Anatomy of the Digestive System Chapter 25. Gastrointestinal (GI) Tract.
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Transcript of Anatomy of the Digestive System Chapter 25. Gastrointestinal (GI) Tract.
Anatomy of the Digestive System
Chapter 25
Gastrointestinal (GI) Tract
Walls of the GI Tract1. 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 juice2. 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
• Rectum– Last 7-8 inches of the large intestine– Anal canal is the last inch
• Mucous lined vertical folds anal columns
– Opening = anus
Divisions of the Large Intestine
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