All living organisms require nutritional support for their survival. Food is one of the basic requirement to provide the energy to all living organisms. Food consists of three major biomolecules of Carbohydrates, proteins, and fats. In addition to these biomolecules, water plays an important role to inhibit dehydration of the body. Biomolecules cannot be taken up by our body in the natural form. In the digestive system, complex food substance is converted into simpler food substance. This process of conversion of complex food molecules to simple absorbable molecules is called as digestion. Digestion is carried on by different types of mechanical and biochemical methods. The alimentary canal plays a critical role in the human digestive system.
Digestion and Alimentary Canal
The alimentary canal is also termed as the digestive tract. The alimentary canal starts from the mouth and ends in the anus. Alimentary canal consists of the following parts.
- Mouth and Oral cavity
- Small intestine
- Large intestine
Mouth and oral cavity
Mouth is a first part of the alimentary canal. It consists of lips, cheeks, tongue, and teeth. Teeth are used to masticate the food in order to increase the surface of the food for digestion. As a result, enzymes from the oral cavity act on the food effectively to increase the rate of digestion. Two sets of tooth form in the human life. These are as follows:
- Milk teeth
- Permanent teeth
Four different types of permanent teeth are present in the human beings.
The tongue is attached to the oral cavity floor. The papillae are present on the upper surface of the tongue which bears the taste buds.
Oval cavity leads to the esophagus. The esophagus is a thin and long portion of the alimentary canal which opens into the pharynx. During swallowing the food, a flap-like structure prevents the food entry into the glottis. This flap-like structure is called as epiglottis.
Oesophagus leads into the stomach through the neck and the diaphragm. Oesophagus opening is regulated by a muscular sphincter into the stomach. The stomach consists of three parts. These are as follows:
- Cardiac portion – It is a portion where esophagus opens into the stomach.
- Fundic portion – It is a region to store the food for long-term digestion.
- Pyloric portion – It is a region where stomach opens into the duodenum.
Pyloric sphincter is used to regulate the stomach opening into the duodenum.
Small intestine measures 6 m long and 2.5 cm thick. It contains the following three regions:
- Duodenum – It is the first portion of the small intestine, which starts from the stomach.
- Jejunum – It is used to absorb the nutrients from the digested food.
- Ileum – It is also used to absorb the nutrients which are not absorbed by the jejunum.
The large intestine measures 1.5 m long. It is the last part of the alimentary canal. The main function of the large intestine is to absorb the water from solid wastes and store the waste materials. These waste materials are removed by defecation. The large intestine consists of five parts. These are as follows:
- Cecum – It is used to absorb the digestive fluids.
- Appendix – It is a vestigial organ. It does not have any specific function.
- Colon – It is used to absorb the water from digested food.
- Rectum – It is used to store the residual wastes.
- Anus – It is used to remove the waste material to the outside of the body through sphincter contraction.
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