Stomach Flashcards
What level does the oesophagus passes through the oesophageal hiatus
T10
What does the muscle around the oesophagus hiatus function as
Sphincter
How long is the abdominal segment of the oesophagus
Less than 2cm
What is the distal oesophagus supplied by
Branches of the left gastric artery
What is the drainage of the distal oesophagus
Systemic system of veins
Via oesophageal veins that drains into the azygos vein
To portal venous system
Via the left gastric veins
What is the distal oesophagus a site of
Portosystemic anastomoses
What does the stomach chemically and mechanically break food down to
Chyme
What are the four parts of the stomach
Cardia
Fundus
Body
Pylorus
What is the oesophagus continuous with
Cardia of stomach
What is the most superior part of the stomach
Fundus
What is the largest part of the stomach
Body
What is the most distal part of the stomach
Pyloric part
What is the area of the pyloric part
Pyloric antrum
Pyloric canal - contains pyloric sphincter
What is the role of the pyloric sphincter
Circular smooth muscle
Regulates the passe if chyme into the duodenum
What is the right border of the stomach called
Lesser curvature
What is the left border of the stomach called
Greater curvature
Where does the stomach lie
Left upper quadrant
What is the stomach covered by
visceral peritoneum
What is the anterior surface of the stomach related to
Anterior abdominal wall
Diaphragm
Left lobe of the liver
What is the posterior surface of the stomach related to
Forms the anterior wall of the lesser sac
What does the lesser omentum connect
Lesser curvature to the liver
What does the free edge of lesser omentum contain
Hepatic artery
Hepatic portal vein
Bile duct
What is posterior to the free edge entrance to
Lesser sac
What does the greater omentum hang from
Greater curvature
What is the stomach supplied by
Branches of the coeliac trunk
Where are G-cells located
Pyloric antra mucosa
What do G-cells produce
Gastrin
What are G-cells activated by
Vagus nerve - Ach (M3R)
What stimulates G-cells
Partially digested proteins
How does Gastrin travel
Hormone through the blood
Where are Parietal cells located
Fundus
What do parietal cells contain a lot of
Mitochondria
What happens with parietal cells
Mitochondria - respiration produces a lot of CO2
CO2 + H20 = H2CO3- = H+ + HCO3-
H+ goes into stomach lumen
HCO3- goes in to blood
What is the enzyme involves in the bicarbonate reaction within the parietal cells
Carbonic anhydrase
What do parietal cells produce
HCl
How is Hydrogen transported out of parietal cells
By H+K+ ATPase pump
What acts on parietal cells
Somatostatin -
Ach +
Histamines +
Gastrin +
PEG2 +
What acts on chief cells and how
Gastrin
increases Ca2+
Vesicle fuses with membrane
Releases pepsinogen
What do chief cells secrete
Pepsinogen
Where are the chief cells located
Fundus
Is pepsinogen active or inactive
Inactive
What is the active form of pepsinogen
Pepsin
How does pepsinogen become active
pH 1.8-3.5
What acts on chief cells
Gastrin +
Histamine +
Ach +
Secretin +
When is secretin released
S-cells in duodenum
To high acidic/fatty chyme
What to antral-D cells respond to
High H+ concentration on outside of cell
What do antral-D cells release
Somatostatin
What is the role of somatostatin
Act on G-cells
Inhibit release of gastrin - to decrease pH
What acts on Antral-D cells
Ach -
Gastrin -
Where are Antral-D cells located
Antrum and Body
What do enterochromaffin like cells secrete
Histamine
What acts on enterochromaffin like cells
Ach +
Somatostatin -
Gastrin +
What are the cells of the stomach
G-cells
Parietal cells
Chief cells
Antral-D cells
Enterochromaffin like cells
Where are enterochromaffin like cells located
Fundus
Cardia
What cell secretes gastrin
G-cells
Enteroendrocrine cells
What cell secretes HCL (h+ and Cl-)
Parietal cells
What cell secretes pepsinogen
Chief cell
What cell secretes somatostatin
Antral-D cells
What cell secretes histamine
Enterochromaffin like cells
What does the body of the stomach secrete
Mucus, pepsinogen and HCl
What does the antrum of the stomach secrete
Mucus, pepsinogen and gastrin
What do mucus cells secrete
Mucous
What cell secrete intrinsic factor
Parietal cell
How much hydrochloric acid is secreted a day
Approx 2 litres
What is gastric acid secretion dependent upon
Energy
What is the concentration of HCl in gastric acid
> 150 mM
Describe the cephalic phase
Turning it on
Parasympathetic NS
Sight, smell, taste of food and chewing
ACh released
ACh acts directly on parietal cells
ACh triggers release of gastrin and histamine
Net effect = increased acid production
Describe the gastric phase
Turning it on
Gastric distension, presence of peptides and amino acids
Gastrin release
Gastrin acts directly on parietal cells
Gastrin triggers release of histamine
Histamine acts directly on parietal cells
Net effect = increased acid production
Describe what happens with proteins in the stomach
Turning it on
Direct stimulus for gastrin release
Proteins in lumen act as a buffer, mopping up H+ ions, causing pH to rise
- decreased secretion of somatostatin
- more parietal cell activity (lack of inhibition)
Describe the turning it off gastric phase
Low luminal pH (high H+)
Directly inhibits gastric secretion
Indirectly inhibits histamine release (via gastrin)
Stimulates somatostatin release which inhibits parietal cell activity
Describe the intestinal phase
Turning it off
In duodenum
- duodenal distension
- low luminal pH
- hypertonic luminal contents
- presence of amino acids and fatty acids
Trigger release of enterogastrones
- secretin (inhibits gastrin release, promotes somatostatin release)
- CCK - cholecystokinin
Short and long neural pathways - reducing Ach release
What is the role of secretin (interstitial phase)
Inhibits gastrin release
Promotes somatostatin release
What is involved in the gastric acid secretion
1 PNs neurotransmitter Ach
1 hormone - gastrin
2 paracrine factors - histamine +, somatostatin -
2 key enterogastrones - secretin -, CCK -
What are the ways in which gastric mucosa defends itself
Alkaline mucus
Tight junctions between epithelial cells
Replacement of damaged cells
Feedback loops
What is the conversion of pepsinogen dependent upon
pH
When is the conversion of pepsinogen to pepsin most efficient
pH <2
What type of feedback loop is the conversion of pepsinogen to pepsin
Positive
Pepsin catalyses the reaction
When is pepsin active
Only at low pH
Irreversible inactivation in small intestine by HCO3-
Is protein digestion dependent upon pepsin
No
Accelerates protein digestion
What % does the role of pepsin in protein digestion account to
Approx. 20%
What does pepsin do
Breaks down collagen in meat - helps shred meat into small pieces with greater surface area for digestion
Describe receptive relaxation
Mediated by PNS acting on enteric nervous plexus
Afferent input via Vagus nerve
Nitric oxide and serotonin released by enteric nerves mediate relaxation
Where do peristaltic waves begin
Gastric body - weak contraction
Where are peristaltic waves more powerful
Gastric antrum
What happens to chyme
Little chyme enters duodenum
Antral contents forced back towards body (mixing)
Describe the basic electrical rhythm for gastric motility
Frequency determined by pacemaker cells in muscularis propria
3/minute
Pacemaker cells undergo slow depolarisation - repolarisation cycles
Depolarisation waves transmitted through gap junctions to adjacent smooth muscle cells
Do not cause significant contraction in empty stomach
Gastric motility what happens if there are more action potentials
The strength of smooth muscle tension and time will increase
What is the strength of peristaltic contractions increased by
Gastrin
Gastric distension
What respond to gastric distension
Mechanoreceptors
What is the strength of peristaltic contractions decreased by
Duodenal distension
Increased duodenal luminal fat
Increased duodenal osmolarity
Decreased luminal pH
Increased sympathetic NS action
Decreased parasympathetic NS action
Describe protease activation
Chief cell secretes pepsinogen
Parietal cell secretes HCl (+ intrinsic factor)
HCl facilitates the activation of pepsinogen to pepsin
Pepsin breaks down proteins to peptides
Describe protease secretion
Chief cells produce pepsinogen
Synthesised in inactive form (zymogen)
Pepsinogen mediated by input from enteric NS (ACh)
Secretion parallels HCl secretion
Luminal activation
What is the blood supply to the stomach
Coeliac trunk
Where does the coeliac trunk leave the aorta
T12
What are the three branches of the coeliac trunk
Left gastric artery
Common hepatic artery
Splenic artery
Where do the left and right gastric arteries run
Lesser curvature of the stomach and anastomose with each other
Where does the left gastric artery arise from
Coeliac trunk
Where does the right gastric artery arise from
Common hepatic artery
Where do the left and right gastro-omental (gastroepiploic) arteries run
Greater curvature of the stomach and anastomose with each other
Where does the left gastro-omental artery arise from
Splenic artery
Where does the right gastro-omental artery arise from
Gastroduodenal artery - branch of the common hepatic artery
What provides parasympathetic fibre to stomach
Vagus nerve
What does parasympathetic stimulation to the stomach promote
Peristalsis and gastric secretion
What provides sympathetic fibres to the stomach
Greater splanchnic nerve
Where does the greater splanchnic nerve leave the spinal cord
Preganglionic fibres
T5-T9
