Transcript gastric acid（HCl）

Digestion in the stomach
Gastric secretion and
regulation
Movement of stomach
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Stomach: a reservoir, mixing,
ingestion and empting
• gastric juice（acid）
• proteins (pepsins )
small
peptides
• absorption of little water
and alcohol
2
Secretion of gastric fluid
Composition and functions of gastric juice
endocrine： G cell — gastrin
D cell-SS (somatostatin)
enterochromaffin-like cell (ECL)-- histamine
cardiac
mucous cell：mucus HCO3 gland
Exocrine
pyloric
mucous cell：
Acidsecrete
gland
colorless、insipidity 、acidity(pH 0.9-
1.5)1.5-2.5L/day
G cell-gastrin
mucus HCO3 Neck mucous cell：mucus
parietal cell：HCI、intrinsic
factor
chief cell：pepsinogen
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Composition and functions of gastric juice
1、gastric acid（HCl）
1）volume ejection of gastric acid
acid secretion（mmol/H）
basic acid output ：on empty stomach
(after fasting overnight)（0-5）
maximal acid output：after food or chemicals
stimulation (20-25）
man> woman young >old
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Secretion of HCL
primary active transporter
parietal cell
antiport carrier
Function of HCL
1. activates pepsinogen, convert it into pepsin.
providing a medium of low pH favoring pepsin
action.
2. kills bacteria
3. promotes pancreatic secretion and
biliation, intestinal secretion.
4. promotes Fe++ and Ca++ absorption in initial
part of small intestine.
5. Degeneration of protein and facilitates digestion.
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proton pump
H+/K+ - ATPase
inactivator—omeprazole
Gastric ulcer
duodenal
ulcer
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2、Pepsinogen ----- precursor of pepsin
HCl and
self activation
pepsinogen
pepsin
protein
proteose, peptone
Ph2 — Ph 5
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3. Mucous-HCO3- barrier
Mucus is secreted by the stomach surface
cells，mucous neck cells，cardiac gland and
pyloric gland． It is strong viscous.
The surface mucous cells also secrete
HCO3- , It can neutralise with H+ from the
lumen of the stomach.
this structure and its function are called
Mucous-HCO3- barrier
Mucous protect mucosa against
mechanical injury by acid-pepsin and other
agent.
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Mucus bicarbonate barrier
Mucosal barrier:
Alcohol，Aspirin，
Epinephrin,
Helicobacter pylori.
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Helicobacter pylori
• For their discovery(1983) of bacterium
Helicobacter pylori and its role in gastritis
and peptic ulcer disease,
•In 2005, they won the Nobel Prize for
physiology.
Helicobacter pylori
• So,
• Awards word said, they are put a chronic
recurrent disease into a short term and
controllable disease in 2005 Nobel Prize
in physiology awards ceremony.
• Great！
4、Intrinsic factor: forming complex with B12,
allowing it to be absorbed in the terminal ileum. the
deficiency of it can cause the disease
macrocytic anemia
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Composition of gastric juice
HCL
pepsinogen
Mucous bicarbonate barrier
Intrinsic factor
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Regulation of gastric juice secretion
Endogenous substance
acting directly on parietal cells that stimulate
gastric secretion:
1. Acetylcholine (Ach):
release from nerve termination,
M3-receptor
Blocking agent --- atropine
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Regulation of gastric juice secretion
2. G cell
gastrin
Parietal cell
H2-receptor
3. ECL cell
histamine
(Enterochromaffin-like cell)
Blocking agent of H2- R：Cimetidine
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Inhibition of gastric secretion
G cell
Parietal cell
SS
(somatostatin)
ECL cell
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Regulation of gastric
secretion in different phase
The major physiological stimulant to
acid secretion is the ingestion of meal.
Gastric secretion after a meal can be
divided into three phases according to
stimulus location.
cephalic
phase
gastric
phase
intestinal phase
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Sham feeding
gastric fistula
esophageal fistula
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cephalic phase
• Sham feeding
• Conducted by Pavlov and his students in 1898
1) unconditional reflex and conditional reflex
2) relationship between the time of sham
feeding and the volume of gastric secretion in
cephalic phase
3) appetite related to cephalic phase of gastric
secretion
4) abolished by bilateral vagotomy
Abolished by bilateral vagotomy
Gastrin
HCL
pepsin
sectioning of the vagi abolishes
nervous reflex
mechanism∶
ⅠⅡⅧ
Vision smell
hearing
receptor
G cell
encephalic
nerves
Conditional
reflex
Sham feeding
oral pharynx
receptor
Ⅴ Ⅶ Ⅸ Ⅹ
nonconditional
reflex
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Ⅹ
Acidsecre
ting
gland
胃
gastric
液
juice
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Characteristics juice in cephalic phase
• Occupy 30% of total quantity of
digestive phase.
• Acidity and pepsin content are very
high.
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Characteristics juice in gastric phase
• Occupy 60% of total quantity of
digestive phase.
• But pepsin content lower than the
content of cephalic phase.
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regulatory mechanism of gastric phase
distension
chemical stimulus
food
long vagovagal reflexes
local enteric reflexes
G cell
Acidsecret
ing
gland
gastrin
gastric
juice
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Characteristics juice in intestinal phase
• Occupy 10% of total quantity of
digestive phase.
Gastrin、entero-oxyntin
• Small intestine
juice
gastric
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• The
acid
secretion
begins
immediately following a meal and
reaches to peak in one or two hours.
The three phases of secretion start
almost simultaneously and overlap
each other.
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Inhibitory regulation of gastric secretion
(1) acid inhibition
duodenum pH<2.5
secretin and bulbogastrone
Gastric antrum pH<1.2-1.5 G cell
Gastric acid
inhibition
D cell
This is a negative feedback mechanism
preventing overloading of the small intestine
with acid content.
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Inhibitory regulation of gastric secretion
(2) Fat inhibition
The inhibitory action of fat on
gastric secretion only be achieved
when fat entered into duodenum.
May be related to some humoral
factors such as enterogastrone.
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Inhibitory regulation of gastric secretion
(3) Hypertonic inhibition
Hypertonic
solution
Osmoreceptor
In intestine
Gastric
acid
Inhibitory
hormones
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Gastric Movement
Forms of movement
1．Receptive relaxation
1）concept：With each swallow of food, the bolus
stimulating the stretch receptors in the
pharynx and esophagus, the smooth muscle
relaxation of the fundus and body in stomach
by a reflex mediated by the vagus nerves.
2)Significance：With the intaking of food,
intragastric pressure retains invariable.
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2.Peristalsis：
Each wave begins in the body (middle part) of the
stomach and produces only a ripple as it spread down
the antrum at a rate of 3 per minute.
At the beginning, the wave is
too weak, but it gets more and
more powerful when it reaches
antrum. The pyloric sphincter
muscles contract upon arrival of
the wave. Only a small amount of
chyme is expelled into the
duodenum with each wave .
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Function of gastric peristalsis：
① mix the chyme with digestive juice
② grind food
③ push chyme gastric emptying
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（3）Migrating motor complex (MMC)
There is a very strong contraction
migrating from the upper to lower stomach
on an empty stomach, 1/90mins.
Significance: sweep the remainder of the stomach.
Gastric emptying and it’s regulation
1. Concept : A process of gastric contents
moving from stomach into duodenum.
2. Motivity
Food
enter
stomach
gastric motility
pyloric sphincter
muscle relax
intragastric pressure >
pressure in duodenum
Gastric emptying
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Effective factor of gastric emptying
The rate at which gastric contents pass into the
duodenum depends on their chemical and physical
characteristics.
1）Characteristics of food
Carbohydrate > protein > fat
finely ground > Coarse food
liquid > solid
isotonic solutions > greater or reduced
osmolality
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2）The promoting factors in stomach
The gastric factors that promote emptying.
chemical stimulus
emptying
mechanical
Vago-vagal reflex
stimulation of food
gastric
motility
G cell-gastrin
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3）the inhibitory factors in duodenum
secretory cell in
the mucosa
secretin
CCK(cholecystokinin )
emptying
Food
entero-gastric
reflexes
gastric motility
receptor in the wall
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• When food enters the duodenum,
multiple nervous reflexes are
initiated from the duodenal wall and
pass back to the stomach to slow or
even stop stomach empting as the
volume of chyme in the duodenum
becomes too much.
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(the inhibitory)
emptying
Entero-gastric Reflex
KEY POINTS
1. Receptive relaxation
2. Gastric emptying
3. Peristalsis
4. Composition and functions of gastric juice
5. The function of HCL.
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