The Human Digestive System

In my second post, I wll be telling you more about the Human Digestive System. The digestive system consists of the elimentary canal (also known as the gut), the salivary glands, the liver, the gall bladder and the pancrease. The journey of food through the alimentary canal begins in the mouth, through this journey, some of the food is digested and absorbes by the body. Undigested food is passed out of the body through the anus.


Mouth
In the human body, the mouth is a specialized organ for receiving food and breaking up large organic masses. In the mouth, food is changed mechanically by biting,chewing and grinding. In the mouth, food is moistened by saliva, a sticky fluid that is produced from the salivary glands. The saliva contains an enzyme called amylase, which digests starch molecules into smaller molecules of maltose.
During chewing, the tongue moves food about and manipulates it into a mass called a bolus. The bolus is pushed back into the throat and is forced through the opening to the oesophagus or in other words, the gullet.

Oesophagus
The oesophagus is a long, narrow, muscular tube located behind the windpipe that extends through the neck and chest to the stomach. The bolus of food moves through the esophagus by peristalsis: a rhythmic series of muscular contractions that propels the bolus along. The contractions are assisted by the pull of gravity.

Stomach
At the junction of the esophagus and stomach, there is a ringlike muscle, called the lower esophageal sphincter, closing the passage between the two organs. As food approaches the closed sphincter, the sphincter relaxes and allows the food to pass through to the stomach.
The stomach has three mechanical tasks. First, it stores the swallowed food and liquid. To do this, the muscle of the upper part of the stomach relaxes to accept large volumes of swallowed material. The second job is to mix up the food, liquid, and digestive juice produced by the stomach. The lower part of the stomach mixes these materials by its muscle action. The third task of the stomach is to empty its contents slowly into the small intestine.
In the stomach, gastric juice is produced by the linings of the stomach and it contains hydrochloric acid and proteases. Proteases in the stomach digest the proteins in the food eaten into shorter chains of amino acids, while the hydrochloric acid provides the acidic condition needed for the proteases to work. The hyfrochloric acid also kills bacteria which may have been swallowed in together with food. The cells lining the stomach also produces a thick layer of mucus which coats the inner stomach walls and prevents the stomach from digesting itself and from the corrosive effects of the hydrochloric acid.

Small Intestine
The small intestine is about 6 meters (20 feet) long. It is coiled in the center of the abdominal cavity . The small intestine is divided into 3 sections: upper, jejunum, and ileum. The lining of the small intestine secretes a hormone called secretin, which stimulates the pancreas to produce digestive enzymes.The small intestine is where the most extensive part of digestion occurs. Most food products are absorbed in the small intestine.

Large Intestine
The large intestine has a larger width but is only 1.5 meters (5 feet) long. The large intestine is divided into 6 parts: cecum, ascending colon, transverse colon, descending colon, sigmoid/transverse colon, and rectum.The large intestine is responsible for absorption of water and excretion of solid waste material. Food and waste material are moved along the length of the intestine by rhythmic contractions of intestinal muscles; these contractions are called peristaltic movements. Waste is solid because most of the water has been removed by the intestines as it travels through them.




In the next post, I will be posting about the digestive systems of birds.