The Digestive System
The digestive system is a group of organs that perform the process by which food, containing nutrients, is eaten and broken down into different components. This breakdown makes it possible for the digested material to pass through the intestinal wall into the blood stream. The digestive process contains many different steps that take place in many different organs.
The first step of digestion begins at the mouth, where the food enters the mouth. Saliva is secreted from the salivary glands. The saliva contains enzymes such as Ptyalin, which starts sugar digestion. The enzymes also provide lubrication to help in the chewing and swallowing of the food. The food then goes down the esophagus and into the stomach, where the next step of digestion takes place.
In the stomach, a mixture of hydrochloric acid and Pepsin, which is secreted by the stomach wall, liquefies the food. At the same time, a substance called intrinsic factor binds Vitamin B in food and various gastric enzymes, such as Pepsin (which begins protein digestion), which are secreted by the stomach wall. Secretions of mucus protect the stomach from its digestive enzymes. The food is then mixed in the stomach, turning it into chyme(digested food). The muscular pumping motion called peristalsis churns the chyme around.
The chyme then passes through the pyloric valve by peristalsis to the first portion of the small intestine, the duodenum. The duodenum is where most of the chemical digestion takes place. Here, bile from the gallbladder and enzymes from the pancreas and intestinal walls combine with the chyme to begin the final part of digestion.
Bile liquid is created in the liver, and stored in the gallbladder. Bile aids in the mechanical digestion of fat. The pancreas and gland cells of the small intestine secrete digestive enzymes that chemically break down complex food molecules into simpler ones. These enzymes include trypsin for protein digestion, amylase for carbohydrate digestion, and lipase for fat digestion. When the food passes through the duodenum, the digestion is complete.
From the duodenum, the chyme passes to the jejunum and ileum, where tiny finger-like objects called villi, cover the walls. These villi start the absorption of food. During the absorption, food molecules enter the blood stream through the walls of the intestine. From the small intestine, the digested products travel to the liver. Liver cells filter the blood of any harmful substances such as alcohol and ammonia.
Once food has passed through the small intestine, it is mostly undigestible material and water. It then enters the large intestine. There are six parts to the large intestine: the cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum. The appendix is attached near the bottom of the cecum. The appendix intercepts pathogenic microorganisms the enter the digestive tract. In the other parts of the large intestine, water and minerals are absorbed. The remaining material is then compacted into feces through peristalsis and passed out of the body through the rectum and the anus.
A peptic ulcer is an open sore in the mucus membrane of the stomach. While and ulcer is developing, part of the surface tissue breaks down, dies, and becomes inflames. There are two types of peptic ulcers. The first is the duodenal, which forms in the duodenum. Gastric ulcers develop in the stomach. The pepsin, located in the stomach, can eat through the lining of the stomach and the duodenum. Pepsin wouild not normally eat through the lining of the stomach and duodenum because of mucus which is normally secreted to protect the walls of them. Most peptic ulcers cause pain in the upper part of the abdomen. Peptic ulcers occur usually when the stomach is empty. People can reduce the risk of ulcers by not smoking and drinking alcoholic beverages.
Constipation is another disorder that affects the digestive system. It is a condition in which the bowel does not get rid of waste materials normally. A symptom of constipation is pain or tenderness over the colon. The constipated person may also suffer from headaches or backaches. Constipation can be caused by weakness of the bowel muscle or by strong, irregular contractions of these muscles. It may also occur when a person uses laxatives too frequently or does not