The stomach Flashcards
describe the anatomy of the stomach
check home screen folder
what is the role in secretion and motility of the lower oesophagus and cardia of the stomach
secrete mucus and HCO3-
prevention of reflux
entry of food
regulation of belching
what is the role in secretion and motility of the fungus and body of the stomach
secrete - H+, intrinsic factor mucus, HCO3-, pepsinogens, lipase
acts as reservoir, tonic force during emptying
what is the role in secretion and ruction of the antrum and pylorus
secrete mucus
role in mixing grinding sieving and regulation of emptying
which part of the stomach accepts and holds food
fundus and body
what is the function of the antrum and pylorus in he stomach
antrum - churning and grinding food as well as involved in emptying
pylorus is involved in emptying
what does accommodation of the stomach require
vago-vagal reflex
what does accommodation of the stomach depend on and what does it involve
depends on stretch receptors signalling the vagus which act on the enteric system resulting in relaxation of the stomach and dilation of the fungus and body
what size particles cannot pass through the pyloric sphincter
larger than 1-2 mm
when the duodenum senses delivery of acid, amino acid and lips what happens
duodenum secretes hormones such as CCK, secretin and GIP which decrease gastric motility
describe what happens in the cephalic reflex
sight, smell, taste or thought of food
sight/thought - cerebral cortex which triggers hypothalamus and medulla (which are directly stimulated by taste and smell)
stimulated vagus nerve - stimulates stomach secretory activity
how does depression affect the cephalic reflex
loss of appetite such as in depression affects cerebral cortex and lack of stimulation of para symp centre which inhibits stomach activity
what happens in the stimulatory gastric phase
stomach distension activates stretch receptors which targets local reflexes and vasovagal reflex - medulla and vagus nerve which all stimulate secretory activity
food chemicals and rise in ph triggers G cells to secrete more gastrin into blood which means more secretory activity
what decreases stomach secretory activity in the gastric phase
excessive acidity - decrease in gastrin secretion
emotional distress increases sympathetic nervous system
what stimulates secretory stomach activity in the intestinal phase
presence of low ph and partially digested food in the duodenum - intestinal gastrin release into blood and more secretory stomach activity
what actions in the intestinal phase inhibit stomach secretory activity
distension of duodenum with presence of fatty, acidic, hypertonic, chyme or irritants
these all lead to local reflexes, pyloric sphincter and vagal nuclei in medulla which stimulate enterogastric reflex and inhibit stomach secretion
describe the anatomy of gastric pits and glands
check home screen folder for diagram
what do mucus cells secrete
mucus and HCO3-
what do parietal cells do and what are they also called
where are they primarily found
oxyntic - secrete HCL and intrinsic factor
found in the fungus and body
what do chief cells do
also called peptic cells and they secrete pepsinogen
what are the two types of gastrin and what is it
peptide hormone released from G cells
G17 - main from secreted from antrum
G34 - C-terminal 17 are the same as G17 - main form secreted from the duodenum
what is gastrin homologous with
CCK-PZ and can share receptors
what simulate release of gastrin
lumen protein / amino acids
para symp input mediated by gastrin releasing peptide and interneurons
what inhibits gastrin release
lumen H+ via negative feedback
what are the main actions of gastrin
stimulate acid secretion and promote mucosal growth
what are the two types of somatostatin
14 and 28 - 28 most common
where is somatostatin released
D cells in stomach, duodenum and pancreas
how does somatostatin reach its target
mainly paracrine and endocrine
what stimulates release of somatostatin - what inhibits it
lumen H+ and inhabited by ACh
what is the role of somatostatin
acts on G cells to inhibit gastrin release and also CCk and secretin
what is the anatomical difference between raton and active parietal (oxyntic)
resting have tubulovesicles
active have canaliculus
what protects the epithelium
bicarbonate and mucus secretion
what is intrinsic factor, where is it released and what do it do
55 kDa glycoprotein
rebased from parietal cells in stomach
binds to cobalamin (vit B12) but not until it reaches the small intestine
essential for cobalamin uptake in the ileum
what mediates effect of gastrin
CCK-a receptors
what are pepsins
family of proteases secreted from the chief and mucus cells
when are pepsins released
in response to ACh H+, minor effects of secretin, cck and gastrin
what are pepsins secreted as and how are they activated
secreted as pro hormones (pepsinogens)
cleaved spontaneously at low pH less than 5 and quickly less than 3
cleaved by pepsin (autolysis)
what is a pepsin(s)
endoproteases - they are cut within the peptide chain rather than going for the terminal amino acid
optimum pH 2-3
denature above 5-7
what is and what is the role of gastric lipase
involve din initial digestion of triglycerides
cleave the outer fatty acids off triglycerides leaving diacyl glycerol
what is the optimum ph for gastric lipase
4 - stable in the stomach but denatured by pancreatic proteases
what does ptyalin a amylase do and is its optimum ph
initial digestion of polysaccharides
optimum ph of 7 and denatured at ph 4
what are the causes of vomiting
vagal afferents in response to irritants
psychogenic (pain, revulsion)
motion sickness (labyrinthine disorders)
drugs or toxins
pregnancy
what is the central role of vomiting
area postrema = chemotrigger zone
what are the consequences of vomiting
salivation, sweating, hyper ventilation
retrograde peristalsis
retching (involuntary contractions of diaphragm and abdominal wall
displacement of the cardia in the thorax
