Stomach Flashcards
the stomach stores
ingested food until it can be emptied into the small intestine at a rate appropriate for optimal digestion.
the stomach secretes
hydrochloric acid (HCl) and enzymes to begin protein digestion.
the stomach mixes
food and gastric secretions to produce chyme – thick liquid mixture that exits the stomach into the duodenum.
These functions are accomplished in a four-step process:
1) Filling
2) Storage
3) Mixing
4) Emptying
what is the stomachs volume when empty?
The stomach has a volume of 50 ml when empty
The stomach has a volume of 50 ml when empty
This can expand to…
… 1 litre during a meal, and yet exhibits little change in wall tension/rise in intragastric pressure.
what happens within deep folds of the stomach when the stomach relaxes?
Deep folds within the stomach gradually flatten as the stomach relaxes with each mouthful of food
Deep folds within the stomach gradually flatten as the stomach relaxes with each mouthful of food
What is this caused by?
caused by the act of eating and mediated by the vagus nerve.
Deep folds within the stomach gradually flatten as the stomach relaxes with each mouthful of food – caused by the act of eating and mediated by the vagus nerve.
It enhances
the stomach’s ability to accommodate extra volume of food with little rise in stomach pressure.
If more than 1 litre of food is consumed, the stomach becomes
over distended and intragastric pressure rises and discomfort is experienced.
what is it called when the stomach relaxes?
Receptive relaxation
whats the function of Interstitial cells of Cajal (ICC) Pacemaker cells ?
- Generate slow wave potentials that sweep down the stomach at an approximate rate of 3 waves per minute.
- This is the Basic Electrical Rhythm (BER) of the stomach.
What is the Basic Electrical Rhythm (BER) of the stomach?
Rhythmic pattern of spontaneous depolarisations
Basic Electrical Rhythm (BER) of the stomach may be accompanied by…
… circular smooth muscle contractions depending upon level of excitability
Fundus area does not usually …
… store food
the fundus area contains…
… a pocket of gas
the Fundus and body is
thin walled leading to mixing movements (stored food not mixed)
how does the wave in the stomach spread?
fundus -> body -> antrum -> pyloric sphincter
food is fed into the
antrum, and mixing takes place here
Peristaltic contraction in
upper fundus
Peristaltic contraction in upper fundus – sweeps down to …
… pyloric sphincter.
Contraction becomes more
vigorous as it reached the thick-muscled antrum.
Strong antral peristaltic contraction propels
chyme forward.
what propels chyme forward?
Strong antral peristaltic contraction propels chyme forward.
Small portion of chyme pushed through
partially open pyloric sphincter into the duodenum.
Small portion of chyme pushed through partially open pyloric sphincter into the duodenum. Stronger than …
… antral contraction = more chyme emptied.
When peristaltic contraction reaches pyloric sphincter, the sphincter
tightly closes = no further emptying.
Chyme hits closed pyloric sphincter and is
tossed back into the antrum.
Chyme hits closed pyloric sphincter and is tossed back into the antrum.
The forward and backward propulsion in antrum with
each peristaltic contraction mixes chyme
Chyme hits closed pyloric sphincter and is tossed back into the antrum.
The forward and backward propulsion in antrum with each peristaltic contraction mixes chyme
– known as ???
retropulsion
Gastric emptying and mixing [FULL]
1) Peristaltic contraction in upper fundus – sweeps down to pyloric sphincter.
2) Contraction becomes more vigorous as it reached the thick-muscled antrum.
3) Strong antral peristaltic contraction propels chyme forward.
4) Small portion of chyme pushed through partially open pyloric sphincter into the duodenum. Stronger than antral contraction = more chyme emptied.
5) When peristaltic contraction reaches pyloric sphincter, the sphincter tightly closes = no further emptying.
6) Chyme hits closed pyloric sphincter and is tossed back into the antrum. The forward and backward propulsion in antrum with each peristaltic contraction mixes chyme – known as retropulsion.
The stomach does NOT
absorb food
what does the stomach absorb?
Alcohol and aspirin ARE!
Alcohol is lipid soluble and diffuses across
the epithelial plasma membranes that line the stomach and enter the blood through the submucosal capillaries
Low pH, acetylsalicylate is lipid soluble – also crosses
the plasma membranes of epithelial cells
What factors modulate Gastric Motility and Emptying within the stomach?
- Volume of Chyme
- Degree of fluidity
what factors modulate Gastric Motility and Emptying outside of the digestive system?
- Emotion
- Intense pain
what factors modulate Gastric Motility and Emptying within the duodenum?
Fat, acids, hypertonicity or distension
Mode of regulation of volume of chyme?
Distension – direct effect, through smooth muscle stretch, intrinsic plexus, vagus nerve and gastrin
effects of Volume of Chyme?
Increased volume stimulates emptying
degree of fluidity mode of regulation?
Direct effect in fluid form
effects of degree of fluidity?
More rapid emptying in less viscous solutions
mode of regulation of Fat, acids, hypertonicity or distension?
Initiates enterogastric reflex or releases enterogastrones (CCK, Secretin)
effects of Fat, acids, hypertonicity or distension?
Inhibit further emptying until duodenum clear
emotion mode of regulation?
Alters autonomic balance
Aggressive / Stressful ↑
Depressive ↓
effects of emotion on Gastric Motility and Emptying?
Stimulates or inhibits motility and emptying
mode of regulation of Intense pain?
Increases sympathetic activity
effects of intense pain on gastric motility and emptying?
inhibits motility and emptying
what is the driving force of gastric emptying?
Antral peristaltic contractions are the driving force for gastric emptying
- Antral peristaltic contractions are the driving force for gastric emptying
- Strength controlled by …
… signals given by both the stomach and the duodenum.
- Antral peristaltic contractions are the driving force for gastric emptying
- Strength controlled by signals given by both the stomach and the duodenum.
- Determine the …
… excitability of the stomach’s smooth muscle – determines the degree of antral peristaltic activity
Gastric Emptying – influenced by 4 important duodenal factors
what are they?
Fat
Acid
Hypertonicity
Distension
whats the primary regulator of gastric motility and emptying?
duodenum
Duodenum must be ready to
receive chyme
Duodenum must be ready to receive chyme. Can delay
gastric emptying
Duodenum must be ready to receive chyme. Can delay gastric emptying by….
- Reducing strength of antral peristalsis
- Influenced by Enterogastrones (Secretin & Cholecystokinin) inhibit forward motion in response to dietary lipids
Fat is digested and absorbed more …
…slowly than other nutrients
- Fat is digested and absorbed more slowly that other nutrients
- Takes place only within …
… the lumen of the small intestine
Triglycerides strongly stimulate …
… duodenal release of CCK
If fat is already present in the duodenum, further gastric emptying of more fatty stomach contents is…
… inhibited – You will feel full for longer
As stomach secretes HCl, chyme is highly
acidic on emptying into duodenum.
acid is neutralized by?
sodium bicarbonate secreted into duodenal lumen by pancreas
Un-neutralized acid irritates …
… duodenal mucosa and inactivates pancreatic digestive enzymes secreted into the duodenal lumen
Un-neutralized acid in duodenum induces
the release of secretin
Digestion of carbohydrates and protein – Large numbers of amino acids and glucose are …
… released
If absorption does not keep pace with digestion, …
… increased osmolarity of duodenal contents
Water enters lumen from
intestinal wall
Water enters lumen from intestinal wall leads to
intestinal distension and circulatory imbalances due to plasma volume reduction -> osmotic diarrheoa (e.g. Sorbitol)
Too much chyme in the duodenum inhibits …
… the emptying of more gastric content.
- Too much chyme in the duodenum inhibits the emptying of more gastric content.
- This inhibition gives…
…the duodenum time to cope with excess volume it already contains.
the neural response is known as the
enterogastric reflex
the two components of the enterogastric reflex?
Autonomic nerves (long reflex)
Intrinsic nerve plexuses (short reflex)
the enterogastric reflex is broken down into
three phases:
- Cephalic phase
- Gastric phase
- Intestinal phae
when is the cephalic phase?
before food reached the stomach
The taste, smell, or thought of food or tactile sensations of food in the mouth stimulate the
medulla oblongata (green arrows).
Vagus nerves carry
parasymphathetic action potentials to the stomach (pink arrow), where enteric plexus neurons are activated.
Postganglionic neurons stimulate
secretion by parietal and chief cells and stimulate gastrin and histamine secretion by endocrine cells.
Gastrin is carried through the
circulation back to the stomach (purple arrow), where, along with histamine, it stimulates secretion.
describe the cephalic phase [FULL]
1) The taste, smell, or thought of food or tactile sensations of food in the mouth stimulate the medulla oblongata (green arrows).
2) Vagus nerves carry parasymphathetic action potentials to the stomach (pink arrow), where enteric plexus neurons are activated.
3) Postganglionic neurons stimulate secretion by parietal and chief cells and stimulate gastrin and histamine secretion by endocrine cells.
4) Gastrin is carried through the circulation back to the stomach (purple arrow), where, along with histamine, it stimulates secretion.
when does the gastric phase occur?
presence of food in the stomach
Distention of the stomach stimulates
mechanoreceptors (stretch receptors)
Distention of the stomach stimulates mechanoreceptors (stretch receptors) and activates a
parasympathetic reflex
- Distention of the stomach stimulates mechanoreceptors (stretch receptors) and activates a parasympathetic reflex.
- Action potentials generated by the mechanoreceptors are carried by…
… the vagus nerves to the medulla oblongata
The medulla oblongata increases
action potentials in the vagus nerves that stimulate secretions by parietal and chief cells and stimulate gastrin and histamine secretion by endocrine cells
Distention of the stomach also activates
local reflexes that increase stomach secretions
Gastrin is carried through the circulation back to
the stomach (purple arrow), where, along with histamine, is stimulates secretion
whats the gastric phase [FULL] ?
1) Distention of the stomach stimulates mechanoreceptors (stretch receptors) and activates a parasympathetic reflex. Action potentials generated by the mechanoreceptors are carried by the vagus nerves to the medulla oblongata (green arrow).
2) The medulla oblongata increases action potentials in the vagus nerves that stimulate secretions by parietal and chief cells and stimulate gastrin and histamine secretion by endocrine cells (pink arrow).
3) Distention of the stomach also activates local reflexes that increase stomach secretions (orange arrow).
4) Gastrin is carried through the circulation back to the stomach (purple arrow), where, along with histamine, is stimulates secretion
when does the intestinal phase occur?
after food has left the stomach
Chyme in the duodenum with a pH less than 2 or containing fat digestion products (lipids) inhibits
gastric secretions by three mechanisms:
Chemoreceptors in the duodenum are stimulated by
H ions (low pH) or lipids
- Chemoreceptors in the duodenum are stimulated by H ions (low pH) or lipids.
- Action potentials generated by the chemoreceptors are carried by
… the vagus nerves to the medulla oblongata, where they inhibit parasympathetic action potentials, thereby decreasing gastric secretions.
Local reflexes activated by
H ions or lipids also inhibit gastric secretions
Secretin and cholecystokinin produced by
the duodenum (brown arrows) decrease gastric secretions in the stomach.
Endocrine hormones released from
the small intestine mucosa
- Endocrine hormones released from the small intestine mucosa
- Secreted in…
… mostly duodenal and some jejunal mucosa
Endocrine hormones released from the small intestine mucosa:
- Secreted in mostly duodenal and some jejunal mucosa
Carried in …
… blood stream
Endocrine hormones released from the small intestine mucosa:
- Secreted in mostly duodenal and some jejunal mucosa
- Carried in blood stream
This inhibits…
And reduces…
inhibits antral contractions
reduces gastric emptying
two enterogastrones release from small intestine mucosa?
- Secretin
- Cholecystokinin (CCK)
what is secretin produced by?
S cells
Cholecystokinin (CCK) is produced by
I cells
Cholecystokinin (CCK) inhibits…
… antral contractions
Cholecystokinin (CCK) induces…
… Induces pyloric sphincter contraction and Gallbladder contraction to release bile
Cholecystokinin (CCK) stimulates…
… pancreas to secrete digestive enzymes from acinar cells
what does secretin do?
- Slows emptying of acidic gastric contents
- Regulates the pH of the duodenum
Secretin regulates the pH of the duodenum by:
1) Inhibiting thegastric secretionof gastric acid from parietal cells in stomach
2) Stimulating the pancreatic production of bicarbonate from intercalated duct cells
what does gastrin stimulate?
Stimulates secretion of gastric acid (HCl) by parietal cells of the stomach
gastrin aids in
gastric motility
gastrin is released by
G cells in the pyloric antrum of the stomach, duodenum, and the pancreas
what does gastrin bind to
CCK B receptors
gastrin secretion stimulated by
peptides in stomach lumen
Stomach secretes how much gastric juice a day?
Stomach secretes 2 litres of gastric juice a day
Luminal surface pitted with
deep gastric pits at the base of which lie the gastric glands.
what are the two gastric glands
1) Oxyntic (fundic) mucosa
2) Pyloric gland area (PGA)
Oxyntic (fundic) mucosa lines the
body/fundus
what are the cells of the Oxyntic (fundic) mucosa?
- Parietal cell HCl
- Intrinsic factor (Vit B12 metab.)
- Pepsinogen – Chief cells
- Mucus – Mucous Cells
Pyloric gland area (PGA) lines the
antrum
Pyloric gland area (PGA) has a small amount of
pepsinogen
what cells in pyloric gland area (PGA)?
mucous cells, which secrete mucus
What is the function of Atrial natriuretic peptide (ANP)?
helps regulate antral somatostatin secretion
what do mucous cells line?
line gastric pits
mucous cells secrete
watery mucus
where are chief cells found?
found in deeper parts of the gastric glands
chief cells secrete?
pepsinogen
Parietal (AKA oxyntic) cells – found in
deeper parts of gastric glands
Parietal (AKA oxyntic) cells secrete
- HCl
- Intrinsic factor
Surface epithelial cells - located between the
pits
Surface epithelial cells, between the pits, secrete…
… a thick viscous alkaline mucus over the surface of the mucosa
H+ and Cl- are actively transported by …
… separate pumps in parietal cell plasma membrane.
H+ concentration within the stomach lumen compared to the blood is
3 million times greater.
Secreted H+ is not transported from the
blood
Secreted H+ is not transported from the blood but is derived from
metabolic processes within the parietal cell.
HCl does not actually
digest any nutrients
HCl does not actually digest any nutrients but it does…
… promote specific functions that aid in digestion.
HCl activates
pepsin
Pepsinogen is the precursor to
the active enzyme pepsin
Pepsinogen is the precursor to the active enzyme pepsin and provides an
acid medium that is optimal for pepsin activity.
HCl aids in
breakdown
HCl aids in the breakdown of …
… connective tissue and muscle fibres.
HCl denatures
protein
HCl uncoils…
…proteins from their complex highly folded state thus exposing more of the peptide bonds for enzymatic attack.
HCl exhibits
antimicrobial activity
HCl kills most of the microorganisms ingested with food – although
some escape and continue to grow and divide in the large intestine
pepsin is a major enzyme mostly secreted into the
stomach lumen as its inactive precursor – pepsinogen.
HCl cleaves a small portion of
pepsinogen
HCl cleaves a small portion of the molecule (44 amino acids) converting it to
the active form – pepsin
Activated pepsin cleaves
other pepsinogen molecules – autocatalytic process.
Secreting the precursor pepsinogen prevents
pepsin from digesting intracellular proteins.
Pepsin cleaves
peptide bonds between hydrophobic and aromatic amino acids to yield small peptides
What is Gastric Intrinsic Factor (GIF)?
Is a second secretory glycoprotein produced from parietal cells
Gastric Intrinsic Factor (GIF) is important for?
vitamin B12 absorption
Gastric Intrinsic Factor (GIF) is essential for?
red blood cell formation
Vitamin B12 can only be absorbed in
combination with gastric intrinsic factor
Once bound, GIF and vitamin B12 are
absorbed by receptor-mediated endocytosis in the ileum (the end of the small intestine)
The stomach receives innervation from
several sources
The stomach receives innervation from several sources:
which are?
1) Sympathetic fibres via splanchnic nerves and celiac ganglion
2) Parasympathetic fibres from the medulla
3) Sensory vagal fibres
Sympathetic fibres via splanchnic nerves and celiac ganglion (synapse) supply
blood vessels and musculature
Parasympathetic fibres from the medulla travel in
the gastric branches of the vagus nerves
90% of parasympathetic fibres are…
… afferent – info transmitting from stomach to CNS
Sensory vagal fibres include those concerned with
gastric secretion.
In addition to the gastric exocrine secretory cells, there are other
secretory cells in the gastric glands that release endocrine and paracrine regulatory factors
G Cells secrete
the hormone gastrin into the blood
G cells are found only
in pyloric gland area (PGA)
Enterochromaffin-like cells (ECL) dispersed among
the parietal and chief cells of oxyntic mucosa
Enterochromaffin-like cells (ECL) secrete…
… the paracrine hormone histamine
what is acetylcholine?
neurotransmitter released from the intrinsic nerve plexus
what do D cells secrete?
secrete the paracrine somatostatin, scattered in the PGA and in duodenum
what cells stimulate HCl secretion?
G cells
Enterochromaffin-like cells (ECL)
Acetylcholine
what cells inhibit HCl secretion?
D cells
the 3 phases of gastric control
cephalic phase - excitory
gastric phase - excitory
Intestinal phase - inhibitory
describe cephalic phase
1) Thinking about tasting, smelling, chewing, and swallowing food increases gastric secretion by vagal nerve activity
2) intrisic plexus
3) acetylcholine release causing release of G cells in PGA, forming into gastrin, and this gastrin then stimulates histamine from ECL cells
5) acetylcholine release and formed gastrin causes increased HCl and pepsinogen production
describe Gastric phase - excitatory
1) Food reaches the stomach – stimulated by the presence of protein, distension, caffeine, and alcohol.
2) intrisic plexus
3) causes acetylcholine release
4) acetylcholine release stimulates g cells to secrete gastrin which stimulates histamine from ECL cells
5) acetylcholine release, gastrin, and histamine from ecl cells causes increased HCl/Pepsinogen production
go look at slide 36
Intestinal phase - inhibitory is importanst in
helping to shut the flow of gastric juices as chyme begins to be emptied into the small intestine:
How does the stomach protect itself from digestion?
Mucus
Luminal membranes of epithelial cells
Tight junctions
Entire stomach lining
how does mucus protect the stomach from digestion?
a protective coating that also traps HCO3- which neutralises acid in the vicinity.
how does luminal membranes of epithelial cells protect the stomach from digestion?
Luminal membranes of epithelial cells impermeable to H+, acid cannot penetrate.
how do tight junction protect the stomach from digestion?
Tight junctions prevent passage of H+ between cells
how does the entire stomach lining protect the stomach from digestion?
Entire stomach lining is replaced every three days – rapid turnover, cells are removed before they can be damaged.
If the barrier is broken and wall is exposed to gastric juices and enzymes
erosion may occur:
causing a peptic ulcer
Helicobacter pylori: the cause of
over 80% of all peptic ulcers
These motile bacteria penetrate (‘tunnel’) through the
alkaline mucus layer (mucosa) where they are protected from the gastric juices.
Helicobacter pylori produce the enzyme…
… urease
Urease acts on urea to
release ammonia and carbonate
Urease acts on urea to release ammonia and carbonate
Leads to…
… the localised neutralisation of acid protecting bacterium.
Helicobacter pylori secretes
toxins: causes a persistent inflammation at the site of colonisation
ulcers weaken…
… the tight junctions: gastric mucosa is leakier than normal
Up until the 1982 stomach ulcers were believed to be caused by
stress and lifestyle factors
Drs Marshall and Warren discovered
colonies of a spiral-like bacteria in the guts of patients with gastritis and gastric ulcers.
- No one believed them
Drs Marshall and Warren discovered colonies of a spiral-like bacteria in the guts of patients with gastritis and gastric ulcers.
- No one believed them
- They successfully…
…cured a patient using antibiotics
- No one believed them
Marshall drank a “cloudy broth” of the bacteria – infecting himself and developing gastritis. Which was then
cured using antibiotics
- No one believed them
A PR company posted about their findings.
They were
awarded a Nobel Prize in Physiology in 2005
Acid and pepsin diffuse into the mucosa and submucosa with
serious consequences
Acid and pepsin diffuse into the mucosa and submucosa with serious consequences:
- Haemorrhage resulting from damage to submucosal capillaries
- Perforation or complete erosion resulting in escape of potent gastric contents into the abdominal cavity
types of Mucus layer breach?
Haemorrhage
Perforation or complete erosion
Mucus layer breach treatments?
- Antibiotics
- H-2 Histamine receptor blockers
- Proton pump inhibitors
- Gastric Surgery
Antibiotics…
… destroy the bacteria
H-2 Histamine receptor blockers examples
ranitidine, blocking histamine binding to its receptor significantly suppresses acid secretion.
Proton pump inhibitors examples
omeprazole, inhibit acid secretion by directly blocking the H+ pump in the parietal cells
what is Gastric Surgery?
Surgery to reduce gastric capacity
How are Laparoscopic Adjustable Gastric Band (LAGB) placed?
Placed using laparoscopic surgery
What is a LAGB?
Adjustable inflatable silicone device
What does LAGB stand for?
Laparoscopic Adjustable Gastric Band
Laparoscopic Adjustable Gastric Band (LAGB)
creates a
small pocket in the upper half of the stomach
Laparoscopic Adjustable Gastric Band (LAGB)
Creates a small pocket in the upper half of the stomach
Fills with…
… food rapidly, and food empties slowly, passes through the rest of the digestive system.
with Laparoscopic Adjustable Gastric Band (LAGB), large meals are not…
… possible
Laparoscopic Adjustable Gastric Band (LAGB)
does not always work in..
… grazers
Gastric bypass is placed using
laparoscopic surgery
Small intestine arranged in a
Y shape
Gastric bypass bypasses the
duodenum
in gastri cbypasses, Food passes from small pocket through the …
… ‘roux limb’
with a gastric bypass, it is physically impossible to
eat a large meal
whay is Ghrelin
hunger stimulating hormone
Ghrelin makes u want to
eat
ghrelin is produced in
fundus
Types of gastric surgeries
- Roux-en-Y Gastric bypass (RYGB)
- Adjustable Gastric Band (AGB)
- Vertical Sleeve Gastrectomy (VSG)
- Biliopancreatic Diversion With a duodenal switch (BPD-DS)
- Biliopancreatic Diversion (BPD).
Different areas of the stomach are affected
