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PowerPoint® Lecture Slides
prepared by Vince Austin,
Bluegrass Technical
and Community College
CHAPTER
Elaine N. Marieb
Katja Hoehn
William A. Simmons
Human
Anatomy
& Physiology
SEVENTH EDITION
23
PART B
The Digestive
System:
Mechanism
Pharynx - know

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
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Esophagus - know

Muscular tube going from the laryngopharynx to
the stomach

Travels through the mediastinum and pierces the
diaphragm

Joins the stomach at the cardiac orifice
http://youtube.com/watch?v=1Om_qQl_SsQ
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Esophagus - understand
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Figure 23.12
Esophageal Characteristics - understand

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)
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Deglutition (Swallowing) - know


Coordinated activity of the tongue, soft palate,
pharynx, esophagus, and 22 separate muscle
groups
Buccal phase – bolus is forced into the oropharynx
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Deglutition (Swallowing) - know
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
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Deglutition (Swallowing) - understand
Bolus of food
Tongue
Pharynx
Epiglottis
Glottis
Trachea
(a) Upper esophageal
sphincter contracted
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Deglutition (Swallowing) - understand
Uvula
Bolus
Epiglottis
Esophagus
(b) Upper esophageal
sphincter relaxed
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Deglutition (Swallowing) - understand
Bolus
(c) Upper esophageal
sphincter contracted
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Deglutition (Swallowing) - understand
Relaxed
muscles
Bolus of
food
Longitudinal
muscles
contract,
shortening
passageway
ahead of bolus
Gastroesophageal
sphincter closed
(d)
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Circular muscles
contract,
constricting
passageway
and pushing
bolus down
Stomach
Deglutition (Swallowing) - understand
Relaxed
muscles
Gastroesophageal
sphincter open
(e)
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Bolus of food
Tongue
Uvula
Pharynx
Epiglottis
Bolus
Epiglottis
Glottis
Esophagus
Trachea
(a) Upper esophageal
sphincter contracted
summary
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
Stomach
(e)
Relaxed
muscles
Gastroesophageal
sphincter open
Stomach - know






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
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Stomach - know




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
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Stomach - know


Nerve supply – sympathetic and parasympathetic
fibers of the autonomic nervous system
Blood supply – celiac trunk, and corresponding
veins (part of the hepatic portal system)
Normal stomach:
http://youtube.com/watch?v=Ln09qihUi3g&feature=related
Stomach ulcer:
http://youtube.com/watch?v=kRwMAMe1IWY&feature=re
lated
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know
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Figure 23.14a
Microscopic Anatomy of the Stomach - understand

Muscularis – has an additional oblique layer that:

Allows the stomach to churn, mix, and pummel
food physically

Breaks down food into smaller fragments
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Microscopic Anatomy of the Stomach - know

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
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Microscopic Anatomy of the Stomach - understand
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Microscopic Anatomy of the Stomach - understand
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Microscopic Anatomy of the Stomach - understand
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Glands of the Stomach Fundus and Body understand

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
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Glands of the Stomach Fundus and Body - know

Chief cells – produce pepsinogen


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
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Stomach Lining - know

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
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Digestion in the Stomach - know

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
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Regulation of Gastric Secretion - know

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
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Cephalic Phase - know


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
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Gastric Phase - know

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
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Gastric Phase - know

Inhibitory events include:

A pH lower than 2

Emotional upset that overrides the parasympathetic
division
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Intestinal Phase - know


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
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Release of Gastric Juice: Stimulatory Events summary
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Release of Gastric Juice: Inhibitory Events summary
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Regulation and Mechanism of HCL Secretion - know

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
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Regulation and Mechanism of HCl Secretion - detail
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Response of the Stomach to Filling - understand

Stomach pressure remains constant until about 1L
of food is ingested

Relative unchanging pressure results from reflexmediated relaxation and plasticity
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Response of the Stomach to Filling - know

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
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Gastric Contractile Activity - understand

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)
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Gastric Contractile Activity - know

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
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Gastric Contractile Activity - summary
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Regulation of Gastric Emptying - understand


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 - know

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 - summary
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Small Intestine: Gross Anatomy - know

Runs from pyloric sphincter to the ileocecal valve

Has three subdivisions: duodenum, jejunum, and
ileum
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Small Intestine: Gross Anatomy - know

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
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Small Intestine: Microscopic Anatomy - know

Structural modifications of the small intestine wall
increase surface area



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
http://youtube.com/watch?v=xu5jDCX2cHM
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Duodenum and Related Organs – be able to label
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Small Intestine: Microscopic Anatomy – be able to
label
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Small Intestine: Histology of the Wall - understand

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
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Small Intestine: Histology of the Wall - know

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 - know

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
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Liver - know



The largest gland inside 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
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Liver - understand

The ligamentum teres:

Is a remnant of the fetal umbilical vein

Runs along the free edge of the falciform ligament
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Liver: Associated Structures - know

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
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Liver: Associated Structures - know

Bile leaves the liver via:

Bile ducts, which fuse into the common hepatic
duct

The common hepatic duct, which fuses with the
cystic duct

These two ducts form the bile duct
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Gallbladder and Associated Ducts – be able to label
http://youtube.com/watch?v=bNMsNHqxszc
&feature=related
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Liver: Microscopic Anatomy - understand

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
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Liver: Microscopic Anatomy - understand

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
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Liver: Microscopic Anatomy - know


Liver sinusoids – enlarged, leaky capillaries
located between hepatic plates
Kupffer cells – hepatic macrophages found in liver
sinusoids
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Liver: Microscopic Anatomy - know


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
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Composition of Bile - know

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
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The Gallbladder - know

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
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Regulation of Bile Release - know

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
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Regulation of Bile Release - know


Cholecystokinin causes:

The gallbladder to contract

The hepatopancreatic sphincter to relax
As a result, bile enters the duodenum
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Regulation of Bile Release - understand
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
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Regulation of Bile Release - understand
1 Acidic, fatty chyme
entering duodenum causes
release of cholecystokinin
and secretin from
duodenal wall
enteroendocrine cells
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Regulation of Bile Release - understand
1 Acidic, fatty chyme
entering duodenum causes
release of cholecystokinin
and secretin from
duodenal wall
enteroendocrine cells
2 Cholecystokinin
and secretin enter the
bloodstream
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Regulation of Bile Release - understand
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
Regulation of Bile Release - understand
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
Regulation of Bile Release - understand
4 Vagal stimulation causes
weak contractions of
gallbladder
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
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3 Bile salts
and secretin
transported via
bloodstream
stimulate liver
to produce bile
more rapidly
Review

http://youtube.com/watch?v=1nFwO9iU5Y&feature=related

http://youtube.com/watch?v=LpaEWpYUdDQ
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Functions of the large intestine

Reabsorb water and compact material into feces

Absorb vitamins produced by bacteria

Store fecal matter prior to defecation
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The Large Intestine
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Figure 24.23a
Figure 24.23 The Large Intestine
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Figure 24.23b, c
The rectum

Last portion of the digestive tract

Terminates at the anal canal

Internal and external anal sphincters
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Histology of the large intestine

Absence of villi

Presence of goblet cells

Deep intestinal glands
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Physiology of the large intestine

Reabsorption in the large intestine includes:

Water

Vitamins – K, biotin, and B5


Organic wastes – urobilinogens and
sterobilinogens

Bile salts

Toxins
Mass movements of material through colon and
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The
Defecation
Reflex
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Figure 24.25
Processing and absorption of nutrients

Disassembles organic food into smaller fragments

Hydrolyzes carbohydrates, proteins, lipids and
nucleic acids for absorption
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Carbohydrate digestion and absorption

Begins in the mouth

Salivary and pancreatic enzymes


Brush border enzymes


Disaccharides and trisaccharides
Monosaccharides
Absorption of monosaccharides occurs across the
intestinal epithelia
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Lipid digestion and absorption

Lipid digestion utilizes lingual and pancreatic
lipases

Bile salts improve chemical digestion by
emulsifying lipid drops

Lipid-bile salt complexes called micelles are
formed

Micelles diffuse into intestinal epithelia which
release lipids into the blood as chylomicrons
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Protein digestion and absorption

Low pH destroys tertiary and quaternary structure

Enzymes used include pepsin, trypsin,
chymotrypsin, and elastase

Liberated amino acids are absorbed
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Absorption

Water


Ions


Nearly all that is ingested is reabsorbed via
osmosis
Absorbed via diffusion, cotransport, and active
transport
Vitamins

Water soluble vitamins are absorbed by diffusion

Fat soluble vitamins are absorbed as part of
micelles
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Digestive Secretion and Absorption of Water
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