The Human Digestive System
* The alimentary canal includes organs such as the mouth, pharynx, oesophagus, stomach, small intestine, large intestine and anus.
* The mouth, the anterior opening of the alimentary canal, leads to the buccal cavity or oral cavity, which contains the teeth and the tongue.
* The tongue helps push the food from the oral cavity into the phaynx, the passageway for air and food.
* The pharynx opens into the windpipe or trachea and the oesophagus.
* The stomach, an important organ of the alimentary canal, is located in the upper left part of the abdominal cavity between the oesophagus and the first part of the small intestine called the duodenum.
* The duodenum, jejunum and ileum make up the small intestine.
* The large intestine is divided into three regions- the caecum, colon and rectum.
* The salivary glands, liver and pancreas are collectively known as the digestive glands.
Digestion of Food
* The teeth, present in the oral cavity, masticate the food, while the tongue mixes it with saliva, which is rich in enzymes, salivary amylase, lysozyme and electrolytes.
* The bolus passes through the pharynx and then into the oesophagus y the process of swallowing or deglutition.
* In the stomach, the bolus mixes with the juices secreted y the gastric glands in the mucosa of the stomach.
* The churning of the stomach walls mixes the bolus with the gastric juice to form a pulp-like substance called chyme.
* The movements generated by the muscularis layer of the duodenum causes the chime to mix with pancreatic juice, bile, and intestinal juice or saccus intericus.
* In the final steps of digestion, the end products synthesised by the action of bile and pancreatic juice are further converted into absorbable molecules by intestinal juice.
Absorption of Digested Products
*Absorption is the process by which the end products of digestion pass through the intestinal mucosa into the blood or lymph.
* Absorption is carried out by passive and active transport mechanisms.
* The organs of absorption are the mouth, stomach, small intestine and large intestine, of which the small intestine is the principal organ for absorption of nutrients.
* The final products of digestion-glucose, fructose, fatty acids, glycerol and amino acids are absorbed through the mucosa into the bloodstream and lymph.
* Assimilation is the process by which absorbed substances finally reach the tissues for utilisation.
* Digestive wastes are eliminated through the rectum through the process of defecation.
* Bacterial, viral and parasitic infections, indigestion, constipation, vomiting, jaundice and diarrhoea are some common disorders of the digestive system.