Name: Absorption and Assimilation of Digested Food
Uploaded: 2019-07-19
Duration: 5 min 57 s
Description: We consume food to get energy. How does food provide energy? Digestion breaks down the food, and the nutrients are absorbed and assimilated into the body to...

Question

Describe human digestive system with a well labelled diagram.

Accepted Answer

The digestive system of human includes two main components-Alimentary canal and digestive glands. Alimentary canal includes the following structures:

Mouth and buccal cavity: The buccal cavity is lined with stratified squamous epithelium and contains teeth and salivary glands.

Teeth: Dentition in humans is diphyodont, thecodont and heterodont. The different types of teeth are incisors, canines, premolars and molars. Tooth has a white shiny capping called enamel. It is the hardest substance in the human body and is secreted by ameloblast.

Salivary glands: There are three pairs of salivary glands. They are parotid glands, submaxillary glands and sublingual glands. They secrete saliva which consists of water, electrolytes, salivary amylase, lysozymes, etc. The digestion of carbohydrates is the first step in digestion and begins in the buccal cavity. The chewed food called bolus is swallowed into oesophagus.

Oesophagus: It is a long tube like structure that runs through the neck and thorax and reaches the stomach. The peristalsis begins from this part in the gut.

Stomach: Stomach is a J-shaped organ that stores and digests food over a period of 4-5 hours. Its lower convex and upper concave surfaces are called greater and lesser curvature respectively. Stomach is divisible into four parts:

Cardiac-It is present near the heart.

Fundus-It is the upper part of the stomach which stores accumulated gases.

Body-It is the main central region of the stomach.

Pyloric-It is the distal part and opens into the first part of the small intestine.

Partial digestion of food takes place in the stomach. Castle's intrinsic factor secreted by the oxyntic cells helps in absorption of vitamin B12. Enzymes like pepsinogen and pro-rennin helps in the breakdown of proteins.

Small intestine: The small intestine is the longest part of the alimentary canal. The three major regions of small intestine are as follows:

Duodenum-It is widest and shortest part of small intestine.

Jejunum-It is the middle part of small intestine which is red and vascular.

Ileum-It is highly coiled and the longest portion of small intestine, which finally opens in large intestine on the right side of abdominal cavity.

Large intestine: The large intestine is around 1.5 m long and is divisible into three parts: caecum, colon and rectum. It is the last part of the alimentary canal where the undigested and unabsorbed food materials are received from the small intestine.

Caecum: It has a vestigial organ called vermiform appendix attached to it. It is a small blind sac which hosts some symbiotic microorganisms like E.coli which break down the undigested food particles and help in the synthesis of some vitamins. There is no secretion of digestive juices.

Colon: It is divided into three parts-ascending, transverse and descending. Mucus is secreted which act as a lubricant for the easy passage of faeces. Reabsorption of water, electrolytes and few drugs takes place.

Rectum: The sigmoid or pelvic colon opens into rectum. The roughage is stored in the rectum region. Rectum opens out through the anus. The egestion of faeces to the outside occurs through the anal opening and the process is called defaecation. It is a voluntary process and is carried out by a mass peristaltic movement.

Describe human digestive system with a well labelled diagram.

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