liver (production of bile) and Pancreas (hormones production and secretes digestive enzymes)
§ Not a part of GI but is attached to the GI
PART 2. DIGESTION
• Micro-nutrients à little or no digestive preparation
• Macronutrients à needs to be broken down into little basic units to allow absorption
o Requires enzyme
• Muscular/Mechanical actions
o Chewing
o Peristalsis à squeezing of oesophagus pushing food down
o Segmentation à squeezing pushing food up
§ Good for when food moved down too quickly & mixing w/ new food
o Stomach action
• Digestive secretions/Chemical actions
o Saliva (moisten foods), gastric juice, bile, pancreatic and intestinal enzymes
Document Summary
Principle organs & functions: mouth: chews and mixes food with saliva, oesophagus: passes food from the mouth to the stomach, stomach: adds acid, enzymes and fluid. Churns and mixes to a liquid mass: small intestine: secretes enzymes that digest all energy-yielding nutrients to smaller molecules, cells of wall absorb nutrients into the blood and lymph, large intestine: reabsorbs water and minerals. Good for when food moved down too quickly & mixing w/ new food: stomach action, digestive secretions/chemical actions, saliva (moisten foods), gastric juice, bile, pancreatic and intestinal enzymes. Carbohydrate digestion little to none required: starch digestion begins in the mouth, no digestion in the stomach. In duodenum pancreatic amylase breaks molecules into disaccharides: final break down occus in the small intestine, enzymes break disaccharides into monosaccharides. Prevent constipation: soluble fibre partially fermented in the large intestine, resistant starch (rs) some starch doesn"t get digested b/c been changed chemically. Ends up as food for bacteria found in processed food.
