gastric physiology Flashcards
functions of stomach min 5
Store and mix food Dissolve and continue digestion Regulate emptying into duodenum Kill microbes Secrete proteases Secrete intrinsic factor Activate proteases Lubrication Mucosal protection
surface of gastric mucosa cells
mucous cells
where is gastric acid made
fundus and body of stomach
names of the three phases of gastric acid secretion
cephalic phase
gastric phase
duodenal phase
what to g cells make and their function
gastrin stimulate secretion of hcl and histamine
what does ach do in the cephalic phase - turning it on
acts on parietal cells to turn them on and triggers the release of gastrin and histamine
What do d cells make derek for
derek for somastin
gastric phase for the production of gastric acid ?
g cells release gastrin acts on parietal cells gastrin triggers release of histamine histamine acts directly on parietal cells net goal= to increase acid production
function of proteins in the lumen
act as a buffer , mopping up H+ ionss causing ph to rise ,decreased secretion of somatostatin
more parietal cell activity due to lack of inhibition
how to stop gastric phase
low luminsl ph inhibits gastrin secretion via a negative feedback loop
inhibits histamine via gastrin
stimulates somastatin release inhibits parietal cell activity
turning off in the intestinal phase
Presence of chyme in duodenum stimulates entero endocrine cells to release cholecystokinin and secretin
Inhibit gastric acid secretion
which nerve innervate ach
VAGUS NERVE
what is a peptic ulcer
a breach in the musocal surface
causes of peptic ulcers
Helicobacter pylori infection
Drugs – NSAIDS
Chemical irritants – alcohol, bile salts, ? Dietary factors
Gastrinoma
treatment for peptic ulcers
tablets for one week
how does gastric mucosa defend itself
alkaline mucus
Tight junctions between epithelial cells
Replacement of damaged cells
Feedback loops
what does Helocobacter pylori do to cause peptic ulcer and treatment
Secretes urease , split urea into co2 and ammonia
Treatment - proton pump inhibitor to lower on
Followed by antibiotics
how do NSAID’s work to cause peptic ulcer
Inhibit cox-1
Reduced production of prostaglandin
More mucosal injury
how do bile salts cause peptic ulcer
Duodeno-gastric reflux
Regurgitated bile strips away mucus layer
Reduced mucosal defence
what cells produce pepsinogen
chief cells
what enzyme does the stomach produce
NO ENZYME
protease activation
positive feedback loop
pepsinogen into pepsin via HCL.
Pepsin is very ph dependant
how does pepsin help in protein digestion
breaks down collagen into meat, helps shred meat into smaller pieces , greater surface area
peristalsis
peristalsis waves- contractions weak at fundus and cardia then towards pylorus they become stronger and then closes
What do the interstitial cells of cajal do
Pacemaker cells
Control the frequency of contractions
3 a minute
what happens if you overfill the duodenum
dumping syndrome, vommiting , cramps, diarrhoea
gastroparesis
delayed gastric emptying
effects of gastroparesis
nausea, anorexia, abdo pain, vomit undigested food
Gastric acid secretion step by step
H20 and co2 combine to produce carbonic acid catalysed by carbonic anhydrase
Carbonic acid dissociates into h+ and bicarbonate ion
H+ moves into stomach via action be transport
HCO3- out the cell and swap with cl-
H and cl to make hcl
How to increase gastric acid production 2 ways
1)Via ach released from the vagus nerve
Direct stimulation of parietal cells
Produced during gastric phase where intrinsic nerves detect distension stimulating ach
2)activation of g cells leads to gastric release
Gastrin released and binds to CCK receptors on parietal cells which elevates calcium levels causing increased vesicular fusion.
How does pepsinogen get converted to pepsin
By hcl
functions of the colon
Absorption of water and electrolytes
Production of vitamins
Excretion of waste
start oof the bowel
ileocaecal valve/ junction
layers of the colonic wall
Mucosa
Submucosa
Muscularis propria
Serosa
histology of colon
columnar epithelium , goblet cells
what is the gastro-colic- reflex
Stomach stretching and food in the jejunum leading to mass movement of the colon
How do we know we need a poo?
Rectum fills
Reflex relaxation of internal anal sphincter
Sampling reflex
To complete defaecation
External sphincter relaxes
Puborectalis relaxes
Rectum contracts
Valsalva maneuver
What do enterochromaffin ecl cells secrete
Histamine
What do H2 receptors do
Histamine binds to them Causing increased gastric aid production in stomach
How many layers of muscle in the stomach
3
two functions of pancreas
Endocrine secretion
Exocrine secretion
Aqueous bicarbonate secretion
Enzyme secretion
what does the enyzme cholecystokinin do
Gallbladder contraction
Inhibition of gastric acid secretion
Delays gastric emptying
where is the enzyme Cholecystokinin produced
I cells of duodenum & jejunum
How does secretin inhibit gastrin and reduce gastric acid production
Release of somastatin
Inhibits release of gastrin in the pyloric antrum
action of the enzyme gastrin
HCl secretion (parietal cells) enzyme release (acinar cells)
consequences of exocrine dysfunction
malnutrition, osteoporosis, increased cardiovascular morbidity,
protein digestion ?
Pepsin initiates in stomach. Trypsin & Chymotrypsin packaged into secretory vesicles as proenzymes; prevents auto digestion
Enterokinase embedded in Smallintestine mucosa. Active trypsin activates chymo and trypsinogen
what is a mesentery
The mesentery attaches your intestines to the wall of your abdomen.
How to work out bmi
Weight / height 2
What is bmr
Basal metabolic rate
The amount of energy needed to stay alive at rest
What can increase your bmr
Being overweight
Male
Pregnancy
Exercise
What can decrease your bmr
Increase in age
Malnutrition
Starving
Hypothyroidism
How is gastric acid produced
Parietal cells have a proton pump that release protons in exchange for k , proton binds with cl in lumen
Ecf cells release histamine which bind to h2 receptors on parietal cells for more proton release
Gastrin also promoted hcl production
Layers of the stomach
Mucosa
Submicosa
Muscularis externa
Serosa
What happens in the cephalic phase
Activated upon seeing , smelling food etc
Stimulation via vagus nerve and ach
Ecl cells secrete histamine , g cells also release gastrin
What happens in the gastric phase
Stomach distension
Triggers gastrin release , activates histamine release
Hcl continues to be secreted in response to distension and amino acids digested due to proteases
What happens in the intestinal phase
Duodenum initially enhances gastrin secretion but soon inhibits it
Enterogastroc reflex, duodenum sends inhibitory impulses to the stomach
What is gastric motility mediated by
Acetylcholine , parasympathetic vagus nerve
Nitric oxide serotonin
What increases the strength of gastric contractions
Gastrin
Distension of stomach
What decreases the strength of gastric contractions
Duodenal distension
Increase in duodenal fat
Decrease in duodenal fat
Increase sympathetic stimulation
Role of pepsinohgen
Pepsinogen as an inactivate Zymogen of Pepsin
Activated by low ph
Increase protein digestion
Shreds meat
What is gastric motility
Peristaltic contraction
Difference between large and small intestine
Small
Smaller
No appendices
Wall smooth
Large Larger Longitudinal muscle is not continuous Has appendices Sacculated
