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One of the basic requirements of all living organisms is food. Carbohydrates, proteins and fats are the major components of our food. Vitamins and minerals are also present in small quantities. Food provides us energy and the organic materials that are required for growth and tissue repair. Water plays an crucial role in metabolic processes. The ingested biomacromolecules cannot be used in their original form. They have to be broken down into simpler molecules. This process of conversion of complex molecules food substance to simpler molecules is called digestion. Digestion is carried by the digestive system.
The digestive system:
The human digestive system consists of the alimentary canal and the associated glands.
Alimentary canal:
The alimentary canals starts with the mouth and ends with anus. The mouth leads to the buccal cavity or oral cavity. The buccal cavity consists of teeth and tongue. An adult human has 32 permanent teeth. There are four types of teeth namely canine, incisor, premolar and molar.
Mastication (digestion) of food is done primarily by the hard chewing surface of the teeth which is made up of enamel. The tongue has small projections, papillae and few of them have taste buds. The oral cavity leads into Pharynx. Pharynx serves as a common passage for both food and air. The windpipe that is oesophagus and the trachea open into the pharynx. Epiglottis, a cartilaginous flap prevents the entry of food into glottis during swallowing. The oesophagus is a thin and long tube which extends posteriorly passing through the neck, thorax and diaphragm. Oesophagus leads to stomach.
Stomach has four parts
1. a cardiac portion –Oesophagus opens into it .
2. a fundic portion
3. body
4.pyloric portion- this portion opens into small intestine.
Small intestine consists of three regions
1. Duodenum- ‘C’ Shaped
2. Jejunum- long coiled
3. Ileum – Highly coiled
Pyloric sphincter guards the opening of stomach into the duodenum. The last portion of small intestine ileum opens into the large intestine .
Large intestine consists of three regions
1. Caecum – small sac where some symbiotic microorganisms live
2. Colon – divided into ascending, transverse, descending and sigmoid colon
3. Rectum – This opens out through anus.
Digestive Glands:
The digestive glands include salivary glands ,the liver and pancreas.
Salivary glands :
Salivary glands produce saliva and is produced by three pairs of glands. They are parotid (cheek), sub maxillary or sub mandibular (lower jaw) and sublingual( below the tongue).
Liver:
Liver is the largest gland in our body. It weighs around 1.2 to 1.5 kg. It consists of two lobes. The liver is situated below the diaphragm. The bile is secreted by hepatic cell and it passes through hepatic ducts and stored in a thin muscular Sac called the Gallbladder . The cystic duct( gallbladder) and hepatic duct forms the common bile duct.
Pancreas:
Pancreas is both exocrine and endocrine gland. Exocrine portion secretes alkaline pancreatic juice which contains enzymes and the endocrine portion secretes hormones insulin and glucagon.
This is the overview of human digestive system .
