Case 1 - Overview of the gastrointestinal tract Flashcards
what is the oral/buccal cavity lined with
lined by oral mucosa, a thick stratified squamous epithelium that is resistant to abrasion
what does the mucosa produce
defensins to inhibit bacterial growth
what type of teeth appear in the first 6-24 months of life
deciduous teeth (n=20) appear within the first months of life
what are the deciduous teeth replaced by
gradually replaced in childhood as the permanent teeth erupt (finish by approx age 12)
what is there lots of in saliva
IgA
diagram showing the location of the different teeth
how many incisors are there and what do they do
2 - slice and cut
how many canines are there and what do they do
1 - tear and rip
how many premolars are there and what do they do
2 - grind and crush
how many molars are there and what do they do
3 - grind and crush (mostly grind)
what is the formula used by dentists for each side of the mouth
formula used to show the 32 teeth in the mouth - 2 incisors in top left, right, bottom left and right and so on
how much of saliva is water
approx 99%
what are the different glands that produce saliva
parotid, sub lingual, and sub mandibular
what lipases and amylases are in saliva
lingual lipases and alpha amylase
is saliva slightly acidic or alkaline and why
slightly acidic (pH 6.75-7) to provide reasonably optimal conditions for enzyme funciton
what act as lubricants in saliva
mucoproteins (mucin)
what is the most abundant immunoglobulin in saliva
IgA
what are included in saliva for dental repair
calcium and phosphate
what is salivation controlled by
salivatory nuclei in the medulla and pons in the brainstem
what stimulates the production of saliva with a high water content
mechanoreceptors and chemoreceptors in the mouth
what is an important feature about mechanoreceptors
they are not food specific - non food objects induce saiation
what can also induce salivation
inout from higher brain centres and lower digestive tract
what are the two intrinsic nerve plexuses
myenteric nerve plexus
submucosal nerve plexus
features of the ENS
the submucosal and myenteric plexuses are not simply nerve fibres from the CNS
they have their own neurones akin to the gut brain
the gut is influenced by the rest of the nervous system, but will function without any input from the brain or spinal cord
what does contraction of the circular smooth muscle do
squeezes the gut contents
what does contraction of the longitudinal muscle do
shortens that portion of the gut
what cells have ‘pacemaker’ activity and what does this mean/do
interstitial cells of Cajal
means that the smooth muscle layers in the gut are spontaneously active
what does loss of the cells of Cajal lead to
gut motor dysfunction disorders
how long is the oesophagus
25cm
what does the submucosa contain
blood vessels, lymphatics, nerves, lymphoid tissue and mucus glands
what is the oesophagus lined with
stratified squamous epithelium to resist abrasion
what kind of muscle is found in the oesophagus
in the first third (voluntary) it is skeletal muscle
in the last third (involuntary) it is smooth muscle
the middle third is mixed
what is the outer layer mostly made up of
adventita
what is the last part beyond the diaphragm covered with
serosa
what does the epithelium change to at the gastro-oesophageal junction
lining changes from squamous to columnar epithelium (glandular)
what happens if there is metaplasia?
Barrett’s oesophagus - change of epithelium from stratified squamous to gastric due to repeated damage form gastric reflux - precursor to oesophageal cancer
diagram showing peristalsis in the stomach
where is peristalsis confined to in the stomach
the lower part
what valve opens and closes here and how is it regulated
the pyloric valve opens and closes and is tightly regulated
what does the action of peristalsis and the pyloric valve result in
vigorous churning of contents and relatively slow gastric emptying
what is the rate of gastric emptying controlled to some extent by
the caloric value of the contents of the duodenum
what forms the numerous longitudinal folds (rugae)
thick mucosal and sub mucosal layers
what happens after a meal in the small intestine
there are small irregular contractions of the small intestine
what happens in the inter digestive state
the small intestine exhibits the migrating motor complex (MMC), which can take up to 2 hours to pass along the small intestine
what is the signal to stop this inter digestive activity
ingestion of food, and this can be mimicked by gastrin and by cholecystokinin (CCK) which are released from the stomach and intestine, respectively
what is CCK
is a potent inhibitor of gastric emptying in response to high caloric value in the duodenum, an example of local integration of activity to meet demand
how active is the colon
active almost continuously, although increased activity can be elicited by particular stimuli
how long is transit time in the colon
2-3 days
what is the major component in terms of transit time (dehydration and storage)
the transverse colon is the major component
what do contractions of the circular muscle cause
haustra - not like peristalsis
what happens as one haustrum fills
as one haustrum fills and distends, this induces contractions that push food into the next
what is the gastrocolic reflex
powerful, propulsive contractions can be elicited by the introduction of food to the stomach
what is the function of the stomach
mixes food
acts as a reservoir
what starts disgestion
the stomach - proteins, nucleic acids
what is the pH of the stomach and what does this do
pH 1-2 and this activates some enzymes
what is the only truly essential function of the stomach
absorbing vitamin B12 using intrinsic factor
what does the stomach absorb
alcohol
some water
some vitamin B12
what produce gastrin
mucous cells and enteroendocrine cells produce gastrin. these are tightly coiled
what are the exocrine gastric secretions
hydrochloric acid
mucus
pepsinogen
intrinsic factor
what are the endocrine secretions
gastrin
somatostatin
what are the main cells of the stomach
goblet cells
mucous cells
parietal cells
chief cells
G cells
D cells
what do goblet cells do
secrete an alkaline mucus
what do mucous cells do
secrete mucus and pepsinogens
what do parietal cells do
secrete gastric acid and intrinsic factor
what do chief cells do
secrete pepsin and gastric lipase
what do G cells produce
gastrin
what do D cells produce and where are they found
found in antrum and produce somatostatin
what does hydrochloric acid do
acidifies the lumen, produces pepsin from pepsinogen
what does mucus do
protects mucosal surface being damaged by HCL
what does pepsinogen do
precursor of pepsin (which acts as an endopeptidase)
what does intrinsic factor do
important in the absorption of Vit B12 and erythropoeisis
what does gastrin do
stimulates acid production
what does somatostatin do
inhibits release of gastrin
what stimulates the release of pepsinogen
acetylcholine i.e vagal input
what controls and stimulates HCL
acetylcholine i.e vagal input
gastrin (from G cells)
histamine (from enterochromaffin cells)
other hormones
what is gastric acid secretion inhibited by
somatostatin (via decreased gastrin release)
secretin (via decreased gastrin secretion)
gastric inhibitory peptide and other enterogastrones (directly on parietal cells)
what are the 3 phases of gastric secretion
cephalic phase
gastric phase
intestinal phase
what is the cephalic stage
through smell, sight, taste of food releases ACh, stimulating the parietal cells and also the G cells - vagally mediated, about 40% of gastric acid secretion occurs here
what is the gastric phase
distension and reflex activation of enteric neurones and vagal outflow stimulate the parietal cells and G cells.
digested proteins in the stomach also stimulate the G cells - about 50% of gastric acid secretion occurs here
what is the intestinal phase
amino acids present in the bloodstream (products of protein digestion) directly stimulate the parietal cells - about 10% of gastric acid secretions occurs here
what is the gastric mechanism for the inhibition of gastric secretion
if proteins are present in the stomach, they act as buffers to keep luminal pH>3
as the stomach empties, therefore, the luminal pH falls below 3. D cells release somatostatin to inhibit gastrin release and thereby reduce acid secretion
what is the duodenal mechanism of gastric secretion
acidification of the duodenal lumen releases secretin, which inhibits gastrin secretion
acidification of the duodenal lumen and the presence of fatty acids and salt in the duodenum release gastric inhibitory peptide, which acts directly on parietal cells to inhibit HCL secretion
main GI hormones - where are they produced and their major actions
ydbsadyb
ehfbeufb eufun
