The Oesophagus and Stomach Flashcards
State the basic plan of the gut wall from the lumen outwards.
- Epithelium,
- lamina propria (loose connective tissue)
- muscularis (thin layer of muscle)
- submucosa,(connective tissue)
There are nerve plexuses in the submucosa - muscularis
smooth msucle layer - Serosa is a mixture of connective tissue and epithelium
Adventitia is only connective tissue
What vertebral level does the oesophagus start at?
C5
How long is the average oesophagus?
25-30 cm
At what vertebral level does the oesophagus pierce the diaphragm?
T10
Describe the cell type in the upper oesophagus and how is this cell type specialised?
Non-keratinising stratified squamous -
this is good for protection - acts as a barrier and prevents the loss of water through the epithelium. It allows damage without loss of funtion
What are the two important sphincters in the oesophagus?
Upper oesophageal sphincter and the lower oesophageal sphincter
Describe the difference in structure of the lower and upper oesophageal sphincters.
- The upper oesophageal sphincter is made up of only skeletal muscle
- the lower oesophageal sphincter consists of both skeletal and smooth muscle.
but mainly smooth muscle
What state are the sphincters in when there is no food in the mouth?
They are tonically active meaning that they are both closed.
What happens when food goes into the mouth?
how does the muscle contract around food?
When food goes into the mouth, a reflex is set up by the swallowing centre in the brain leading to peristalsis.
the circular muscle contracts above the food and it relaxes below the food
How does muscle type change as you pass down the oesophagus?
You go from skeletal to smooth muscle as you move down the oesophagus.
How does the innervation change as you pass down the oesophagus?
It goes from motor neurones to autonomic nervous system as you move down the oesophagus.
What two types of muscle are in the oesophagus?
Circular and longitudinal
What is the difference between the primary and secondary peristaltic waves?
Secondary peristaltic wave is initiated after the primary if the food gets stuck if the bolus of food is very large
The lower oesophageal sphincter is not considered a true anatomical sphincter. What is it formed by?
Diaphragm (muscular part),
greater curvature of the stomach folding inwards, difference in pressure between the thorax and abdomen
- stops acid reflux from coming up
What are the gastric folds in the stomach lining called and what is the point in them?
Rugae - they increase surface area
-allows the stomach to expand as the folds can stretch out
Describe the transition in epithelium from the oesophagus to the stomach.
- Oesophagus is made up of non-keratinising stratified squamous epithelia
- the stomach epithelium is made up of simple columnar epithelium
What are the 4/5 regions of the stomach?
Cardiac and pyloric regions
entering leaving
body and the fundus
middle of stomach
Pyloric Antrum
bottom of stomach
Certain substances are produced in certain regions of the stomach.
State which substances are produced in which regions.
Cardiac and Pyloric regions - mucus only
Fundus and Body - pepsinogen, HCl, mucus
Antrum - gastrin
What feature do the mucus secreting cells of the stomach have that protects them from the acidity of the stomach?
They secrete bicarbonate (HCO3)
HCO3 sits on top of these cells and neutralises the acid that comes into contact with its surface
How much acid is produced by the stomach per day and what is the concentration of protons?
which area produces the acid?
2 L
150 mM
the body and the fundus
What do Gastric Chief Cells produce?
State some histological features of Gastric Chief Cells?
Gastric Chief Cells produce pepsinogen
- They have a lot of RER
( due to protein secretion) - They have Golgi apparatus
( allows modification of the proteins)
for packaging and modifying for export - They have a lot of vesicles at the apical membrane
State three structural features of the resting parietal cell.
(not producing acid)
- Numerous mitochondria - provide energy for the active transport of protons into the lumen of the stomach
- Cytoplasmic Tubulovesicles - contain H+/K+ ATPase channels
- Internal Canaliculi - fluid filled reservoirs present within the resting parietal cell
What is the role of parietal cells?
Parietal cells pump protons into the lumen of the stomach and make it more acidic
*****Describe the mechanism by which active parietal cells increase the proton concentration in the stomach.
- Co2 diffuses into the cell from the blood and reacts with water with the action of carbonic anhydrase to produce bicarbonate and a proton.
- NA/K ATPase brings one potassium in and one sodium out. The K+ follows the concentration gradient and diffuses into the canaliculi.
- HCO3-/Cl- pump, pumps bicarbonate out and chloride into the gastric lumen.
- Then, ATP is used to actively transport H+ into the gastric lumen with K+ moving out.
H+ + Cl - = HCL
There is a massive ATP driven movement of protons into the stomach lumen.
What is the effect of inhibiting carbonic anhydrase?
This reduces the acid producing ability of the parietal cells because it is no longer able to convert water and carbon dioxide into bicarbonate
What two proteins do you need a lot of to increase the acidity of the stomach?
- Carbonic Anhydrase and
- H+/K+ ATPase
How does pepsinogen turn into pepsin?
pepsinogen in an acidic environment is broken down into pepsin
so the pepsinogen is activated by th HCL secreted by the pariateal cells
What are the two stimuli for gastrin production?
- Acid production itself
- Local peptide hormones that are being produced by pepsin
What is the effect of gastrin?
Gastrin is produced in the pyloric antrum and passes into the bloodstream before returning to the lumen of the stomach where it causes an increase in acid secretion by the stomach epithelium.
How can gastrin indirectly increase acid secretion?
Gastrin stimulates the release of histamine from chromaffin cells (in the lamina propria) - this stimulates acid secretion
What are the three phases of gastric secretion?
Cephalic, Gastric, Intestinal
Describe the cephalic phase of gastric secretion.
- This is before the food even enters your mouth.
- The vagus nerve from the medulla stimulates
i) parietal cells to secrete acid
ii) ECL cells to release histamine
iii) Releases gastrin releasing peptide on G-cells.
iv) Inhibits somatostatin release from D-cells.
-all results in MORE acid
Describe the gastric phase of gastric secretion.
- requires a mechanical stimulus
- food in stomach causes stretch and chemoreceptors send messages to the brain.
- The brain then activates the vagus nerve and increases pepsin and acid production.
- then the enteric nervous system will take over and cause churning of the stomach.
Describe the intestinal phase of gastric secretion.
- Chyme enters the small intestine and if the pH is < 2 or the chyme has a high lipid content,
- this acts as a stimulus that goes up to the brain and switches off acid and pepsin production.
also causes the enterogastric reflex
What are the three hormones produced in the enterogastric reflex? What is the name given to this group of hormones?
Gastric Inhibitory Peptide, Cholecystokinin and Secretin
These are enterogastromes
- They decrease the production of acid and pepsin
- The enterogastric reflex is a reflex that is controlled by hormones
Describe the excitatory process when chyme has a high protein content.
- If the chyme entering the small intestine has a high protein content it will stimulate the release of gastrin
- more acid is produced hence more pepsinogen is converted to pepsin so the proteins will be better digested.
State two drugs that decrease acid secretion and their targets.
Omeprazole - proton pump inhibitor
Ranitidine - histamine receptor antagonist
Which of the following structures within the
parietal cell contains the most H+/K+ ATPase?
Canaliculi Carbonic anhydrase Golgi body Mitochondria Tubulovesicles -->
Which of the following stimuli would be most likely to
decrease acid secretion in the stomach?
Chyme fatty acid content --> Increased acetylcholine secretion Increased gastrin secretion Protein content of the meal Stomach distension
what is the gastro oesophageal junction?
what function does it have?
There is an epithelial transition at the Z-line from stratified squamous to simple columnar.
Reflux is prevented by the diaphragm.
what are the main functions of the stomach?
- to break down food
- to hold food
- kill parasites/bacteria
what are the two types of stomach contraction?
- peristalsis 20%
- propels the chyme towards the colon
- the autonomic nervous system is essential
- segmentation 80%
this is weaker
fluid chyme goes towards pyloric sphincter
solid chyme goes towards the body
what are the features of a secreting parietal cell?
- Tubovesicles fuse with the membrane and microvilli project into the canaliculi.
