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The Human Digestive System

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The Human Digestive System - Lesson Summary

The body depends on the digestive system to break down the bio macromolecules in food into absorbable molecules.
 
The human digestive system consists of the alimentary canal and the digestive glands. The alimentary canal starts with the mouth, which contains the teeth and the tongue. The teeth masticate the food and the tongue pushes the food from the oral cavity into the pharynx. The food is passed from the pharynx to the stomach through the oesophagus. The stomach is made of a fundic region, a cardiac portion and a pyloric portion. The pyloric sphincter regulates the flow of the churned food from the stomach into the duodenum, which is followed by the jejunum and ileum that make up the rest of the small intestine.
 
The large intestine is divided into caecum, colon and rectum. The caecum hosts symbiotic micro-organisms and open into an ascending, transverse and descending colon. The descending part of the colon leads to the rectum, which stores faeces. The faeces is egested through the last part of the alimentary canal, called the anus.
 
The wall of the anus and other organs of the alimentary canal is made of four layers of tissues, the serosa, muscularis, sub-mucosa and mucosa. The serosa is made up of a thin mesothelium along with some connective tissues. It is followed by the muscularis, a muscle layer made up of a circular inner layer and a longitudinal outer layer of smooth muscle cells. Adjoining the muscularis is the sub-mucosa, which is a soft connective tissue layer containing blood vessels, nerve endings and lymphatic vessels. The innermost layer of the alimentary canal is mucosa, which lines the lumen of the alimentary canal. Mucosa forms gastric glands and rugae in stomach, whereas in the small intestine, mucosa forms villi and microvilli. Both villi and microvilli considerably increase the absorptive surface area of the small intestine.

Apart from the alimentary canal, the digestive glands consists of the salivary glands, the liver and the pancreas There are three pairs of salivary glands – the parotid gland located in the cheek, the sub-maxillary or sub-mandibular glands found in the lower jaw and the sub-lingual gland located below the tongue, which secrete saliva. The liver secretes bile and is stored in the gall bladder.

The exocrine portion of the pancreas secretes enzymes and the endocrine portion secretes hormones. The pancreatic juices and bile pour into the duodenum through hepato-pancreatic duct, guarded by the sphincter of Oddi. 

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