The document summarizes key aspects of the stomach's physiology including its structure, storage function, gastric juice production, motility, and emptying. The stomach has three sections - the fundus, body, and antrum. Food storage relies on receptive relaxation which increases stomach size through passive stretching and active mechanisms involving vagus nerve stimulation. Gastric juice contains hydrochloric acid, pepsin, mucus and other factors. Acid secretion involves parietal cells and is regulated by vagus nerve and hormones. Stomach motility mixes food and empties contents through contractions controlled by pacemaker cells. Emptying is promoted by gastric factors but inhibited by duodenal stretch, acidity, and hormones like CCK that

2. University of Bakht Alruda
Faculty of Medicine
Department of Physiology

3. Stomach

4. Contents
Storage of stomach
Gastric juice
Gastric motility
Gastric emptying

5. Stomach
Storage of food
 Three anatomic
divisions of the
stomach:
1. The fundus
2. The body
3. The antrum
Fundus
Body
antrum
Pyloric sphincter
Pylorus
Greater curvature
Lesser curvature

6. Storage of food
 When food enters the stomach, the fundus and upper portion
of the body relax and accommodate the food with little if any
increase in pressure (receptive relaxation).
 Intragastric pressure does not change as the volume of
stomach content is increased from (1/2 – 3 ) Liter
1 1.5 2 2.5 3
0.5 3.5 4 5
Liter
6 7
Intragastric
pressure
0
1
2
mmHg
(receptive relaxation

7. Storage of food
Receptive Relaxation
Passive mechanism Active mechanism

8. Storage of food
 Passive mechanism (plasticity)
increasing size of stomach

9. Active mechanism
vagal nerve
vagal nerve
vagovagal reflex
VIP

10. Active mechanism
 Mechanoreceptors detect distention of the
stomach and trigger vagovagal reflex
 vagovagal reflex, meaning that both afferent
and efferent limbs of the reflex are carried in
the vagus nerve
 The neurotransmitter released from these
postganglionic vagal nerve fibers is VIP
 VIP increases length of the muscle (increase
size of stomach)

11. Gastric juice
 Gastric juice
1. Gastric gland
2. Contents of Gastric juice
3. Mechanism of HCL secretion
4. Control of HCL secretion

12. neck cell
Parietal cell
chief cell
Gastric pits
1
2
3
Gastric pits

13. Gastric gland
 Gastric glands are found mainly in the fundus and
body of the stomach
 They are tubular glands each 3-7 glands open together
into the gastric pits
 Gastric pits open in lumen of the stomach
 Each gastric gland contains three type of cells:
1. Mucous producing cell (neck cell)
2. HCL producing cell (Parietal or oxyntic cell)
3. Proteolytic enzyme secreting cell (chief of peptic cell)

14. Contents of Gastric juice
 Gastric juice formed of:-
1. HCL
2. Pepsinogens
3. Gastric lipase
4. Intrinsic factors
5. Mucous

15. Contents of Gastric juice
 Hydrochloric acid
 Functions of HCL:-
1. Break connective tissue and muscle fiber e.g.
found in meat so it helps enzyme action
2. Activation of pepsinogen
3. Provide optimum PH for pepsin
4. Bactericidal properties
5. Help absorption of iron

16. Mechanism of HCL secretion
CO2
metabolism
ECF H2O
+
H2CO3
CL-
C.A
HCO3
H+
K+
CL-
K+
Parietal cell Canaliular Lumen
HCL

17.  Pepsinogens
 The are inactive precurors of pepsin
 Pepsinogens are activated by
1. HCL
2. Pepsin (Autocatalysis)
Contents of Gastric juice
Pepsin
Pepsinogens
Activated
converted

18.  Pepsinogens
 Optimum PH for pepsin is 1.8-3.5
 Pepsin hydrolysis protein into short chain
peptide
 They are endopeptidase and prefer to
break the peptide bond at phenylalanine
Contents of Gastric juice

19.  Gastric lipase
 This enzyme hydrolysis TAG
 It has optimum PH of 4-7
 It act mainly TAG with short chain FAA
.e.g. Butric acid found in Butter
 It is much less important than pancreatic
lipase
Contents of Gastric juice

20. Intrinsic factors
 This is secreted by parietal cell
 It is glycoprotein that combine with Vit-B12
 For protected its passage in small intestine
 It also help absorption Vit-B12 at the distal part of
ileum
 Deficiency of Vit-B12 causes megaloplastic anaemia
 This occur in atrophy of parietal cell or remove large
portion of the stomach
 In these cases the Vit-B12 should be given in an inject
able
Contents of Gastric juice

21.  Mucous
Contents of Gastric juice
HCO3 PH=7
Mucous
HCL Pepsin

22. Control of HCL secretion
 Control of HCL secretion can considered to occur in
three phases:-
1. Cephalic phase when food is present above the
stomach
2. Gastric phase when food is present at level the stomach
3. Intestinal phase when food is present in the intestine

23. smell
taste
sight
chewing
swallowing
Thinking
HCL
Gastrin
His
G cell
Parietal cell
ECL
HCL
HCL
Cephalic phase
About 20% of Gastric juice is produce during cephalic phase

24. Sham feeding
About 20% of Gastric juice is produce during cephalic phase

25. Gastric phase
 Gastric phase includes :-
1. Long pathway (vagovagal reflex )
2. Short pathway mediated by local nerve in stomach
wall
 Protein digestive products and other substance like
ethanol stimulate G cell to secrete Gastrin hormone
which increase HCL
 Such substance are known as secretogages

26. Gastric phase
vagovagal reflex
About 70% of Gastric juice is produce during Gastric phase

27. Intestinal phase
 About 10% of Gastric juice is produce during
intestinal phase
 In duodenum wall there are a large number of
scattered endocrine cells that secrete different
hormone
 Gastrin is produced by some of these cells and
therefore stimulates parietal cell to secrete HCL
 CCK is another hormone that has structural similarly
to Gastrin in small dose can stimulate Gastrin
receptor

28. Parietal cell
Gastrin hormone receptor
H2 receptor for His
Muscarinic receptor of Ach
Gastrin
Ach

29. H2
Parietal cell
Ca++
H+
K+
ATP
cAMP
K+
CL-

30. Gastric motility
 Purpose
1. Mixing food with gastric juice
2. Emptying of food into the duodenum
 Structure of the Stomach wall
 The stomach has three layers of muscle:
1. outer longitudinal layer
2. middle circular layer
3. inner oblique layer
 The thickness of the muscle wall increases from the
proximal stomach to the distal stomach.

31. Innervation of the Stomach
 The innervation of the stomach
includes
 Extrinsic innervation by the
autonomic nervous system
 Intrinsic innervation from the
myenteric and submucosal
plexuses.
 The myenteric plexus receives
parasympathetic innervation via
the vagus nerve and
sympathetic innervation via
fibers originating in the celiac
ganglion.
 vagus nerve release VIP and
Ach
Longitudinal
layer
Circular
layer
celiac ganglion.
Gastric motility
Parasymp. innervations
Symp. innervations

32.  The fundus + Body (Proximal Part) = Storage part
 The Body (Distal Part) + Pylorus = mixing movement
3 contraction /min
Gastric motility

33. Introduction (slow waves)
 Slow waves are a unique feature of the
electrical activity of gastrointestinal smooth
muscle.
 Slow waves are not action potentials, but
rather oscillating depolarization and
repolarization of the membrane potential of
the smooth muscle cells
 It is believed that slow waves originate in the
interstitial cells of Cajal (greater curvature),
which are abundant in the myenteric plexus.

34. threshold

35. ms
mV
separate contraction or twitch

36. ms
mV twitches summate
threshold

37. Slow waves (BER) reach to threshold by:-
 Ach (vagus nerve )
 Gastrin )G-cell)
Gastrin Hormone
1. Increasing force of contraction smooth
muscle
2. Increasing rate of contraction
3. Constricts LOS but relaxes pyloric sphincter
Slow waves (BER)

38. Ach (vagus nerve )
1. Increasing fore of contraction smooth muscle
2. Dose not increasing rate of contraction
Summary :vagus nerve
1.Increase size of stomach (VIP)
2.Mixing waves contraction (Ach)
Slow waves (BER)

39. Antral part of stomach have two function:-
1. Retropulsion
 most of the gastric contents are propelled back into
the antrum for further mixing and further reduction
of particle size
2. Empty of liquefied chyme
Gastric motility

40. Stomach Emptying

41. Regulation of
Stomach Emptying
Gastric
Factors
Duodenal
Factors
promote Emptying inhibite Emptying

42. Gastric Factors That Promote
Emptying
1. Emptying of the stomach is controlled by
stomach factors such as :-
 The degree of filling in the stomach
 The excitatory effect of gastrin on stomach
peristalsis.

44. -
celiac ganglion.
Osmoreceptors
Enterogastric reflex
osmolality
acidity
Chemoreceptors
distention
Stretch receptor

45. Duodenal Factors That Inhibit Stomach Emptying
 enterogastric inhibitory reflexes
 Stretch receptor → distension
 Osmorecptor → Osmolarity
 Chemoreceptors → Acidty
hormonal feedback by:-
 CCK → constriction of pyloric sphincter
 GIP → Decrease gastric motlitiy
 Secreting → Decrease gastric motlitiy

46. Stomach Emptying
Gastric Factors
(Promote Emptying)
Duodenal Factors
(Inhibit Emptying)
Gastrin
Volume& Liquids
food
enterogastric
inhibitory reflexes
distention
acidity
osmolality
Hormonal
CCK
GIP
Secretin

47.  Presence of fat and their digestive products in
duodenum delay gastric emptying
1. The effect of fat is mediated by CCK, which is
released when fatty acids arrive in the duodenum .
(CCK contracts pyloric sphincter )
2. The effect of fat is mediated by GIP which
decreasing gastric motility
3. Fat in duodenum activate local nerve network in
duodenal wall (increasing duodenal motility that
resist empty)
Stomach Emptying

48. Enterogastric (inhibitory) reflex
 A variety of stimuli act on the duodenum
to initiate enterogastric reflexes that slow
gastric emptying
 Purpose entrogastric reflexes prevent the
flow of chyme from exceeding ability of
intestine to handle it
 Causes High or low osmolality, low PH and
distension of duodenal wall all excite an
enterogastric reflex

49. References
Concise Human Physiology 2th Edition
Guyton Medical Physiology 11th Edition
Physiology by Costanzo
Physiology by Robert
NMS Physiology 3th Edition
Ganong Medical Physiology 23th Edition
Human Physiology The Mechanisms of
Body Function (9th ed).