Histology of the Esophagus and Stomach Flashcards
4 layers of GI tract from lumen —> superficial
Mucosa
Submucosa
Muscularis/muscularis externa
Serosa/adventitia
What is the difference between serosa and adventitia?
Serosa = covered by peritoneum
Adventitia = retroperitoneal
3 components of mucosal layer of GI tract
Lining epithelium (varies segment to segment)
Underlying lamina propria (vascularized loose CT)
Muscularis mucosae (thin layer of smooth muscle that controls mobility of mucosa/mucosal glands)
2 major components of submucosal layer of GI tract
Dense irregular CT with neurovasculature and lymphatics
Glands may be present (esophagus and duodenum)
The muscularis/muscularis externa layer of GI tract has 2 layers of smooth muscle, and inner circular layer and an outer longitudinal layer. Neurovascular plexuses reside between layers. What are the differences in function of these muscular layers?
Contraction of circular layer constricts lumen
Contraction of longitudinal layer shortens the tube
The serosa/adventitia is comprised of loose CT. When digestive tube is suspended by a mesentery/peritoneal fold, the adventitia is covered by _______ forming the ______ layer
Those without mesothelium covering have an _______. Organs may have adventitia and/or serosa, depending on location
Mesothelium; serosa
Adventitia
The digestive tube is innervated by what 2 major components?
Extrinsic = parasympathetics and sympathetics
Intrinsic = enteric component
Important parasympathetics for GI innervation
Vagus nerve (until splenic flexure)
Pelvic splanchnics (splenic flexure —> inferiroly)
Fibers in vagus and pelvic splanchnics are presynaptic; ganglion and postsynaptic fibers are intermural (postganglionic)
Important sympathetics for GI innervation
Branches from greater, lesser, least, and lumbar splanchnics
Synapse in prevertebral ganglia (celiac, SM, aorticorenal, and IM ganglia)
Postsynaptic nerves travel to organs via blood vessels on peri-arterial plexuses
Intrinsic/enteric innervation involves what 2 interconnected plexuses, formed by sensory and motor neurons but linked by interneurons?
Submucosal plexus of Meissner (submucosa)
Myenteric plexus of Auerbach, located between inner circular and outer longitudinal layers (muscularis)
The intrinsic/enteric innervation responds to local stimuli and input from extrinsics. They regulate and control what 2 major gut functions?
Peristaltic contractions of the muscularis and movements of muscularis mucosae
Secretory activities of the mucosal and submucosal glands
_________ axons of the parasympathetics increase gut motility
________ axons of the sympathetics decrease gut motility
Preganglionic
Postganglionic
Does the esophagus have serosa or adventitia?
Both!
Thoracic esophagus has adventitia with adipose tissue. Inferior to the diaphragm, it has serosa
Describe the 2 major types of glands found in the esophagus
Cardiac esophageal glands - reside in LP (mucosa)
Submucosal glands - consist of small lobules with mucous and serous cell types, drained by a single duct
Describe mucosal layer of esophagus
Stratified squamous epithelium overlying a lamina propria
Numerous folds
Muscularis mucosa only present in lower segment
Describe submucosa of esophagus
Network of collagen and elastic fibers, many small blood vessels
Submucosal venous plexuses drain into both the systemic and portal venous system
Increased pressure in the submucosa of the esophagus may lead to what condition?
Esophageal varices - dilation of the submucosal venous sinuses
Describe muscularis layer of esophagus
Inner circular and outer longitudinal layers have segment dependent variation!
Upper third = skeletal muscle
Middle third = skeletal and smooth
Lower third = smooth muscle
What forms the unique divider between the esophagus and stomach?
Gastroesophageal junction
Describe the epithelial transition that occurs at the gastroesophageal junction
Stratified squamous nonkeratinized epithelium —> simple columnar
Epithelium in the stomach is glandular with pits and glands
The esophagus has 2 sphincters, what are their specific functions?
Upper esophageal sphincter (UES) - anatomical, swallowing reflex
Lower esophageal sphincter (LES) - functional, prevents reflux of gastric contents
What is GERD
Gastroesophageal reflux disease
Causes chronic inflammation, ulceration, and difficulty swallowing (dysphagia) due to reflux of gastric contents
What happens to the stratified squamous epithelium of the gastroesophageal junction transition zone if GERD is a chronic issue?
It may be replaced at the lower end by a columnar mucus-secreting/glandular form, Barrett’s esophagus/metaplasia
Metaplastic epithelium is at high risk of developing dysplasia or carcinoma!
4 regions of the stomach
Cardia (2-3cm, near esophageal opening)
Fundus (projects to left of cardia)
Body (extensive central region)
Pyloric antrum (ends at gastroduodenal orifice)
2 areas of stomach based on motility characteristics
Orad area = fundus and upper part of body, relaxes during swallowing
Caudad area = lower portion of body and antrum, participates in regulation of gastric emptying
The stomach contains gastric mucosal folds called ______, which are covered by gastric _____. A gastric mucosal barrier protects the mucosal surface
Rugae; pits
The mucosa of the stomach is lined with _____ epithelium. The lamina propria contains cardiac, gastric, and pyloric _______.
_____ and _____ fibers predominate, and the ______ mucosae facilitates release of gastric gland secretions
Secretory simple columnar; glands
Reticular; collagen; muscularis
Describe the submucosal layer of the stomach
Dense irregular CT with collagen and elastic fibers
Arterioles, venous plexuses, and lymphatics
Meissner’s plexus
Describe muscularis/muscularis externa layer of stomach
3 layers of smooth muscle: oblique, circular, and longitudinal (poorly defined)
Circular muscle layer thickens in pyloric region, forming pyloric sphincter
Does the stomach have adventitia or serosa?
Serosa - with loose CT and blood vessels (bc stomach is intraperitoneal)
Describe cardiac glands found in the stomach
Glands are tubular with coiled end (appear similar to sweat glands)
Opening is continuous with gastric pits
Extend only a few centimeters from gastroesophageal junction
Lined with mucus-secreting cells similar to those in esophagus
The major contributors of gastric juice in the stomach are the glands of the fundus/body. Describe these glands
Straight tubular with 2-7 opening into single gastric pit (bc many shared connection/exit points)
3 major regions of glands found in fundus/body of stomach
Pit (foveolar), lined by surface mucous cells
Neck, lined by mucous neck cells, stem cells, and parietal cells
Body, upper andlower portions contain different proportions of cells
What type of cell predominates in the pit of glands of fundus/body of stomach?
Surface mucous cells
What type of cell predominates in the neck of glands of fundus/body of stomach?
Mucous neck cells
What type of cell predominates in the upper portion of the body of glands of fundus/body of stomach?
Parietal cells (some chief cells and stem cells as well, but these don’t predominate until lower portion of body)
What type of cell predominates in the lower portion of the body of glands of fundus/body of stomach?
Chief cells and enteroendocrine cells
Some parietal cells
Both surface mucous cells and mucous neck cells produce _____ (glycoproteins)
A mucous layer containing this substance forms and insoluble gel that attaches to surface of mucosa, neutralizing the microenvironment to an ________ pH
Mucins
Alkaline
Condition associated with TGF-alpha induced hyperplasia of surface mucous cells leading to nausea, vomiting, epigastric pain, GI bleeding, and diarrhea
Menetrier’s disease
What 2 things do parietal cells produce?
HCl of gastric juice
Intrinsic factor (glycoprotein that binds vitamin B12)
3 distinctive features of parietal cells
Abundant mitochondria
Secretory/intracellular canaliculus
H/K dependent ATPase rich tubulovesicular system
What is the significance of abundant mitochondria found in parietal cells?
Produce ATP to pump H+ into secretory canaliculus
Chief cells predominate in the lower 1/3 of gastric glands, EXCEPT in which areas of the stomach?
Chief cells are not present in cardiac glands and are seldom found in the pyloric antrum
The basal region of chief cell cytoplasm contains extensive ______. Numerous _______ granules (secretory) are located in the apical region.
RER; zymogen
Numerous zymogen granules are located in the apical region of chief cell cytoplasm. What proenzyme is stored in these zymogen granules? What is its significance?
Pepsinogen
Released into the lumen of the gland via exocytosis (stimulated by feeding) and converted to pepsin by acidic environment; pepsin digests most proteins
Enteroendocrine cells release what 3 major peptide hormones that regulate GI tract?
Somatostatin
Gastrin
Ghrelin
What cells produce gastrin and what is its function?
Produced by G cells in pyloric antrum
Stimulates production of HCl by parietal cells
What cells produce somatostatin and what is its function?
Produced by D cells
Inhibits gastrin action
Where is ghrelin produced and what is its function?
Produced in gastric fundus
Binds its receptor in pituitary and stimulates GH secretion
An increase in plasma levels of what hormone during fasting trigger hunger?
Ghrelin
Describe appearance of pyloric glands
Simple tubular and branched at distal end
How are the gastric pits of pyloric glands different from gastric pits in cardia or fundus region of the stomach?
Gastric pits are deeper, they extend halfway through the depth of the mucosa
Pyloric glands have larger lumen and are highly branched
Pyloric glands are lined by mucus-secreting cells (resemble mucous neck cells) which contain large and pale secretory mucus, as well as secretory granules containing _______, a bacterial lytic enzyme
Lysozyme
T/F: Enteroendocrine cells and gastrin-secreting G cells are abundant in pyloric antrum, and lymphoid nodules can be seen in the lamina propria (GALT)
True
What condition occurs when body produces autoantibodies specific to H, K-dependent ATPase, a parietal cell antigen, and intrinsic factor (all produced by parietal cells)?
Autoimmune gastritis
Autoimmune gastritis causes destruction of parietal cells. What does this destruction result in?
A marked decrease in HCl in gastric juice = achlorhydria
Without synthesis of intrinsic factor, patient develops vitamin B12 deficiency which disrupts RBC formation in the bone marrow, leading to pernicious anemia
Flagellated bacterium that resides in mucus layer lining the gastric epithelium (especially pyloric antrum), despite hostile environment
Helicobacter pylori
H pylori survives and replicates in the gastric lumen and is mainly associated with what 2 conditions?
Peptic ulcers
Adenocarcinoma
What are the 3 phases of pathogenesis of H pylori infection?
- Active phase = motile bacteria increase gastric pH by producing ammonia
- Stationary phase = bacterial attachment to receptors on mucous surface cells of pyloric region; production of cytotoxic proteases for nutrient supply and attraction of leukocytes; production of ammonia and cytotoxic proteases leads to peptic ulcer formation
- Colonization phase = detach from epithelium, replicate within mucus blanket and remain attached to glycoproteins
Most people infected with H pylori do not have symptoms. What are the symptoms when they do occur?
Intense, sudden, persistent stomach pain; hematemesis and/or melena
