Homostasis - Nutrition part 2 (The digestive system) - 23 August 2012

The Digestive System 

The alimentary canal

It is a series of connected tubes which functions to carry out digestion

It consists of the mouth, esophagus (previously known as gullet in primary school), stomach, small intestine, large intestine, rectum and anus. 

The accessory organs 

It consists of salivary glands, gall bladder, liver and pancreas.

Digestion 

There are two types of digestion - mechanical digestion and chemical digestion.

Mechanical digestion

In simple terms, it means moving parts breaking down food substances.

Example: Mouth and stomach from the alimentary canal.

Chemical digestion 

Chemical digestion refers to the breaking down of food substances chemically. Note that chemical digestion requires enzymes. 

Example: Mouth, stomach and small intestine from the alimentary canal.

Enzymes = chemical substances that break things down. Therefore, they are involved in chemical digestion. 

The different digestion and where it takes place in our human body

We learn 3 different digestion in sec 1, namely Carbohydrate digestion, Protein digestion and Fat digestion.

Mouth: Only carbohydrate digestion takes place here, where polysaccharides are broken down into smaller polysaccharides and/or maltose)

Stomach: No carbohydrate digestion and fat digestion take place in the stomach; only protein digestion takes place. It is also where protein digestion starts. Proteins are broken down into small polypeptides here.

Lumen of small intestine: Carbohydrate digestion takes place. Polysaccharides are broken down into maltose and other disaccharides by an enzyme from the pancreas. Protein digestion also takes place; polypeptides are broken down into amino acids. Fat digestion takes place here too. Fat droplets are broken down into glycerol and fatty acids by an enzyme from pancreas.

Epithelium of small intestine: Carbohydrate digestion takes place. Disaccharides are broken down into monosaccharides by an enzyme which comes from the small intestine. Protein digestion takes place; polypeptides are broken down into amino acids. Fat digestion also takes place, fat droplets are broken down into glycerol and fatty acids by an enzyme from pancreas.

Note that the enzymes from the pancreas take part in carbohydrate digestion and lipid digestion (fat digestion). Bile is produced in the gall bladder and salivary amylase is produced in the salivary glands. 

The small intestine 

The small intestine is approximately 6 meters long. 

Duodenum: Where the fat globules are broken up into fat droplets by bile salts.

Ileum: More digestion, less absorption as most of the food substances are not simple substances.

Jojenum: Less digestion, more absorption as most of the food substances have been digested already.

Villi 

Villus is a single protrusion.

 

Epithelial cells in the small intestine

- Has microvilli

 

(taken from cellfunctioning.wikispaces.com, edited by me)