The Digestive System
Chapter 22
Anatomy of the Digestive System
• A tube within a tube.
• The body wall is the outer covering, then the coelom (cavity),
then the gut, and then the lumen of the gut.
mouth
coelom
gut
body wall
anus
mouth
• Ingestion – Taking food into the
pharynx
digestive tract by mouth.
• Digestion – the breakdown of
food into smaller and smaller
particles.
– Mechanical digestion
– Chemical digestion
esophagus
• Propulsion – smooth muscle
stomach
contract/relax and propel food
toward anus.
• Absorption – broken down
materials pass into epithelial cells of
GI tract.
• Egestion – elimination of
indigestible materials and bacteria
through anus.
Let’s Draw!
small
intestine
large
intestine
anus
• Ingestion – Taking food into the
digestive tract by mouth.
• Digestion – the breakdown of
food into smaller and smaller
particles.
– Mechanical digestion
– Chemical digestion
• Propulsion – smooth muscle
contract/relax and propel food
toward anus.
• Absorption – broken down
materials pass into epithelial cells of
GI tract.
• Egestion – elimination of
indigestible materials and bacteria
through anus.
Salivary Glands
• Saliva – keep mouth and pharnyx moist.
• When eating - lubricates, dissolves, and begins chemical
breakdown of food.
• Defense - antibodies, lysozymes, and cytokines (attract
defensive cells).
• Parasympathetic innervation.
Salivary Glands
• Parotid gland – saliva secreted through parotid duct and
enters vestibule.
• Submandibular gland – duct opens at base of lingual
frenulum.
• Sublingual gland – ducts open into floor of mouth.
•
•
•
•
•
•
•
•
Crown – tooth proper above gum
line.
Enamel – dentin covering of
calcium phosphate and calcium
carbonate.
Dentin – main portion of tooth
comprised of calcified C.T.
Pulp cavity – filled w/ blood
vessels, nerves, and lymph vessels.
Root – anchorage into alveolar
processes.
Periodontal ligament – lines each
socket w/ fibrous C.T. Helps anchor
tooth and acts as shock absorber.
Cementum – covering of dentin in
root.
Apical foramen – opening at
bottom of root canal.
Dental Formula
2I
2I
1C
1C
2M
2M
upper
=
lower
2I 1C 2P 3M
upper
=
2I 1C 2P 3M
lower
× 2 = 20 teeth
× 2 = 32 teeth
Esophagus
• Muscle
– Skeletal
– Mixed
– Smooth
• Leads to stomach
Stomach
• Connects esophagus to duodenum.
• Functions:
– secretes gastric juice which contains HCl, pepsin, lipase
– mix food w/ gastric juice to form chyme
– little absorption
• Stomach lining protected by thick layer of mucous.
Stomach
• Cardiac – junction from esophagus and stomach
• Fundus – ballooned section above body
• Body – main/central region of stomach bounded by fundus
and pyloric region
• Lesser and Greater curvature – borders of stomach
• Pylorus – connects stomach to duodenum
• Pyloric sphincter – valve that “communicates” with
duodenum
• Rugae – large folds of stomach
Small Intestine
• Approx. 90% of
nutrient absorption
occurs in small
intestine.
• Has many loops and
coils and fills much of
the abdominal cavity.
• Receives secretions
from both the
pancreas and liver.
Small Intestine
• 3 portions of the small
intestine.
– Doudenum
• 5%, 2 cm diameter
– Jejunum
• 40%, greater diameter
– Ileum
• 60%, final portion and
joins w/ large intestine
at the ileocecal
sphincter.
plicae (circulares)
villi
microvilli
All increase absorption by increasing surface area of intestine.
Colon: Large Intestine
• Functions:
– Completion of water
absorption from chyme.
– Manufacture of vitamin K
and some B vitamins by
bacteria.
– Expulsion of undigested
foods (defecation).
Colon: Large Intestine
• Extends from ileum to
anus.
• Larger diameter than
small intestine and
approx. 5 feet in
length.
• Frames small
intestine on 3 sides.
• Villi largely absent,
why?
Cecum – blind pouch, which marks the beginning of large intestine.
Vermiform appendix - a narrow, dead-end tube (3-8 inches long) that hangs
off of the cecum. No digestive function but aides immune system.
4 main portions of the colon: ascending, transverse, descending
and sigmoid colon.
Rectum – last 20cm of GI tract, the terminal section is called the
anal canal that terminates at the anus.
Anal sphincter – 2 sphincter muscles (external and internal)
located in walls of anal canal.
Internal under ANS control and external under voluntary control.
Haustrum – one of the pouches into which the large intestine is divided .
Tenia coli muscle – muscle bands penetrate the circular layer at irregular
intervals. These discontinuities in the muscularis externa allow segments of the
colon to contract independently.
Accessory Digestive Structures
•
•
•
•
•
Liver
Gall bladder
Pancreas
Peritoneum
Portal System
Liver produces bile that is stored in gallbladder. It is then pumped into
doudenum to reduce the size of fat globules in a process called
emulsification.
The pancreas serves two functions:
exocrine - it produces pancreatic juice containing digestive enzymes
endocrine - it produces several important hormones, namely insulin
Pancreasneutralizes
acids from
stomach by
production of
bicarbonate
ions.
Bile
Liver
Gallbladder
Bile
Acid chyme
Pancreatic juice
Duodenum of
small intestine
Pancreas
Membranes of the Lower Digestive Organs
• Peritoneum – largest serous membrane of the body located
below the diaphragm in the abdominopelvic cavity.
– Visceral peritoneum – covers some organs in the abdominal-pelvic
cavity.
– Parietal peritoneum – lines the wall of the abdominopelvic cavity.
Membranes of the Lower Digestive Organs
• Peritoneum – largest serous membrane of the body located
below the diaphragm in the abdominopelvic cavity.
– Mesentery – double layered extension of the peritoneum.
• Provides passage of blood vessels, lymphatics, and nerves.
• Holds organs in place and stores fat.
The End