miércoles, 8 de diciembre de 2010

The digestive system

Nutrients in the foods you eat are needed by the cells of your body, we eat foods to obtein nutrients. But:
What organs and processes break down the foofs into nutrients that the body can use for fuel?
What organs and processes let the nutrients enter your bloodstream so they can travel to the cells where they are needed?
The basic processes involved are digestion and absorption. The organs involved are the organs of the digestive system.
Organs that make up the digestive system are shown in figure. Most of the organs form the gastrointestinal tract. Other digestive organs are called accessory organs.

Organs of the digestive system.
1. Gastrointestinal Tract
The gastrointestinal (GI) tract is a long tube that connects the mouth with the anus. It is more than 9 meters long in adults. The upper GI tract includes the mouth, pharynx, esophagus, and stomach. The lower GI tract includes the small and large intestines. Food enters the mouth, passes through the upper and lower GI tracts, and then exits the body as feces through the anus.

The organs of the GI tract are covered by two layers of muscles that enable peristalsis. Peristalsis is a rapid, involuntary, wave-like contraction of muscles. It pushes food through the GI tract.
The inside of GI tract is lined with mucous membranes. Mucous membranes can secrete and absorb substances. The ability to secrete and absorb substances is necessary for the functions of the digestive system.
2. Accessory Organs of the Digestive System
They are additional organs that play important roles in digestion. Food does not pass through them, but they make substances needed for digestion. The accessory organs are the salivary glands, the liver and the pancreas.

  • The salivary glands are found in and around your mouth and throat. We call the major salivary glands the parotid, submandibular, and sublingual glands.They all secrete saliva into your mouth .
  • The liver is a large organ next to the stomach. It produces digestive substances that are carried by tubes,to the small intestine and gall bladder. The gall bladder is a small, pear-shaped structure below the liver. It stores substances (bile) from the liver until they are needed by the small intestine.
  • The pancreas is a gland below the stomach. It produces digestive substances that are carried by a duct to the small intestine.

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