Histology of the GIT Flashcards
What comprises the mucosa?
- epithelium
- simple columnar or stratified squamous
- can include endocrine cells, hormone secreting cells
- renewed every 5-6 days by local stem cells
- lamina propria
- loose CT
- contains nerves, small blood vessels, immune cells
- muscularis mucosae
- thin layer of smooth muscle, facilitates mixing
- boundary of mucosa
- it is the most diverse layer of the gut
What comprises the submucosa?
- dense, irregular connective tissue
- fibroblasts, collagen
- gives structural stability, strength, and elasticity
- contains nerves, small ganglia, blood vessels
- sometimes glands and immune cells
What comprises the muscularis externa?
- two layers of smooth muscle:
- inner circumferential
- outer longitudinal
- small myenteric ganglia between layers
- responsible for gut movement
What comprises the serosa and adventitia?
serosa - ‘non-stick’ surface
- not attached to anything
- fluid secreting surface
- simple squamous flattened epithelium w/ thin layer of CT underneath
- prevents organ adhesion
adventitia
- in some parts of the gut where the gut is connected to other organs
- top of oesophagus and rectum
- connective tissue, no secretive surface
The enteric nervous system is a component of the
ANS
Nerves of the ENS are in
submucosa: regulate absorptive and secretory processes
(between the 2 layers of) smooth muscle: myenteric ganglia
contain sensory neurons, motor neurons, and interneurons
The ENS regulates
absorption and secretion via the submucous ganglia
smooth muscle activity via the myenteric ganglia
The oesophagus epithelium is comprised of
non-keratinised squamous epithelium
What are the layers of the oesophagus?
non-keratinised squamous epithelium
lamina propria
submucosal glands (mucous-secreting)
two muscle types: striated (voluntary) muscle @ top, smooth (involuntary) muscle @ bottom
What characterises the structure of the stomach?
gastric glands (infoldings of epithelial cells, containing multiple cell types)
extra layer of oblique muscle (varies between regions)
pyloric sphincter
What are the 4 main types of cells in the gastric glands?
- mucous cells - secrete mucus
- parietal cells - secrete hydrochloric acid
- chief cells - secrete proenzymes (pepsinogen)
- enteroendocrine cells - secrete hormones (gastrin)
In the stomach, mucous cells are primarily located
surface, pale staining
some lower down amongst other cell types
In the stomach, parietal cells are located
scattered through gastric glands, never at the surface
Parietal cells secrete
hydrochloric acid
Chief cells secrete
pro-enzymes eg pepsinogen
In the stomach, chief cells are located
at the base of the gastric glands
Enteroendocrine cells secrete
hormones (eg gastrin) into the bloodstream
In the stomach, enteroendocrine cells are
scattered amongst other cells of the gastric glands
seen with special stains
The small intestine is responsible for what percentage of absorption?
85%
What is the general structure of the small intestine?
muscularis externa
submucosal connective tissue w/blood vessels folded into plicae circulares (valves of Kerckring), covered w/villi (mucosa)
How is the surface area of the small intestine increased?
folds of submucosa (plica circulares/valves of Kerckring)
covered in villi (projections of mucosa)
villi covered by enterocytes (simple columnar epithelium), each w/microvilli
What is the structure of the villi of the small intestine?
absorptive zone
- simple columnar epithelium w/multiple cell types (some goblet cells, fewer than stomach)
- lamina propria (connective tissue) at core of villi
- projections of muscularis mucosae for movement
- blood vessels, lymph vessels, and immune cells
secretory zone
- crypts of Lieberkuhn - tubular glands between villi secreting fluid and mucous into the lumen
What cell types are found within the epithelial cells of the small intestine?
- enterocytes - fluid transport, absorption
- goblet cells - mucus secretion
- enteroendocrine cells - hormone secretion (don’t look different)
- paneth cells - special to SI, seen on EM w/special stain, deep in glands, secrete anti-microbial peptides (immune system)
- stem cells - renew epithelium
What are the distinctive features of the duodenum?
Brunner’s glands in submucosa
lower plica circulares, longer villi
What is the function of Brunner’s glands?
secrete alkaline mucus from submucosa into the glands at the base of the crypts to inactivate stomach enzymes and acid that may enter the duodenum
What are the distinctive features of the ileum?
Peyer’s patches
short villi, +goblet cells
What are Peyer’s patches?
aggregates of immune cells in submucosa of the ileum
What are the general features of the large intestine?
muscularis externa (lognitudinal) in taeniae coli, not a continuous sheath
more goblet cells in the rectum
immune cells
What comprises the mucosa of the large intestine?
no villi
straight tubular glands w/lamina propria in between (non-motile)
simple columnar epithelium
What comprises the epithelial layer of the large intestine?
- enterocytes - fluid transport, absorption
- goblet cells - mucus secretion
- enteroendocrine cells - hormone secretion (unknown function)
- stem cells - renew epithelium (deep)
compared to small intestine:
- fewer paneth cells
- higher proportion of goblet cells
- some differences in enteroendocrine cell types (different hormones)
- no villi
What is the cell type of the anal mucosa?
stratified squamous epithelium (like oesophagus)
