Transcript Gastric Anatomy & Physiology

Gastric Anatomy & Physiology
Medical ppt
http://hastaneciyiz.blogspot.com
Anatomy
In adult life, stomach located T10 and
L3 vertebral segment
Can be divided into anatomic regions
based on external landmarks
4 regions
Cardia
Fundus
Corpus (body)
Antrum
Anatomy
Cardia- region just
distal to the GE
junction
Fundus- portion
above and to the left
of the GE junction
Anatomy
Corpus- region between
fundus and antrum
Margin not distinctly
external, has arbitrary
borders
Antrum- bounded
distally by the pylorus
Which can be
appreciated by palpation
of a thickened ring of
smooth muscle
Anatomy
Position of the
stomach varies with
body habitus
In general- it is fixed
at two points
Proximally at the GE
juction
Distally by the
retroperitoneal
duodenum
Anatomy
Anterior- in contact with Left
hemi-diaphragm, left lobe and
anterior segment of right lobe
of the liver and the anterior
parietal surface of the
abdominal wall
Posterior- Left diaphragm, Left
kidney, Left adrenal gland, and
neck, tail and body of pancreas
The greater curvature is near
the transverse colon and
transverse colon mesentery
The concavity of the spleen
contacts the left lateral portion
of the stomach
Vasculature
Vasculature
Well vascularized organ
Arterial flow mainly derived from Celiac Artery
3 Branches
Left Gastric Artery
Supplies the cardia of the stomach and distal esophagus
Splenic Artery
Gives rise to 2 branches which help supply the greater curvature
of the stomach
Left Gastroepiploic
Short Gastric Arteries
Common Hepatic or Proper Hepatic Artery
2 major branches
Right Gastric- supples a portion of the lesser curvature
Gastroduodenal artery
-Gives rise to Right Gastroepiploic artery
-helps supply greater curvature in conjunction
with Left Gastroepiploic Artery
Anatomy
Venous Drainage
Parallels arterial supply
Lymphatic drainage
Lymph from the proximal portion of the stomach drains along the lesser
curvature first drains into superior gastric lymph nodes surrounding the Left
Gastric Artery
Distal portion of lesser curvature drains through the suprapyloric nodes
Proximal portion of the greater curvature is supplied by the lymphatic
vessels that traverse the pancreaticosplenic nodes
Antral portion of the greater curvature drains into the subpyloric and
omental nodal groups
In general- The lymphatic drainage of the human stomach, like its
blood supply, exhibits extensive intramural ramifications and a number
of extramural communications. Therefore spread beyond is often
beyond region of origin at a distance from the primary lymphatic zone
Anatomy
Nerve Supply
Left and Right Vagus Nerves descend
parallel to the esophagus within the thorax
before forming a peri-esophageal plexus
between the tracheal bifurcation and the
diaphragm
From this plexus, two vagal trunks coalesce
before passing through the esophageal
hiatus of the diaphragm
Anatomy
Left (anterior) Vagus
Nerve
Left of the
esophagus
Branches
Hepatic Branch
Supplies liver
and Biliary
Tract
Anterior gastric or
Ant. Nerve of
Latarget
Anatomy
Right (posterior)
Vagus Nerve
Right of the
esophagus
Branches
Celiac
Posterior Latarget
Innervates
posterior
gastric wall
Anatomy
Parasympathetic innervation of
Stomach- Vagus Nerve
90% of fiber in vagal trunk is afferent (info
transmitting from stomach to CNS)
Sympathetic innervation of StomachSplanchnic Nerve
Derived from spinal segement T5-T10
Anatomy
Microscopic Anatomy
Glandular portions of stomach
Lined by simple columnar epithelium
This luminal surface is interrupted at intervals by gastric
pits
Opening into these gastric pits are one or more gastric
glands that have functional significance
Mucosa has three types of gastric glands
-Cardiac
-Oxyntic
-Antral
Microscopic Anatomy
Cardiac Glands
Location- Cardia
Contain mucous
Function- secrete
mucous (provides a
protective coat for lining
of stomach)
Oxyntic Glands
Most distinctive feature
of the stomach
Location- Fundus and
Corpus
Contains many cell types
Microscopic Anatomy
Parietal cells
Location- neck of gastric
pit
Stimulated by Ach,
Histamine and Gastrin
Secretes HCl + Intrinsic
Factor
Chief Cells
Location- base of gastric
pit
Stimulus- Vagal
Secretes Pepsinogen
(eventually leads to
pepsin- digestive
enzyme)
Microscopic Anatomy
Antral Glands
Gastrin cells
Location- mucosa of distal stomach
Stimulus- amino acids
Secretion- Gastrin (stimulates HCl production by way of
parietal cells)
Somatostatin
Location- mucosa of distal stomach + Duodenum
Stimulus- HCl or low pH in duodenum
Actions- Inhibits gastric emptying, Pancreatic secretions,
and gallbladder contraction
Physiology
The stomach contains a number of
biologically active peptides in nerves and
endocrine cells
Ex. Gastrin, somatostatin, vasoactive intestinal
peptide (VIP), substance P, and glucagon, etc
The two peptides of greatest importance to
human disease and clinical surgery are
Gastrin
Somatostatin
Physiology
Gastrin
Most important stimulus is a meal
amino acids that results from proteolysis
Fat and carbohydrates are not stimuli for gastrin
secretion
Gastric distention that occurs from a meal will stimulate
cholinergic neurons thereby releasing gastrin
Gastrin will then prompt Parietal cell to secrete HCl
Once Gastric distention diminishes, VIP-containing
neurons are activated causing stimulation of
somatostatin, thus attenuating Gastrin secretion
Overall, a lumen pH >3.0 will potentiate gastrin
release, whereas a pH <3.0 will inhibit its release
Physiology
Somatostain
Like Gastrin, plays an integral role in gastric
physiology
Also, used for important therapeutic applications
in treatment of digestive diseases
Main stimulus is a low or acidic (<3.0)luminal pH
Many peptides have shown to release somatostatin
Ex. Secretin, Cholecystokinin and gastrin
In contrast, stimulation of Vagal nerves along with
cholinergic neurons inhibit somatostatin
Overall, the most important gastric function of
somatostatin is to regulate acid secretion and
gastrin release
Gastric Acid Secretion
Gastric Acid Secretion
Basolateral membrane of the parietal cell
contains specific receptors for the three major
stimulants of acid production
Histamine
Gastrin
Acetylcholine
Each stimulant has its own 2nd messenger
system which allows for stimulation of the
parietal cell
Gastric Acid Secretion
Humans normally secrete 2 to 5 mEq/h of HCl
in the fasting state, constituting basal acid
secretion
Both Vagal tone and ambient Histamine secretion
are presumed to regulate basal acid secretion
Gastrin is not thought to play a role in basal acid
secretion
Therefore, a Vagotomy or use of H2 blockers (ex.
Cimetidine) will decrease basal acid production
Gastric Acid Secretion
Stimulated acid secretion begins with
Cephalic phase
Thought, sight or smell of food stimulates acid
secretion
Mediated by Vagal stimulation
Vagal discharge
Directs the cholinergic mechanism for stimulation
Can be inhibited by Atropine (anticholinergic)
Inhibits release of somatostatin
Vagal effects inhibit tonic inhibition that is
provided by somatostatin
Gastric Acid Secretion
Gastric Phase
Begins when food enters the stomach
The following are responsible for stimulation of acid
secretion
Presence of partially hydrolyzed food constituents
Gastric distention
Gastrin is the most important mediator of this phase
Ends when Antral muscosa is exposed to acid
When luminal pH is <2.0 in the antrum, gastrin release
stops
Somatostatin release is increased
Entry of digestive products into the intestine begins the
intestinal-phase inhibition of gastric acid secretion
Gastric Acid Secretion
Intestinal Phase
Also, releases HCl by way of Gastrin
Releases secretin to inhibit Gastrin which
ultimately decreases Acid production
Other Factors
Pepsin
Secreted from gastric chief cells
Contributes to the overall coordination of
the digestive process
Main function is to initiate protein
digestion, usually is incomplete
Partially hydrolyzed protein by pepsin are
important signals for release of
Gastrin
Cholecystokinin
Other Factors
Intrinsic Factor (IF)
Located in the parietal cells (oxyntic gland)
Main function is to absorb cobalamin
(Vitamin B12) form ileal mucosa and then
transported to the liver
Secretion of IF is similar to acid secretion
stimulated
Ach
Histamine
Gastrin
Other Factors
Bicarbonate
Secreted from the gastric
mucosa
Theory is that bicarbonate is
secreted to maintain a
neutral pH at the mucosal
surface, even if acidic in
lumen
Cholinergic agonist, vagal
nerve stimulation have been
shown to increase gastric
bicarbonate production
Gastric Motility
To understand gastric motility the stomach is divided
into two functional terms as two different regions
which have distinctive smooth muscle
Proximal 1/3
3 layers of smooth muscle
Outer longitudinal
Middle Circular
Inner Oblique
Distal 2/3
Only a distinctive outer longitudinal layer
Gastric smooth muscle ends at the pylorus, a septum
of connective tissue marks the change from pylorus
to the duodenum
Gastric Motility
Proximal 1/3
Have prolonged and tonic gastric contractions
No action potentials or pacesetter
Thus no peristalsis
Distal 2/3
In general, gastric smooth muscle exhibit
myoelectric activity based on a highly regular
pattern, called slow waves
Slow waves set a maximum rate at which contrations can
occur (3 contractions/min); they do not cause
contractions
Gastric Motility
Contraction occur when action potential
are phase locked with a crest of a slow
wave pattern
When an action potential is combined with
a pacesetter potential (partially depolarized
smooth muscle cells) a ring of smooth
muscle cell contraction moves with
peristalsis
Coordination of Contraction
Receptive Relaxation
Vagally mediated relaxation of fundus (proximal
stomach) when degluttination occurs
Allows the proximal stomach to act as a storage
site for ingested food in the immediate
postprandial period
Meal is accepted without a significant increase in intragastric pressure
Soon proximal contractile activity increases eventually
leading to compressive movement of gastric content
form fundus to antrum
Coordination of Contraction
Food enters antrum
Food peristaltically propelled toward the pylorus
Pylorus closes before the antral contraction
This coordinated closing allows for small bolus of liquid
and food particles to pass, while the main bulk of the
gastric content undergoes retropulsion back into the
antrum
Next, there is a churning action in the antrum that
mixes the ingested food particle, gastric acid and
pepsin
Solid food particles >1mm will not pass through the
pylorus
Coordination of Contraction
Overall, Liquids are empty more quickly than solid
Liquids empty exponentially
Solids endure this “lag period” or antral contraction (empties
linearly)
In general
Proximal stomach is the dominant force in determining liquid
emptying based on the gastroduodenal pressure gradient
generated by proximal gastric contractions
Distal stomach is postulated as controlling emptying of solids
through its grinding and peristaltic actions
Medical ppt
http://hastaneciyiz.blogspot.com