Anatomy of the Digestive System

Chapter 25Target 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 3/9-10/11Announcements:1. Make up test ASAP2. No tutoring/make ups today after school3. Progress Report grades due this Friday4. Bring book & packet on FridayWarm 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 today3. Packet due block day4. 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 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– 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

• 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

3/22/11Announcements:1. Packet due block day2. Quiz block day3. 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