Intro and Basic GI Concepts

Question 1

What are the three basic gastric functions?

Answer 1

1. Filling - acts as a reservoir for food and liquid
2. Mixing - mixing food w/ gastric secretions begins digestion
3. Emptying - gradually empties partially digested food into the intestine

Question 2

What are the components of the gastric mucosal barrier?

Answer 2

• surface mucus
• bicarb
• epithelial cells
• mucosal blood flow
• prostaglandins
• basal membrane

Question 3

How does disruption of the gastric mucosal barrier result in damage?

Answer 3

• results in pain, failure to distend normally, nausea and vomiting
• mucosal erosions or ulcers
  
  • occurs in gastric dz, liver dz, uremia, hypoxia, shock, sepsis

Question 4

What is the physiology of the vomiting reflux?

Answer 4

• it is a spontaneous forceful ejection of gastric contents through the mouth
• occurs when vomiting center receives sufficient stimulation to reach threshold and initiate the reflex
  
  • nausea, retching, vomiting (3 phases)

Question 5

How is the emetic center stimulated?

Answer 5

• anxiety, anticipation > cerebral cortex
• apomorphine, uremic toxins, hepatotoxins, endotoxins, cardiac glycosides > chemoreceptor trigger zone
• motion > oculovestibular system
  
  • connects to chemoreceptor zone (dogs)
  • connects to emetic center (cats)

all three of these stimulate the emetic center

Question 6

Describe the processes going on with intestinal fluid secretion and absorption

Answer 6

• most water absorption and secretion occurs in the SI
  
  • secretion = villous crypts
  • absorption = villous tips
• intake is typically only about 1/3 of fluids in the body, the majority is from endogenous secretions

Question 7

What are the pathophysiologic mechanisms of diarrhea?

Answer 7

• Osmotic: excess of osmotically active molecules retained in bowel lumen –> failure to digest/absorb nutrients; e.g. EPI, intestinal dysbiosis
• Secretory: stim of excess secretion overwhelms absorption, often persists despite fastin
• Exudative: incr mucosal permeability, leakage of tissue fluid, serum proteins, or blood; d/t lymphangiectasia, decr oncotic pressure, incr hydrostatic pressure
• Disordered motility - secondary role
• Mixed - most diarrhea

Question 8

What causes dysfunction of gastric filling?

Answer 8

• inflammatory and neoplastic dz
  
  • failure to relax
  • incr in postprandial intragastric pressure –> causes pain, nausea, and vomiting

Question 9

What determines the speed of gastric empyting?

Answer 9

• physical and chemical composition of a meal and food type, pH and osmolarity
  
  • caloric content of food
• stomach only empties when intragastric pressure exceeds duodenal pressure and pyloric resistance

Question 10

What occurs with gastric emptying dysfunction?

Answer 10

• can be disrupted in gastric and SI dz
• most delay emptying and cause vomiting
• gastric outlet obstruction results in gastric distension and stasis
• normal emptying time for a dog fed its caloric requirement once daily = 12-14h