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Figure 22.17 Neural and hormonal mechanisms that regulate release of gastric juice.
Inhibitory events
Stimulatory events
Cephalic
phase
1 Sight and thought
of food
Cerebral cortex
Conditioned reflex
2 Stimulation of
taste and smell
receptors
Gastric
phase
1 Stomach
distension
activates
stretch
receptors
Hypothalamus
and medulla
oblongata
Vagovagal
reflexes
Intestinal
phase
Stimulate
Inhibit
© 2014 Pearson Education, Inc.
Vagus
nerve
Vagus
nerve
Local
reflexes
2 Food chemicals
(especially peptides and
caffeine) and rising pH
activate chemoreceptors
1 Presence of
partially digested
foods in duodenum
or distension of the
duodenum when
stomach begins to
empty
Medulla
Lack of
stimulatory
impulses to
parasympathetic
center
G cells
Intestinal
(enteric)
gastrin
release
to blood
Gastrin
release
to blood
Gastrin
secretion
declines
G cells
Overrides
parasympathetic
controls
Sympathetic
nervous
system
activation
1 Loss of
appetite,
depression
1 Excessive
acidity
(pH < 2)
in stomach
2 Emotional
stress
Stomach
secretory
activity
Enterogastric
reflex
Brief
effect
Cerebral
cortex
Local
reflexes
Vagal
nuclei
in medulla
Pyloric
sphincter
Release of
enterogastrones
(secretin, cholecystokinin,
vasoactive intestinal
peptide)
1 Distension
of duodenum;
presence of
fatty, acidic, or
hypertonic
chyme; and/or
irritants in
the duodenum
2 Distension;
presence of
fatty, acidic,
partially
digested food
in the
duodenum
Figure 22.17 Neural and hormonal mechanisms that regulate release of gastric juice.
Inhibitory events
Stimulatory events
Cephalic
phase
1 Sight and thought
of food
Cerebral cortex
Conditioned reflex
2 Stimulation of
taste and smell
receptors
Gastric
phase
1 Stomach
distension
activates
stretch
receptors
Hypothalamus
and medulla
oblongata
Vagovagal
reflexes
Intestinal
phase
Stimulate
Inhibit
© 2014 Pearson Education, Inc.
Vagus
nerve
Vagus
nerve
Local
reflexes
2 Food chemicals
(especially peptides and
caffeine) and rising pH
activate chemoreceptors
1 Presence of
partially digested
foods in duodenum
or distension of the
duodenum when
stomach begins to
empty
Medulla
Lack of
stimulatory
impulses to
parasympathetic
center
G cells
Intestinal
(enteric)
gastrin
release
to blood
Gastrin
release
to blood
Gastrin
secretion
declines
G cells
Overrides
parasympathetic
controls
Sympathetic
nervous
system
activation
1 Loss of
appetite,
depression
1 Excessive
acidity
(pH < 2)
in stomach
2 Emotional
stress
Stomach
secretory
activity
Enterogastric
reflex
Brief
effect
Cerebral
cortex
Local
reflexes
Vagal
nuclei
in medulla
Pyloric
sphincter
Release of
enterogastrones
(secretin, cholecystokinin,
vasoactive intestinal
peptide)
1 Distension
of duodenum;
presence of
fatty, acidic, or
hypertonic
chyme; and/or
irritants in
the duodenum
2 Distension;
presence of
fatty, acidic,
partially
digested food
in the
duodenum
Figure 22.15b Microscopic anatomy of the stomach.
Gastric pits
Surface epithelium
(mucous cells)
Gastric
pit
Mucous neck cells
Parietal cell
Gastric
gland
Chief cell
Enteroendocrine cell
© 2014 Pearson Education, Inc.
Enlarged view of gastric pits and
gastric glands
Figure 22.15c Microscopic anatomy of the stomach.
Pepsinogen
HCI
Pepsin
Mitochondria
Parietal cell
Chief cell
Enteroendocrine
cell
Location of the HCl-producing parietal cells
and pepsin-secreting chief cells in a gastric
© 2014 Pearson Education, Inc.
gland
Figure 22.18 Mechanism of HCl secretion by parietal cells.
Gastric gland
Blood
capillary
CO2
Chief cell
Stomach lumen
CO2 + H2O
H+-K+
ATPase
H2CO3
Carbonic
anhydrase
H+
K+
HCO3−
Alkaline
tide
Parietal cell
H+
K+
HCI
HCO3−
Cl−
Interstitial
fluid
© 2014 Pearson Education, Inc.
HCO3−- Cl−
antiporter
Cl−
Cl−
Figure 22.15c Microscopic anatomy of the stomach.
Pepsinogen
HCI
Pepsin
Mitochondria
Parietal cell
Chief cell
Enteroendocrine
cell
Location of the HCl-producing parietal cells
and pepsin-secreting chief cells in a gastric
© 2014 Pearson Education, Inc.
gland
Figure 22.16 Photographs of a gastric ulcer and the H. pylori bacteria that most commonly cause it.
Bacteria
Mucosa
layer of
stomach
A gastric ulcer lesion
© 2014 Pearson Education, Inc.
H. pylori bacteria
Figure 22.17 Neural and hormonal mechanisms that regulate release of gastric juice.
Inhibitory events
Stimulatory events
Cephalic
phase
1 Sight and thought
of food
Cerebral cortex
Conditioned reflex
2 Stimulation of
taste and smell
receptors
Gastric
phase
1 Stomach
distension
activates
stretch
receptors
Hypothalamus
and medulla
oblongata
Vagovagal
reflexes
Intestinal
phase
Stimulate
Inhibit
© 2014 Pearson Education, Inc.
Vagus
nerve
Vagus
nerve
Local
reflexes
2 Food chemicals
(especially peptides and
caffeine) and rising pH
activate chemoreceptors
1 Presence of
partially digested
foods in duodenum
or distension of the
duodenum when
stomach begins to
empty
Medulla
Lack of
stimulatory
impulses to
parasympathetic
center
G cells
Intestinal
(enteric)
gastrin
release
to blood
Gastrin
release
to blood
Gastrin
secretion
declines
G cells
Overrides
parasympathetic
controls
Sympathetic
nervous
system
activation
1 Loss of
appetite,
depression
1 Excessive
acidity
(pH < 2)
in stomach
2 Emotional
stress
Stomach
secretory
activity
Enterogastric
reflex
Brief
effect
Cerebral
cortex
Local
reflexes
Vagal
nuclei
in medulla
Pyloric
sphincter
Release of
enterogastrones
(secretin, cholecystokinin,
vasoactive intestinal
peptide)
1 Distension
of duodenum;
presence of
fatty, acidic, or
hypertonic
chyme; and/or
irritants in
the duodenum
2 Distension;
presence of
fatty, acidic,
partially
digested food
in the
duodenum
Figure 22.14a Anatomy of the stomach.
Cardia
Fundus
Esophagus
Muscularis
externa
• Longitudinal layer
• Circular layer
• Oblique layer
Serosa
Body
Lumen
Lesser
curvature
Rugae of
mucosa
Greater
curvature
Duodenum
© 2014 Pearson Education, Inc.
Pyloric sphincter
(valve) at pylorus
Pyloric
canal
Pyloric
antrum
Figure 22.19 Peristaltic waves in the stomach.
Pyloric
valve
closed
1 Propulsion: Peristaltic
waves move from the fundus
toward the pylorus.
© 2014 Pearson Education, Inc.
Pyloric
valve
closed
2
Grinding: The most
vigorous peristalsis and mixing
action occur close to the pylorus.
Pyloric
valve
slightly
opened
3
Retropulsion: The pyloric end of
the stomach acts as a pump that
delivers small amounts of chyme into
the duodenum, simultaneously forcing
most of its contained material backward
into the stomach.
Figure 22.30c Mesenteries of the abdominal digestive organs.
Greater omentum
Transverse colon
Transverse
mesocolon
Descending colon
Jejunum
Mesentery
Sigmoid
mesocolon
Sigmoid colon
Ileum
© 2014 Pearson Education, Inc.
Figure 22.22a Structural modifications of the small intestine that increase its surface area for digestion and absorption.
Vein carrying
blood to
hepatic portal
vessel
Muscle
layers
Circular
folds
Villi
© 2014 Pearson Education, Inc.
Lumen
Figure 22.22b Structural modifications of the small intestine that increase its surface area for digestion and absorption.
Microvilli
(brush border)
Absorptive
cells
Lacteal
Villus
Goblet
cell
Blood
capillaries
Mucosaassociated
lymphoid
tissue
Intestinal
crypt
Muscularis
mucosae
Duodenal
gland
© 2014 Pearson Education, Inc.
Enteroendocrine
cells
Venule
Lymphatic vessel
Submucosa
Figure 22.22c Structural modifications of the small intestine that increase its surface area for digestion and absorption.
Absorptive cells
Goblet
cells
Villi
© 2014 Pearson Education, Inc.
Intestinal crypt
Figure 22.21 The duodenum of the small intestine, and related organs.
Right and left
hepatic ducts
of liver
Cystic duct
Common hepatic duct
Bile duct and sphincter
Accessory pancreatic duct
Mucosa
with folds
Tail of pancreas
Pancreas
Jejunum
Gallbladder
Major duodenal
papilla
Hepatopancreatic
ampulla and sphincter
© 2014 Pearson Education, Inc.
Main pancreatic duct and sphincter
Duodenum
Head of pancreas
Figure 22.28 Mechanisms promoting secretion and release of bile and pancreatic juice.
1 Chyme enter
-ing duodenum
causes duodenal
enteroendocrine
cells to release
cholecystokinin
(CCK) and
secretin.
2 CCK (red
dots) and
secretin (yellow
dots) enter the
bloodstream.
3 CCK induces
secretion of
enzyme-rich
pancreatic juice.
Secretin causes
secretion of
HCO3− -rich
pancreatic juice.
© 2014 Pearson Education, Inc.
4 Bile salts and,
to a lesser extent,
secretin
transported via
bloodstream
stimulate Liver to
produce bile more
rapidly.
5 CCK (via
blood stream) causes
gallbladder to
contract and
Hepatopancreatic
Sphincter to
relax. Bile Enters
duodenum.
6 During cephalic
and gastric phases,
vagal Nerve stimulates gallbladder to
contract weakly.
CCK secretion
Secretin secretion
Figure 22.29a Gross anatomy of the large intestine.
Left colic
(splenic) flexure
Transverse
mesocolon
Right colic
(hepatic) flexure
Transverse colon
Epiploic
appendages
Superior
mesenteric artery
Haustrum
Descending colon
Ascending colon
IIeum
Cut edge of
mesentery
IIeocecal valve
Tenia coli
Sigmoid colon
Cecum
Appendix
Rectum
Anal canal
© 2014 Pearson Education, Inc.
External anal sphincter
Figure 22.29b Gross anatomy of the large intestine.
Rectal valve
Rectum
Hemorrhoidal
veins
Levator ani muscle
Anal canal
External anal
sphincter
Internal anal
sphincter
Anal columns
Pectinate line
Anal sinuses
Anus
© 2014 Pearson Education, Inc.
Figure 22.31 Defecation reflex.
Impulses from
cerebral cortex
(conscious
control)
Sensory
nerve fibers
Voluntary motor
nerve to external
anal sphincter
Sigmoid
colon
Rectum
External anal
sphincter
(skeletal muscle)
Stretch receptors in wall
2 A spinal reflex is initiated in which
parasympathetic motor (efferent) fibers
stimulate contraction of the rectum and
sigmoid colon, and relaxation of the
internal anal sphincter.
Involuntary motor nerve
(parasympathetic division)
Internal anal sphincter (smooth muscle)
3 If it is convenient to defecate,
voluntary motor neurons are inhibited,
allowing the external anal sphincter to
relax so feces may pass.
© 2014 Pearson Education, Inc.
1 Feces move into and
distend the rectum,
stimulating stretch receptors
there. The receptors transmit
signals along afferent fibers
to spinal cord neurons.