Download Anatomy of the Digestive System

Anatomy of the Digestive
System
Chapter 25
Gastrointestinal (GI) Tract
Walls of the GI Tract
1. Mucosa
– inner lining of tract
– secretes mucous
– Highly folded – increased surface area for
absorption
• Microvilli
2. Submucosa
– Mainly connective tissue
– Contains:
• Exocrine glands
– Secretes acids & enzymes
Walls of the GI Tract
3. Muscularis
–
Smooth muscle
•
2 layers
–
–
–
Longitudinal (outer)
Circular (inner)
Move particles by peristalsis
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 - Problems
• 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
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 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
• 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
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
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
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 through the
lobules 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 digestion &
absorption of lipids)
• 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