Histology of the GI Tract Flashcards
What are the 4 layers of the GI tract ?
mucosa, submucosa, muscularis externa, adventitia/serosa
Define Mucosa
- innermost layer, contains the epithelial cells important in lubrication & absorption
Define Submucosa
- this layer contains the support network of blood vessels & immune cells to keep the mucosa healthy in addition to attaching it to the muscular layers below
Define Muscular Externa
the muscles necessary for peristalsis are contained in this layer
Define Adventitia/Serosa
- the outermost layer which allows the GIT to interact with other tissues around it
What are the 2 adaptions of the oesophagus ?
- mucosa is stratified squamous epithelium, the remainder of the GI tract is simple columnar
- outermost layer of oesophagus is an adventitiam, remainder of tract is serosa
What is the benefit of the stratified squamous epithelium of the oesophagus ?
- more adapted to resist mechanical abrasion
Describe peristalsis
- facilitated by the muscularis externa layer of GI tract
- contains 2 sheets of muscle that work in opposite directions to maximise efficiency of peristalsis
- muscle runs around circumference of GI tract, circular muscle
- the other runs down it’s length the longitudinal muscle
Where does the oesphagus terminate ?
in the stomach
Describe the mucosa of the stomach
- columnar epithelium, and forms ‘glands’ which house a range of important cell types
Describe the muscular layer of the stomach
- contains 3 layers of muscles, this ensures efficient mixing, churning & emptying
What are the functions of the stomach?
- digestion
- disinfection = the acidic environment in the stomach helps to kill any microbes
- mechanical breakdown = churning of the stomachs muscular contractions help to further macerate food
What does the epithelium of the stomach form?
- forms pits which house gastric glands
What cells are present in the stomach?
- Mucus cells
- Parietal cells
- Chief cells
- G cells
What do mucus cells do?
- protects the stomach from the low pH environment
What do parietal cells do?
- produce the sotmachs HCL, also makes intrinsic factor
What is the function of Chief cells?
- produces pepsinogen, the zymogen of pepsin
What is the function of G cells?
- secrete gastrin, which stimulates pepsinogen & HCL production
What controls the passage of chyme from the stomach?
- the pyloric sphincter
What are the 3 parts of the small intestine?
duodenum = major site of digestion
jejunum & ileum = 90% of absorption carried out in jejunum & ileum
Where is bile produced?
in the liver
Where is bile stored?
in the gall bladder
How does bile enter the duodenum?
- squeezed into duodenum via the common bile duct where it can exert its role in fat digestion
Describe the location of the pancreas
- lies posterior to stomach, running from the duodenum towards the spleen
What are the endocrine & exocrine functions of the pancreas?
endocrine = acts on distant cells via circulation (secretion of insulin)
exocrine = acts via ducts or channels rather than blood (digestive enzymes into duodenum)
What is the key cell of the endocrine part of the pancreas?
- beta-islet cells
- which produce insulin
What is the key cell of the exocrine part of the pancreas?
- Acinar cells
- which produce digestive enzymes
Describe Microvilli
- increase surface area of cell for nutrient absorption
- approximately 0.1 um & 1 um tall
- microvilli can also bud from their tips & this allows them to release useful substances they contain
What are some cells present in the intestine?
- intestinal stem cells
- paneth cells
- goblet cells
- enterocytes
- transit amplifying cells
- enteroendocrine cells
Whats the function of intestinal stem cells?
replace lost/damaged intestinal cells
What’s the function of paneth cells?
involved in intestinal defence
What’s the function of transit amplifying cells?
intermediates bewteen stem cells & enterocytes
What’s the function of goblet cells?
produce lubricating mucus
What’s the function of enteroendocrine cells?
secretes hormones
What’s the function of enterocytes?
absorbs nutrients
What is a Lacteal ?
- villi contain them
- they’re capillaries of the lymphatic system
- lipids are transported away from the GI tract by lacteals
Describe the Large Intestine
- horseshoe shaped
- begins at exit of ileum & terminates at the anus
- runs around outside of small intestine
- 1.5 metres long & 7.5 cm wide
What are the functions of the large intestine ?
- reabsorption of water & electrolytes from intestinal juices
- compaction of intestinal contents into faeces
- storage of fecal material
- absorption of important vitamins produced by bacteria (biotin. B12, folic acid)
