digestive system

three main secretions of the stomach

1. mucus: lines the stomach

2. hydrochloric acid: creates acidity

3. pepsinogen: converts into pepsin which chemically digests proteins

brush border enzymes

proteases, lactase (disaccharides), and bicarbonate

ghrelin

hormone that induces hunger

leptin

hormone that causes satiety

insulin

found in beta cells in pancreas

induces cellular uptake of glucose and stores glucose as glycogen, lowering BGL

glucagon

found in alpha cells in pancreas

stimulates breakdown of stored glycogen into glucose, raising BGL

1. ingestion of food in the mouth

mechanical digestion — chewing

mucus lubricates food

chemical digestion — amylase digests starch and lipase digests lipids

2. deglutition

food is packaged into a bolus and swallowed

3. bolus passes through pharynx

epiglottis closes the tracheal opening

bolus enters the esophagus

4. peristalsis

smooth muscle contractions move bolus through gastric sphincter to stomach

lower esophageal (cardiac) sphincter pervents reflux

5. mechanical digestion in stomach

forms chyme which moves through pyloric sphincter into the small intestine

6. small intestine — duodenum (small intestine)

chemical digestion of chyme — bicarbonate from pancreas and bile from the liver/gall bladder

breakdown of fats, proteins, and carbohydrates

produces brush border enzymes

7. small intestine — jejunum and ileum

jejunum: villi and microvilli absorb nutrients, carbohydrates, proteins into the blood

ileum: absorbs lipids, vitamin B12, bile salts, and products of digestion

8. blood travels from small intestine to liver

hepatic portal duct

glucose stored as glycogen

metabolizes proteins and carbohydrates

produces bile (breaks down lipids in small intestine)

9. colon

ascending: absorbs remaining water and salts

transverse: stores digested food

descending: carries solid waste to the rectum

10. elimination

waste accumulates in the rectum and ejects through the anus

gall bladder

stores bile produced by the liver

pancreas

produces pancreatic juices that neutralize and aid breakdown of chyme

gastrin

stomach hormone

stimulates gastric glands to secrete pepsinogen and hydrochloric acid

response to protein digestion

cholecystokinin

small intestine hormone

digests fats and proteins

stimulates release of bile from gall bladder

secretin

duodenum hormone

pH regulation — inhibits gastric acid secretion (stomach) and stimulates bicarbonate production (pancreas)

bile

produced by liver and stored in gall bladder

encourages digestion of fats