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Figure 22.17 Neural and hormonal mechanisms that regulate release of gastric juice.

Lack ofstimulatoryimpulses toparasym-patheticcenter

Gastrinsecretiondeclines

Overridesparasym-patheticcontrols

Sympatheticnervoussystemactivation

Cerebralcortex

G cells

Emotionalstress

Excessiveacidity(pH < 2)in stomach

Loss ofappetite,depression

Entero-gastricreflex

Localreflexes

Pyloricsphincter

Vagalnucleiin medulla

Distensionof duodenum;presence offatty, acidic, orhypertonicchyme; and/orirritants inthe duodenum

Release ofenterogastrones(secretin, cholecystokinin,vasoactive intestinalpeptide)

Distension;presence offatty, acidic,partiallydigested foodin theduodenum

Intestinal(enteric)gastrinreleaseto blood

Briefeffect

Gastrinreleaseto blood

Vagusnerve

Vagusnerve

Conditioned reflex

Localreflexes

Vagovagalreflexes

G cells

Presence ofpartially digested foods in duodenumor distension of theduodenum when stomach begins to empty

Stimulate

Inhibit

Hypothalamusand medullaoblongata

Cerebral cortex

Medulla Stomachdistensionactivatesstretchreceptors

Food chemicals(especially peptides andcaffeine) and rising pHactivate chemoreceptors

Stimulation oftaste and smellreceptors

Sight and thoughtof food

1

1

2

1

2

1

2

1

2

1

Stimulatory events Inhibitory events

Cephalicphase

Gastricphase

Intestinalphase

Stomachsecretoryactivity

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Figure 22.17 Neural and hormonal mechanisms that regulate release of gastric juice.

Lack ofstimulatoryimpulses toparasym-patheticcenter

Gastrinsecretiondeclines

Overridesparasym-patheticcontrols

Sympatheticnervoussystemactivation

Cerebralcortex

G cells

Emotionalstress

Excessiveacidity(pH < 2)in stomach

Loss ofappetite,depression

Entero-gastricreflex

Localreflexes

Pyloricsphincter

Vagalnucleiin medulla

Distensionof duodenum;presence offatty, acidic, orhypertonicchyme; and/orirritants inthe duodenum

Release ofenterogastrones(secretin, cholecystokinin,vasoactive intestinalpeptide)

Distension;presence offatty, acidic,partiallydigested foodin theduodenum

Intestinal(enteric)gastrinreleaseto blood

Briefeffect

Gastrinreleaseto blood

Vagusnerve

Vagusnerve

Conditioned reflex

Localreflexes

Vagovagalreflexes

G cells

Presence ofpartially digested foods in duodenumor distension of theduodenum when stomach begins to empty

Stimulate

Inhibit

Hypothalamusand medullaoblongata

Cerebral cortex

Medulla Stomachdistensionactivatesstretchreceptors

Food chemicals(especially peptides andcaffeine) and rising pHactivate chemoreceptors

Stimulation oftaste and smellreceptors

Sight and thoughtof food

1

1

2

1

2

1

2

1

2

1

Stimulatory events Inhibitory events

Cephalicphase

Gastricphase

Intestinalphase

Stomachsecretoryactivity

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Figure 22.15b Microscopic anatomy of the stomach.

Enteroendocrine cell

Enlarged view of gastric pits andgastric glands

Chief cell

Parietal cell

Mucous neck cells

Surface epithelium (mucous cells)

Gastric pits

Gastricpit

Gastricgland

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Figure 22.15c Microscopic anatomy of the stomach.

Mitochondria

Parietal cell

Chief cell

Enteroendocrine cell

Location of the HCl-producing parietal cellsand pepsin-secreting chief cells in a gastricgland

HCIPepsinPepsinogen

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Figure 22.18 Mechanism of HCl secretion by parietal cells.

HCIParietal cell

Interstitialfluid

HCO3−- Cl−

antiporter

Alkalinetide

H+-K+

ATPase

Stomach lumenChief cell

Gastric gland

H+

K+

CO2 CO2 H2O

H2CO3

+

HCO3−

H+

K+

Carbonicanhydrase

HCO3−

Bloodcapillary

Cl− Cl− Cl−

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Figure 22.15c Microscopic anatomy of the stomach.

Mitochondria

Parietal cell

Chief cell

Enteroendocrine cell

Location of the HCl-producing parietal cellsand pepsin-secreting chief cells in a gastricgland

HCIPepsinPepsinogen

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Figure 22.16 Photographs of a gastric ulcer and the H. pylori bacteria that most commonly cause it.

A gastric ulcer lesion H. pylori bacteria

Bacteria

Mucosalayer ofstomach

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Figure 22.17 Neural and hormonal mechanisms that regulate release of gastric juice.

Lack ofstimulatoryimpulses toparasym-patheticcenter

Gastrinsecretiondeclines

Overridesparasym-patheticcontrols

Sympatheticnervoussystemactivation

Cerebralcortex

G cells

Emotionalstress

Excessiveacidity(pH < 2)in stomach

Loss ofappetite,depression

Entero-gastricreflex

Localreflexes

Pyloricsphincter

Vagalnucleiin medulla

Distensionof duodenum;presence offatty, acidic, orhypertonicchyme; and/orirritants inthe duodenum

Release ofenterogastrones(secretin, cholecystokinin,vasoactive intestinalpeptide)

Distension;presence offatty, acidic,partiallydigested foodin theduodenum

Intestinal(enteric)gastrinreleaseto blood

Briefeffect

Gastrinreleaseto blood

Vagusnerve

Vagusnerve

Conditioned reflex

Localreflexes

Vagovagalreflexes

G cells

Presence ofpartially digested foods in duodenumor distension of theduodenum when stomach begins to empty

Stimulate

Inhibit

Hypothalamusand medullaoblongata

Cerebral cortex

Medulla Stomachdistensionactivatesstretchreceptors

Food chemicals(especially peptides andcaffeine) and rising pHactivate chemoreceptors

Stimulation oftaste and smellreceptors

Sight and thoughtof food

1

1

2

1

2

1

2

1

2

1

Stimulatory events Inhibitory events

Cephalicphase

Gastricphase

Intestinalphase

Stomachsecretoryactivity

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Figure 22.14a Anatomy of the stomach.Cardia

EsophagusMuscularisexterna

Lessercurvature

DuodenumPyloric sphincter(valve) at pylorus

Pyloriccanal

Pyloricantrum

Greatercurvature

Rugae ofmucosa

Lumen

Body

Serosa

Fundus

• Oblique layer• Circular layer• Longitudinal layer

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Figure 22.19 Peristaltic waves in the stomach.

Pyloricvalveclosed

Pyloricvalveslightlyopened

Pyloricvalveclosed

Grinding: The most vigorous peristalsis and mixing action occur close to the pylorus.

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.

2 Propulsion: Peristaltic waves move from the fundus toward the pylorus.

1 3

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Greater omentum

Transverse colon

Transversemesocolon

Descending colon

MesenterySigmoid mesocolon

Jejunum

Sigmoid colon

Ileum

Figure 22.30c Mesenteries of the abdominal digestive organs.

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Figure 22.22a Structural modifications of the small intestine that increase its surface area for digestion and absorption.

Vein carryingblood tohepatic portalvessel

Musclelayers

Circularfolds

Villi

Lumen

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Figure 22.22b Structural modifications of the small intestine that increase its surface area for digestion and absorption.Microvilli(brush border)

Absorptivecells

VillusLacteal

GobletcellBloodcapillariesMucosa-associatedlymphoidtissueIntestinalcryptMuscularismucosae

Duodenalgland

Enteroendocrinecells

VenuleLymphatic vessel

Submucosa

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Figure 22.22c Structural modifications of the small intestine that increase its surface area for digestion and absorption.

Gobletcells

Absorptive cells

Villi

Intestinal crypt

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Figure 22.21 The duodenum of the small intestine, and related organs.

Right and left hepatic ducts of liver

Common hepatic ductBile duct and sphincterAccessory pancreatic duct

Tail of pancreasPancreasJejunum

Main pancreatic duct and sphincter

Head of pancreasHepatopancreaticampulla and sphincter Duodenum

Mucosawith folds

Gallbladder

Major duodenalpapilla

Cystic duct

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Chyme enter-ing duodenum causes duodenalenteroendocrine cells to release cholecystokinin(CCK) and secretin.

CCK (red dots) andsecretin (yellow dots) enter the bloodstream.

CCK inducessecretion of enzyme-richpancreatic juice. Secretin causes secretion of HCO3

− -rich pancreatic juice.

Bile salts and, to a lesser extent, secretintransported viabloodstream stimulate Liver to produce bile more rapidly.

CCK (via blood stream) causes gallbladder to contract and HepatopancreaticSphincter to relax. Bile Enters duodenum.

During cephalicand gastric phases,vagal Nerve stimu-lates gallbladder tocontract weakly.

CCK secretion

Secretin secretion

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3

4

5

6

Figure 22.28 Mechanisms promoting secretion and release of bile and pancreatic juice.

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Figure 22.29a Gross anatomy of the large intestine.

Right colic(hepatic) flexure

Transverse colon

Superiormesenteric artery

Ascending colonIIeum

IIeocecal valve

Cecum

Appendix

Left colic(splenic) flexureTransversemesocolon

Epiploicappendages

Descending colon

Cut edge ofmesenteryTenia coli

Sigmoid colon

RectumAnal canal External anal sphincter

Haustrum

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Figure 22.29b Gross anatomy of the large intestine.

Rectal valveRectumHemorrhoidalveins

Levator ani muscle

Anal canal

External analsphincterInternal analsphincterAnal columnsPectinate lineAnal sinuses

Anus

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Figure 22.31 Defecation reflex.

Impulses fromcerebral cortex(consciouscontrol)

Voluntary motornerve to externalanal sphincter

External analsphincter(skeletal muscle)

Sensorynerve fibers

Sigmoidcolon

Stretch receptors in wall

Involuntary motor nerve (parasympathetic division)Internal anal sphincter (smooth muscle)

Feces move into anddistend the rectum,stimulating stretch receptorsthere. The receptors transmitsignals along afferent fibersto spinal cord neurons.

A spinal reflex is initiated in whichparasympathetic motor (efferent) fibersstimulate contraction of the rectum andsigmoid colon, and relaxation of theinternal anal sphincter.

If it is convenient to defecate,voluntary motor neurons are inhibited,allowing the external anal sphincter to relax so feces may pass.

1

2

3

Rectum