Structure Small intestine

 Structure Small intestine

          It is about 7 meter long tube from stomach to large intestine that is surrounded by large intestine at navel region. Its first section as the shape of hoarse nal (English alphabet C) and about 25 cm in length surrounds pancreas, which is called duodenum. Common bile duct and pancreatic duct open in it.

 In this way, food reaches in small intestine and is mixed with pancreatic juice, bile secreting from liver and intestinal juice.          In this way, food reaches in small intestine and is mixed with pancreatic juice, bile secreting from liver and intestinal juice.

The walls of small intestine are made up of such types of four layers, from which the stomach wall is being formed, but few modifications are found in this case.

1.     The external serous layer is made up of peritoneum.  

2.     The muscular layer is made up of involuntary muscles, in which the layer of long fibers are present on outside and the layer of circular fibers are present in the lower section of it. In the section between both these fibrous layers, the network of blood vessels, lymphatic tubes and nerves are present. Peristaltic movement takes place by the contraction of the layer of circular fibers; as a result of it, the chyme moves towards the large intestine. 

3.     Submucosal layer is made up of areolar tissue having the network of many blood vessels, lymphatic tubes, glands and nerves. The network of nerves is called Meissner’s plexus. In the duodenum, few special types of glands are found in small bunches (groups), called Bruner’s glands. They produce a type of sticky alkaline fluid that protects the internal layer of duodenum from sour substances of stomach. 

Mucosa- This layer has three advantages (features) that make the processes of digestion and absorption faster in small intestine-

(i) It has plicae circulares like a fringe (frill) that increase the area of mucosa for absorption. They are stable comparison to stomach plicae and also do not disappeared by expansion of intestine. They are found more near the joint junction of duodenum and jejunum. 

 (ii) There are many protuberances about 0.5 to 1 mm in length like fingers in it, called villi. Due to these villi, mucosa appears as velvet as well as they increase the absorption area of mucosa. In between the bases of villi, tubular intestinal glands forms by curing epithelium inward resulting surface area is increased more. Inside every villus, blood vessels and a lymph duct are present. This duct is called bacteal and plays an important role in the absorption of fat.       

  1. Normal tubular glands are present inside the mucosa. They secrete many types of enzymes that help in the digestion of carbohydrate, protein and fat. Mucus glands (crypts of Lieberkuhn) are reached in lamina propria (the layer of connective tissue that supports epithelium). The glands that reach in the submucosa, called Brunner’s glands and are found only in the duodenum. These glands secrete sticky, alkaline mucus secretions that protect mucosa inside the intestine by the acidic chyme of stomach.

        In the entire mucosa of the small intestine, solitary follicles are present everywhere, called solitary glands. These follicles are found in groups inside the ileum, known as aggregated lymph follicles or Peyer’s patches. These are round and oval in shape. They are become inflamed in case of typhoid fever. These lymphoid glands help in killing the micro bactera that are absorbed by the small intestine with food.