What are the four general consistent layers to the G.I. tract?
3: Muscularis Externa
4: Serosa / Adventitia
What determines the difference between serosa and adventitia?
Serosa is covered by peritoneum, adventitia is retroperitoneal.
What is the lamina propria?
Vascularized loose connective tissue
What is the function and location of the muscularis mucosae?
It is located in the mucosal layer of the G.I. tract, and is a thin layer of smooth muscle which squeezes mucosal glands.
What is the submucosal layer comprised of?
Where do we see glands in the submucosal layer?
Dense irregular connective tissue with neurovasculature and lymphatics
in the esophagus and duodenum
In which layer are the muscles which aid in gastrointestinal peristalsis located?
In the muscularis externa.
Of the two layers to the muscularis externa – a circumferential and a longitudinal layer – which is the outer layer, and which is the inner layer?
The inner layer of the muscularis externa is circumferential
The outer layer of the muscularis externa is longitudinal
Where are the neurovascular plexes located in the muscularis externa?
Between the inner circular and outer longitudinal layers of muscle.
What nerves make up the parasympathetic portion of the extrinsic nervous system of the G.I.?
The vagus nerve – up to the splenic flexure
The pelvic splanchnics – after the splenic flexure
Are the fibers from the vagus nerve and pelvic splanchnics presynaptic or postsynaptic?
They are presynaptic
What nerves provide sympathetic autonomic innervation to the G.I.?
Branches from the greater, lesser, least, and lumbar splanchnic nerves.
Where do the sympathetic nerves for the G.I. synapse?
The celiac, superior mesenteric, inferior mesenteric, and aorticorenal ganglia.
What is the location and function of the plexus of Meissner?
The (submucosal) plexus of Meissner is located in the submucosa, and controls glandular secretion via control of the muscularis mucosae.
What is the location and function of the myenteric plexus of Auerbach?
The myenteric plexus of Auerbach is located in between the layers of the muscularis externa and controls peristalsis.
In terms of motility of the G.I., what would be the function of a presynaptic axon?
Preganglionic axons (of the parasympathetics) increase motility.
Where are the cardiac esophageal glands located?
In which histological layer are they found?
The cardiac esophageal glands are located in the terminal portion of the esophagus (near the cardia of the stomach).
The cardiac esophageal glands are located in the lamina propria of the mucosa.
How might submucosal glands of the esophagus be able to regulate the viscosity of their secretion?
They contain both mucus and serous cell types, and are drained by a single duct.
What is Barrett's esophagus?
Barrett's esophagus is when GERD becomes chronic, and the stratified squamous epithelium of the esophagus becomes mucus-secreting simple columnar epithelium.
What characterizes the gastroesophageal junction?
A drastic change in epithelium from stratified squamous epithelium of the esophagus, to the simple columnar epithelium of the stomach.
Where do we find the cardiac, gastric, and pyloric glands of the stomach histologically?
In the lamina propria of the mucosa
What are gastric pits?
Openings of the cardiac, gastric, and pyloric glands into the lumen of the stomach.
What is different about the muscularis externa of the stomach?
It contains an external longitudinal layer, a middle circular layer, and an extra inner oblique layer.
Histologically, what is the pyloric sphincter made of?
A thickening of the inner circumferential layer of the muscularis externa of the stomach
Is a muscularis mucosae present in the stomach?
Yes, in some sections
What is the function of the isthmus of the gastric pit/gland?
Is the location of undifferentiated stem cells, which mostly differentiate into the surface mucous cells of the gastric pit.
What cell type is contained in the gastric pit?
Surface mucous cells
What cell types are contained in the neck of a gastric gland?
Mucus neck cells
What cell types are contained in the fundus of a gastric gland?
Parietal cells (some)
What is the difference between an "open" and "closed" enteroendocrine cell?
Open enteroendocrine cells have a thin protrusion of cytoplasm with microvilli that can receive signals from the lumen of the gland.
Closed enteroendocrine cells do not reach the lumen of the gland, and must be regulated by paracrine and neural mechanisms.
What is different about the orientation of cardiac glands and gastric glands?
Cardiac glands are tubular, coiled, and less branched.