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DIGESTIVE
SYSTEM
Peritoneum: Membrane of the abdominal
cavity
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Parietal Peritoneum covers the
abdominal wall
• Visceral Peritoneum covers the
inner organs
Branching from the peritoneum:
– Lesser omentum—attaches
the liver to the lesser
curvature of stomach
– Greater omentum: (Apron)
Contains fat to insulate,
cushion, and protect
abdominal organs
The Digestive System Functions
• Ingestion—taking in food
• Digestion—breaking food down both
physically and/or chemically
• Absorption—movement of nutrients into
the bloodstream
• Defecation—rids the body of indigestible
waste
Organs of the Digestive System
• Two main groups of organs
– Alimentary canal (gastrointestinal or GI tract)—
continuous coiled hollow tube from mouth to
anus
– Accessory digestive organs (aid in digestion but
food does not pass through)
Organs of the Alimentary Canal
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Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Anus
Accessory Digestive Organs
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Teeth
Salivary glands
Pancreas
Liver
Gallbladder
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
Mouth Physiology
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Mastication (chewing) of food
Mixing masticated food with saliva
Initiation of swallowing by the tongue
Allows for the sense of taste
Salivary glands
• They make as much as a quart
of saliva each day.
• Saliva helps with
– swallowing
– protects your teeth against bacteria
– aids in the digestion of food.
Enzymes found in saliva
• Amylase – breaks down startches
• Lysozyme – breaks down cell walls of
bacteria (also secreted in eyes and
nose)
• Lipase – starts the breakdown of fats,
specifically triglycerides
Pharynx Anatomy
• Nasopharynx—not part of the
digestive system
• Oropharynx—posterior to oral
cavity
• Laryngopharynx—below the
oropharynx and connected to
the esophagus
Pharynx Physiology
• Serves as a passageway for air and food from
mouth to esophogus
• Food is propelled to the esophagus by two
muscle layers
– Longitudinal inner layer
– Circular outer layer
• Food movement is by alternating contractions
of the muscle layers (peristalsis)
Esophagus Anatomy and Physiology
• Anatomy
– About 10 inches long
– Runs from pharynx to stomach through the diaphragm
• Physiology
– Conducts food by peristalsis (slow rhythmic
squeezing)
– Passageway for food only (respiratory system
branches off after the pharynx)
https://www.youtube.com/watch?v=rJS-Kh5wCQU
Layers of Alimentary Canal Organs
 Mucosa
 Innermost, moist
membrane , smooth
muscle layer
 Submucosa
 Just beneath the mucosa,
contains blood vessels and
nerve endings
• Muscularis externa—
smooth muscle
– Inner circular layer and
outer longitudinal layer
• Serosa—outer membrane
Stomach Anatomy
• Located on the left side of the abdominal cavity
• Food enters at the cardioesophageal sphincter
– Food empties into the small intestine at the pyloric
sphincter (valve)
Stomach Physiology
• Temporary storage tank for food
• Site of food breakdown – HCl acid
• Chemical breakdown of protein begins by the
enzyme pepsin Delivers chyme (processed
food) to the small intestine
Small Intestine
• The body’s major digestive organ
• Muscular tube extending from the pyloric
sphincter to the ileocecal valve
• Site of nutrient absorption into the blood
• Suspended from the posterior abdominal wall
by the mesentery ( a membrane within the
small intestine)
Subdivisions of the Small Intestine
• Duodenum
– Attached directly to the stomach
• Jejunum
– Attaches anteriorly to the duodenum
• Ileum
– End portion of the small intestine extends from
jejunum to large intestine
Chemical Digestion in the Small Intestine
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Chemical digestion begins in the
small intestine
– Bile, formed by the liver,
enters via the bile duct
breaks down fats
– Enzymes in the small
intestine are secreted by the
pancreas and the intestinal
cells
*Peptidases (breaks proteins
into amino acids
*Sucrase breaks down sucrose
sugar
*Lactase breaks down lactose in
milk
*Maltase breaks down maltose
into glucose
Amylase breaks down starch
Nucleases break down nucleic
acids
Small Intestine Anatomy
• Three structural modifications that increase
surface area
– Microvilli—tiny projections of the plasma
membrane (create a brush border appearance)
– Villi—fingerlike structures formed by the mucosa
– Circular folds (plicae circulares)—deep folds of
mucosa and submucosa
Small Intestine Anatomy
• Structural modifications that
increase surface area
– Microvilli—tiny projections
of the plasma membrane
(create a brush border
appearance)
– Villi—fingerlike structures
formed by the mucosa
Large Intestine
• Larger in diameter, but shorter in length, than
the small intestine
• Frames the internal abdomen
Large Intestine Anatomy
• No villi present
• Goblet cells produce alkaline (high pH)mucus
which lubricates the passage of feces
• Muscularis externa layer is reduced to three
bands of muscle called teniae coli
• These bands cause the wall to pucker into
haustra (pocketlike sacs)
Large Intestine Anatomy
• Cecum—saclike first part of the large intestine
• Appendix (you can live without an appendix)
– Accumulation of lymphatic (immune system)
tissue that sometimes becomes inflamed
(appendicitis)
– Hangs from the cecum
– Nursery for important digestive bacteria
Large Intestine Anatomy
• Colon
– Ascending—travels up right
side of abdomen
– Transverse—travels across
the abdominal cavity
– Descending—travels down
the left side
– Sigmoid—enters the pelvis
• Rectum and anal canal—also in
pelvis
Large Intestine Anatomy
• No villi present
• Goblet cells produce alkaline mucus which
lubricates the passage of feces
• Anus—opening of the large intestine
– Double sphincter
– These sphincters are normally closed except
during defecation
Liver
• Produces bile so the small intestine can break down
fats and proteins
• Makes blood cells
• Helps in creating blood clot factor
• Carbs are stored in the liver as glycogen – when no
glucose is available and energy is needed this is
released
• Stores vitamins A,D,E,K and iron
• Removes hormones like estrogen and drugs and
alcohol
• Has immune cells that destroy pathogens that enter
the liver from the gut.
• Makes albumin – a protein for transporting hormones
Gall bladder
• Stores bile for release into the intestines
Pancreas
• Secretes many enzymes that act in the small
intestine
• Part of the endocrine system – maintain
homeostasis by producing insulin (to allow the
uptake of glucose into cells) and glucagon (when
too little glucose available it takes stored
glycogen from the liver and breaks it down)When
glycogen runs out, muscles will be broken down.