Monday, July 13, 2009

2nd entry: Our digestive system (continued)



As mentioned on my last post, after the food is being chewed and soften by our mouth, the food is led to the Oesophagus.

The Oesophagus
It is a muscular tube in our chest that connects the mouth and throat to the stomach.

The muscles in the wall of our oesophagus contracts and relaxes to push the bolus(chewed and soften food) to our stomach. This muscular movement is called peristalsis. NO digestion occurs in the oesophagus.


The stomach
The stomach lies between the oesophagus and the duodenum.



For us humans, our stomach has a relaxed, empty volume of about 45 ml. When it expands,it can hold about 1 litre of food. The stomach is surrounded by parasympathetic and orthosympathetic plexuses(networks of blood vessels and nerves in the anterior gastric, posterior, superior and inferior, celiac and myenteric), which regulate both the secretions activity and the motor activity of its muscles.


The stomach produces strong enzymes called 'gastric juice' which helps in disgestion.


The muscular walls of the stomach helps to move the food and acid around, causing them to mix together properly. When the acid mixes well with the food, the food will break down into smaller, easier to digest fragments.


The small intestine


The small intestine is more than 6 meters long, known to be the longest organ in our human body and it is located within the middle of the abdomen. It has three sections, the duodenum, jejunum and ileum.


Duodenum

It is the first part of the small intestine. It is C-shaped and about 25 cm long.

The duodenum receives the thick liquid mixture of partly-digested food and acid from the stomach. It neutralise the mixture in the alkaline environment. The duodenum also receives bile from the gall bladder and other enzymes from the pancreas. Glands in the duodenum produces mucus which is coated around mixture to make the passage down easier and smoother.

Jejunum and Ileum

The jejunum is the 1-2 m long, coiled mid-section of the small intestine.
The ileum is the final portion of the small intestine. It measures 2-4 m in length.

The inner linings of the jejunum and ileum contain very small finger-like bumps called 'villi'.
The bumps helps increase surface area and improves the small intestine's ability to absorb nutrients. The last stage of digestion is completed, when food and liquids are fully broken down into their nutrient components. For example:

-glucose from carbohydrates,
amino acids from proteins,
fatty acids and cholesterol from fats
-vitamins
-minerals
-salts
-water

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There are some food which could not be digested fully. We can call them 'undigested food'. They as well, have to undergo processes to be released out of our body as they should not be staying inside. I will talk about all this on my 3rd entry.


posted by Neo Jin at 3:32 PM

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