Introduction to Gastrointestinal Physiology I, II, & III

Question 1

Location of ENS plexuses

Answer 1

Meissner’s (submucosal) plexus: in submucosa

Auerbach’s (myenteric) plexus: between circular and longitudinal muscle layers within muscularis propria

Question 2

Parasympathetic innervation of GI tract (location of preganglionic fiber and NT at postganglionic synapse)

Answer 2

Vagus nerve innervates upper GI tract

Pelvic nerve innervates lower GI tract

Preganglionic fibers synapse at myenteric and submucosal plexuses

Postganglionic neurons are cholinergic or peptidergic

Question 3

Sympathetic innervation of GI tract (location of preganglionic and postganglionic fibers)

Answer 3

Preganglionic fibers synapse in ganglia outside of GI tract

• Celiac, superior mesenteric, inferior mesenteric, and hypogastric ganglia

Postganglionic fibers are adrenergic and synapse on myenteric/submucosal plexuses or dirrectly innervate smooth muscle, endocrine, or secretory cells

Question 4

Contents of saliva

Answer 4

• HCO₃^-, K⁺
• α-Amylase and lingual lipase
• Mucus
• RNase and DNase
• Hypotonic solution

Question 5

Contents of gastric (stomach) secretions

Answer 5

• HCl
• Pepsinogen
• Intrinsic factor (IF)

Question 6

Contents of pancreatic secretions

Answer 6

• HCO₃^- (isotonic)
• Pancreatic lipase
• Amylase
• Proteases

Question 7

Contents of bile

Answer 7

• Bile salts
• Bilirubin
• Phospholipids
• Cholesterol

Question 8

Upper versus lower esophagus

Answer 8

Upper esophageal sphincter (UES)

• First 1/3 of esophagus
• Composed of skeletal muscle but not under voluntary control
• Prevent reflux of esophageal content into pharynx to gaurd airway aspiration

Lower esophageal sphincter (LES)

• Lower 2/3 of esophagus
• Composed of smooth muscle
• Prevents reflux of gastric contant into esophagus and mouth

Question 9

Achalasia

Answer 9

Caused by impairment in lower esphageal sphincter (LES) relaxation and/or loss of peristaltic sequencing of esophageal contraction (motor disorder)

• Dysphagia, chest pain, regurgitation

Question 10

Vagovagal reflex

Answer 10

Causes relaxation (increase in volume) in orad stomach in response to distention

• Mechanoreceptors in caudad stomach (vagal afferent) signal to dorsal vagal complex
• Vagal efferent signals cause relaxation of orad region via VIP and NO secretion
• Vagal efferent signals also cause contraction of caudad region via Ach

Question 11

Gastroporesis

Answer 11

Delayed gastric emptying

• Cause: Obstruction, nerve damage to pyloric sphincter, or other nerve damage
• Symptoms: nausea, vomiting, bloating

Question 12

Dumping syndrome

Answer 12

Upper portion of small intestine fills too quickly with undigested food from the stomach

• Cause: certain gastric surgeries and precipitated by high sugar foods
• Symptoms: distention (pain), osmotic diarrhea, alimentary hypoglycemia (due to sudden increase in insulin release)

Question 13

Proteins secreted into gastric lumen (and cells they are secreted by)

Answer 13

Cheif cells

• Produce, store, and secrete pepsinogen

Parietal cells

• Secrete HCl and intrinsic factor (IF)

Mucous cells

• Secrete mucous and HCO₃^-