DIGESTIVE SYSTEM
Digestive System
1. Structure
2. Enzymatic Activity (goblet cells - make and secrete enzymes)
3. Absorption, exchange & assimilation
SURFACE AREA TO VOLUME RATIO!
1. INGESTION
2. MECHANICAL AND CHEMICAL DIGESTION
3. TRANSPORT
4. ABSORPTION (absorbed from gut to blood)
5. ASSIMILATION (becoming part of body component)
6. EGESTION
Phases of Digestion
IN SMALL INTESTINE
Goblet cells increase
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as you go down
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Villi & micro-villi increases
Enzymes
1. Salivary Amylase - Starch in mouth (7-7.8)
2. Pepsin - Proteins in stomach (2)
3. Pancreatic amylase - Carbohydrates in duodenum (7.2 - 7.5)
4. Lipase - Fats in duodenum (7.2-7.5)
5. Trypsin - Proteins (polypeptides to amino acids) in duodenum (7.2 - 7.5)
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Trypsin and pepsin need to be activated!
(i) Trypsinogen --(bile)--> trypsin
(ii) Pepsinogen --(HCl)--> pepsin
Bile produced by liver (broken down RBCs) and stored in the gall bladder neutralizes acid (HCl) and emulsifies fat
Liver, pancreas, and gallbladder are accessory organs...
ACID IN STOMACH
1. Immune defense mechanism
2. Helps break down bonds on a molecular level
3. Mucus produced by epithelial lining to protect muscular lining of the stomach
EMULSIFICATION OF FATS
Stomach
- HCl in stomach lowers pH to approx 2, killing bacteria and denaturing proteins.
- Pepsin enzyme starts protein digestion
- Muscular action helps in digestion (mechanical digestion)
- Stretch receptors in muscular wall trigger release of enzymes
when stomach is full
- Gastric pit releases gastric acid
Small Intestine
- Chyme enters duodenum. Bile from gall bladder is emptied here - neutralizes acid and emulsifies fat.
- Pancreatic enzymes are released (amylase, trypsin)
- Further enzymes are released in jejunum
- Illeum is last stage of small intestine (most villi) -> empties into cecum
most absorption of digested food
- Peristalsis moves digested and undigested mixture of food going through
1) Epithelial - Single outer layer of cells on each villus
2) Mucosa - Inner lining including villi
3) Submucosa - Connective tissue (btwn mucosa and muscle)
4) Muscular layer - Inner circular and longitudinal muscles [peristalsis]
5) Serosa - Protective fluid outer layer (prevents friction)
Large Intestine
- Undigested food pushed into large intestine
- Reclaim as much water as possible before egestion of solid faeces.
- Maximizes SA:V by being long and folded.
- Mucus secreted to lubricate passage of faeces
- A diet rich in fibres helps clear out waste products and dead cells, reducing risks of colon cancer.
Villi (adaptation for absorption)
- Single cell thick
- Blood capillaries
- Interstitial fluid (site for chemical reactions)
- Lacteal (part of lymphatic network - lipids, fatty acids, and glycerol)
- Microvilli (SA:V)
1. The Digestive System
