The Digestive System The mysterious process uncovered!

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.

Down the hatchet (or Pharynx and esophagus)! Pharynx – Commonly called the throat. – Intersection of the glottis and opening to the esophagus is found here. – Epiglottis is 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.

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

Stomach Photo

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.

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.

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

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!