The document summarizes the digestion and absorption of fats and other nutrients in the small intestine. It discusses how fats are emulsified by bile salts and lecithin in the duodenum and broken down by pancreatic lipase. The breakdown products are absorbed via micelles and transported as chylomicrons through lacteals. It also describes the absorption of water, sodium, chloride, bicarbonate and iron in the small intestine and the limited absorption that occurs in the large intestine through bacterial breakdown.

1. Digestion and Absorption of Fats Agitation in the stomach breaks the large drops of fats into small drops and disperses them throughout the chyme, this process called emulsification Most of the emulsification occurs in the duodenum under influence of bile Bile salts and lecithin are important for emulsification of fat The structure of bile salt and lecithin consist of hydrophobic in one side and hydrophilic on the other side

2. Digestion and Absorption of Fats Pancreatic lipase breaks down triglycerides to monoglyceride and free fatty acids Another function of bile salts and lecithin is to surround fatty acid and monoglyceride to form micelles The bile salt micelles also acts as transport medium to carry monoglyceride and free fatty acids to brush borders Monoglyceride and free fatty acids are absorbed into the blood but the bile salts released back to the chyme

3. Digestion and Absorption of Fats Triglycerides are reassemble inside the cells and packaged into chylomicrons Chylomicrons are composed of 90% triglyceride, 5% cholesterol, 4% phospholipid, 1% protein. Chylomicrons leave the cells and enter lymph vessels called Lacteals Short and medium chain fatty acids are absorbed by simple diffusion and can directly enter capillary

4. Digestion and Absorption of Fats Fat Bile + Agitation Emulsified Fat Emulsified Fat Pancreatic lipase Fatty acid & 2 monoglyceride

5. Transport of Lipids Across Intestinal Epithelium

6. Fatty Acid Absorption

7. Water and Na absorption Most of the water and Na enters the GI tract are absorbed in the small intestine The brush border is permeable to both water and Na ion Na and water absorbed by transcellular transport through intestinal epithelial cells or by paracellular transport through tight junction At the basal and lateral membranes of the cells, Na ions are transported into extracellular fluid of tissue and blood vessels This causes osmosis of water

8. Aldosterone enhances Na absorption During dehydration, large amount of aldosterone secreted Aldosterone causes increased Na absorption by intestinal epithelium and this in turn causes increases in absorption of Cl ions and water The function of aldosterone in the intestinal tract is the same as that of aldosterone in the renal tubules

9. Absorption of Chloride Chloride absorbed by diffusion in the upper part of the small intestine Transport of chloride ions follow the sodium ions

10. Absorption of Bicarbonate in the Small Intestine When Na ions are absorbed, moderate amount of hydrogen ions are secreted into the lumen of the gut Hydrogen ions combine with bicarbonate ions to form carbonic acid Carbonic acid dissociate to form water and carbon dioxide Carbon dioxide absorbed into the blood and expired through the lungs

11. Absorption of Iron Iron absorbed in the small intestine Iron combines with blood plasma to form transferrin and can be released to tissue cells In the cell, iron combines with protein apoferritin to form ferritin The iron stored as ferritin is called storage iron Total body iron is regulated mainly by altering the rate of absorption

12. Absorption in the Large Intestine Cells and secretions of the large intestine have no digestive functions Resident bacteria break down some of the indigestible carbohydrate and use released nutrients These bacteria synthesize some B complex vitamin and vitamin K that are absorbed The colon absorbs small amounts of salts and water