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14
PART A
The Digestive System
and Body Metabolism
PowerPoint® Lecture Slide Presentation by Jerry L. Cook, Sam Houston University
ESSENTIALS
OF HUMAN
ANATOMY
& PHYSIOLOGY
EIGHTH EDITION
ELAINE N. MARIEB
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The Digestive System and Body
Metabolism
Functions of digestive system:
 Ingestion: Taking in food.
 Digestion: Breaking down food physically
and chemically.
 Absorption: Absorption of nutrients into
the blood.
 Defecation: Ridding the body of
indigestible remains.
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Organs of the Digestive System
Figure 14.1
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Organs of the Alimentary Canal -a.k.a.
gastrointestinal (GI) tract
 Mouth
 Pharynx
 Esophagus
 Stomach
 Small intestine
 Large intestine
 Anus
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Mouth (Oral Cavity) Anatomy
 Lips (labia) – protect
the anterior opening
 Cheeks – form the
lateral walls
 Hard palate – forms
the anterior roof
 Soft palate – forms
the posterior roof
 Uvula – fleshy
projection of the
soft palate
Figure 14.2a
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Mouth (Oral Cavity) Anatomy
 Vestibule – space
between lips and
teeth/gums.
 Oral cavity – area
contained by the teeth.
 Tongue – muscle
attached at hyoid and
styloid processes of the
skull.
 Tonsils - Palatine and
lingual.
 Lingual Frenulum – fold
of membrane that secures
tongue to floor of mouth.
Figure 14.2a
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Processes of the Mouth
 Mastication (chewing) of food
 Mixing masticated food with saliva
 Initiation of swallowing by the tongue
 Taste
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Pharynx Anatomy
 Nasopharynx
(not part of the
digestive system)
 Oropharynx
 Laryngopharynx
Figure 14.2a
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Pharynx Function
 Passageway for air and food
 Two muscle layers alternately contract to
propel food (peristalsis):
 Longitudinal inner layer
 Circular outer layer
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Esophagus
 Runs from pharynx to stomach
 Conducts food by peristalsis
 Passageway for food only
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4 Tissue Layers of Alimentary Canal Organs
1. Mucosa – moist innermost layer.
2. Submucosa – lies beneath mucosa made of
connective tissue with blood vessels, nerve
endings and lymph tissue.
3. Muscularis externa –smooth muscle
containing both circular (inner) and
longitudinal (outer) layers.
4. Serosa - Outermost (visceral) layer that
contains serous fluid-producing cells
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Layers of Alimentary Canal Organs
Figure 14.3
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Stomach Anatomy
 Food enters at the cardioesophageal sphincter
 Regions of the stomach
 Cardiac region
 Fundus
 Body
 Pylorus
 Food empties into the small intestine at the
pyloric sphincter
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Stomach Anatomy
Rugae – internal stomach folds of the mucosa
Lesser curvature: concave medial surface.
Greater curvature: convex lateral surface.
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Stomach Anatomy
Figure 14.4a
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Stomach Functions
 Food storage tank
 Food breakdown
 Chemical breakdown of protein begins
 Delivers chyme (processed food) to the small
intestine
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Specialized Mucosa of the Stomach
Made of simple columnar epithelium
containing:
 Gastric pits – formed by folds in mucosa
 Gastric glands (secrete gastric juice)
 Chief cells – produce protein-digesting
enzymes (pepsinogens)
 Parietal cells – produce HCl
 Endocrine cells – produce gastrin
 Mucosa secretes sticky mucus.
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Structure of the Stomach Mucosa
Figure 14.4b–c
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Small Intestine
 Body’s major digestive organ extending from
pyloric sphincter to the ileocecal valve.
 Site of nutrient absorption into the blood
 Suspended from the posterior abdominal wall
by the mesentery (fan-shaped membrane)
 Average length: 2.5 – 7 meters
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3 Subdivisions of the Small Intestine
1. Duodenum: “twelve finger-widths long”
(smallest)
a. Attached to the stomach
b. Curves around the head of the pancreas
2. Jejunum: “empty”
a. Attaches anteriorly to the duodenum
3. Ileum: “twisted intestine” (largest)
a. Extends from jejunum to large intestine
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Chemical Digestion in the Duodenum
 Pancreatic enzymes enter duodenum through the
pancreatic duct.
 Bile from the liver enters duodenum through bile
duct.
 Pancreatic ducts and bile ducts join to form
hepatopancreatic ampulla.
 Pancreatic enzymes and bile then travel through
duodenal papilla together to enter duodenum.
 Small intestine cells also secrete some enzymes in
duodenum.
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Chemical Digestion in the Small Intestine
Figure 14.6
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Absorption of the Small Intestine
Three structures that
increase absorption:
1. Microvilli –
extensions of the cell
membrane (makes it
seem “fuzzy”)
2. Villi: Fingerlike
structures formed by
the mucosa (more
surface area)
3. Circular folds: (a.k.a.
plicae circulares) deep
folds of small
intestine.
Figure 14.7a
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Large Intestine
 Larger in diameter, but shorter than the small
intestine
 Frames the internal abdomen
 Extends from ileocecal valve to anus
 Function:
 Absorption of water
 Eliminates indigestible food from the body as
feces
 Does not participate in digestion of food
 Goblet cells produce mucus to act as a lubricant
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Large Intestine
Figure 14.8
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Structures of the Large Intestine
 Cecum – saclike first part of the large intestine
 Appendix - lymphatic tissue hanging from cecum
that sometimes becomes inflamed (appendicitis)
 Colon
 Ascending
 Transverse
 Descending
 Sigmoid Colon
 Rectum
 Anus – contains external anal sphincter which is
kept closed except during defecation.
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Accessory Digestive Organs
Salivary glands – empty saliva secretions into mouth to aid in
food breakdown and taste.
 Parotid (anterior to ears)
 Submandibular
 Sublingual
Teeth
 Two sets of teeth (“baby” teeth (20)and adult teeth (32
with wisdom))
Pancreas
 Secretes enzymes into duodenum through pancreatic duct
 Produces hormone insulin
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Accessory Digestive Organs
Liver
 Largest gland in the body
 Contains 4 lobes
 Suspended by diaphragm and abdominal wall by
falciform ligament.
 Produces bile through common hepatic duct; enters
duodenum through bile duct.
Bile: contains many substances that break down fats
(yellowish-green in color).
Gallbladder
 Located on inferior surface of liver
 Stores bile when digestion is not occurring
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Processes of the Digestive System
1. Ingestion – getting
food into the mouth
2. Propulsion – moving
foods from one region
of the digestive system
to another (peristalsis
(a)/segmentation (b)).
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Processes of the Digestive System
3. Mechanical digestion
 Mixing of food in the mouth by the tongue
 Churning of food in the stomach
 Segmentation in the small intestine
4. Chemical Digestion: enzymes break down
food molecules into their building blocks
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Processes of the Digestive System
5. Absorption: products of digestion are
absorbed in the blood or lymph.
6. Defecation: elimination of indigestible
substances as feces
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Processes of the Digestive System
Figure 14.11
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Control of Digestive Activity
 Mostly controlled by the parasympathetic
division
 Chemical and mechanical receptors in organ
walls
 Production of hormones (p. 475)
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