- List, in order, the structures through which food passes in the human digestive tract.
- Distinguish clearly between the structure of the stomach and the small intestine.
- Describe how the digestive system helps maintain out internal environment.
On average it takes 24-33 hours for each meal to complete its passage through the digestive tract
Parts of the Human Digestive TractEdit
In mammals the mouth has a number of teeth arranged along the upper and lower jaws
The number and structure of teeth vary with each species
The upper surface of the tongue is covered with pimple-like structures called papillae which house most of the taste buds
The uvula which hangs from the middle of the back edge of the soft palate prevents food from entering the pharynx when swallowing
In the mouth food comes in contact with saliva which is secreted by three pairs of salivary glands
Saliva helps in the chemical process of digestion and moistens food so it can pass through the esophagus more easily
The two parotid glands located below and in front of the ears are the largest salivary glands
The smallest are the sublingual glands in the floor of the mouth inside of the incisors
The third pair are submaxillary glands and are below and behind the sublingual glands
The glands open into the mouth by ducts, tubular canals for carrying glandular secretions from one part of the body to another
- The Esophagus
- Food passes through a tube called the esophagus. It is lined with circular and longitudinal muscles along its length, which is about 24 cm. The muscles work together to push the food along.
- Mucin is secreted by a number of small, tubular glands located in the back of the throat and in the walls of the esophagus.
- The circular muscle ring at the lower end of the esophagus is thickened considerably to give its owner some involuntarycontrol over the flow of food into or out of the stomach.
- The movement of food out of the stomach, up the esophagus, and out of the mouth is called regurgitation.
- The stomach is a muscular, J-shaped, sac-like organ whose interior lining is packed with millions of gastric glands. These glands secrete the gastric juice so important in digestion.
- The stomach has a third layer of muscle fibres called the oblique layer. Muscles lining the stomach work to break food physically into smaller pieces and mix it with the gastric juices. This makes a thick liquid called chyme.
- The circular muscle layer at the junction of the stomach and the next part of the digestive tract is also thickened. The muscle layer forms a valve called the pyloric sphincter, which contracts and relaxes to controlthe flow of food leaving the stomach.
The Small IntestineEdit
The Large IntestineEdit
Undigested and unabsorbed materials are put in Large intestine from small Intestine