Lecture 7-Histology Of Esophagus And Stomach Flashcards
Four layers of the GI tract
-Mucosa-3 components?
Epithelium, lamina propria, muscularis mucosa
Four layers of the GI tract
-Submucosa?
Connective tissue that contains glands, blood vessels, nerves
Four layers of the GI tract
-Muscularis externa?
Two to three layers of smooth muscles
Four layers of the GI tract
- Adventitia and serosa
- Where are each of these seen?
- What are they?
Adventitia-esophagus, most of duodenum
Serosa-rest of GI tract
CT that supports and binds other organs
The mucosa has three components?
- A lining epithelium with mucosal and submucosal glands and ducts
- An underlying lamina propria consisting of a vascularized loose CT
- A thin layer of smooth muscle, the muscularis mucosae
Mucosa
- Epithelium histology?
- Function?
- Stratified squamous and simple columnar
- Function
- selectively permeable barrier
- transport, digestion, absorption
- produces hormones
Mucosa
- Lamina propria
- what is found here?
- What is special about the lamina propria found in the small and large intestines?
- Vascularized loose CT
- Lymphatic nodules and scattered immunocompetent cells
- Lamina propria of the small and large intestines is a relevant site of immune responses (peyer’s patch or GALT)
Mucosa
- Muscularis mucosae
- What is it?
- Functions?
- A thin double layer of smooth muscle is often present
- Increases contact area with food
- Propel and mix food in GI tract
Submucosa
- Consists of?
- Glands are present in the submucosa of what GI organs?
- Consists of a dense irregular CT with large blood vessels, lymphatics, and nerves branching into the mucosa and muscularis
- Glands are present in the submucosa of the esophagus and duodenum
Mucosa and submucosa in the stomach compared to mucosa and submucosa in the small intestine?
Mucosa and submucosa extend into the lumen as folds
- stomach-rugae
- small intestine-plicae
Mucosal gland-function?
Increase secretory capacity
Mucosa alone can extend into the lumen-called?
Fingers/villi
Muscularis externa
-2 layers of? What are they called?
-Contains two layers of smooth muscle-circular layer and longitudinal layer
Muscularis externa
- Circular layer
- Description?
- Function?
- Circular layer-inner layer is arranged around the tube lumen
- Contraction of the smooth fibers of the circular layer reduces the lumen
Muscularis externa
- Longitudinal layer
- Description?
- Function?
- Longitudinal layer- fibers of the outer layer are disposed along the tube
- contraction of the fibers of the longitudinal layer shortens the tube
Adventitia
- Outside the peritoneal cavity
- Binds to the body wall
- Loose CT
- Blood vessels and nerves
Serosa
- Within the peritoneal cavity
- Loose CT
- Simple squamous epithelium
- Blood vessels, nerves adipose tissue
Innervation of the GI tract allows it to respond to?
Both local stimuli and ANS input
GI tract innervation
-Extrinsic (ANS)-Effect of sympathetic (TL)?
Decreases motility and secretions
GI tract innervation
-Extrinsic (ANS)-Effect of parasympathetic (Vagus)?
Increases motility/secretions
GI tract innervation
- Intrinsic/enteric
- Myenteric plexus is between what 2 layers?
Between the inner/circular and outer/longitudinal layers of muscularis externa
GI tract innervation
- Intrinsic/enteric
- description?
- Contains what 2 plexi?
- Distinct, interconnected neuronal circuits
- Meissner’s plexus
- Myenteric plexus
GI tract innervation
- Intrinsic/enteric
- Functions?
- Peristaltic contractions to move bolus
- Secretory activity of mucosal and submucosal glands
Esophagus-Location?
Lies posterior to the trachea in the thoracic cavity, except for its distal end, which passes through the diaphragm into the abdominal cavity
Lower esophageal sphincter
Just anterior to the gastroesophageal junction, helps prevent reflux and regurgitation of stomach contents through contraction and must relax to allow food passage with swallowing
-There is also a upper esophageal sphincter near the cricopharyngeus muscle
Esophagus
-What happens at the gastroesophageal junction?
- At the gastroesophageal junction, the mucosa transitions from the stratified squamous epithelium of the esophagus to simple columnar epithelium and glandular secretory mucosa
- The muscularis mucosa, submucosa, and muscularis propria are continuous through this junction
Portal-caval anastomoses
-Increase in portal venous pressure?
-Increase in portal venous pressure results in dilation of veins (esophageal varices)
Mucosal and submucosal glands
-Continuously produce?
Continuously produce a thin layer of mucous to lubricate the epithelial surface
Muscularis externa in the esophagus
- Inner circular and outer longitudinal
- Segment dependent variation
- Upper 1/3-skeletal muscle
- Middle 1/3-transition, primarily smooth muscle
- Lower 1/3-smooth muscle
Esophagus has 2 sphincters
-Upper sphincter?
Anatomically defined, cricothyroid
Participates in initiation of swallowing
Esophagus has 2 sphincters
-Lower esophageal?
Functionally defined, gastroesophageal sphincter
Prevents gastric reflux
Barrett’s Esophagus
- Condition in which an abnormal columnar epithelium replaces the stratified squamous epithelium that normally lines the esophagus
- Most severe histologic consequence of chronic GERD
GERD
Change in epithelium to columnar (like stomach), chronic esophagitis/ulceration, dysphagia, fibrosis a/o esophageal strictures
Digestive tube (made up of 4 organs-esophagus, stomach, small intestine, and large intestine) -Each of these organs is made up of four concentric layers (inside to outside)?
Mucosa, submucosa, muscularis externa, and adventitia/serosa
Adventitia for esophagus and most of duodenum
Serosa for rest of GI tract
Stomach
-Protective layer of mucous protects surface epithelium from?
- Mechanical ingestion by ingested foods
- Destructive effects of acids and hydrolytic enzymes
Gastric glands
-Contain 5 major cell types?
- Mucous neck cells
- Chief cells
- Parietal cells
- Stem cells
- Gastroenteroendocrine cells
- The gastric mucosa contains of the fundus-body has 2 classes of mucus-producing cells?
- Where are they each located?
- Surface mucous cells lining the pit
- Mucous neck cells located at the opening of the gastric gland into the pit
Both types of mucous cells produce?
Mucins with glycoproteins to form a protective mucus layer
Surface and neck mucous cells produce:
-Protective mucus layer-function?
-Traps bicarbonate ions and neutralizes the microenvironment adjacent to the apical region of the surface mucous cells to an alkaline pH
Chief cells
-Where are they located in the gastric gland?
- Predominate in the lower third of the gastric gland
- Chief cells are not present in cardiac glands and are seldom found in the pyloric antrum
Chief cells-What do they secrete?
Pepsinogen which is then converted to pepsin by the acidic environment
Parietal cells secrete?
HCl and intrinsic factor
Autoimmune gastritis
- Caused by?
- What results from this?
- Autoantibodies to H+K+-dependent ATPase, a parietal cell Ag, and autoantibodies to intrinsic factor
- Destruction of parietal cells causes a reduction in HCl in the gastric juice (achlohydria) and a lack of synthesis of intrinsic factor
- Vitamin B12 deficiency–>disrupts formation of RBCs–>pernicious anemia
Secretion of HCl by parietal cells is stimulated by what substances?
-These substances are produced by?
The parasympathetic mediator ACh and the peptide gastrin produced by enteroendocrine cells of the pyloric antrum
-ACh also stimulates gastrin release
Gastric juice
-A combination of two separate secretions?
- An alkaline mucosal gel protective component-always present
- HCl and pepsin-levels vary because the levels increase after food intake
H. pylori
-Where is the stomach particularly vulnerable to this organism?
- In the gastric epithelium particularly in the pyloric antrum
- Survives and replicates in the gastric lumen
H. pylori
-Presence of this bacteria is associated with?
Acid peptic ulcers and adenocarcinoma of the stomach
The function of the alimentary tube is regulated by what 2 substances?
-What are each of these produced by?
- Peptide hormones produced by gastroenteroendocrine cells
- Neuroendocrine mediators produced by neurons
Peptide hormones produced by gastrointestinal endocrine cells have the following general functions?
- Regulation of water, electrolyte metabolism, and enzyme secretion
- Regulation of GI motility and mucosal growth
- Stimulation of the release of other peptide hormones
Peptide hormones
-Secretin-released by? When?
Cells in the duodenal glands of Lieberkuhn when the gastric contents enter the duodenum
Secretin-function?
- With CCK?
- With ACh?
- Stimulates pancreatic and duodenal (Brunner’s glands) bicarbonate and fluid release
- Together with CCK secretin stimulates the growth of the exocrine pancreas
- Secretin and ACh stimulates chief cells to secrete pepsinogen, and inhibits gastrin release to reduce HCl secretion in the stomach
Gastrin
-produced by? Where are these cells located?
G cells located in the pyloric antrum
Gastrin-main function?
- Stimulates the production of HCl by parietal cells
- Can also activate CCK to stimulate gall bladder contraction
CCK-where is it produced?
In the duodenum
CCK-function?
Stimulates gall bladder contraction and relaxation of the sphincter of Oddi when protein and fat rich chyme enters the duodenum
GIP-where is it produced?
In the duodenum
GIP-function?
Stimulates insulin release when glucose is detected in the small intestine
Motilin
- release is regulated by?
- released by?
A neural control mechanism-released cyclically (every 90 mins) during fasting from the upper small intestine
Motilin-function?
Stimulates GI motility
Ghrelin-where is it produced?
Stomach (fundus)
Where does Ghrelin bind?
-To its receptor in growth hormone secreting cells in the anterior hypophysis
Ghrelin-function?
Stimulates the secretion of growth hormone
When do ghrelin levels increase?
-What does this trigger?
Ghrelin plasma levels increase during fasting triggering hunger by acting on hypothalamic feeding centers
Mucosa, submucosa, and muscularis externa
- Lamina propria
- types of fibers?
- types of cells?
- Reticular and collagen fibers predominate in the lamina propria
- Cells-fibroblasts, lymphocytes, mast cells, eosinophils, and plasma cells
Submucosa consists of?
- Dense irregular CT-abundant collagenous and elastic fibers
- Large number of arterioles, venous plexuses, and lymphatics
- Meissner’s plexus
Muscularis externa
- Consists of three poorly defined layers of what type of muscle?
- what are the layers?
Smooth muscle-circular, oblique, and longitudinal
Muscularis externa-which layer of muscle forms the annular pyloric sphincter?
The circular muscle
Meissner’s plexus is located in what layer?
Submucosal layer
