A short PDF on histology of the digestive system

This system develops from the embryonic endoderm &it consists of the oral cavity, esophagus, 

stomach, small and large intestine, rectum and anus. It also includes accessory glands such as 

the salivary gland, liver and pancreas. 

The system functions as to receive food substances through the mouth, prepare it for digestion, 

digest the food and then absorb it mainly by the small intestine. 

The walls of the digestive system components are made up of 4 main layers; the mucosa, 

submucosa, muscularis and serosa (adventitia). 

MUCOSA: This layer is made of an epithelium and underlying lamina propria. 

The epithelium is simple columnar all over the gastrointestinal tract except at the pharynx, 

mouth, esophagus and over parts of anal canal which are stratified squamous non keratinized

to prevent abrasion. 

The epithelium serves protective function at esophagus and anal canal, secretory function at oral 

cavity, esophagus, stomach and intestine & absorptive function at the intestine. 

Functions include production of mucus for lubrication and protection, production of hormone, 

facilitation of food transport, digestion and absorption.

The lamina propria is made up of loose connective tissue (reticular and collagen fibers) rich in 

blood vessels and lymphatic vessels, lymphocytes, capillary nerves and smooth muscle cells. 

Sometimes they contain mucoserous glands (esophagus).

MUSLCULARIS MUCOSAE: There is a thin layer of smooth muscle that separates the mucosa from 

the submucosa layer. 

Around the lumen of the tract is a layer of circularly arranged muscle fibers which is surrounded 

on the outside by longitudinal muscle fibers. 

The muscles function as to contract the mucosa which results in the movement and folding of 

the mucosa to facilitate digestion and absorption of food. 

SUBMUCOSA: It is a loose connective layer (the looseness is to permit mobility of the mucosa)

with large blood vessels and lymph vessels. It is found between the muscularis mucosa and 

muscularis externa. Between the submucosa and the muscularis externa is the submucosa 

meissner's plexus which supplies the muscularis mucosae and the mucosal glands.

MUSLCULARIS EXTERNA: It is the most substantial layer made of 2 smooth muscle layer *except 

at the upper part of the esophagus where the muscle are striated. 

The muscles are arranged circularly on the inside and longitudinal on the outside. Between them 

(the 2 muscle layers) is the myenteric (Auerbach's) plexus. The plexus supply the externa and 

with the meissner's plexus, it forms the local enteric nervous system of the digestive tract. The 

externa carries out rhythmic contraction called PERISTALTIS which propels food down the tract. 

SEROSA OR ADVENTITIA: The serosa is a thin layer of loose connective tissue that is covered by 

mesothelium (simple squamous epithelium). Blood vessels, lymphatic vessels and adipose tissue 

can be found here. When the organ covered by the serosa is attached to an organ (such as when 

posterior abdominal wall is attached to the intestine), the serosa becomes adventitia, which is 

thick and lacks mesothelium.

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