The Digestive System

1. The Digestive System Ben Coltharp

2. Overview The Digestive system is composed of three major sections: Large Intestine, Small Intestine, and the Salivary Glands, which make up the mouth. Each of these sections each have at least three organs/glands, with the Large Intestine having eight.

3. Salivary Glands Mouth- Food enters through this, which is a mucous membrane-lined cavity. The lips, cheeks, hard palate, and the soft palate all help to protect the mouth. Tongue- Has several bony attachments, two of these are to the hyoid bone and the styloid processes of the skull. The lingual frenulum, mucous membrane fold, secures tongue to floor of mouth.

4. Other Major Organs Pharynx- from the mouth, the food passes posteriorly into the oropharynx and laryngopharyns; both of which are common passageways for food, fluids, and air. The walls of the pharynx contain two skeletal muscle layers. Alternating contractions of these two muscle layers propel food through the pharynx. Esophagus- Runs from the pharynx through the diaphragm to the stomach. 25 cm (10 inches) long, it’s a passageway that conducts food to the stomach.

5. Other Major Organs contd. Stomach- Cardiac region, which surrounds the cardioesophageal sphincter, where food enters. Varies in size from 15-25 cm (6-10 inches) in length. Diameter and volume depend on how much quantity of food it contains. When full, it can hold about 4 liters ( 1 gallon). Acts as a “storage tank” for food and food breakdown. Its wall contains a third, (other two being longitudinal and circular muscle layers) obliquely arranged layer in the themuscularisexterna. Allows not only to move along the tract, but to churn, mix , and pummel the food. In addition, chemical breakdown takes place also. The stomach wall is composed of columnar epithelium mucous cells that produce protective layer of bicarbonate-rich alkaline mucus that clings and protects the stomach wall from being damaged by acid and digested by enzymes.

6. Small Intestine Small Intestine- Major body digestive organ. Muscular tube extending from the pyloric sphincter to the large Intestine. Longest section of the alimentary tube, with an average length of 2-4 m, (7-13 feet :O). The SI has three subdivision: Duodenum, Jejunum, and Ileum. SI is able to process only a small amount of food at one time. Pyloric sphincter (gatekeeper) controls food movement into the SI from the stomach and prevents the SI from being overwhelmed. Enzymes that are produced by the pancreas and then ducted into the duodenum through the pancreatic ducts, completing the chemical breakdown. Duodenum- about 25–38 cm (10–15 inches) long connecting the stomach to the jejunum. Jejunum- gives the bowel great mobility within the abdomen. It also contains circular and longitudinal smooth muscle which helps to move food along Ileum- mainly to absorb vitamin B12 and bile salts and whatever products of digestion were not absorbed by the jejunum.

7. Small Intestine

8. Large Intestine Much larger in diameter than SI, but shorter in length. Extends from the ileocecal valve to the anus. Major Functions: dry out indigestible food residue by absorbing water and to eliminate these residues from the body as feces. Subdivisions- Cecum, appendix, colon, rectum, and anal canal. Because the “vermiform” appendix is usually twisted, it’s an ideal location for bacteria to accumulate and multiply. Usually leading to appendicitis. The anal canal ends at the anus. The anal canal has an external voluntary sphincter composed of skeletal muscle and an internal involuntary sphincter formed by smooth muscle. These sphincters open and close the anus, which are usually closed, except during defecation.

9. Large Intestine contd.