Digestive System I: Organs and Structure
 General functions
 Organs of the Alimentary
Canal
• Mouth and Teeth
• Swallowing
• Pharynx, Esophagus
o Propulsion
• Stomach
• Linings and Mesentaries
• Small Intestine
• Large Intestine
The Digestive System and Body Metabolism
 Digestion
• Six essential activities
1. Ingestion
2. Propulsion
3. Mechanical digestion
4. Chemical digestion
Ingestion
Mechanical
digestion
• Chewing (mouth)
• Churning (stomach)
• Segmentation
(small intestine)
Chemical
digestion
5. Absorption
6. Defecation
Food
Pharynx
Esophagus
Propulsion
• Swallowing
(oropharynx)
• Peristalsis
Stomach (esophagus,
stomach,
small intestine,
large intestine)
Absorption
Lymph
vessel
Small
intestine
Large
intestine
Defecation
Blood
vessel
Mainly H2O
Feces
Anus
Organs of the Digestive System
Organs of the Alimentary Canal

Mouth

Pharynx

Esophagus

Stomach

Small intestine

Large intestine

Anus
Accessory Digestive Organs

Salivary glands

Teeth

Pancreas

Liver

Gall bladder
Digestive System I: Organs and Structure
 General functions
 Organs of the Alimentary Canal
• Mouth and Teeth
• Swallowing
• Pharynx, Esophagus
o Propulsion
• Stomach
• Linings and Mesentaries
• Small Intestine
• Large Intestine
Mouth (Oral Cavity) Anatomy
Processes of the Mouth
 Mechanical Processes
• Mastication (chewing)
of food using temporal
and masseter muscles
and teeth
• Wetting masticated food
with saliva
• Initiation of swallowing
by the tongue
 Chemical Processes
• Allowing for the sense
of taste
• Digestion of some
starch by salivary
amylase in saliva
Teeth
 The role is to masticate (chew) food
 Humans have two sets of teeth
• Deciduous (baby or milk) teeth
• 20 teeth are fully formed by age two
 Permanent teeth
• Replace deciduous teeth beginning
between the ages of 6 to 12
• A full set is 32 teeth, but some people
do not have wisdom teeth
 Classification of Teeth
• Incisors (clipping, nibbling)
• Canines (siezing)
• Premolars (grinding)
• Molars (grinding)
Regions of a Tooth
 Crown – exposed part
• Outer enamel
• Dentin
• Pulp cavity
 Neck
• Region in contact with the
gum
• Connects crown to root
 Root
• Periodontal membrane
attached to the bone
• Root canal carrying blood
vessels and nerves
Pharynx Anatomy and Function
Digestive System I: Organs and Structure
 General functions
 Organs of the Alimentary Canal
• Mouth and Teeth
• Swallowing
• Pharynx, Esophagus
o Propulsion
• Stomach
• Linings and Mesentaries
• Small Intestine
• Large Intestine
Deglutition
Bolus of food
Tongue
Pharynx
Epiglottis
Glottis
Trachea
1 Upper esophageal sphincter is contracted. During
the buccal phase, the tongue presses against the hard
palate, forcing the food bolus into the oropharynx
where the involuntary phase begins.
Figure 23.13, step 1
Deglutition
Uvula
Bolus
Epiglottis
Esophagus
2 The uvula and larynx rise to prevent food from
entering respiratory passageways. The tongue blocks
off the mouth. The upper esophageal sphincter
relaxes, allowing food to enter the esophagus.
Figure 23.13, step 2
Deglutition
Bolus
3 The constrictor muscles of the pharynx contract,
forcing food into the esophagus inferiorly. The upper
esophageal sphincter contracts (closes) after entry.
Figure 23.13, step 3
Digestive System I: Organs and Structure
 General functions
 Organs of the Alimentary Canal
• Mouth and Teeth
• Swallowing
• Pharynx, Esophagus
o Propulsion
• Stomach
• Linings and Mesentaries
• Small Intestine
• Large Intestine
Esophagus
 Runs from pharynx to stomach
through the diaphragm
 Conducts food by peristalsis
(slow rhythmic squeezing)
 Passageway for food only
(respiratory system branches off
after the pharynx)
 Esophageal mucosa contains
stratified squamous epithelium
• Changes to simple columnar
at the stomach
 Esophageal glands in submucosa
secrete mucus to aid in bolus
movement
Propulsion
 Peristalsis – alternating
waves of contraction
 Segmentation – moving
materials back and forth to
aid in mixing
Peristalsis Movie Online
Peristalsis X-ray movie
Digestive System I: Organs and Structure
 General functions
 Organs of the Alimentary Canal
• Mouth and Teeth
• Swallowing
• Pharynx, Esophagus
o Propulsion
• Stomach
• Linings and Mesentaries
• Small Intestine
• Large Intestine
Stomach Anatomy and Function
cardiac region
serosa
cardiac sphincter
fundus region
body region
pylorus region
rugae of
mucosa
Muscularis
externa
Functions of the Stomach
 Acts as a storage tank for food
 Site of initial food breakdown
 Chemical breakdown of protein begins
 Delivers chyme (processed food) to the
small intestine
Propulsion in the Stomach
 Food must first be well mixed
 Rippling peristalsis occurs in the lower stomach
 The pylorus meters out chyme into the small intestine (30 ml
at a time)
 The stomach empties in four to six hours
Stomach peristalsis interactive animation online
Figure 14.15
Specialized Mucosa of the Stomach
 Simple columnar epithelium
• Mucous neck cells –
produce a sticky alkaline
mucus
• Gastric glands – secrete
gastric juice
• Chief cells – produce
protein-digesting
enzymes (pepsinogens)
• Parietal cells – produce
hydrochloric acid
• Endocrine cells –
produce gastrin
Chief Cells Utilize Blood CO2 and Interstitial Cl to Produce HCl
Blood
capillary
Chief cell
CO2
CO2 + H2O
Carbonic
H2CO3 anhydrase
H+
K+
Stomach lumen
H+-K+
ATPase
H+
K+
HCO3–
Alkaline
tide
HCI
Parietal cell
HCO3–
Cl–
Cl–
HCO3–- Cl–
antiporter
Cll–
Interstitial
fluid
Figure 23.18
Serous Membranes- Thin linings of organs and body wall
Mesenteries are double layers of peritoneum
•Routes for blood vessels, lymphatics, and
nerves; holds organs in place and stores fat
• Parietal serosae line
internal body walls
• Visceral serosae
cover internal organs
Retroperitoneal organs lie posterior to the
peritoneum (e.g. the liver); intraperitoneal
(peritoneal) organs are surrounded by the peritoneum
Mesenteries of the Stomach
Layers of peritoneum (serosa) attached
to the stomach = mesentaries
 Lesser omentum –
attaches the liver to the
lesser curvature
 Greater omentum –
attaches the greater
curvature to the
posterior body wall
 Contains fat to insulate,
cushion, and protect
abdominal organs
Lesser
omentum
Greater
omentum
Digestive System I: Organs and Structure
 General functions
 Organs of the Alimentary Canal
• Mouth and Teeth
• Swallowing
• Pharynx, Esophagus
o Propulsion
• Stomach
• Linings and Mesentaries
• Small Intestine
• Large Intestine
Small Intestine
 The body’s major digestive organ
 Site of nutrient absorption into the blood
 Muscular tube extending form the pyloric
sphincter to the ileocecal valve
 Suspended from the posterior abdominal wall
by the mesentery (omenta)
 Regions of the Small Intestine
• Duodenum
o
Attached to the stomach
o
Curves around the head of the pancreas
• Jejunum
o
Attaches anteriorly to the duodenum
• Ileum
o
Extends from jejunum to large intestine
Four Tunics of the Alimentary Canal
1.
2.
3.
4.
Absorption in the Small Intestine



Absorptive Structures
•
Absorptive cells
•
Blood capillaries
•
Lacteals (specialized lymphatic capillaries)
•Intestinal crypt epithelium
•Secretory cells that produce intestinal juice
• Cells that make antimicrobial chemicals
•Stem cells
Folds in the Small Intestine
•
Called circular folds or plicae circulares
•
Deep folds of the mucosa and submucosa
•
Do not disappear when filled with food
Peyer’s patches in submucosa (collections of lymphatic tissue)
Digestive System I: Organs and Structure
 General functions
 Organs of the Alimentary Canal
• Mouth and Teeth
• Swallowing
• Pharynx, Esophagus
o Propulsion
• Stomach
• Linings and Mesentaries
• Small Intestine
• Large Intestine
Functions of the Large Intestine
Structures
 Cecum – saclike first part of the large intestine
 Appendix
•
Accumulation of lymphatic tissue that sometimes
becomes inflamed (appendicitis)
•
Hangs from the cecum
 Colon
•
Ascending
•
Transverse
•
Descending
•
S-shaped sigmoidal
 Rectum
 Anus – external body opening
Functions
 Absorption of water
 Elimination of indigestible food from the body as feces
 Does not participate in digestion of food
 Goblet cells produce mucus to act as a lubricant
Left colic
(splenic) flexure
Transverse
mesocolon
Epiploic
appendages
Right colic
(hepatic)
flexure
Transverse
colon
Superior
mesenteric
artery
Haustrum
Descending
colon
Ascending
colon
IIeum
Cut edge of
mesentery
Teniae coli
IIeocecal
valve
Cecum
Vermiform appendix
Sigmoid
colon
Rectum
Anal canal
(a)
External anal sphincter
Figure 23.29a
Modifications to the Muscularis Externa in
the Large Intestine
 Longitudinal smooth
muscle is reduced to
three bands (teniae coli);
circular muscles still
present
 Muscle bands have some
degree of tone
 Walls are formed into
pocketlike sacs called
haustra
Digestive System I: Organs and Structure
 General functions
 Organs of the Alimentary Canal
• Mouth and Teeth
• Swallowing
• Pharynx, Esophagus
o Propulsion
• Stomach
• Linings and Mesentaries
• Small Intestine
• Large Intestine