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Human Biology: Digestive System Lesson 3: Absorption and Digestion in the Intestines Today’s Objectives Analyse the functional inter-relationships of the structures of the digestive system, including: Describe the functions of anaerobic bacteria in the colon Describe how the small intestine is specialized for chemical and physical digestion and absorption Describe the structure of the villus, including microvilli, and explain the functions of the capillaries and lacteals within it Digestion in the Duodenum The small Intestine is about 7 meters long The first 25 cm is the duodenum Digestive actions in the Duodenum: Stomach chyme is neutralized (sodium bicarbonate) Bile breaks down fat into fat droplets Pancreatic juice: amylase breaks down starch; trypsin breaks down protein; lipase breaks down fat droplets after bile has emulsified the fat Digestion in the Small Intestine Remainder of small intestine is also has digestive actions: Despite this, the primary function of the small intestine is absorption of molecules: Final digestion of protein and carbohydrates by intestinal juices (peptidases and maltase) from millions digestive glands Amino acids Glucose Fatty acids Glycerol Other disaccharides are digested in the small intestine by their own enzymes (lactase aids in lactose digestion, which is a sugar in milk) Absorption in the Small Intestine Small Intestine is specialized for absorption: Extremely long with convoluted (folded) walls Walls have villi (finger-like projections along the walls) Villi themselves have tiny microvilli on columnar epithelial cells Within each villus are blood vessels and a small lymph vessel called a lacteal which absorbs fluids and returns it to the veins later on Absorption occurs across the walls of each villus by active transport (uses energy): Sugars and amino acids enter the blood vessels and travel to the liver Glycerol and fatty acids enter the lacteals which will go back into the bloodstream later at the subclavian veins Villi and Microvilli The folded walls, villi and microvilli all greatly increase the surface area of the interior of the small intestine Greater surface area means more surface for absorption to occur Absorption in the Large Intestine The Large Intestine’s main function is the absorption of water Some vitamins may also be absorbed in the large intestine The large intestine also contains a large population of E. Coli bacteria which consume any substances that were not digested earlier When the bacteria break down these substances, they give off odorous molecules that cause the characteristic odor of feces or “passing gas” Bacteria in the Large Intestine Some vitamins, amino acids, and other growth substances required by the body (growth factors) are produced by these bacteria The growth factors are absorbed by the lining of the gut (intestine) E. Coli helps us metabolize what our bodies were unable to metabolize, thereby providing us with a vital service