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prepared by Vince Austin,
Bluegrass Technical
and Community College
CHAPTER
Elaine N. Marieb
Katja Hoehn
23
PART B
Human
Anatomy
& Physiology
SEVENTH EDITION
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
The Digestive
System
Pharynx

From the mouth, the oro- and laryngopharynx
allow passage of:

Food and fluids to the esophagus

Air to the trachea

Lined with stratified squamous epithelium and
mucus glands

Has two skeletal muscle layers

Inner longitudinal

Outer pharyngeal constrictors
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Esophagus

Muscular tube going from the laryngopharynx to
the stomach

Travels through the mediastinum and pierces the
diaphragm

Joins the stomach at the cardiac orifice
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Esophagus
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.12
Esophageal Characteristics

Esophageal mucosa – nonkeratinized stratified
squamous epithelium

The empty esophagus is folded longitudinally and
flattens when food is present

Glands secrete mucus as a bolus moves through
the esophagus

Muscularis changes from skeletal (superiorly) to
smooth muscle (inferiorly)
PLAY
InterActive Physiology®:
Secretion, page 6
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Digestive Processes in the Mouth

Food is ingested

Mechanical digestion begins (chewing)

Propulsion is initiated by swallowing

Salivary amylase begins chemical breakdown of
starch

The pharynx and esophagus serve as conduits to
pass food from the mouth to the stomach
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Deglutition (Swallowing)


Coordinated activity of the tongue, soft palate,
pharynx, esophagus, and 22 separate muscle
groups
Buccal phase – bolus is forced into the oropharynx
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Deglutition (Swallowing)
Pharyngeal-esophageal phase – controlled by the
medulla and lower pons


All routes except into the digestive tract are sealed
off
Peristalsis moves food through the pharynx to the
esophagus
PLAY
InterActive Physiology®:
Motility, pages 4-5
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Bolus of food
Tongue
Uvula
Pharynx
Epiglottis
Bolus
Epiglottis
Glottis
Esophagus
Trachea
(a) Upper esophageal
sphincter contracted
Bolus
(b) Upper esophageal
sphincter relaxed
Relaxed
muscles
Bolus of
food
Longitudinal
muscles
contract,
shortening
passageway
ahead of bolus
Gastroesophageal
sphincter closed
(d)
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(c) Upper esophageal
sphincter contracted
Circular muscles
contract,
constricting
passageway
and pushing
bolus down
Relaxed
muscles
Gastroesophageal
sphincter open
Stomach
(e)
Figure 23.13
Deglutition (Swallowing)
Bolus of food
Tongue
Pharynx
Epiglottis
Glottis
Trachea
(a) Upper esophagea
sphincter contracted
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.13
Deglutition (Swallowing)
Uvula
Bolus
Epiglottis
Esophagus
(b) Upper esophageal
sphincter relaxed
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.13
Deglutition (Swallowing)
Bolus
(c) Upper esophageal
sphincter contracted
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.13
Deglutition (Swallowing)
Relaxed
muscles
Bolus of
food
Longitudinal
muscles
contract,
shortening
passageway
ahead of bolus
Gastroesophageal
sphincter closed
Circular muscles
contract,
constricting
passageway
and pushing
bolus down
Stomach
(d)
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.13
Deglutition (Swallowing)
Relaxed
muscles
Gastroesophageal
sphincter open
(e)
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.13
Bolus of food
Tongue
Uvula
Pharynx
Epiglottis
Bolus
Epiglottis
Glottis
Esophagus
Trachea
(a) Upper esophageal
sphincter contracted
Bolus
(b) Upper esophageal
sphincter relaxed
Relaxed
muscles
Bolus of
food
Longitudinal
muscles
contract,
shortening
passageway
ahead of bolus
Gastroesophageal
sphincter closed
(d)
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
(c) Upper esophageal
sphincter contracted
Circular muscles
contract,
constricting
passageway
and pushing
bolus down
Relaxed
muscles
Stomach
(e)
Figure 23.13
Stomach






Chemical breakdown of proteins begins and food
is converted to chyme
Cardiac region – surrounds the cardiac orifice
Fundus – dome-shaped region beneath the
diaphragm
Body – midportion of the stomach
Pyloric region – made up of the antrum and canal
which terminates at the pylorus
The pylorus is continuous with the duodenum
through the pyloric sphincter
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Stomach




Greater curvature – entire extent of the convex
lateral surface
Lesser curvature – concave medial surface
Lesser omentum – runs from the liver to the lesser
curvature
Greater omentum – drapes inferiorly from the
greater curvature to the small intestine
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Stomach


Nerve supply – sympathetic and parasympathetic
fibers of the autonomic nervous system
Blood supply – celiac trunk, and corresponding
veins (part of the hepatic portal system)
PLAY
InterActive Physiology®:
Motility, page 6
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.14a
Microscopic Anatomy of the Stomach

Muscularis – has an additional oblique layer that:

Allows the stomach to churn, mix, and pummel
food physically

Breaks down food into smaller fragments
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Microscopic Anatomy of the Stomach

Epithelial lining is composed of:

Goblet cells that produce a coat of alkaline mucus


The mucous surface layer traps a bicarbonaterich fluid beneath it
Gastric pits contain gastric glands that secrete
gastric juice, mucus, and gastrin
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Microscopic Anatomy of the Stomach
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.15a
Microscopic Anatomy of the Stomach
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.15b
Microscopic Anatomy of the Stomach
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.15c
Glands of the Stomach Fundus and Body

Gastric glands of the fundus and body have a
variety of secretory cells

Mucous neck cells – secrete acid mucus

Parietal cells – secrete HCl and intrinsic factor
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Glands of the Stomach Fundus and Body

Chief cells – produce pepsinogen


PLAY
Pepsinogen is activated to pepsin by:

HCl in the stomach

Pepsin itself via a positive feedback
mechanism
Enteroendocrine cells – secrete gastrin, histamine,
endorphins, serotonin, cholecystokinin (CCK), and
somatostatin into the lamina propria
InterActive Physiology®:
Secretion, page 8
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
PLAY
InterActive Physiology®:
Motility, page 6
Stomach Lining

The stomach is exposed to the harshest conditions
in the digestive tract

To keep from digesting itself, the stomach has a
mucosal barrier with:


A thick coat of bicarbonate-rich mucus on the
stomach wall

Epithelial cells that are joined by tight junctions

Gastric glands that have cells impermeable to HCl
Damaged epithelial cells are quickly replaced
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Digestion in the Stomach

The stomach:

Holds ingested food

Degrades this food both physically and chemically

Delivers chyme to the small intestine

Enzymatically digests proteins with pepsin

Secretes intrinsic factor required for absorption of
vitamin B12
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Regulation of Gastric Secretion

Neural and hormonal mechanisms regulate the
release of gastric juice

Stimulatory and inhibitory events occur in three
phases

Cephalic (reflex) phase: prior to food entry

Gastric phase: once food enters the stomach

Intestinal phase: as partially digested food enters
the duodenum
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Cephalic Phase


Excitatory events include:

Sight or thought of food

Stimulation of taste or smell receptors
Inhibitory events include:

Loss of appetite or depression

Decrease in stimulation of the parasympathetic
division
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Gastric Phase

Excitatory events include:

Stomach distension

Activation of stretch receptors (neural activation)

Activation of chemoreceptors by peptides, caffeine,
and rising pH

Release of gastrin to the blood
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Gastric Phase

Inhibitory events include:

A pH lower than 2

Emotional upset that overrides the parasympathetic
division
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Intestinal Phase


Excitatory phase – low pH; partially digested food
enters the duodenum and encourages gastric gland
activity
Inhibitory phase – distension of duodenum,
presence of fatty, acidic, or hypertonic chyme,
and/or irritants in the duodenum

Initiates inhibition of local reflexes and vagal
nuclei

Closes the pyloric sphincter

Releases enterogastrones that inhibit gastric
secretion
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Release of Gastric Juice: Stimulatory Events
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.16.1
Release of Gastric Juice: Inhibitory Events
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.16.2
Regulation and Mechanism of HCl Secretion

HCl secretion is stimulated by ACh, histamine, and
gastrin through second-messenger systems

Release of hydrochloric acid:


Is low if only one ligand binds to parietal cells

Is high if all three ligands bind to parietal cells
Antihistamines block H2 receptors and decrease
HCl release
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Regulation and Mechanism of HCl Secretion
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.17
Response of the Stomach to Filling

Stomach pressure remains constant until about 1L
of food is ingested

Relative unchanging pressure results from reflexmediated relaxation and plasticity
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Response of the Stomach to Filling

Reflex-mediated events include:



Receptive relaxation – as food travels in the
esophagus, stomach muscles relax
Adaptive relaxation – the stomach dilates in
response to gastric filling
Plasticity – intrinsic ability of smooth muscle to
exhibit the stress-relaxation response
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Gastric Contractile Activity

Peristaltic waves move toward the pylorus at the
rate of 3 per minute

This basic electrical rhythm (BER) is initiated by
pacemaker cells (cells of Cajal)
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Gastric Contractile Activity

Most vigorous peristalsis and mixing occurs near
the pylorus

Chyme is either:

Delivered in small amounts to the duodenum or

Forced backward into the stomach for further
mixing
PLAY
InterActive Physiology®:
Motility, page 10
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Gastric Contractile Activity
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.18
Regulation of Gastric Emptying


Gastric emptying is regulated by:

The neural enterogastric reflex

Hormonal (enterogastrone) mechanisms
These mechanisms inhibit gastric secretion and
duodenal filling
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Regulation of Gastric Emptying

Carbohydrate-rich chyme quickly moves through
the duodenum

Fat-laden chyme is digested more slowly causing
food to remain in the stomach longer
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Regulation of Gastric Emptying
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.19
Small Intestine: Gross Anatomy

Runs from pyloric sphincter to the ileocecal valve

Has three subdivisions: duodenum, jejunum, and
ileum
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Small Intestine: Gross Anatomy

The bile duct and main pancreatic duct:

Join the duodenum at the hepatopancreatic ampulla

Are controlled by the sphincter of Oddi

The jejunum extends from the duodenum to the
ileum

The ileum joins the large intestine at the ileocecal
valve
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Small Intestine: Microscopic Anatomy

Structural modifications of the small intestine wall
increase surface area



PLAY
Plicae circulares: deep circular folds of the mucosa
and submucosa
Villi – fingerlike extensions of the mucosa
Microvilli – tiny projections of absorptive mucosal
cells’ plasma membranes
InterActive Physiology®:
Anatomy Review, page 5
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Duodenum and Related Organs
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.20
Small Intestine: Microscopic Anatomy
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.21
Small Intestine: Histology of the Wall

The epithelium of the mucosa is made up of:

Absorptive cells and goblet cells

Enteroendocrine cells

Interspersed T cells called intraepithelial
lymphocytes (IELs)

IELs immediately release cytokines upon
encountering Ag
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Small Intestine: Histology of the Wall

Cells of intestinal crypts secrete intestinal juice

Peyer’s patches are found in the submucosa

Brunner’s glands in the duodenum secrete alkaline
mucus
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Intestinal Juice

Secreted by intestinal glands in response to
distension or irritation of the mucosa

Slightly alkaline and isotonic with blood plasma

Largely water, enzyme-poor, but contains mucus
PLAY
InterActive Physiology®:
Secretion, page 13
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Liver



The largest gland in the body
Superficially has four lobes – right, left, caudate,
and quadrate
The falciform ligament:

Separates the right and left lobes anteriorly

Suspends the liver from the diaphragm and anterior
abdominal wall
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Liver

The ligamentum teres:

Is a remnant of the fetal umbilical vein

Runs along the free edge of the falciform ligament
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Liver: Associated Structures

The lesser omentum anchors the liver to the
stomach

The hepatic blood vessels enter the liver at the
porta hepatis

The gallbladder rests in a recess on the inferior
surface of the right lobe
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Liver: Associated Structures

Bile leaves the liver via:

Bile ducts, which fuse into the common hepatic
duct

The common hepatic duct, which fuses with the
cystic duct

PLAY
These two ducts form the bile duct
InterActive Physiology®:
Secretion, pages 11-12
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Gallbladder and Associated Ducts
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.20
Liver: Microscopic Anatomy

Hexagonal-shaped liver lobules are the structural
and functional units of the liver

Composed of hepatocyte (liver cell) plates
radiating outward from a central vein

Portal triads are found at each of the six corners of
each liver lobule
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.24c
Liver: Microscopic Anatomy

Portal triads consist of a bile duct and


Hepatic artery – supplies oxygen-rich blood to the
liver
Hepatic portal vein – carries venous blood with
nutrients from digestive viscera
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.24d
Liver: Microscopic Anatomy


Liver sinusoids – enlarged, leaky capillaries
located between hepatic plates
Kupffer cells – hepatic macrophages found in liver
sinusoids
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Liver: Microscopic Anatomy


Hepatocytes’ functions include:

Production of bile

Processing bloodborne nutrients

Storage of fat-soluble vitamins

Detoxification
Secreted bile flows between hepatocytes toward
the bile ducts in the portal triads
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Microscopic Anatomy of the Liver
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.24c, d
Composition of Bile

A yellow-green, alkaline solution containing bile
salts, bile pigments, cholesterol, neutral fats,
phospholipids, and electrolytes

Bile salts are cholesterol derivatives that:

Emulsify fat

Facilitate fat and cholesterol absorption

Help solubilize cholesterol

Enterohepatic circulation recycles bile salts

The chief bile pigment is bilirubin, a waste product
of heme
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
The Gallbladder

Thin-walled, green muscular sac on the ventral
surface of the liver

Stores and concentrates bile by absorbing its water
and ions

Releases bile via the cystic duct, which flows into
the bile duct
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Regulation of Bile Release

Acidic, fatty chyme causes the duodenum to
release:

Cholecystokinin (CCK) and secretin into the
bloodstream

Bile salts and secretin transported in blood
stimulate the liver to produce bile

Vagal stimulation causes weak contractions of the
gallbladder
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Regulation of Bile Release


Cholecystokinin causes:

The gallbladder to contract

The hepatopancreatic sphincter to relax
As a result, bile enters the duodenum
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Regulation of Bile Release
4 Vagal stimulation causes
weak contractions of
gallbladder
3 Bile salts
and secretin
transported via
bloodstream
stimulate liver
to produce bile
more rapidly
5 Cholecystokinin
(via bloodstream)
causes gallbladder
to contract and
hepatopancreatic
sphincter to relax;
bile enters
duodenum
1 Acidic, fatty chyme
entering duodenum causes
release of cholecystokinin
and secretin from
duodenal wall
enteroendocrine cells
2 Cholecystokinin
and secretin enter the
bloodstream
6 Bile salts reabsorbed into blood
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.25
Regulation of Bile Release
1 Acidic, fatty chyme
entering duodenum causes
release of cholecystokinin
and secretin from
duodenal wall
enteroendocrine cells
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.25
Regulation of Bile Release
1 Acidic, fatty chyme
entering duodenum causes
release of cholecystokinin
and secretin from
duodenal wall
enteroendocrine cells
2 Cholecystokinin
and secretin enter the
bloodstream
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.25
Regulation of Bile Release
3 Bile salts
and secretin
transported via
bloodstream
stimulate liver
to produce bile
more rapidly
1 Acidic, fatty chyme
entering duodenum causes
release of cholecystokinin
and secretin from
duodenal wall
enteroendocrine cells
2 Cholecystokinin
and secretin enter the
bloodstream
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.25
Regulation of Bile Release
4 Vagal stimulation causes
weak contractions of
gallbladder
3 Bile salts
and secretin
transported via
bloodstream
stimulate liver
to produce bile
more rapidly
1 Acidic, fatty chyme
entering duodenum causes
release of cholecystokinin
and secretin from
duodenal wall
enteroendocrine cells
2 Cholecystokinin
and secretin enter the
bloodstream
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.25
Regulation of Bile Release
4 Vagal stimulation causes
weak contractions of
gallbladder
5 Cholecystokinin
(via bloodstream)
causes gallbladder
to contract and
hepatopancreatic
sphincter to relax;
bile enters
duodenum
3 Bile salts
and secretin
transported via
bloodstream
stimulate liver
to produce bile
more rapidly
1 Acidic, fatty chyme
entering duodenum causes
release of cholecystokinin
and secretin from
duodenal wall
enteroendocrine cells
2 Cholecystokinin
and secretin enter the
bloodstream
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.25
Regulation of Bile Release
4 Vagal stimulation causes
weak contractions of
gallbladder
3 Bile salts
and secretin
transported via
bloodstream
stimulate liver
to produce bile
more rapidly
5 Cholecystokinin
(via bloodstream)
causes gallbladder
to contract and
hepatopancreatic
sphincter to relax;
bile enters
duodenum
1 Acidic, fatty chyme
entering duodenum causes
release of cholecystokinin
and secretin from
duodenal wall
enteroendocrine cells
2 Cholecystokinin
and secretin enter the
bloodstream
6 Bile salts reabsorbed into blood
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 23.25