Case 2 - yaffas Flashcards
how is the stomach divided physiologically
orad portion - first 2/3 of the body
caudad portion - last 1/3 of the body
explain of the storage function of the stomach works
food entering forms concentric circles of food in the orad portion of the stomach
the newest food is closest to the oesophageal opening, whilst the old food lies nearest the outer wall of the stomach
when this food stretches the stomach wall, a vagovagal reflex occurs
signals are sent from the stomach to the brainstem and back, reducing the muscle tone of the muscular wall of the body of the stomach so that the wall can expand outwards progressively
what is the max volume of the stomach
0.8-1.5 litres
what are digestive juices of the stomach secreted by
the gastric glands whcih are present in almost the entire wall of the body of the stomach except along the lesser curvature of the stomach
what do these digestive juices come into direct contact with
the food lying against the mucosal surface of the stomach
explain the mixing of the stomach contents
as long as food is in the stomach, weak peristaltic constrictor waves, called mixing waves begin in the mid to upper portions of the stomach wall and move toward the antrum about once every 15 seconds
what are these waves initiated by
the gut wall basic electrical rhythm, consisting of slow waves that occur spontaneously in the atomach wall
what happens as the constrictor waves progress from the body into the antrum
they become more intense
what do these extremely intense waves provide
powerful peristaltic action potential driven constrictor rings that force the antral contents under higher and higher pressure towards the pylorus
what is an exceedingly important mixing mexhanism in the stomach
the moving peristaltic constrictive ring, combined with this upstream squeezing action called retropulsion
what is the upstream squeezing action
the antral contents are squeezes upstream through the peristaltic ring toward the body of the stomach and not through the pylorus
what is chyme
the mixture of food that passes down the gut, after it has been mixed with the stomach secretions
what do the peristaltic waves do
cause mixing in the stomach
provide a pumping action called the pyloric pumo
what is the pylorus
the distal opening of the stomach
what does stretching of the stomach wall elicit
local myenteric reflexes in the wall that greatly accentuate activity of the pyloric pump and at the same time inhibit the pylorus
where are the G cells that secrete gastrin found
the antral mucosa
what are the duodenal reflexes that inhibit stomach emptying mediated by
directly from the duodenum to the stomach through the ENS in the gut wall
through extrinsic nerves that go to the prevertebral sympathetic ganglia and then back through inhibitory sympathetic nerve fibres to the stomach
through the vagus nerve to the brainstem, where they inhibit the normal excitatory signals transmitted to the stomach through the cvagi
what do these pathways do
strongly inhibit the pyloric pump propulsive contractions
increase the tone of the pyloric sphincter
what is cholecytokinin CCK
the hormone that has the most potent effect in regards to hormonal feedback to inhibit gastric emptying
where is CCk released and when
released from the duodenal and jejunal mucosa in response to fatty substances in the chyme
what does it act as
an inhibitor to block increased stomach motility caused by gastrin
what is secretin
released from duodenal mucosa (S cells in the crypts of Lieberkuhn)
released in response to gastric acid passed from the stomach through the pylorus
what is gastric inhibitory peptide (GIP)
this has a general but weak effect of decreased GI motility
released from the duodenal and jejunal muscosa
released in response to fat in the chyme, but to a lesser extent carbohydrates aswell
although GIP weakly decreases GI motility, its primary function is to stimulate secretion of insulin by the pancreas
summary of regulation of stomach emptying
emptying of the stomach is controlled only to a moderate degree by stomach factors such as the degree of filling in the stomach and the excitatory effect of gastrin on stomach peristalsis
probably the most important control of stomach emptying resides in inhibitory feedback signals from the duodenum, including both enterogastric inhibitory nervous feedback reflexes and hormonal feedback by CCK
these feedback mechanisms work together to slow the rate of emptying
what is the rate of stomach emptying limited to
the amount of chyme that the small intestine can process
what are two ways that there can be increased stomach emptying
increased stretching of the stomach leads to increased pressure in the stomach
gastrin - enhanced pyloric pump + increased HCL production in parietal cells
how can nervous reflexes lead to decreased stomach emptying
inhibit pyloric pump and increase pyloric sphincter tone
how does hormonal feedback lead to decreased stomach emptying
because of the following hormones that are secreted due to the presence of fat in the duodenum
secretin - inhibits gastrin
CCk - inhibits gastrin
GIP - weakly decrease GI motility
what are the two types of tubular glands found in the stomach mucosa
oxyntic glands
pyloric glands
what are the three types of cells found in oxyntic glands
mucous neck cells - secrete mucus
chief cells - pepsinogen
parietal, oxyntic cells - HCL and intrinsic factor
where are these cells located
on the inside surface of the body and fundus of the stomach, constituting to the proximal 80% of the stomach
what do pyloric glands do
mainly secrete mucus for protection and they also secrete gastrin
where are pyloric glands located
in the antral portion of the stomach - distal 20% of the stomach
what do the oxyntic cells contain
large branching intracellular caniculi
where is the HCL formed
villus-like projections inside these canaliculi and is then conducted through the canaliculi to the secretory end of the cell (the apical end)
what is the movement and exchange of ions in and out of parietal cells primarily powered by
ATP from the numerous mitochondria present in the parietal cells
what is the first step in the mechanism of HCL seceretion
Cl- ions are actively transported from parietal cell cytoplasm into the lumen of the canaliculus via a chloride pump. Na+ ions are actively transported out of the canaliculus into the cytoplasm of the parietal cell via a sodium pump. This creates a negative potential (-40 to -70 mV) in the canaliculus. This causes K+ ions (and some Na+ ions) to enter the canaliculus from the cytoplasm. Thus, in effect, mainly KCl and smaller amounts of NaCl enter the canaliculus.
what is the second step in the mechanism of HCL secretion
Water dissociates into hydrogen ions (H+) and hydroxyl ions (OH-) in the cytoplasm. H+ ions are actively secreted into the canaliculus in exchange for K+ ions. This is catalysed by the H+/K+ ATPase (proton pump).
Also, Na+ ions are ions are actively reabsorbed by a separate sodium pump. Therefore, the Na+ ions and K+ ions that were initially secreted into the canaliculus have ben reabsorbed, whilst H+ ions have been added to the canaliculus. This gives us the HCl in the canaliculus.
what is the third step in the mechanism of HCL secretion
Water passes into the canaliculus by osmosis because of the increased ionic concentration in the canaliculus. The final secretion from the canaliculus contains water, HCl (conc = 150-160mEq/L), KCl (conc = 15mEq/L) and small amounts of NaCl.
what is the fourth step in the mechanism of HCL secretion
OH- combines with CO2 under the influence of carbonic anhydrase to form bicarbonate ions (HCO3-). These diffuse into the extracellular fluid in exchange for Cl- ions.
what is the pepsinogen function and how is it activated
it has no digestive activity
as soon as it comes into contact with HCL, it is activated to form active pepsin
what does pepsin function as and what is an optimum pH condition for this
Pepsin functions as an active proteolytic enzyme for protein digestion, in an acid medium.
Optimum pH is 1.8 - 3.5 but above a pH of 5 it has almost no proteolytic activity and becomes completely inactivated is a short time.
regulation of pepsinogen secretion by peptic cells in the oxyntic cells is regulated in response to what two types of signals
stimulation of peptic cells by acetylcholine released from the vagus nerves on the gastric enteric nervous plexus
stimulation of peptic cell secretion in response to acid in the stomach
how does acid stimulate this secretion (second point on last card)
it doesnt stimulate the peptic cells directly, instead it elicits additional enteric nervous reflexes that support the original nervous signals to the peptic cells
what is the rate of pepsiogen secretion influenced by
the amount of acid in the stomach
what is intrinsic factor essential for
the absorption of vitamin B12 in the ileum
what is intrinsic factor secreted by
oxyntic cells along with HCL
what happens when a person has chronic gastritis
when the acid producing parietal cells are destroyed, the person not only develops achlorhydria but often also pernicious anaemia because of failure of maturation of the red blood cells in the absence of the vitamin b12 stimulation of the bone marrow
what do the surface mucus cells secrete
large quantities of viscid mucus that coats the stomach mucosa, thus providing protection for the stomach and lubrication
what do ECL cells secrete as well as HCL
histamine
what does the histamine bind to
H2 histamine receptors of parietal cells
this activates the parietal cells to form and secrete HCL
rate of formation and secretion of HCL is dependent on the amount of histamine secreted bt ECL cells
when is hypochorhydria diagnosed
when the pH of the gastric secretions fails to decrease below 6.5 after maximal stimulation
what are the different treatments for H pylori
Standard Triple Therapy
2 antibiotics + 1 PPI.
“CAP” = Clarityromycin (500mg bd) + Amoxicillin (1g bd) + PPI (standard dose bd)
Metronidazole (400mg bd) can be used instead of Amoxicillin
Modern Bismiuth-Based Regimens
2 antibiotics + 1 bismuth compound.
“CAR” = Clarithromycin (500 mg bd) + Amoxicillin (1 g bd) + Ranitidine bismuth citrate (400 mg bd)
Metronidazole (400 mg bd) can be used instead of Amoxicillin.
Retreatment:
Standard triple therapy
As above using a regimen different from that first employed
Quadruple Therapy
PPI (standard dose bd) + Tetracycline (4× 500 mg) + Metronidazole (3× 400 mg/ 500 mg) + Ranitidine Bismuth Citrate (400 mg bd).
Bismuth Subcitrate (4× 100 mg)/ Bismuth Subsalicylate (4× 600 mg) can be used instead of Ranitidine Bismuth Citrate
features of first generation PPIs
Example - Omeprazole
Lipid soluble, weak base – enters & accumulates in acid spaces (canaliculi of parietal cell).
Activated in acid - chemically altered by H+ to an active sulphenamide form.
Sulphenamide = cationic so trapped in canaliculi.
Forms irreversible S-S bond with H+,K+ ATPase, therefore blocks its action permanently.
features of second generation PPIs
Example – Esomeprazole / Nexium
1st generation PPIs (e.g. omeprazole) are a mixture of optical (R and S) isomers.
The S-isomer is more active in humans.
Purified S-isomer is ‘esomeprazole/nexium’
what is referred pain to do with peritonitis
can cause irritation of the diaphragm. This will cause referred pain into the right shoulder via the C3, 4, 5 dermatome.
