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Layers of the GI tract, Defense mechanisms and Innervation

                                                                                            

gafacom image result for Layers of the GI tractThe GI tract from the esophagus to the anal canal is comprised of 4 layers or tunics. Each layer performs specific functions in the digestive process.

These layers are :
1.                  Mucosa- the innermost layer lines the lumen of the GI tract. It is both absorptive and secretory in function.It contains lymph nodes as well as goblet cells which secrete mucous. There is also a thin layer of smooth muscle in this tunid.
2.                  Submucosa- this is the second layer, much thicker than the mucosa. It is primarily vascular and nerve containing. Absorbed molecules pass through the mucosa to enter blood or lymph vessels here. The submucosa contain glands and  a nerve plexus (Meissner’s plexus) which provides autonomic innervation to the muscle layer in the mucosa.



3.                  Tunica muscularis- This is  the primary smooth  muscle layer of the GI tract which is responsible for peristalsis. It has an inner circle and an outer longitudinal layer of muscle. Contraction of this layer causes the movement of food as well as helping to pulverize and churn the food with digestive enzymes. There is a large nerve plexus (Aurebach’s plexis ) located between the 2 muscle layers. It provides both sympathetic and parasympathetic innervation.
4.                  Serosa- is the outermost layer of  the GI tract wall. It is binding an protective in function.

Defense mechanisms of the GI tract

The GI tract has several mechanisms for protecting against harmful materials ingested. The lining of the stomach produces  concentrated hydrochloric acid which can kill some organisms. The mucous lining of the GI tract serves as a protective layer as well producing copious amounts of mucous that may dilute harmful substances. The most helpful mechanism is vomiting which is a reflexive response to toxins and irritants. Diarrhea can also help remove harmful substances as well.

Innervation of the GI tract

The GI tract is innervated by the sympathetic and parasympathetic divisions of the nervous system. The vagus nerves are the source of parasympathetic activities in the esophagus, stomach, pancreas, gall bladder, small intestine and part of the large intestine. The lower portion of the large intestine receives parasympathetic innervation from spinal nerves of the sacral region. Stimulation of the parasympathetic nerves increases peristalsis and GI tract secretions. Sympathetic nerve fibers pass through the submucosal  and myeteric plexuses that innervate the GI tract. The effect of sympathetic nerves is in opposition to parasympathetic nerves. Sympathetic impulses inhibit peristalsis, reduce secretions and constrict muscle sphincters along the GI tract.
Layers of the GI tract, Defense mechanisms and Innervation Layers of the GI tract, Defense mechanisms and Innervation Reviewed by gafacom on June 03, 2019 Rating: 5

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