oesophagus and stomach Flashcards
anatomy of oesophagus
oesophageal sphincter and epiglottis direct food and air to the right place
epiglottis covers the opening of the trachea during swallowing
upper oesophageal sphincter relaxes - allowing it to fit in the oesophagus
oesophagus is a conduit tube
close proximity with the lungs and major bv
oesophageal sphincter
constrictor pharyngeal medius - commonality with circular muscle layer of GI tract
constrictir pharynges inferior - commonality with longitudinal muscle layer
physiology of the oesophagus
25cm long
wall made of skeletal and sm
upper oesophagus = skeletal muscle only
lower = sm
middle third = mixture of 2 as the proportion of skeletal muscle tapers along its length
under -ve pressure, stomach under +ve pressure
lining - non-keratinised straitifed sqaumous cells - all the way to the lower oesophageal sphincter where cells are arranged as simple columnar epithelium to9 resist strong stomach acid
the epithelial change occurs within the spincter along a jagged line called Z line
lower oesophageal sphincter
split into:
internal component - built into circular smooth muscle of oesophageal wall
external component - formed by right crus of diaphragm
swallowing
stage 0 - oral phase - chewing and saliva help prepare bolus for swallowing - both sphincters are constricted
stage 1 - pharyngeal phase [- bolus moves to back of pharynx, the pharengeal musculature helps to guide it towards the oesophagus. Both oesophageal sphincters open.
stage 2 - upper oesophageal phase - upper sphincter closes, superior rings of circular muscle contract as inferior rings dilate, Sequential contractions of longitudinal muscle help guide the food down the gullet.
stage 3 - lower oesophageal phase - food passes through the lower sphincter that too closes, the peristaltic wave continues to push food into the stomach
anatomical levels of the oesophagus
start from C5
close to trachea, aorta, recurrent laryngeal nerves
travel through diaphragm, only short region in abdo before reacing stomach
function
conduit for food
secretions from pharynx to stomach
epithelia organisation
non-keratinising
wear and tear lining
stratified squamous
lubrication - mucous secreting glands
muscle organisation - skeletal/smooth
sphincters - upper and lower oesophageal
tonically active - closed at rest
swallowing centre - recognise swallowing - more powerful effect on upper, cause to open
upper - skeletal muscle
lower - smooth/skeletal
layers of muscle
longitudinal near bottom of slide
circular near top
peristalsis in oesophagus
local effect
nerve stimulate contraction above bolus, relaxation below
if food not moved - 2nd peristaltic signal from brain
function of the gastrooesophageal sphincter
allow movement of food and fluids into the stomach, but ensure acidic contents of the stomach are separate from the vulnerable oesophageal tissue
z line - gastrooesophageal sphincter
visible threshold between epithelia and the oesophagus - stratified squamous and stomach - simple columnar
stomach and oesophageal lining
oesophageal epithelium - light pink - wear and tear lining
stomach epi - bright red - more resistant to low pH
mucosal gel lining of the stomach provides protection against corrosive acid
function of gastro-oesophageal sphincter
acid reflux stopped by the diaphragm
failure of the gastro-oesophageal sphincter
in pregnancy stomach pushed up = oesophagus pushed up pressure difference inn thorax and abdomen acid reflux
structure of the gastro-oesophageal sphincter
epithelia change from stratified squamous to simple columnar because need to absorb
gastric folds/rugae - allow expansion
lower sphincter is less well defined than upper sphincter - it is made of diaphragm and fold in stomach - when stomach is empty, opening is narrow
functions of the stomach
digestion of macronutrients - chemical and mechanical
storage reservoir - until down stream organs are ready to receive stomach contents
immunological protection - strong acid helps to destroy ingested pathogens
structure of stomach
lined with columnar epithelia and it invaginates into gastric pits - contain exocrine and endocrine celks
anatomical regions
pyloric canal pyloric antrum body fundus cardia
where is gastric acid secreted from
fundus and body in high volume
stomach wall
extra oblique layer of smooth muscle inside circular layer - aids in performance of complex grinding motions
in empty state - stomache contracted - mucosa and submucosa are in folds called rugae
when full - rugae are stretched -flat
rugae allow it to undertake resevoir function
cardiac and pyloric region
when immediately enter and leave respectively
mucus secretion
body and fundus
mucus
HCl
pepsinogen
Antrum
gastrin -endocrine hormone
purpose of HCO3- in mucus gel
neutralise acid that comes into contact with the cell wall
pH at epithelial surface 6-7
pH at lumen 1-2
stomach secretions
2L /day
150 mM H+
peristalsis in stomach
propel chime to colon
more peowerful proximally
ANS essential
‘move food from 1 end of tube to other’
segmentation in stomach - movement
weaker than peristalsis
move fluid chime to pyloric sphincter - it is digested so can move onto the next bit
solid chime pushed back up
stretching activates enteric nervous system - local
what are gastric pits
deep pores within stomach mucosa
lead to multiple gastric glands - house functional secretory cells of stomach
contain cells for secreting gastric juice - cocktail of hydrochloric acid, enzymes and enzyme zymogens
cells also secrete mucous, paracrine siugnals and hormones
mucous cells
abundant
secrete a bicarbonate-rich mucous which helps to protect the stomach lining
keeps pH next to lining near 7 rather than 2-3
protects lining form active lipase and proteases which may interfere with lipid bilayer and membrane transporters
parietal cells
acid secreting cells
quiescent until activated
then tubovesicles in the cytoplasm fuse with the small invaginations on the apical surface to make canalicular surface with large SA for acid secretion
rich in mt
secrete intrinsic factor - a glycoprotein essential for absorption of vitamin B12
HCL function
kill ingested pathogens
activate protease zymogens
alter protein structure to help digestion
chief cells
produce protease zymogen - pepsinogen
and a lipase - gastric lipase
pepsinogen is activated to pepsin in the presence of HCl in gastric lumen
precurser stops it autodigesting the chief cells
pepsin breaks dietry proteins into smaller peptide chains
gastric lipase is an enzyme that digests fats by removing a fatty acid from triacylglyceride molecule
G cells
enteroendocrine cells
at bottom of gastric pit release hormone gastrin into blood stream in response to the presence of peptides in the stomach, and stomach distension.
gastrin
travels through blood to receptor cells in stomach
stimulates gastric secretion and motility
stimulation of smooth muscles by gastrin leads to stronger contraction and the opening of the pyloric sphincter to move food into the duodenum
also binds to receptors on pancreas and gall bladder - increases secretion of pancreatic juice and bile
Enterochromaffin-like cells
ECL
neuroendocrine cell in gastric glands
in vicinity of parietal cells
secrete histamine - stimulates the secretion of acid from the parietal cells
D cells
enteroendocrine cells secrete somatostatin - inhib affect of GI func
somatostatin inhibits ECL production of histamine and parietal cell activity - both inhibit the secretion of HCl
gastric stem cells
`pluripotent stem cells are capable of differentiating into all the stomach cells
structure of chief cell
abundant RER
Golgi
apical secretion granules
features of parietal cells
tubovesicles contain H+/K+ ATPase
internal canaliculi - internal reservoir near lumen
parietal cell secreting
tubovesicles fuse with membrane and microvilli
canaliculi combine and project into the lumen of the stomach
action of parietal cell
CO2 enter - carbonic anhydrase: CO2 + H2O -> HCO3- + H+
bicarbonate is exchanged for chloride
chloride diffuse into canaliculi
k enters cell in exchange for na
canaliculi absorb K for exchange
K+/H+ ATPase take H+ into canaliculi and K+ out - active transport
H+ secreted
gastrin and histamine
gastrin stimulates histamine release from chromaffin cells
3 phases of the activities of the stomach
cephalic phase
gastric phase
intestinal phase
cephalic phase
Afferents: Sight, smell, taste and thought of food
efferents: vagus nerve stimulate secretion from mucous cells, chief cells, parietal cells and G-cells via the submucosal plexus, gastrin and histamine also stimulate parietal cell secretion
effects: small secretion for new minutes
gastric phase
afferents: distention of stomach and chemoreception of nutrients and a reduced pH.
efferents: Vagus nerve (neurons secreting ACh) stimulate secretion from mucous cells, chief cells, parietal cells and G-cells via the submucosal plexus and increase motility (mixing waves) via the myenteric plexus, gastrin and histamine also stimulate parietal cell secretion
effect: 3-4 hours of gastric activity and mechajnical digestion
intestinal phase
Afferents: Duodenal stretch and chemodetection of reduced pH and duodenal distension
efferents: I-cells secrete cholecystokinin (CCK) and S-cells secrete secretin into the blood. decrease parietal secretion and inhibit gastric motility and emptying, stretch receptors input into enteric nervosu system which reduces activation of the stomach
effect: Gastric emptying slows down to allow downstream organs to deal with current contents.
cephalic phase processes
vagus nerve release ACh
stimulate histamine
causes cAMP to enter cell
gastric phase processes
stretch and chemo receptors - activate tissue
activate muscle and gland to release mucin and acid
stomach distension - switch on vagus
intestinal phase
mainly inhibitory
chime in intestine - intestine respond to pH and consistency - inhibit stomach if lipid conc is high
enterogastric reflex: inhibited by gastric inhibitory peptide, cholecytokinin, secretin, enterogastric reflex.
inhib from vagus nerve - centrally inhibited
if protein conc high - stim gastrin secretion
pharmacology
ranitidine - histamine receptor antagonist
omeprazole - protein pump inhibitor
