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