Anatomy of the Digestive
System
Chapter 25
Target Test Date (Chapters 25
& 26): Block Days 4/6-4/7
Gastrointestinal (GI) Tract
Walls of the GI Tract
1. Mucosa
– inner lining of tract
– secretes mucous
– Highly folded – increased surface area for
absorption
• Microvilli
– Composed of 3 layers
• Mucous epithelium, lamina propria, muscularis
mucosae
Walls of the GI Tract
2. Submucosa
– Mainly connective tissue
– Contains:
• Exocrine glands
– Secretes acids & enzymes
• Parasympathetic nerves form the submucosal
plexus
Walls of the GI Tract
3. Muscularis
–
Smooth muscle
•
2 layers
–
–
–
–
Longitudinal (outer)
Circular (inner)
Move particles by peristalsis
Myenteric plexus: found between 2 layers
of smooth muscle
Walls of the GI Tract
4. Serosa
–
–
–
Outermost layer
Connective tissue and peritoneum (visceral
layer)
Mesentery connects the parietal &
visceral portions of the peritoneum
Walls of the GI Tract – Cell
Modifications
• Although the layers remain the same
throughout the GI tract, the cell types
may change
– Ex: Mucosa layer of the esophagus is
composed of stratified squamous cells to
resist abrasion, but transitions to simple
columnar cells for absorption and secretion
Mouth
• Also called
the oral or
buccal cavity
• Composed
of:
– Lips, cheeks,
tongue, hard
palate, soft
palate
Tongue
• Skeletal muscle covered by mucous membrane
• Helps in chewing (mastication), swallowing
(deglutition) and speech
• Papillae cover upper portion of the tongue
– Vallate: posterior portion of tongue; contain taste
buds
– Fungiform: sides and tip of tongue; contain taste
buds
– Filiform: anterior 2/3 of tongue; do not contain
taste buds
Tongue
• Frenulum – anchors tongue to floor of
the mouth
– Ankyloglossia: frenulum is too short;
results in speech problems; “tongue-tied”
• Floor of mouth and underside of tongue
are very vascular
– Sublingual drugs (nitroglycerin, morphine)
Salivary Glands
• Parotid
– Upper jaw; anterior & inferior to
external ear
– watery saliva containing enzymes
• Sublingual
– floor of the mouth
– Mostly mucous saliva
• Submandibular
– Opens on either side of the
frenulum
– Mixture of watery (enzymes) and
mucous secretions
Teeth
• Organs of mastication
• Increase surface area that digestive
enzymes can work on food
• 3 main sections:
– Crown: exposed portion; covered by enamel
– Neck: surrounded by the gingivae (gums)
– Root: fits into the alveolar process of the
jaw (gomphosis)
Teeth
• Children - 20 teeth
– deciduous or primary
• 16 teeth per jaw - 32 total (adult)
– Incisors (4)
• blade shaped - used to tear food
– Canines (Cuspids) (2)
• Pointed teeth - used to tear food
– Premolars (Bicuspids) (4)
• 2 points - used to tear and grind food
– Molars (6)
• 4 points - used for grinding
• Last set called wisdom teeth
Esophagus
• Collapsible, muscular, mucous-lined tube
• 25cm; extends from pharynx to
stomach
• Posterior to trachea
• Upper esophageal sphincter (UES) –
prevents air from entering during
respiration
• Lower esophageal sphincter or cardiac
sphincter
Esophagus
• Esophageal hiatus – hole in the diaphragm
through which the esophagus enters the
abdominal cavity
– Enlargement results in lower portion of
esophagus and stomach bulging upward into
the chest  hiatal hernia
• Gastroesophageal reflux disease (GERD) –
backward flow of stomach acid through
the cardiac sphincter into the lower
esophagus
Warm Up 3/9-10/11
Announcements:
1. Make up test ASAP
2. No tutoring/make ups today after school
3. Progress Report grades due this Friday
4. Bring book & packet on Friday
Warm Up:
1. Name the 4 layers of the GI tract (inner to outer).
List one fact about each layer.
2. Name the 3 salivary glands. What type of saliva is
produced from each?
3. What is a hiatal hernia?
4. On what areas of the tongue are taste buds found?
Warm Up 3/11/11
Announcements:
1. You need your book and packet – go get it.
Warm Up:
1. True/False: The layers of the GI tract and
cell types are consistent from mouth to
anus.
2. Name 3 functions of the tongue.
3. True/False: The tongue is poorly vascular.
4. How does the number of teeth differ
between children and adults?
3/21/11
Announcements:
1. Welcome Back!!
2. No warm up today
3. Packet due block day
4. Quiz block day (covers chapter 25
notes through tomorrow)
5. Practical Friday (cat digestive organs
and labeling)
Stomach
• Elongated, pouch-like structure
• Mostly in LUQ
• After eating the stomach walls distend;
when empty size of large sausage
• In adults holds 1-1.5 liters
Stomach Landmarks (fig 25-10)
•
•
•
•
Fundus – enlarged upper left portion
Body – central portion
Pylorus – lower portion
Lower esophageal sphincter (also
cardiac sphincter)
• Pyloric sphincter
• Lesser curvature
• Greater curvature
Modifications of the Stomach Wall
•
Gastric Muscosa
–
–
–
Arranged into folds which allow for
distention (Rugae)
Contains gastric glands which are surrounded
by gastric pits
Gastric glands secrete gastric juice
•
3 major secretory cells:
1. Chief cells: secrete enzyme of gastric juice
2. Parietal cells: secrete hydrochloric acid (HCl)
3. Endocrine cells: secrete ghrelin (stimulate hypothalamus
to increase appetite) and gastrin (influences digestive
functions)
Modifications of the Stomach Wall
• Gastric Muscle
– Muscularis layer is composed of 3 smooth
muscle layers
– Superficial to deep
• Longitudinal
• Circular
• Oblique
– Allows stomach to contract at many
different angles
Modifications of the Stomach Wall
• Serosa Layer
– Visceral layer forms the greater omentum
(over intestines) and lesser omentum
(connects stomach to liver)
Small Intestine
• 1 inch in diameter; 20 feet in length
• 3 divisions:
– Duodenum
• 10 inches
• C shaped
– Jejunum
• 8 feet
• Begins where the sm. intestine turns forward and
downward
– Ileum
• 12 feet
Walls of the Small Intestine
• Mucosa lining has circular folds  plicae
• Small projections called villi (singular –
villus) cover plicae
– 1 mm in height
– Contain an arteriole, venule and lymph vessel
– Epithelial cells on the surface of villi contain
approx 1700 microvilli per cell
• Villi and microvilli increase surface area
for absorption
Walls of the Small Intestine
• Goblet cells are located on villi and in
crypts
– Secrete mucus
• Secretory cells in each crypt produce an
enzyme that prevents bacterial growth
in the small intestine
Large Intestine
• 2.5 inches in diameter; 5-6 feet in
length
• Divisions
– Cecum
– Colon
– rectum
Divisions of the Large Intestine
• Cecum
– First 2-3
inches of
the large
intestine
– Blind pouch
in right
quadrant
Divisions of the Large Intestine
• Colon (4 divisions)
– Ascending
• Vertical position in right quadrant
• Ileum joins superior to cecum
• Ileocecal valve allows material to pass into the
large intestine
– Transverse
• Horizontal position below liver, stomach &
spleen
• Extends from the hepatic flexure to the splenic
flexure
Divisions of the Large Intestine
– Descending
• Vertical position in the left quadrant
• Extends to the level of the iliac crest
– Sigmoid colon
• Below iliac crest
• Means “s-shaped”
• Bends from L to R
Divisions of the Large Intestine
• Rectum
– Last 7-8 inches of the large intestine
– Anal canal is the last inch
• Mucous lined vertical folds  anal columns
– Opening = anus
Walls of the Large Intestine
• Intestinal mucous glands
– Secrete mucous that coats feces
• Longitudinal muscles are grouped into
tape-like strips called taeniae coli
• Circular muscles are grouped into rings
which form pouches  haustra
• Circular muscles in the rectum form
rectal valves
3/22/11
Announcements:
1. Packet due block day
2. Quiz block day
3. Practical (identification & labeling) Friday
Warm Up:
1. The folds in the stomach which allow for distention
are called:
2. Name 3 modifications of the stomach wall.
3. List the divisions of the small intestine from superior
to inferior.
4. The transverse colon extends from the _________
to the ___________.
5. Name the 3 modifications in the small intestine which
increase surface area (from largest to smallest).
Vermiform Appendix
• Attached to the cecum in the RLQ
• 3-4 inches in length
• “breeding ground” for intestinal or
normal flora
– Nonpathogenic bacteria
– Aids in digestion and absorption
Appendicitis
• Mucous lining becomes inflamed
• Fecal matter or food becomes trapped
causing irritation and inflammation
• Rupturing of the appendix results in
infectious materials in the abdominal
cavity
– May cause infection of the peritoneum
and/or other abdominal organs
Appendicitis
• S/S
– Nausea/vomiting
– RLQ pain (McBurney’s Point)
– Rebound tenderness
• An enlarged appendix can be removed
through a laparoscopic surgical
procedure
Peritoneum
• Continuous sheet of serous membrane
– Lines walls of abdominal cavity (parietal layer)
– Outer layer of abdominal organs (visceral layer)
• Binds abdominal organs together
– Mesentery: projection of the parietal layer
• Attached to small intestine
• Allows free movement without becoming tangled (volvulus)
– Greater omentum: continuation of the stomach’s
serosa layer
• Covers small intestines
– Lesser omentum
• Attaches from the liver to the stomach
Liver
• Largest gland in the body
• Weighs 3-4 pounds
• RUQ
Anatomy of the Liver
• Two lobes connected by the falciform
ligament
– Left lobe 1/6 the size of the right lobe
– 3 divisions of the right lobe
• Right lobe proper, caudate lobe and quadrate
lobe (seen inferiorly) (fig 25-22)
Anatomy of the Liver
Anatomy of the Liver
• Hepatic lobules – anatomical units of the liver
– Pentagon-shaped cylinders
• Blood enters the lobules from the hepatic artery
& hepatic portal vein
– Arterial blood oxygenates
– Venous blood passes for inspection
• Kupffer cells remove bacteria, old RBCs, dissolved toxins
• Venous blood continues to the inferior vena cava
– Bile formed by hepatic cells passes though the
canaliculi to the bile ducts
Fig
25-23,
page
758
Bile Ducts
• Small bile ducts merge to form R and L
hepatic ducts
– R and L hepatic ducts form common hepatic
duct
– Cystic duct and common hepatic duct form
common bile duct
– Common bile duct opens into the duodenum
– Fig 25-25
Bile Ducts
Liver Functions
• Detoxification
• Bile secretion (aids in the absorption of
fats)
• Protein, fat and carbohydrate
metabolism
• Hematopoisesis (blood cell production)
Gallbladder
•
•
•
•
•
•
Pear-shaped sac
3-4 inches long
Can hold 30-50mL of bile
Located on inferior surface of the liver
Rugae (similar to stomach)
Functions:
– Stores and concentrates bile
– Contracts and ejects bile into duodenum during
digestion
Cholecystitis
• Inflammation of the gallbladder
• Often caused by gallstones
(cholelithiasis)
– Solid precipitants; mostly cholesterol
– High incidence in obese individuals and those
undergoing rapid weight loss
• Treatment:
– Laparoscopic cholecystectomy
– Ultrasound lithotripsy
– Oral medications (Actigall)
Pancreas
• 6-9 inches long
• LUQ; behind stomach extending to the
spleen
• Endocrine & Exocrine tissue
• Exocrine tissue arranged in a compound
acinar formation (grapelike)
– Release digestive enzymes into microscopic
ducts which join to the main pancreatic duct
– Pancreatic duct empties into the duodenum