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Overview of the Digestive Tract
What is the Digestive System?
• Consists of the muscular digestive tract
assisted by various accessory organs
• Digestive functions include:
• Ingestion
• Mechanical processing
• Digestion
• Secretion
• Absorption
• Excretion
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Overview of the Digestive Tract
What are the Digestive Tract
Components?
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Oral cavity
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Rectum
Anus
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Overview of the Digestive Tract
The Components of the Digestive System and
Their Functions
Figure 16-1
Overview of the Digestive Tract
What is the Histological Organization—
Four Layers?
• Mucosa
• Epithelium
• Submucosa
• Connective tissue, nerves, blood vessels
• Muscularis externa
• Serosa (in peritoneal cavity)
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Overview of the Digestive Tract
The Structure of the Digestive Tract
Figure 16-2(a)
Overview of the Digestive Tract
The Structure of the Digestive Tract
Figure 16-2(b)
Overview of the Digestive Tract
What is the Movement of Digestive
Materials?
• Involuntary control of smooth muscle of
muscularis externa
• Two kinds of movement
• Peristalsis propels material along the tract
• Segmentation churns material in the
small intestine
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Contraction of circular
muscles behind food mass
Longitudinal
muscle
Circular
muscle
Contraction
From
mouth
To
anus
Contraction of longitudinal
muscles ahead of food mass
Contraction
Contraction
Contraction of circular muscle
layer forces food mass forward
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 16-3
1 of 4
The Oral Cavity
What are the Functions of the Oral
Cavity?
• Mechanical processing using teeth,
tongue, and palate
• Lubrication of food by mucus in saliva
• Enzymatic digestion by enzymes in
saliva
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Oral Cavity
What are the Functions of the
Tongue?
• Mechanical processing of food
• Manipulation to assist chewing and
swallowing
• Sensory analysis (taste, texture)
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Oral Cavity
The Oral
Cavity
Figure 16-4(a)
The Oral Cavity
The Oral Cavity
Figure 16-4(b)
Panoramic xray
Child- around 9 years old
3rd molar impaction with cyst
3rd molar impaction
Root canal therapy
Extensive dental caries(decay)
Implants
Dental caries
The Oral Cavity
What are the Salivary Glands?
• Three pairs of glands
• Parotid
• Sublingual
• Submandibular
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The Oral Cavity
The Salivary Glands
Figure 16-5
The Oral Cavity
Teeth
• Participate in mastication of food
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Oral Cavity
Teeth: Structural Components and Dental
Succession
Figure 16-6(a)
The Oral Cavity
Teeth: Structural Components and Dental
Succession
Figure 16-6(b)
The Oral Cavity
Teeth: Structural Components and Dental
Succession
Figure 16-6(c)
The Pharynx
What is the Function of the
Pharynx?
• Common passageway for food,
drink, and air
PLAY
Digestive Movie
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Esophagus
What is the Anatomy of the Esophagus?
• Muscular tube about 25 cm long
• Lined by stratified squamous epithelium
• Posterior to trachea
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The Esophagus
What is Swallowing (Deglutition)—Three
Steps?
1. Oral phase
2. Pharyngeal phase
• Bending of epiglottis, closing of glottis
3. Esophageal phase
• Peristalsis pushes bolus toward
stomach
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Oral
phase
Pharyngeal
phase
Nasopharynx
Esophageal
phase
Peristalsis
Soft
palate
Bolus enters
stomach
Thoracic cavity
Lower
esophageal
sphincter
Bolus
Epiglottis
Trachea
Tongue
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Esophagus
Stomach Diaphragm
Figure 16-7
1 of 5
The Stomach
What are the Functions of the
Stomach?
• Temporary storage of ingested food
• Mechanical breakdown of food
• Forms chyme, a liquid suspension
• Breakage of chemical bonds in food
by action of acid and enzymes
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Stomach
What are the Regions of the
Stomach?
• Cardia
• Closest to heart
• Fundus
• “Hump” on top
• Body
• Shaped like the letter “C”
• Pylorus
• Pyloric sphincter guards the exit
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Stomach
The Anatomy of the Stomach
Figure 16-8(a)
The Stomach
What are the Secretions of the Gastric
Glands?
• Parietal cells
• Secrete HCl (strong acid), intrinsic factor
• Chief cells
• Produce pepsinogen, an inactive enzyme
• HCl activates pepsinogen to pepsin
• Goblet cells
• Produce mucus
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Stomach
The Anatomy
of the
Stomach
Figure 16-8(c)
The Stomach
The Anatomy
of the
Stomach
Figure 16-8(d)
The Stomach
The Phases of Gastric Secretion
Figure 16-9 (1 of 3)
The Stomach
The Phases of Gastric Secretion
Figure 16-9 (2 of 3)
The Stomach
The Phases of Gastric Secretion
Figure 16-9 (3 of 3)
The Stomach
Key Note
The stomach provides for the physical
breakdown of food that must precede
chemical digestion. Pepsin and acid
begin the digestion of proteins. For a
variable period of time after food arrives
in the stomach, starch continues the
digestion that began with salivary
amylase.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Small Intestine
What are the Regions of the
Small Intestine?
• Duodenum
• Jejunum
• Ileum
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The Small Intestine
The Segments of the Small Intestine
Figure 16-10(a)
The Small Intestine
The Segments of
the Small Intestine
Figure 16-10(b)
The Small Intestine
What is the Intestinal Wall?
• Plicae have small projections, villi
• Both increase surface area of mucosa
for absorption
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Small Intestine
The Intestinal Wall
Figure 16-11(a)
The Small Intestine
The Intestinal Wall
Figure 16-11(b)
The Small Intestine
The Intestinal Wall
Figure 16-11(c)
The Small Intestine
What is Intestinal Secretion?
• Intestinal juice
• Moistens chyme
• Buffers stomach acid
• Dissolves digestive enzymes
• Dissolves products of digestion
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Small Intestine
What are the Intestinal
Hormones?
• Gastrin
• Secretin
• Cholecystokinin (CCK)
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The Small Intestine
The Activities
of Major
Digestive Tract
Hormones
Figure 16-12
The Small Intestine
Key Note
The small intestine receives chyme
from the stomach and raises its pH.
It then absorbs water, ions,
vitamins, and the products released
from food molecules by the action
of digestive enzymes produced by
intestinal glands and the pancreas.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Pancreas
The Pancreas
Figure 16-13(a)
The Pancreas
The Pancreas
Figure 16-13(b)
The Pancreas
What are the Secretions of the
Pancreas?
• Endocrine secretion (hormones)
• Insulin
• Glucagon
• Exocrine secretion (digestive)
• Water
• Ions
• Enzymes
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Pancreas
Key Note
The exocrine pancreas produces
a mixture of buffers and enzymes
essential for normal digestion.
Pancreatic secretion is stimulated
by hormones (secretin and CCK)
released from the duodenum.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Liver
What is the Overview of
the Liver?
• Largest visceral organ
• Over 200 known functions
• Four Lobes
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The Liver
The Surface
Anatomy of the
Liver
Figure 16-14(a)
The Liver
The Surface Anatomy of the Liver
Figure 16-14(b)
The Liver
Liver Histology
Figure 16-15(a)
The Liver
Liver Histology
Figure 16-15(b)
The Liver
Liver Histology
Figure 16-15(c)
The Liver
What are the Functions of the
Liver?
• Metabolic control
• Release nutrients as needed
• Hematological control
• Plasma protein production
• Production of bile
• Required for fat breakdown
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Gallbladder
• Gall bladder stores and concentrates
bile for release into duodenum
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Gallbladder
Key Note
The liver is the body’s center for
metabolic regulation. It produces bile
that will be ejected by the gallbladder
into the duodenum under stimulation of
CCK. Bile is essential for the efficient
digestion of lipids; it emulsifies fats so
that individual lipid molecules can be
readily attacked by digestive enzymes.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Gallbladder
The Gall
Bladder
Figure 16-16(a)
The Gallbladder
The Gall Bladder
Figure 16-16(b)
The Large Intestine
What is the Overview of the Large
Intestine?
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Reabsorbs water and compacts feces
Absorbs vitamins made by bacteria
Stores feces before defecation
Consists of three parts
• Cecum
• Colon
• Rectum
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Large Intestine
The Large Intestine
Figure 16-17(a)
The Large Intestine
The Large Intestine
Figure 16-17(b)
The Large Intestine
What are the Functions of the
Large Intestine?
• Absorption
• Water
• Ions
• Vitamins
• Organic wastes
• Bile salts
• Toxins
• Bacterial growth
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Large Intestine
Key Note
The large intestine stores digestive
wastes and reduces their volume by
reabsorbing water. Bacteria that live in
the large intestine are an important
source of vitamins, especially vitamin
K, biotin, and vitamin B5.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Digestion and Absorption
The Digestion
and Absorption
of Carbohydrates
Figure 16-18(a) (1 of 2)
Digestion and Absorption
The Digestion
and Absorption
of Carbohydrates
Figure 16-18(a) (2 of 2)
Digestion and Absorption
The Digestion
and Absorption
of Lipids
Figure 16-18(b) (1 of 2)
Digestion and Absorption
The Digestion
and Absorption
of Lipids
Figure 16-18(b) (2 of 2)
Digestion and Absorption
The Digestion
and Absorption
of Proteins
Figure 16-18(c) (1 of 2)
Digestion and Absorption
The Digestion
and Absorption
of Proteins
Figure 16-18(c) (2 of 2)
Aging and the Digestive System
What are Age-Related Changes in
the Digestive System?
• Thinner, more fragile epithelium
• Reduced epithelial stem cell division
• Weaker peristaltic contraction
• Reduced smooth muscle tone
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings