Esophagus And Stomach Histology Flashcards
What are the 4 layers of the GI tract?
From external -> internal
1) mucosa
2) Submucosa
3) muscularis externa
4) Serosa
Details about the mucosa layer
Has three sub-layers (most inner -> most outer)
1) ectoderm derived epithelial tissue
2) lamina propria: loose CT and scattered smooth muscle with blood vessels/lymph vessels and small secretory glands
3) muscularis mucosae: thin layer of smooth muscle that provides localized tone and movement of the mucosa
Details about the Submucosa
Is a layer of dense irregular CT with larger blood and lymph vessels
- possess the submucosal “Meissener” plexus*
- intrinsic nerve fibers and cell bodies with extrinsic nerve fibers
- functions = provides motor control over muscularis mucosae, regulates secretory cells and glands of mucosa and relays sensory feedback to myenteric “Auerbach” plexus
What layer of the GI tract is the Gut-associated lymphoid tissue (GALT) located?
Submucosa layer
Details of the Muscularis externa layer
Is a thick layer of both skeletal and smooth muscles arranged in two sub layers that provides the muscular contractions of peristalsis and segmentation that moves and churns chyme
Possess 3 sub layers:
1) internal sublayer: muscle cells/fibers that are circumferential
2) Myenteric “Auerbach” plexus
- is a collection of intrinsic and extrinsic neurons and nerve fibers
- has 3 functions: provides motor control to muscularis externa, regulates secretory cells and glands of mucosa, and receives input from CNS and ENS to modulate activity
3) external sublayer: muscle cells/fibers that are longitudinal
Details about the serosa layer
Serosa membrane/adventitia
Serous membrane that lines the entire GI tract except for the esophagus
Has two layers:
1) loose CT: contains blood/lymph vessels and nerves just external to the muscularis externa
2) mesothelium: mesoderm-derived layer of simple squamous epithelium adhering to underlying CT
Difference between adventitia and peritoneum
Both are subsets of the serosa membrane layer in the GI tract
Adventitia = organs not suspended within the body cavity. Does not have a mesothelium layer and instead only has a thick loose CT layer
Peritoneum = lining of the peritoneal cavity and is continuous with the mesenteries that secures the visceral organs to the body wall.
What is fusion fascia?
Any region where two AP posing peritoneal serosa or mesenteries are in close contact and fuse together
- they lose serous properties in that region but apples more anchoring ANS support
fusion fascia of Toldt = ascending and descending mesocolon fusion fascia. One of the most clinically importaint ones
Details about the enteric nervous system (ENS)
Intrinsic plexus of neurons that reside within the walls of the digestive tract that monitor and respond to local stimuli and modulate regional glandular/muscular activity
Acts independently for the most part, but also takes input from the AND (both parasympathetic and sympathetic)
Circular vs longitudinal fibers with actions
Circular = peristalsis and movement of the bolus
Longitudinal fibers = churn and produce chyme/mix the bolus
Difference between anatomical and physiological sphincters
Anatomical = is still present at death
- will still be constricted and/or will be obvious it is was there
- example = pyloric sphincter
Physiological = is not still present at death
- will not be constricted and/or will not be obvious it is there
- example LES And UES
How does the muscles in the esophagus change as it travels towards the stomach?
Near the mouth/pharynx = all skeletal muscle
Near the stomach = all smooth muscle
transitions from skeletal -> smooth muscle as it moves down
GERD
Weakening of the LES which leads to chronic reflux esophagitis (heart burn)
- leads to corrosion of the mucosal lining of the distal esophagus
- *is highly associated with asthma
Chronically, will lead to metaplasia of the esophageal mucosa and progress into Barrett esophagus -> then dysplasia
- can also lead to adenocarcinomas of the esophagus
can be caused due to direct muscle issue or a nervous issue
Barretts esophagus
Due to chronic GERD
Replaces stratified squamous epithelial tissue (esophagus tissue) with simple columnar tissues (gastric tissues)
How does the muscularis mucosa layer change in the stomach from the esophagus
Stomach = 3 layers of muscles
- oblique
- circular
- longitudinal
Esophagus = 2 layers of muscles
- circular
- longitudinal
What determines the absence or presence of the gastric rugae?
The direct degree of gastric distention (how full is the stomach?)
Also the indirect elasticity and compliance of the Submucosa.
- NOT muscularis externa
What cells are seen in each region of a standard gastric gland
1) Gastric pit (most superficial)
- contains surface mucous cells
- secretes alkaline fluid with mucin to protect the stomach from gastric acid
2) neck
- contains mucous neck cells
- secretes acidic fluids with mucin to better digest food
3) neck (continue)
- contains parietal cells
- secrete intrinsic factors and hydrochloride acid to better digest food and destroy pathogens
4) fundus
- contains G-cells (enteroendocrine cells) which secrete gastrin into the blood
- also contains chief cells which secrete pepsinogen and gastric lipase to help metabolize proteins and lipids
Pepsinogen vs pepsin
Pepsinogen = inactive form
- found in fundus of the gastric glands
- has no effect
Pepsin = active form
- found in lumen and gastric pit of the gastric glands
- cleaves proteins once activated by acids
How to differentiate pyloric glands from cardiac glands?
You have to know the region of the stomach they originated from
- they look very similar histologically
What epithelial cells are never seen in pyloric or cardiac stomach glands?
Parietal and chief cells
What is the direct action steps of a parietal cell?
1) water is hydrolyzed into hydrogen ions (H+) and hydroxide ions (OH-)
2) H+ is pumped into the lumen of the gastric gland via H+/K+ pumps
3) OH- bonds with CO2 -> bicarbonate (HCO3-)
4) bicarbonate is transferred out of the cell and at the same time Cl- is transferee into the lumen oft he gastric gland via secondary active transport
5) H+ combines with Cl- -> HCL
What is the functional role of intrinsic factor?
Is secreted via parietal cells and functions to Facilities absorption of vitamin B12 within the small intestines
if it doesnt work or insufficient amounts are produced = pernicious anemia
What are the products of chief cells?
Pepsinogen and gastric lipase
Gastric ulcers
Painful erosive lesions of the mucosa which can extend into deeper layers.
- if left untreated that can perforate the wall fo the organ
Common causes:
- overproduction of HCL or pepsin
- lowered production of mucus or bicarbonate
- prolonged exposure to NSAIDs
- bacterial infections (especially helicobacter pylori)
