The Digestive System

1. The Digestive System T. Zack Crawford

2. Function of the Digestive System • To break down large food molecules into smaller ones the body can use such as proteins, carbohydrates, fats, vitamins and minerals

3. Components of the Digestive System – The Mouth • The mouth is the first portion of the digestive system where food enters the body. • It contains the cavity between the lips and the pharynx where food can be broken down physically by a crushing force from the jaw and teeth and chemically by saliva. • Salivary glands will secrete saliva into the mouth which will break down the food with chemical enzymes wile simultaneously cleaning the mouth. • The tongue will form the food into a ball-shaped bolus for swallowing.

4. The Pharynx and Esophagus • The pharynx is the part of the neck and throat behind the mouth and nasal cavity where both air and food pass. • Located in the pharynx, the epiglottis closes over the trachea while food is swallowed to prevent asphyxiation. • The esophagus is the muscular tube connecting the pharynx and stomach as the only pathway for the food. The bolus remains in the esophagus for only about 7 seconds.

5. The Stomach • The stomach is the muscular pouch which stores and breaks down the food both physically by churning and chemically by enzymes such as pepsin. • Gastric acid provides an optimal pH for the reaction with pepsin, along with killing any microorganisms digested with the food, and denaturing proteins. • After leaving the stomach, the food is now in a semi-liquid form known as chyme.

6. The Small Intestine • After leaving the stomach via the pyloric sphincter, the chyme enters the small intestine, about 6 meters of tubing folded thousands of times to fit in al small amount of volume. • Inside this tubing, there are millions of small finger-like projections called villi. These are important for increasing the surface area inside the intestines for absorption of molecules.

7. The Small Intestine • The small intestine is split into three parts. • The duodenum is the first section of the small intestine where secretions from the liver and pancreas are received and chemical digestion occurs. • The next two sections, the jejunum and the ileum are similar in most ways. The ileum is paler in color, thinner in diameter, and contains a large number of cells of the immune system, such as lymphocytes.

8. The Large Intestine • After leaving the small intestine, the remaining food material enters the large intestine where it is retained over time for its fermentation by gut bacteria. Some of this leftover material may be broken down and absorbed before being hardened and concentrated into feces. • The large intestine is a 1.5 meter tube surrounding the small intestine in an upside down “U” shape.

9. The Large Intestine and Anus • The large intestine is split into 5 parts. • The first three of these parts are the ascending, transverse, and descending colon, which are named after the direction in which the remaining material flows. • The sigmoid colon lies directly above the rectum, within the pelvis. • The rectum is the final, straight portion of the large intestine where feces will be stored before defecation. • The feces will be held within the rectum by the anal sphincter.

10. Accessory Digestive Organs • The Liver creates bile to break down fats and detoxifies the blood. • The Gallbladder is a small sack hanging from the liver which stores bile created by the liver. • The Pancreas is a long organ, behind the stomach, that produces insulin and also enzymes that assist in digestion within the small intestine.

11. The Breakdown of Nutrients (Proteins) • Proteins are digested into polypeptides within the stomach and duodenum by three enzymes. Pepsin within the stomach, along with trypsin and chymotrypsin from the pancreas. • The resulting polypeptides will be broken into amino acids by exopeptidases and dipeptidasesfound in the small intestine.

12. The Breakdown of Nutrients (Fats and Carbohydrates) • Fats are broken down into fatty acids by lingual liptase in saliva, pancreatic liptase, and bile. • Salivary and pancreatic amylase break down carbohydrates from polysaccharides to simple sugars such as glucose and maltose to be absorbed in the small intestine. • Also, lactase and sucrase break down lactose and sucrose (respectively) so that they may be absorbed by the small intestine.

13. Physical vs. Chemical Digestion

14. Digestive Disorders – Lactose intolerance • Lactose intolerance is the inability to make lactase, and sub sequentially break down lactose, found in milk, into glucose and galactose. • Symptoms include bloating, cramps, flatulence, diarrhea, nausea, and vomiting after consumption of lactose. Severity generally increases with an increase in consumption. • The disorder is prevalent in approximately half of the adult population. • The only real treatment for this disorder is to avoid consumption of lactose, especially in high concentration. Try to avoid dairy products, especially with lactose additives such as low-fat milk.

15. Digestive DisordersGastroesopageal Reflux Disease(GERD) • GERD refers to transient or permanent damage caused by stomach acid flowing into the esophagus, usually caused by abnormal relaxation of the lower esophageal sphincter (LES) above the stomach or a hiatus hernia (a protrusion of the upper part of the stomach into the thorax via a weakness in the diaphragm) • Symptoms include heartburn, vomiting, and trouble swallowing • GERD could be prevalent in up to 20% of the western population • GERD can be prevented or treated by eating smaller, less acidic meals, losing weight, or elevating your upper body. • As a last resort, GERD can be suppressed by a surgery known as Nissen fundoplication where the LES is strengthened by wrapping the upper part of the stomach around it.

16. Bibliography http://en.wikipedia.org/wiki/Digestive_system http://science.nationalgeographic.com/science/health-and-human-body/human-body/digestive-system-article/ http://en.wikipedia.org/wiki/Human_mouth http://upload.wikimedia.org/wikipedia/commons/c/c5/Digestive_system_diagram_edit.svg http://en.wikipedia.org/wiki/Jejunum and http://en.wikipedia.org/wiki/Ileum http://en.wikipedia.org/wiki/Sphincters http://en.wikipedia.org/wiki/Lactose_intolerance http://en.wikipedia.org/wiki/Gastroesophageal_reflux_disease All accessed on 1/21/13