general structure of GI tract micrograph

It is a muscular tube lined by a special layer of epithelial cells. The entire tract has a similar basic structure with regional variations. The wall has four basic layers/tunics. These are:

mucosa

submucosa

muscularis externa

serosa

Mucosa

innermost layer of the digestive tract

highly folded

degree of folding varies regionally

has 3 sublayers

mucous membrane/epithelium

lamina propria,

muscularis mucosa.

    Mucous membrane

epithelium layer of the mucosa

usually columnar cells

rich in mucus secreting cells

serves as a protective surface

has both exocrine and endocrine glands

    Lamina propria

a layer of connective tissue on which the epithelium rests

has small blood vessels, lymphoid tissue, and nerve fibers

houses the gut/mucosa-associated lymphoid tissue which is

important in the defense against intestinal bacteria and other

pathogens

    Muscularis mucosa

a sparse layer of smooth muscle

lies adjacent to the submucosa

Submucosa

thick connective tissue layer

provides the digestive tract with its distensibility and elasticity

surrounds the muscularis mucosa

contains large blood and lymph vessels

contains a specialized nerve plexus called the submucosal plexus or Meissner’s plexus which help regulate local gut activity

Muscularis externa/muscularis

surrounds the submucosa

major smooth muscle layer of the GIT

made up of an inner circular and outer longitudinal layers separated by the myenteric plexus or Auerbach’s plexus