Digestive SystemPart I - Digestive Tract

Part II - Liver, GB, and Pancreas

Nestor T. Hilvano, M.D., M.P.H.

Part I - Learning Objectives 1. Describe the functions of the digestive system.2. Identify the layers of the digestive tract.3. Discuss the importance of the mesenteries.4. Discuss the neural control of salivation and swallowing.5. Differentiate the anatomy and functions of the oral cavity,

pharynx, and esophagus. 6. Describe the composition and functions of saliva.7. Correlate the anatomy and functions of the stomach. 8. Discuss the 3 phases of gastric secretion.9. Compare and contrast the anatomy and functions of the small

and large intestines.10. Discuss the chemical digestion and absorption of organic

nutrients11. Explain the neurological control of defecation.

Digestive System• Acquires nutrients from environment• Digestive tract (GIT)

– 30 foot long tube, from oral cavity to anal canal• Accessory organs: liver, gallbladder, pancreas, salivary

glands• Digestive functions

- ingestion

- mechanical processing

and digestion

- secretion and absorption

- excretion (defecation)

Peritoneum and Mesentery • ___- lines inner surfaces of body wall• ___ - covers organs • ___ - provides lubrication, separates peritoneal

surfaces and allows sliding without friction• ___ - double sheet of peritoneal membrane

separated by loose C.T.a. mesentery b. visceral peritoneum

c. parietal peritoneum d. peritoneal fluid

• Only duodenum, pancreas and parts of large intestine (ascending and descending colon, rectum) are retroperitoneal

• Dorsal mesentery (mesogastrium, mesocolon, etc.)

• Ventral mesentery (lesser and greater omentum)

Importance of Mesentery

• Support and stabilize the organs in the abdominopelvic cavity

• Provide route for blood vessels, nerves, and lymphatic vessels.

Regulation of Digestive Function• Neural mechanisms

– short myenteric reflexes (swallowing)– long vagovagal reflexes (parasympathetic

stimulation of digestive motility and secretion)• Hormonal mechanisms

– messengers diffuse into bloodstream, distant targets (ex. gastrin, secretin, etc.)

• Local mechanisms (Paracrine secretions)– messengers diffuse to nearby target cells (ex.

prostaglandins, histamine)

Layers of GI Tract• Mucosa

– epithelium– lamina propria– muscularis mucosae

• Submucosa - glands - Meissner’s plexus

• Muscularis externa– inner circular layer– outer longitudinal layer– Myenteric plexus

• Serosa or Adventitia – Mesothelium or areolar tissue

Oral Cavity• Lining epithelium – _________

• Cheeks and lips - keep food between teeth for chewing; essential for speech and suckling in infants

• ___ What is the space between the cheeks (lips) and the teeth?

• Hard and soft palate• ___ - sensitive, muscular manipulator of food• Fauces – dividing line between oral cavity and

pharynx• Functions of oral cavity: ____

a. tongue b. oral vestibule

c. simple columnar d. stratified squamous

Dentition• Baby teeth (20) by 2 years; Adult (32) between 6

and 25• _____ – cut and bite off pieces of food, located at

front• _____ – grasp and tear food, also known as

cuspids• _____ – bicuspids, grinding teeth• _____ – crush and grind food, typically have 3 or

more roots a. incisors b. canine

c. premolar d. molar

Tooth Structure• Periodontal ligament

• Enamel is noncellular secretion

• Cementum and dentin are living tissue

• Root canal leads into pulp cavity– nerves and blood vessels

• What is the hardest structure?

Saliva• Functions of saliva – moisten, begin digestion,

cleanses teeth, inhibites bacteria, binds food together into bolus.

• Hypotonic solution of 99.5% water and solutes– salivary amylase, begins digestion of ______.– lingual lipase, starts digestion of __________.– mucus, aids in swallowing– lysozyme, enzyme kills _______________. – Immunoglobulin _______, inhibits bacterial growth– electrolytes = Na+, K+, Cl-, phosphate and bicarbonate

• pH of 6.8 to 7.0 a. IgA b. bacteria c. fats d. carbohydrates e. proteins

Salivation• Total of 1 to 1.5 L of saliva per day

• Food stimulates receptors that signal salivatory nuclei in medulla and pons– parasympathetic stimulation salivary glands

produce thin, watery, rich in enzymes– sympathetic stimulation produce small

amount of thick, more mucus saliva

• Higher brain centers stimulate salivatory nuclei so sight, smell and thought of food cause salivation

Salivary Glands

__________ = stensen’s ducts, empty into the vestibule at level of 2nd upper molar, produce serous secretion, salivary amylase__________ = wharton’s ducts*__________ = rivinus’ ducts*

* Mixed secretion

a. Sublingual gland b. submandibular gland c. parotid gland

- empty on either side of lingual frenulum

Pharynx• Function: common passageway for_____. • 3 Regions: nasopharynx, oropharynx, and

laryngopharynx• Pharyngeal constrictors muscles involved in

____________.

a. speech b. swallowing c. mastication d. digestion

Esophagus• Straight muscular tube 25-30 cm long• Extends from ________________• Lower esophageal sphincter closes

orifice to reflux• Histology: ________________

Stomach• Most dilated digestive tract• Functions: _______• Soupy mixture is called chyme• 4 regions

• cardia • fundus • body • pylorus

– antrum and pyloric canal• Pyloric sphincter

– regulates the release of chyme into the duodenum

Unique Features of Stomach Wall

• Mucosa– Folds: ___________– LE: ______________– lamina propria is filled with ______________

• Muscularis externa has 3 layers• Serosa

a. simple columnar b. gastric glands

c. rugae d. brunner’s glands

Cells of Gastric Glands• Mucous (Neck mucous) cells secrete mucus for

lubrication• Parietal (oxyntic) cells

– secrete _____ and _______• Chief cells

– secrete __________ • Enteroendocrine cells: secrete hormones

– G cells: _________– D cells : _________a. pepsinogen b. HCl & Intrinsic factor

c. somatostatin d. gastrin

Regulation of Gastric Function1. ____ phase- sight, smell, taste or thought of food; vagus

nerve stimulates gastric secretion and motility

2. ____ phase- activated by presence of food in the stomach; secretion stimulated by

• ACh (from parasympathetic fibers), histamine (from gastric

enteroendocrine cells) and gastrin (from pyloric G cells)

3. ____ phase- enterogastric reflex - duodenum inhibits stomach; chyme stimulates duodenal cells to release secretin, cholecystokinin (CCK) and gastric inhibitory peptide

• all 3 suppress gastric secretion and motility

a. gastric b. intestinal c. cephalic d. all

Small Intestine• ___ - first part (10 in.)

• ___ - middle part (8 ft.)

• ___ - last part (12 ft.) a. Ileum b. jejunum c. duodenum d. cecum

• Functions = ___________a. secretion of water b. final digestion & reabsorption of nutrients

c. compaction of undigested materials d. elimination of waste products

Features of Small Intestine

• _________ - circular folds of mucosa• _________ - projections of mucosa contain

blood vessels and lymphatics • ________ - microvilli on cells a. Striated border

b. Plica circulares

c. Plica semilunares

d. Intestinal villi

Features of Small Intestine • Intestinal crypts or glands

– Absorptive (columnar) cells, goblet cells (mucus secreting), paneth cells (characteristic cells)

• Brunner’s glands secrete bicarbonate mucus; found in ____________.

• Peyer patches in the ____________. • Secrete 1-2 L of intestinal juice/day (water and

mucus, pH 7.4-7.8) a. Ileum c. duodenum

b. Jejunum d. all of the above

Intestinal Motility • Segmentation

- random ringlike constrictions that mix and churn contents with intestinal secretions

• Peristalsis - waves of muscular contractions, moves bolus further down

Large Intestine• 5 feet long and 2.5 inches in diameter in cadaver• Begins as _____ in lower right corner, with

appendix, a slender hollow appendage• ___, ___, and ___ colon • _______ is S-shaped portion • _______ - straight portion (terminal part)a. rectum b. cecum

c. sigmoid colon d. ascending, transverse, and descending

• Transit time is 12 – 24 hours

• Functions: ______ a. secretion of water b. elimination of waste products

c. compaction of undigested materials d. all of the above

Features of Large Intestine• Mucosa

- lack villi, lined by simple columnar w/ abundant goblet cells

- mucosal folds – ____.

- intestinal glands produce mucus only. • Wall of colon forms a series of pouches - ______• Muscularis externa

– Longitudinal bands of smooth muscle called ____. • Transverse and sigmoid have a serosa, the rest

retroperitoneal • Fatty tissues on serosa of large intestine are ___.• a. epiploic appendages b. taenia coli

c. haustra d. plica semilunares

Anal Canal

• Anal canal is 3 cm total length• Anal columns of Morgagni are

longitudinal ridges separated by mucus secreting anal sinuses

• ____________ are permanently distended veins

Neural Control of Defecation

1. Filling of the rectum

2. Reflex contraction of rectum and relaxation of internal anal sphincter

3. Voluntary relaxation of external sphincter

Part II – Learning Objectives

1. Describe the gross and microscopic anatomy of liver, gallbladder, bile duct system, and pancreas.

2. Describe the digestive secretions and functions of the liver and pancreas.

3. Explain how hormones regulate secretions of the liver and pancreas.

Gross Anatomy of Liver• Largest visceral organ, 3 lb. organ located

inferior to the diaphragm• 4 lobes: R, L, caudate, quadrate

– ____________ ligament separates left and right lobes

– ____________ ligament, remnant of umbilical vein

a. round ligament b. falciform ligament

• __________ - pear shaped, adheres to ventral surface between right and quadrate lobes

• Blood supply – 1/3 hepatic artery and 2/3 portal vein

Microscopic Anatomy of Liver• Hepatic lobules• Portal triad consist of = _______ • Functions = metabolic regulation; waste product

removal (ammonia converted into urea); vitamin storage (fat soluble & B12); mineral storage (convert iron into ferritin); drug inactivation

• Hepatocytes• What are Kupffer cells?

Ducts of Gallbladder, Liver, Pancreas

• Bile passes from bile canaliculi to right and left hepatic ducts

• Right and left hepatic ducts join to form common hepatic duct

• cystic duct from gallbladder joins common hepatic duct to form common bile duct

• Duct of pancreas and CBD combine and empty into duodenum at major

duodenal papilla– guarded by sphincter of Oddi

Gallbladder and Bile• 500 to 1000 ml. bile are secreted daily from

_______. • _______ stores and concentrates bile• Bile = yellow-green fluid containing minerals,

bile acids, cholesterol, bile pigments and phospholipids– bilirubin pigment from hemoglobin breakdown

• intestinal bacteria convert to urobilinogen = brown color

– bile acid (salts) emulsify fats and aid in their digestion

a. Gallbladder b. Liver c. Pancreas d. Duodenum

Anatomy of Pancreas• Retroperitoneal gland posterior to stomach• Endocrine and exocrine gland

– secretes 1500 mL pancreatic juice into duodenum• water, enzymes, zymogens, and sodium

bicarbonate• Wirsung (main) duct runs length of gland to

open at sphincter of Oddi• Santorini (accessory) duct opens independently

on duodenum

Pancreatic Acinar Cells

• Panceatic acini – lined by simple cuboidal• Zymogens (proteases)

– trypsinogen– chymotrypsinogen– procarboxypeptidase

• Other enzymes– amylase– lipase– nucleases

Hormonal Control of Secretion & CCK

• Cholecystokinin released from duodenum in response to arrival of acid and fat– causes contraction of GB, secretion of

pancreatic enzymes, relaxation of hepatopancreatic sphincter

• Secretin released from duodenum in response to acidic chyme– stimulates all ducts to secrete more

bicarbonate

Homework (Self-Review) 1. Define the following: peritoneum, mesentery, lesser

omentum, greater omentum, peristalsis, segmentation, epiploic appendages, enamel, periodontal ligament, taenia coli, haustra, intestinal villi, rugae, plicae circulares, bile acids, kupffer cell, parietal cell, chief cell, absorptive cell, and anal columns of Morgagni.

2. Describe briefly the stages of gastric function.

3. Identify organs/structures that correspond to the following: a) secretes bile, b) stores bile, c) regulated by pyloric sphincter, d) has peyer’s patches, e) has brunner’s gland, f) numerous goblet cells and no villi, g) muscular tube behind the trachea, h) largest salivary, serous secreting gland.

4. List the components of portal triad.