Histology Of Esophagus And GI Tract Flashcards
Where does the alimentary canal run
What are its 4 layers (starting from innermost)
Mucosa, submucosa, muscularis externa, and serosa
Three components of the mucosa (innermost layer)
- Lining epithelium
- Lamina propria (connective tissue layer)
- Muscularis mucosae (smooth muscle) (in between mucosa and submucosa)
Submucosa consists of
Dense irregular connective tissue
Muscularis externa consists of
Two layers of smooth muscle
What kind of epithelium is serosa composed of
Parts of the esophagus and GI tract that do not have peritoneum (serosa) have?
Simple squamous epithelium
Adventitia (only connective tissue without a mesothelium)
What is mesothelium
Simple squamous epithelium that lines the serous membrane
What does lamina propria contain
Glands and vessels
- Structure of the muscularis mucosae
2. Function
- Consists of smooth muscle cells arranged in inner circular and outer longitudinal layers
- Contractions move mucosa that facilitate absorption and secretion (independent movement of peristaltic movement of entire wall)
Difference in structure between the muscularis mucosae and muscularis externa?
Similar arrangement but muscularis externa is much thicker
Submucosa
- Function of its blood vessels
- Glands in submucosa are located in what two parts of alimentary canal?
- What is the nerve plexus here called and what does it innervate
- Sends branches to mucosa, muscularis externa and serosa
- Duodenum and esophagus
- Submucosal/Meissners; innervates blood vessels and controls muscularis mucosae
Nerve plexus of the muscularis externa is called?
Myenteric or Auerbach’s plexus
Function of the muscularis externa
Its contractions mix and propel contents of digestive tract
Esophagus:
Function of longitudinal folds of esophagus
Allows lumen distention without mucosal injury when bolus of food passes through
Esophagus:
What kind of cells are in the mucosa
Nonkeratinized stratified squamous epithelium
Where is the muscularis mucosa thickest in the esophagus?
In proximal esophagus (probably aids in swallowing)
Esophageal submucosa is similar to other submucosa; what does it contain in the esophagus and function?
Esophageal glands; produces mucus that lubricates esophageal epithelial lining
Explain the muscularis externa composition throughout the esophagus
Upper 1/3 = striated muscle
Middle 1/3= mix of striated and smooth muscle
Lower 1/3= smooth muscle
Difference between cervical/thoracic parts of esophagus and abdominal part?
Cervical/thoracic part has an adventitia; abdominal part is covered by serosa
What is chyme
Mixing and partial digestion of food in the stomach creates a fluid mix called chyme
Histologically, the stomach is divided into what 3 parts. Parts of stomach were divided based on?
Cardiac region, pyloric region and fundic region
Divided based on type of glands in the gastric mucosa
Cardiac region
- Location
- Gland?
- Near esophageal orifice
2. Contains cardiac glands
Pyloric region:
- Location
- Gland
- Just proximal to pyloric sphincter
2. Pyloric glands
Fundic region
- Location
- Glands
- Between cardiac and pyloric regions (largest part)
2. Fundic (gastric) glands
What type of epithelium is on both sides of the esophagogastric junction?
Esophagus - stratified squamous epithelium
Stomach- simple columnar epithelium (of gastric mucosa)
Stomach as the same general structural plan - recap - what is it
Mucosa, submucosa, muscularis externa and serosa
What two parts are the rugae composed of
Function of rugae
Submucosa and mucosa
Accommodate expansion and filling of stomach
Mucosal surface is characterized by?
Numerous openings (gastric pits/foveolae). Fundic, cardiac, and pyloric glands open into bottom of gastric pits
Type of epithelium of stomach and gastric pits?
Simple columnar (known as surface mucous cells)
Function of surface mucous cells
Feature of these types of cells?
Produce thick, gel like mucus that adheres to epithelial surface and protects against abrasion from chyme.
High bicarbonate concentration to protect epithelium from acidity of gastric juice
Which glands produce gastric juice
Where do these glands extend from
Fundic (gastric) glands
Bottom of gastric puts to muscularis mucosae
Fundic glands consist of what 3 segments
Which of the 3 is most recognizable
Isthmus, neck segment and fundic segment
Fundic segment
Fundic glands:
Function of isthmus
Fate of the cells?
Site of stem cell location which replicate/differentiate
Cells destined to be surface mucus cells migrate upward in gastric pits to stomach surface; other cells migrate down to maintain population of fundic gland epithelium
- Main component of gastric juice
- Function of this component
- This component is produced by
- HCl
- Initiates digestion of proteins and converts inactive pepsinogen to active pepsin
- Parietal cells
(Inactive) pepsinogen is produced by
Chief cells
Function of pepsin (active)
Hydrolyzes proteins into small peptides
What two things do parietal cells produce
HCl and intrinsic factor
What is intrinsic factor essential for
Vitamin B12 absorption in distal ileum (binds to it)
- What can lead to intrinsic factor deficiency
2. What would this cause clinically
- Autoantibodies directed against intrinsic factor or parietal cells
- Pernicious anemia
Fundic glands have 5 functionally different cell types
- Which one gives rise to the other 4?
- What are the other 4?
- Undifferentiated adult stem cells
2. Parietal (oxyntic) cells, chief cells, enteroendocrine cells, mucous neck cells
Where are parietal cells located in relation to mucous neck cells
Parietal cells are usually interspersed between groups of mucous neck cells
Compare mucous neck cells to surface mucus cells
Mucous neck cells are shorter and contain less mucinogen and secrete less alkaline mucus
Chief cells:
- Location
- What do 3 things do they secrete?
- What gives them a basophilic appearance
- Apical cytoplasm contains?
- Mostly in deeper part of fundic glands
- Protein, pepsinogen and a weak lipase
- Abundant rER in basal cytoplasm
- Secretory vesicles (zymogen granules) that contain enzyme precursors