DMH Part 1 > Esophagus and Stomach Histology > Flashcards
Esophagus and Stomach Histology Flashcards
Layers of a Hollow Organ (General)
The lower sphincter of the esophagus is a [] sphincter.
The lower sphincter of the esophagus is a physiologic sphincter.
- diaphragm
- abdominal pressure
Esophagus - Stomach Junction
Parietal cells secrete [].
Parietal cells secrete HCl and Intrisic Factor.
Outer Layer
The outer layer is made up either of an adventitia of loose connective tissue, where the tract lies outside the body cavity, or where the tract lies within the body cavity, of a serosa of simple squamous epithelium overlying a thin layer of connective tissue.
Muscularis Propria
The muscularis propria (=muscularis externa) is responsible for the peristaltic contractions that move food through the tract. It consists usually of an outer longitudinal layer and an inner circular layer of smooth muscle, with a few minor variations depending on the region. Lying between inner and outer muscle layers is the myenteric plexus (=Auerbach’s plexus), comprised of sympathetic fibers and parasympathetic fibers and cell bodies.
Submucosa
The submucosa is a thick layer of loose connective tissue which acts as a “service corridor”, carrying arteries, veins and larger lymphatics to supply the muscularis propria and the mucosa. There is a submucosal nerve plexus (=Meissner’s plexus) which, like the myenteric plexus, is composed of sympathetic fibers, as well as parasympathetic fibers and cell bodies and together with the myenteric plexus comprises the enteric nervous system. In the esophagus and duodenum the submucosa contains multicellular mucous glands, the submucosal glands, which drain via ducts into the gut lumen.
Mucosa
The mucosa is made up of 3 layers:
- The muscularis mucosae is a thin layer of smooth muscle which, like the muscularis propria, is organized into inner circular, outer longitudinal fibers.
- The lamina propria is a layer of loose CT containing capillaries and nerves that supply the epithelium. Diffuse lymphoid tissue and lymphoid follicles (described later) are common in this layer.
- The epithelium is the innermost layer of the mucosa, and its structure varies greatly in different regions of the digestive tract, as described below.
Outer Layer of Esophagus
The outer layer of most of the esophagus is an adventitia of loose connective tissue; the short portion of the lower esophagus within the abdominal cavity is covered by a serosa.
Muscularis Propria of Esophagus
The muscularis propria of the upper esophagus is composed of skeletal muscle which is involved in the voluntary act of swallowing. In the lower esophagus the muscularis is made up of smooth muscle. The muscularis propria of the esophagus is of approximately uniform thickness (i.e. it does not enlarge to form sphincters), but there is a physiological sphincter (indicated by manometric recordings of intraluminal pressures) at both upper and lower ends of the esophagus. The upper esophageal sphincter is at the level of the cricopharyngeus muscle. The lower esophageal sphincter is at the level of the diaphragm.
Submucosa of the Esphagus
In the esophagus, the submucosa contains esophageal mucous glands.
Mucosa of Esophagus
The mucosa of the esophagus has a non-keratinized, stratified squamous epithelium. At either end of the esophagus, the lamina propria contains branched mucous glands. At the inferior end these are called the cardiac glands of the esophagus. They have a morphology similar to that of the submucosal mucous glands of the esophagus but they are located in the mucosa.
Outer Layer of Stomach
The outer layer of the stomach is a serosa.
Muscularis Propria of Stomach
The muscularis propria of the stomach consists of outer longitudinal, middle circular and inner oblique layers of smooth muscle. At the pyloric - duodenal junction, the circular layer is enlarged to form the pyloric sphincter.
Mucosa of Stomach
The mucosa has a simple columnar epithelium which is invaginated to form the stomach glands.
Composition of the Stomach Glands
The stomach epithelium is invaginated to form gastric pits. Each gastric pit branches at its base to form the deeper cardiac, gastric and pyloric glands proper. Thus the gastric pits can, in a sense, be regarded as ducts of the deeper glands. The pits themselves are also glandular, however, being lined by mucous cells.
Cardiac Glands
The cardiac glands of the stomach are situated in the stomach mucosa near the junction with the esophagus. They are coiled tubular glands made up of mucous cells and scattered enteroendocrine cells.
Pyloric Glands
The pyloric glands, like the cardiac glands, are coiled tubular glands made up of mucous cells and scattered enteroendocrine cells. The pyloric region can be distinguished from the cardiac region in sections by the difference in the depth of gastric pits in the two regions: the gastric pits in the pyloric region are deeper (longer) than those in the cardiac region.
Gastric Glands
The gastric (aka fundic or oxyntic) glands are straight branched tubular glands made up of mucous cells (in the neck), parietal cells (mainly in neck, also in base), chief cells (mainly in base, also in neck), and enteroendocrine cells (scattered throughout glands).
Mucous Cells
Have a light, foamy cytoplasm. The quality (and staining properties) of mucin in the granules varies in different regions of the stomach. Mucus functions mainly to lubricate and protect the stomach mucosa against mechanical damage. It forms a layer (the unstirred layer) adjacent to the stomach epithelium that limits (but does not prevent) access of stomach contents to the stomach epithelium.
Parietal Cells
(=oxyntic cells) secrete HCl, which creates an optimal pH for stomach enzymes and protects against some bacteria and viruses. They also produce intrinsic factor that is necessary for absorption of vitamin B12. They have a very acidophilic cytoplasm, and their apical membrane is invaginated to form intracellular canaliculi.
•Parietal cell function is diminished in disorders such as atrophic gastritis (an autoimmune disease) and stomach cancer. The decreased production of intrinsic factor under these circumstances results in diminished absorption of Vitamin B12 from the small intestine. This condition, known as pernicious anemia (Vitamin B12 is required for normal red blood cell production) is sometimes the first clinical indication of a serious stomach problem.
Chief Cells
(=peptic) secrete pepsinogen. Pepsinogen is a precursor of pepsin - a digestive enzyme that hydrolyzes proteins into smaller peptides. Pepsinogen is converted to pepsin by the acid pH of the stomach. Chief cells have a basophilic basal cytoplasm, with secretory granules present in the apical cytoplasm.
Enteroendocrine Cells
secrete hormones that influence gut function; (see p. 488 in Ross et al.). Some have a free apical surface while others do not contact the gut lumen. Enteroendocrine cells have a neutrophilic cytoplasm. Their secretory granules are accumulated in the basal cytoplasm, since these cells exocytose their secretory granules through the basal membrane. These cells are not visible in the light microscope without special stains. Gastrin, a hormone secreted by enteroendocrine cells in the stomach, stimulates stomach motility and HCl production by parietal cells.
Stem Cells
are undifferentiated columnar epithelial cells located at the base of the gastric pits near the opening of the glands in all regions of the stomach. They are actively dividing cells that migrate up into the gastric pits and down into the deeper glands to replace differentiated cells as they are sloughed into the lumen. Mucous cells at the stomach surface are replaced by stem cells approximately every 6 days. Parietal cells and chief cells have a much slower turnover rate.
