Lecture 5: The upper gastrointestinal tract Flashcards
What are the three major layers of the mucosa found throughout the GI tract?
Epithelium, lamina propria, muscularis mucosae
What is the role of the muscularis mucosae?
Local movement and folding of the mucosa
What three things are found in the submucosa?
Nerves, blood vessels, supporting connective tissue
What name is given to the contractions of the GI tract to help move food along?
Peristalsis
What does the epithelium line?
The lumen of the GI tract
Why does the epithelium change in colour along the GI tract?
Different types of epithelial cell
What are the two layers of the muscularis propria?
Outer longitudinal layer
Inner circular layer
What layer of muscularis propria is found only in the stomach and helps with mechanical digestion?
Third inner oblique layer
What name is given to the outermost layer of loose supporting tissue?
Adventitia
What is the name of the outermost layer supporting the muscularis layer in the stomach?
Serosa
What type of cells make up the serosa?
Simple squamous
The serosal layer that covers intraabdominal structures is known as
Visceral peritoneum
What structure binds the digestive tracts to the abdominal wall?
Mesentery
Where is protective mucosa found in the GI tract?
Esophagus, anal canal
Where is secretory mucosa found in the GI tract?
Stomach, small and large intestine
Where is absoptive mucosa found in the GI tract?
Small intestine (dudenum: brunner’s gland)
Where is absorptive/protective mucosa found in the GI tract?
The whole large intestine
What type of epithelial cells make up protective mucosa?
Stratified squamous
What structures differentiate absorptive/protective mucosa?
Lots of mucus secreting cells
What is the oesophagus?
Muscular tube which transports food from mouth to the stomach
How is transport in the oesophagus driven?
Peristaltic contractions
What sphincters contribute to food movement control in the oseophagus?
Lower oesophageal sphincter and upper oesophageal sphincters
What type of epithelial cells line the oesophagus?
Non-keratinised squamous epithelium
What are oseophageal glands?
Small groups of mucus-secreting glands in the sub-mucosa of the oesophagus
What is the purpose of the oseophgeal glands secreting mucus?
Lubrication and protection
What glands are found in the oseophagus nearer to the stomach?
Oesophgeal cardiac glands are found within the lamina propria and secrete mucus
What happens to the mucosa at the junction of the oesophagus and the stomach?
Abruptly changes to glandular secretory (simple columnar epithelial cells)
Why is the stomach split into different regions?
These have different functions
What is the name of the region of the stomach located at the transition from esophagus to the stomach?
Cardia
What is the shape and size of the cardia?
A narrow circular band, <1.5-3cm
What do most glands of the gastric cardia secrete?
Mucus and lysozyme
What type of cardiac glands does the mucosa of the cardia contain
Simple or branched, coiled with large lumens
What does lysozyme do?
Attacks bacterial cell walls
What other cells are found in the gastric cardia?
Parietal cells
What are the glands of the cardia similar to?
Cardiac glands of the oesophagus
What type of mucosa makes up the gastric cardia?
Protective mucosa
What is found in the lamina propria of the fundus and body of the stomach?
Abundant number of gastric glands
How are epithelial cells distrubuted in the fundus and body of the stomach?
Not uniformly
What are the three main areas of each gastric gland?
Isthmus, neck, base
What is the structure at the top of the gastric gland called?
Gastric pit/foveolus
What cells make up the isthmus?
Parietal cells
What type of cells make up the neck of the neck of the gastric gland?
Neck mucous cells, stem cells, parietal cells
What type of cells are found in the base of the gastric gland?
Peptic cells, parietal cells, neck mucous cells, neuroendocrine cells
Parietal cells stain in an H&E
Light
Chief cells stain in an H&E
Dark
Why are stem cells found in the isthmus and neck of the gastric gland?
Cells are exposed to acid to are replaced regularly (high turn over rate)
Where do stem cells move to?
Upwards to replace mucous cells
Downwards to differentiate into parietal, chief or endocrine cells
Mucous cells have a _ to _ day turnover, parietal, chief and endocrine cells are replaced less often
4 to 7
Mucous neck cells are arranged how?
Clusters or single cells in the neck of gastric glands
How are mucous neck cells different to superfical mucous glands?
Larger secretory granules
Parietal cells are called
oxyntic
Where are parietal cells present mainly?
in the upper half of gastric glands
What is the structure of parietal cells in gastric glands?
Large round cells with eosiophilic cytoplasm
What do parietal cells secrete?
Hydrochloric acid
Parietal cells are metabolically active so have
Numerous mitochondria and intracellular canaliculi
Chief cells are aclled
Zymogenic cells
Where do chief cells predominate?
Lower part of tubular glands
What features are abundant in chief cells?
Rough endoplasmic reticulum, condensed basal nuclei (pushed to one side), basophilic (purple) granular cytoplasm
What do chief cells secrete?
Pepsinogen (inactive enzyme)
What happens to pepsinogen once secreted?
Rapidly converts to active form pepsin
Pepsin is what type of enzyme?
proteolytic
What else do chief cells secrete?
Lipase, to help break down fat
Name 4 types of neuroendocrine cells
- Enterochromaffin cells
- G cells
- Delta cells
- Other
What does enterochromaffin cells secrete?
- Chromogranin (induces secretions)
- Calbindin (Ca2+ binding)
What do G cells secrete?
Gastrin (stimulates acid secretion)
What do delta cells do?
Inhibit secretions
What does calcitonin do?
Ca2+ metabolism
What region of the stomach is found before the deodeum?
Pylorus
How do gastric pits differ in the pylorus?
Deeper, communicate with pyloric glands
What is secreted in the pylorus?
Mucus, lysozyme, gastrin
What do D cells in the pylorus secrete?
Somatostain (helps inhibit acid secretion)
What type of cell secrets gastrin?
G cells
What does gastrin do?
Activates parietal cells
What type of stimulation makes G cells secrete gastrin?
Parasympathetic stimulation
Stomach distension and amino acids directly stimulate
What stimulates D cells to secrete somatostain?
HCl, to counterbalance acid secretion
