HUMAN TEETH AND DIGESTIVE SYSTEM

Human Teeth and Digestive System



Human Teeth and Digestive System

The digestive system is the series of tubelike organs that convert our meals into body fuel. In all there's about 30 feet (9 meters) of these convoluted pipeworks, starting with the mouth and ending with the anus. Along the way, food is broken down, sorted, and reprocessed before being circulated around the body to nourish and replace cells and supply energy to our muscles.

Food on the plate needs to become a mashed-up, gooey liquid for the digestive system to be able to split it up into its constituent parts: proteins, carbohydrates, fats, vitamins, and minerals. Our teeth start the process by chewing and grinding up each mouthful, while the tongue works it into a ball-shaped bolus for swallowing.

Moistening saliva fed into the mouth from nearby glands starts the process of chemical digestion using specialized proteins called enzymes. Secreted at various points along the digestive tract, enzymes break down large molecules of food into smaller molecules that the body is able to absorb.

Once we swallow, digestion becomes involuntary. Food passes down the throat to the esophagus, the first of a succession of hollow organs that transport their contents through muscular contractions known as peristalsis.

The esophagus empties into the stomach, a large, muscular chamber that mixes food up with digestive juices including the enzymes pepsin, which targets proteins, and lipase, which works on fats. Hydrochloric acid likewise helps to dissolve the stomach contents while killing potentially harmful bacteria. The resulting semifluid paste—chyme—is sealed in the stomach by two ringlike sphincter muscles for several hours and then released in short bursts into the duodenum.

The first of three sections of the small intestine, the duodenum produces large quantities of mucus to protect the intestinal lining from acid in the chyme. Measuring about 20 feet (6 meters) in length, the small intestine is where the major digestion and absorption of nutrients take place. These nutrients are taken into the bloodstream, via millions of tiny, fingerlike projections called villi, and transported to the liver.

What's left in the digestive tract passes into the large intestine, where it's eaten by billions of harmless bacteria and mixed with dead cells to form solid feces. Water is reabsorbed into the body while the feces are moved into the rectum to await expulsion.

In the human body, the mouth (oral cavity) is a specialized organ for receiving food and breaking up large organic masses. In the mouth, food is changed mechanically by biting and chewing. Humans have four kinds of teeth: incisors are chisel-shaped teeth in the front of the mouth for biting; canines are pointed teeth for tearing; and premolars and molars are flattened, ridged teeth for grinding, pounding, and crushing food. The soupy mixture called chyme spurts from the stomach through a sphincter into the small intestine. An adult's small intestine is about 23 feet long and is divided into three sections: the first 10 to 12 inches form the duodenum; the next 10 feet form the jejunum; ...