Salivary glands, oesophagus and stomach microanatomy Flashcards
What are the general layers of the gut tube from inner most (closest to lumen), and what are their general functions?
Mucosa - protection (many layers) and often cells specialised for secretion or absoprtion
lamina propria - supportive function below mucosal cells.
Physical support - connective tissue, functional support -blood vessels and nerves
muscularis mucosae - provides movement independent of peristalsis
submucosa - same supportive function as lamina propria
muscularis externis - contracts to help churn and move food through the GI tract. Often involved in peristalsis as it is smooth muscle which involuntarily contracts.
Often consists of outer longitudinal and inner circular.
Also forms the sphincters in the GI tract.
serosa/adventitia -
What are the three major salivary glands?
Sublingual (just under tongue)
Submandibular (further towards back of mouth and lower down than sublingual by the jaw bone)
Parotid (up infront of the ear)
What are the relative contributions of each of the glands to the saliva?
Sublingual 5%
Submandibular 70%
Parotid 25%
What type of secretion do the three main salivary glands produce?
Sublingual and Submandibular = serous and mucous (mixed)
Parotid = serous only
What type of epithelium lines the oesophagus?
Stratifies squamous epithelium (non keratinized) which allows for layers to be “brushed” off as sacrificial layers. It transitions into simple cuboidal near the stomach.
Describe the muscularis externis layer of the oesophagus?
The upper third is skeletal muscle, the middle third is a transition zone and contains both and the lower third is just smooth muscle.
What are the two type of gastric glands found in the stomach?
Parietal or oxyntic glands (found in the body and majority of upper portion of the stomach
Pyloric glands (found in the antrum area just before the pyloric region)
What cell types are found in the parietal glands? List these from most superficial to most deep
Mucous cells/ mucous neck cells Parietal cells Enteroendocrine cells Chief cells Some D cells (although most are in antrum in pyloric glands)
What are the cell types found in the pyloric glands? List these from the most superficial to most deep
Mucous cells/ mucous neck cells
G cells
Some D cells (not many)
What is the function of the mucous cells near the surface of gastric galnds?
They secrete mucous which acts as a physical barrier to acidic chyme as well as secreting bicarbonate which acts as a buffer to try and neutralise the acidic contents of the stomach
What is the function of the parietal cells?
They secrete HCL which is important for sterilising the bacteria from the food entering the stomach as well as the HCL allowing the conversion of pepsinogen to pepsin.
These cells also produce intrinsic factor which binds to and forms a complex with vitamin B12 so it can be absorbed. If B12 cannot be absorbed then it results in pernicious anaemia.
What is the function of chief cells?
Important in secreting the digestive enzymes of the stomach.
Pepsin - secreted from these cells in their inactive form (pepsinogen) and are converted to active form by the acidic environment of the stomach. Pepsin is responsible for digesting proteins.
Gastic lipase - digests fats
What is the function of enteroendocrine cells?
Secretes histamine which then stimulates the production of gastric acid and activates most of the other cells of the stomach (eg parietal, chief cells to secrete)
What is the function of G cells?
Secrete gastrin which stimulates gastric acid secretion.
What do D cells do?
Inhibit gastric acid secretion
What are the three phases of gastric secretions during digestion?
Cepahlic
Gastic
Intestinal
What occurs during the cephalic phase of gastric secretion?
when you taste of smell food or even just the tactile sensation of food, it will send nervous information to the medulla oblongata which stimulates the parasympathetic nervous system to send info via the vagus nerve.
This stimualtes the stomach to produce HCL and pepsin and also gastrin to be secreted in the lower part of the stomach. The gastrin then travels through the blood stream to stimulate the release of more HCL and pepsin.
What occurs during the gastric phase of secretion?
Once in the gastric phase the food has entered the stomach and caused it to become distended. The distension activates a parasympathetic nervous response via the medulla oblongata and also directly stimulates the gastric glands. The result is considered secretion of HCL and pepsin.
What occurs during the intestinal phase of secretion?
Once in the intestinal phase the chyme has entered the duodenum so gastric secretion is no longer needed. If the chyme contains lipids from the digestion of fats of ph is below 2 then it inhibits the secretion of gastrin by 3 possible ways. Decreases parasympathetic stimualtion, local reflexes in nerves in gut wall and also by secreting three enzymes into the blood which travel up to the gastric glands to inhibit gastric secretion - these are secretin, gastric inhibitory peptide and cholecystokinen
What are two important hormones released in the duodenum during the intestinal phase of gastric secretion?
Secretin and cholecystokinin
What is secretin stimulated by?
HCL
What is cholecystokinin stimulated by?
Partially digested fats and proteins
What is the common action/function of secretin and cholecystokinin?
To inhibit the secretion of gastric acid
What is the additional action of secretin?
Stimulates the pancreas and bile ducts to release HCO3-
Secretin produces HCO3- which is important as the chyme that is entering the duodenum is very acidic and so it needs to be neutralilsed so it dosent damage the endothelium of the duodenum.
What is the additional action of cholecystokinin?
Stimulates the release of pancreatic enzymes and gallbladder to release enzymes
Connecting the trachea to the oesophagus is connective tissue - is this dense or loose and why?
Loose connective tissue to allow the oeosophagus to stretch/distend when a bolus of food passes down it.
Is there serosa or adventitia surrounding the oesophagus?
On the side of the oesophagus adjacent to the trachea there is adventia as it holding to structures together but on the side of the oesophagus that is most ventral it is serosa as it holding/interfacing with the body wall.
By looking at the muscularis externis muscle layer in the oesophagus how can you tell where the lumen would be?
Look for the inner circular layer (if it is a transverse section then you will see the circular muscle as long striations whereas the longitudinal layer will be seen as circles or muscle). The lumen will be closest to the inner circular layer.
What effect will contraction of the inner circular muscle produce?
Closing in/narrowing of the gut tube
What effect will contraction of the outer circular muscle have?
Shortening of the gut tube
What type of connective tissue is found in the submucosa of the oesophagus?
Dense irregular connective tissue - reflects its supportive function.
What type of epithelium lines the lumen of the oesophagus ?
Stratified squamous epithelium - protective feature of the oesophagus which means several layers can be slothed off
What are the rugae like in the stomach? and how do the rugae change when the stomach is empty and full?
In the empty state, the stomach is contracted and its mucosa and submucosa are thrown up into distinct folds called rugae; when distended with food, the rugae are “ironed out” and flat. The image to the right shows rugae on the surface of a dog’s stomach.
