Exercise 38
Anatomy of the
Digestive System
Objectives
•
•
•
•
•
Overall function
Organs of alimentary canal
Accessory digestive organs
General functions of organs/structures
Histological structure of alimentary canal
wall
• Stomach and small intestine specializations
• Enzymes produced
• Deciduous and permanent teeth
Digestive System
• Provides body with nutrients, water,
electrolytes essential for health
• Organs ingest (take in),
digest (break down), &
absorb (take into bloodstream) food,
and eliminate the undigested remains
Alimentary Canal
• Hollow tube extending from mouth to
anus (gastrointestinal tract or GI tract)
• Various accessory organs/glands
empty into
• “Disassembly Line”
Alimentary Canal Histology
• Mucosa (mucous membrane)
Inner layer, lines lumen; secretion of
enzymes, absorption of nutrients,
protection
LUMEN
OUTER
surface
– Surface epithelium: simple columnar
– Lamina propria: areolar connective
– Muscularis mucosa: smooth muscle—
local movements of mucosa
– Lacteals: in villi (small fingerlike
projections) of small intestine,
lymphatic capillaries—transport fatty
acids to bloodstream
Lacteals will be
in here
ONE VILLUS
Fig. 24-3
Alimentary Canal Histology
• Submucosa (superficial to mucosa;
nutrition, protection)
– Blood, lymph vessels, nerve fibers
– Submucosal plexus is it’s intrinsic nerve supply
Fig. 24-3
Alimentary Canal Histology
• Muscularis externa
– Bilayer of smooth muscle:
• Circular layer of muscle (deep)
• Longitudinal layer of muscle (superficial)
– Myenteric plexus = another intrinsic nerve
plexus, controls these muscle layers  major
controller of GI motility
Fig. 24-3
Alimentary Canal Histology
• Serosa (visceral peritoneum)
– Outermost tunic
– Mesothelium, areolar connective tissue
– Reduces friction as GI organs slide across one
another and cavity’s walls, protects and
anchors organs also
Fig. 24-3
Alimentary Canal Organs
Fig. 24-1
Alimentary Canal Organs
• Oral cavity (mouth)
– Labia (lips)
– Hard palate (anterior roof of mouth)
– Soft palate (posterior roof of mouth)
– Uvula (fingerlike projection of soft palate)
– Tongue (floor of oral cavity)
Fig. 24-6
Pharynx
Nasopharynx (behind nasal cavity)
Oropharynx (behind oral cavity)
Laryngopharynx (epiglottis to larynx)
Fig. 24-6
Esophagus
From pharynx through diaphragm to
gastroesophageal sphincter at
esophagus-stomach junction,
controls food passage into stomach
STOMACH
• (left side of abdominal cavity)
– Cardiac region: upper region, through
which food ENTERS stomach
– Fundus: superior & lateral to cardiac
– Body: middle portion, inferior to fundus
– Pyloric region: terminal part of stomach,
continuous w/small intestine
– Pyloric sphincter: between stomach &
small intestine
Alimentary Canal Organs
• Stomach (left side of abdominal cavity)
– Greater curvature: lateral, convex
– Lesser curvature: medial, concave
– Rugae: prominent folds in the mucosa
when stomach’s empty
Fig. 24-12
SMALL INTESTINE
~2m long
– Duodenum: from pyloric sphincter around
pancreas
– Jejunum: umbilical region of abdomen
– Ileum: terminal portion, joins lg intestine
– Plicae circularis: like rugae, deep folds
– Ileocecal valve: between small and large
intestine
Fig. 24-16
Fig. 24-17
LARGE INTESTINE
~1.5m long
Encircles the small intestine on 3
sides
– Cecum: 1st region, expanded pouch
– Appendix:  attached to cecum,
~3.5” long
– Ascending colon: up the right side
– Transverse colon: across the top
– Descending colon: down the left side
Fig. 24-23
LARGE INTESTINE
– Sigmoid colon: S-shaped curve
(behind bladder) between descending
colon and
– Rectum: last 6” of digestive tract
– Anus: exit of the anal canal
– Anal sphincter: muscle layers (2)
surrounding the anus
Fig. 24-23
LARGE INTESTINE
–Teniae coli: 3 external
longitudinal muscle bands of
muscularis, shorter than rest of
wall, cause it to pucker into
–Haustra: small pocketlike sacs
Fig. 24-23
ACCESSORY Digestive Organs
• Teeth
– Deciduous: appear 6 months-2.5
years; begin to lose teeth around 6
years old
• 20 teeth
Each SIDE of the jaw
• 2, 1, 0, 2 x 2 = 20 Upper: 2I, 1C, 0 PM, 2M
2, 1, 0, 2
Lower: 2I, 1C, 0 PM, 2M
SIDES of the jaw
TEETH
– Permanent: gradually replaces the
1st set to age 12
• 32 teeth
• 2, 1, 2, 3 x 2 = 32
2, 1, 2, 3
Each SIDE of the jaw
Upper: 2I, 1C, 2 PM, 3M
Lower: 2I, 1C, 2 PM, 3M
Permanent Teeth
Central incisors
For biting
Lateral incisors
Canines (cuspids)
1st premolars (bicuspids)
2nd premolars (bicuspids)
For chewing
1st molars
2nd molars
3rd molars
Fig 24-9
Fig. 24-8
Teeth
• Anatomical crown: entire area of
tooth covered by enamel
• Clinical crown: portion of tooth
visible above the gum
• Root: inferior portion (base) of the
tooth (below the gum)
Fig. 24-8
Teeth
• Enamel: “white” mineral (calcium salt)
outer covering of crown
• Dentin: like bone, but no cells; under
enamel, it’s most of the tooth
• Pulp, pulp cavity: interior chamber of
the tooth—has blood vessels & nerves
Fig. 24-8
SALIVARY GLANDS
• Parotid glands: inferior to zyg.
arch, lateral/posterior mandible
• Submandibular glands: floor of
mouth, along inside of mandible
• Sublingual glands: floor of mouth,
more anterior & under tongue
Fig. 24-7
LIVER
• Right, left, caudate, quadrate lobes
Fig. 24-19
LIVER
• Falciform ligament: divides Rt/Lt
lobes
Fig. 24-19
LIVER
• Round ligament: thickened
posterior part of falciform ligament
Fig. 24-19
LIVER
• Hepatic ducts: right, left—collect bile
(secreted by liver) from all bile ducts of
lobes, unite to form the
• Common hepatic duct which leaves the
liver…bile then flows to
• Cystic duct which leads to the gallbladder
(stores/concentrates bile)
….OR goes to the
• Common bile duct which is formed by
union of cystic and common hepatic
ducts--empties into the duodenum (sm
intest),
Fig. 24-21
PANCREAS
• Posterior to stomach, extends laterally off
the duodenum toward the spleen
• Secretes digestive enzymes and buffers
via the
• Pancreatic duct into the duodenum
• Accessory pancreatic duct branches off
the larger pancreatic duct, also empties
into duodenum
• Hepatopancreatic sphincter (muscle)
controlling entrance of substances (from
common bile duct, pancreatic duct) into
duodenal ampulla
Fig. 24-18
Fig. 24-21
Microscope Work
• Stomach
– Gastric pits: shallow depressions, open
onto gastric surface; mucous cells at base
of each one mitotically active—shed into
chyme (acidic “soup” of stomach
secretions and food)
Fig. 24-13
Fig. 24-13
Microscope Work
• Small intestine
– Villi: fingerlike projections all over the
plicae circulares
One VILLUS
Fig. 24-17
Microscope Work
• Large intestine (no villi in colon)
– Goblet cells (unicellular glands) abundant
• secrete mucus to help GI motility
Fig. 24-24