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The Small Intestine
-major site of digestion and absorption
-Diameter= 2.5cm, Length= 6-7m
Components of the Small Intestine
• Duodenum
– first 25-30cm
• most of digestion occurs here
• enzymes from pancreas and bile from gall bladder enter to digest:
– lipids, carbohydrates, proteins
Sodium Bicarbonate in the Duodenum
• The enzymes in the duodenum require a basic pH=9.0 to function. Stomach acid has a pH=2.0. Sodium bicarbonate from the pancreas alters the pH to accommodate these enzymes.
http://www.execulink.com/~ekimmel/secretin_0.htm
• Jejunum
–digestion and absorption
• Ileum
–absorption
–moves undigested material into large intestine
Cross Section of Small Intestine
Structure related to Function• Circular Folds, Villi and Microvilli
– all increase SA to maximize absorption of nutrients
• Length– increases time available for nutrient absorption
• Capillary Beds– absorb nutrients and transport to body cells
• Lacteals– absorb lipids into lymphatic system
The Large Intestine (Colon)• D = 7.6 cm, L = 1.5 m
– reabsorbs water, salt, minerals
• it takes 5.6 L of water to digest our food each day, Why?
• 1. Dissolve digestive enzymes
• 2. Lubricate food material
• 3. Dissolve nutrients to allow absorption
The Large Intestine (Colon)
• all but 0.2 L is reabsorbed in the large intestine
• feces (undigested food material) are usually very solid, low water content
The Large Intestine
Bacteria in the large intestine
Bacteria in the large intestine
• bacteria can’t survive in the harsh environments of the stomach and small intestine
– the damp colon is a good breeding ground
• some are useful, produce vitamins B12, K
• some are harmful, e. coli
Escherchia coli
Where does E.coli come from?
-present in the feces of most mammals
-most strains are harmless
How does E.coli get into lakes?
-runoff waters after heavy rains
-sewage contamination
What are the symptoms of an E.coli infection?
E. Coli Infection• Causes severe diarrhea, How?
– peristalsis speeds up
– not enough time for water re-absorption to occur
• Treatment?– drink lots of fluids
– antibiotics prescribed