stomach Flashcards
what is deglutition
swallowing = propulsion of food from oral cavity into oesophagus
process of swallowing
food molded into bolus by tongue and moved upwards and backwards to pharynx - forces soft palette up to seal of nasal cavity - voluntary
pressure-sensitive sensory cells stimulated
swallowing centre in medulla initiates swallowing reflex - involuntary
epiglottis closes off trachea
complicated contraction/relaxation of muscles forces food into oesophagus
what are the layers of the oesophagus
mucosal
submucosal
muscular
serosal
what is the mucosal layer composed of
stratified squamous epithelium
what is the muscular layer composed of
striated and smooth muscle
what is the serosal layer composed of
adventitia - loose connective tissue only in neck
what is the process of food being transported down the oesophagus
upper oesophageal sphincter closes behind food bolus
complicated peristaltic contractions force food down oesophagus
lower oesophageal sphincter opens to allow passage of food into stomach
what is the lower oesophageal sphincter
cardiac sphincter
physiological - except in horses = anatomical
prevents regurgitation of acidic stomach contents
what is emesis
vomiting - active propulsion of stomach contents into oral cavity
where is the vomiting centre
medulla
what is vomiting stimulated by
pharyngeal/gastric distension or irritation
what is gastric torsion
stomach rotates 90-360 degrees
seals off cardiac sphincter preventing vomiting
what animals does gastric torsion occur in
horses and dogs with wide chests
what happens if rotation compromises blood supply in gastric torsion
gastric tissue becomes hypoxic and in severe cases necrotic
what are the functions of the simple stomach
digestion
protection
storage
mechanical breakdown
what is the ruminant equivalent of the simple stomach
abomasum
what is the embryological regions of the stomach and what do they secrete
oesophageal - non-glandular, stratified squamous epithelium
cardiac - mucous
fundic -mucous and gastric juices
pyloric - mucous
what is the cardia region
entrance to stomach
what is the fundus
blind-ending part
what is the corpus
body of stomach
what is the pylorus
exit from stomach
stomach cell types
mucous
parietal
chief
entero-endocrine
function of mucous cells (goblet)
secrete mucus to protect against HCL
function of parietal cells (oxytinic)
secrete HCL to digest protein
function of chief cells (peptic)
secrete pepsinogen to digest protein
function of entero-endocrine cells
secrete hormones
what does motility do
prepare stomach to receive a meal
mix and mechanically break down chyme
empty stomach contents into small intestine
prevent regurgitation of stomach contents into oesophagus
what is the transmitter that allows initial relaxation of stomach smooth muscle to accommodate the meal
vasoactive intestinal peptide
what is the main type of contraction involved in motility
peristalsis
process of motility
fundus weak contractions
propogate down corpus
pyloric sphincter opens to allow chyme into duodenum
when contraction reach pylorus the pyloric sphincter closes
food forced back into corpus helps mixing
what is stomach emptying regulated by
strength of contraction
opening/closing of pyloric sphincter
stimulation and inhibition of emptying
what stimulates emptying of stomach
neural regulation - expansion of stomach increases strength of contraction
hormonal regulation - release of gastrin increases strength of contraction and dilates pyloric sphincter
what inhibits emptying of the stomach
increased pressure in duodenal walls, low PH, high fat/peptide contraction, high osmolarity.
neural regulation by increased sympathetic activity/decreased parasympathetic activity
hormonal regulation via secretin, CCK and GIP.
what is digestion
enzymatic breakdown of nutrient macromolecules into smaller units that can be absorbed
what is starch digested by and at what pH
amylase
only active at pH greater than 6
what is protein digested by and at what pH
pepsin
active at low pH
what is starch made from
amylose and amylopectin - complex carb
what is starch digestion initiated by
salivary amylase in mouth
what allows starch digestion to continue for a while
acid secreted from stomach walls so gradual decline in pH from centre of stomach to edge
level of starch in omniverous diets
high
level of starch in herbiverous diets
low
levels of starch in carniverous diets and why
low - saliva does not contain amylase
what does pancreas also produce
amylase
what does gastric juices consist of
HCL and pepsinogen (inactive form of pepsin)
what leads to ulceration
breach of mucosal barrier
functions of HCL
convert inactive pepsinogen into active form pepsin
provides required acidic environment for pepsin to digest protein
prevents fermentation by killing microbes
degrades large chunks of connective and muscle tissue into smaller more digestible particles
when does maximum secretion of HCL occur
2-3 hours after a meal
what is duration and volume of HCL dependent on
species
dog produce 0.5-1L per hour where as horse produces 20-30L
why does urine pH increase after a meal
delay between food passing stomach to pancreas
how does pepsin initiate degradation of protein and collagen
breaking peptide links adjacent to aromatic amino acids
what can pepsin activate
more pepsinogen
what stimulates secretion
reflex arcs - long via vagus and short locally
histamine, chief, parietal and mucin cells amplify each other
gastrin
what is cephalic phase caused by
sight, smell, taste, presence of food in mouth
what does cephalic phase stimulate and how
secretion
directly via acetylcholine
indirectly via gastrin in blood
what is gastric phase caused by
stomach expansion
peptides in lumen
what does gastric phase stimulate
secretion
directly via acetylcholine
indirectly via gastrin in blood
what is stimulation/inhibition in the intestinal phase dependent on
acidity of chyme
food components
how is intestinal phase stimulated
neural (cholinergic) and hormonal (gastrin and CCK) signals
what are most intestinal responses
inhibitory
what is hormonal stimulation mediated by
gastrin
