The Digestive System

1. The Digestive System The mysterious process uncovered!

2. The Beginning • Oral cavity: • Both physical and chemical digestion takes place in the mouth. • Saliva: • secreted to moisten food, • protect the mouth from abrasions • buffer against acids in food, kill some forms of bacteria • begin carbohydrate digestion with the enzyme SALIVARY AMYLASE. • Tongue: • is used for taste, manipulates food while chewing and • prepares food for swallowing by forming it into a ball called a bolus.

3. Down the hatchet (or Pharynx and esophagus)! • Pharynx • Commonly called the throat. • Intersection of the glottis and opening to the esophagus is found here. • Epiglottisis a flap that closes the glottis when the act of swallowing occurs. • Esophagus • Connects the pharynx and the stomach. • Peristalsis, wave-like contractions of the smooth muscles push food down toward the stomach. • Connects with the stomach at the CARDIAC SPHINCTER.

4. Into The Stomach • J shaped expandable organ located on the left side of the abdominal cavity. • Stores up to 2 liters of food while mixing and digesting it. • The epithelial cells secrete GASTRIC JUICES and HCl making the pH around 2. • PEPSINOGEN : an enzyme used to partially hydrolyze protein; pepsinogen reacts with HCL to form pepsin. • The hormone GASTRIN is secreted by the stomach cells to regulate the production of gastric juices. • Fat Digestion:Bile emulsifies fat. This creates a larger surface area for the enzyme lipase to digest it. • Carbohydrate Digestion: Disaccharide digestion is under the control of the enzymes maltase, lactase, sucrase, all of which are mainly found in saliva. • The stomach is closed at its posterior end by the PYLORIC SPHINCTER

5. Stomach Photo

6. Small Intestine and Villi • Most hydrolysis of macromolecules occur here • It is more than 6 meters in length with smaller diameter than large intestine. • It is divided into 3 sections: duodenum, jejunum, and ileum • Pancreas, Liver, and Gall Bladder: • accessory organs, add digestive enzymes, juices and hormones into the small intestine. • The hormone Cholecystokinin (CCK) is released from the intestinal cells causing the gall bladder to release bile. It also causes the pancreas to release its digestive enzymes.

7. Absorption • Absorption and distribution of nutrients: • Small intestine is lined with small finger-like projections called Villi • Each villus contains a net of capillaries and a large lymph vessel called a lacteal • The nutrients except fat are absorbed into the capillaries, while the fat enters the lacteal. • All the contents of the blood enter the liver via the Hepatic portal vein. • The liver regulates the contents of the blood.

8. Pancreas and Villi

9. Large Intestine • Colon is connected to the small intestine at a T junction called the cecum. • The appendix is found attached to the end of the cecum. • The main function of the colon is to reabsorb water from the small intestinal material. • The bacteria Escherichia coli live in this area of the body. They produce odor, and Vitamin K. • Waste is excreted through the rectum and out through the anus

11. Now, who’s hungry? • Digestion Transit Times: • Mouth: • one minute • Esophagus: • two to 3 seconds • Stomach: • 2-4 hours • Small Intestine: • 1-4 hours • Large Intestine: • 10 hours to several days! • Digestion is now complete, time to eat again! • Review rubric for digestion t-shirt and digestion creative writing assessment!