Digestion

Digestion is the break down of large, insoluble food molecules into small, soluble food molecules so that they can be absorbed into the blood stream

The digestive system

The digestive system also known as the gut is essentially a long tube about 9 metres long. It starts at the mouth and ends at the anus. There are many different parts to the digestive system but each part has its’ specific function.

Mouth

The mouth is the beginning of the digestive tract. In fact, digestion starts here as soon as you take the first bite of a meal. Chewing breaks the food into pieces that are more easily digested, while saliva mixes with food to begin the process of breaking it down into a form your body can absorb and use.

Throat

Also called the pharynx, the throat is the next destination for food you've eaten. From here, food travels to the esophagus or swallowing tube.

Esophagus

The esophagus is a muscular tube extending from the pharynx to the stomach. By means of a series of contractions, called peristalsis, the esophagus delivers food to the stomach. Just before the connection to the stomach there is a "zone of high pressure," called the lower esophageal sphincter; this is a "valve" meant to keep food from passing backwards into the esophagus.

Stomach

The bolus enters the stomach. The stomach cells makes gastric juices which mix with the food.

• The gastric juices contain a protease enzyme called pepsin which breaks down proteins into amino acids.
• The juices also contain hydrochloric acid, this is because pepsin works best in an acidic environment of pH 2.
• The acid in the juices also kills any germs.

The muscular walls of the stomach churn the food and mix it well with the secretions. After 2-3 hours of churning the food is a thick liquid called chyme.

Small Intestine

Made up of three segments, the duodenum, jejunum, and ileum, the small intestine is a long tube loosely coiled in the abdomen (spread out, it would be more than 20 feet long). The small intestine continues the process of breaking down food by using enzymes released by the pancreas and bile from the liver. Bile is a compound that aids in the digestion of fat and eliminates waste products from the blood. Peristalsis (contractions) is also at work in this organ, moving food through and mixing it up with digestive secretions. The duodenum is largely responsible for continuing the process of breaking down food, with the jejunum and ileum being mainly responsible for the absorption of nutrients into the bloodstream.

Large Intestine

Any indigestible or non absorbed chyme passes into the large intestine. Excess water and salts are absorbed and the remaining chyme is converted into faeces. The faeces is stored in the rectum until it is excreted through the anal canal.