Gastric Physiology & Motility - Prunuske Flashcards
What gastric motile processes promote receptive relaxation?
- Rugae relax to create additional space.
- Dorsal Vagal Complex integrated input to alter gastric secretion and relaxation of the stomach via Enteric Nervous System.
- part of the swallowing reflex => activate gastric mechanoreceptors allowing storage of 2-4 L.
What gastric motile processes promote receptive mixing?
- Gastric motility patterns uses phasic contractions (3 cycles/min) to mix, triturate and sieve gastric contents.
- circumferential contraction => sweeps toward the pylorus resulting in anterograde and retrograde propulsion of material
- second similar contraction follows
- this contraction is sufficient to cause transient and partial opening of the pylorus, allowing small particles to exit the stomach.
- Larger particles are propelled back into the stomach to be further dispersed by contraction
- second similar contraction follows
- Further cycles of contraction against a closed pylorus continue mixing and grinding until all of the meal is emptied from the stomach
What gastric motile processes promote receptive gastric emptying?
- Contractions strengthen and speed up as they approach the closed pyloric sphincter
- Multiple repetitive contractions are sufficient to cause transient and partial opening of the pylorus, allowing small particles to exit the stomach.
- Larger particles are propelled back into the stomach to be further dispersed by contraction
What neural and hormonal processes increase receptive relaxation, mixing, and gastric emptying?
- Rapid emptying is caused by:
- tonic contractions of the reservoir
- deep peristaltic waves along the gastric body
- deep constrictions of the antral waves
- a wide opening of the pylorus
- a duodenal receptive relaxation
- peristaltic duodenal contractions
What neural and hormonal processes decrease receptive relaxation, mixing, and gastric emptying?
- Delayed emptying due to feedback inhibition is caused by:
- a prolonged relaxation of the reservoir
- shallow peristaltic waves along the gastric body
- shallow antral waves
- a small pyloric opening
- a lacking duodenal relaxation
- segmenting duodenal contractions
Is vagal release of ACh during accommodation associated with contraction or relaxation of the stomach?
relaxation
Expansion of the stomach signals forward along the enteric nervous system to signal what downstream effects?
EMPTY MORE DISTAL SEGMENTS.
- Gastroileal reflex: causes ileoceccal valve to relax transfer contents from small to large bowel
- Gastrocolic reflex: induces the need to defecate after ingesting a meal
What are the four components of gastric digestion?
- Low pH facilitates protein denaturation
- Pepsin endopeptidase releases peptides
- Gastric lipase (optimal at pH 3-6) produces free fatty acids
- Mechanical movements are important for emulsification and reducing the size of any solids
What is the extent of gastric absorption?
Gastric absorption is minimal!
Lipid soluble substance such as alcohol and aspirin can be absorbed by diffusion but there is no active transport
Absorption of these substances is associated with gastritis.
What is gastric trituration?
- Emptying of liquids involves proximal stomach (tonic) and of solids involves antral pump (phasic).
- Food must be smaller than 2mm in diameter to pass through the pylorus
Gastric motility
- Gastric motility patterns uses phasic contractions (3 cycles/min) to mix, triturate and sieve gastric contents.
- circumferential contraction => sweeps toward the pylorus resulting in anterograde and retrograde propulsion of materialsecond similar contraction follows
- this contraction is sufficient to cause transient and partial opening of the pylorus, allowing small particles to exit the stomach.
- Larger particles are propelled back into the stomach to be further dispersed by contraction
- circumferential contraction => sweeps toward the pylorus resulting in anterograde and retrograde propulsion of materialsecond similar contraction follows
- Further cycles of contraction against a closed pylorus continue mixing and grinding until all of the meal is emptied from the stomach
How does peristalsis of the stomach occur?
- Peristalsis occurs at the Basic Electrical Rhythm
- (BER) is 3 to 5 waves per minute in the stomach.
- This establishes the maximum frequency of the wave that is propagated over the stomach.
- The amplitude of the BER can be altered by neural (ACh causes calcium influx) and hormonal (Gastrin) input.
- The number of action potentials on the crests of the slow waves determines the magnitude of the contraction.
- Contractions strengthen and speed up as they approach the closed pyloric sphincter.
What factors of gastric and duodenal motility co-operate and modulate gastric emptying?
- A. Rapid emptying is caused by tonic contractions of the reservoir, deep peristaltic waves along the gastric body, deep constrictions of the antral waves, a wide opening of the pylorus, a duodenal receptive relaxation and peristaltic duodenal contractions.
- B. Delayed emptying due to feedback inhibition is caused by a prolonged relaxation of the reservoir, shallow peristaltic waves along the gastric body, shallow antral waves, a small pyloric opening, a lacking duodenal relaxation and segmenting duodenal contractions.
What is the rate of gastric emptying for a glucose solution vs. protein solution vs. solid meal?
- FASTEST: Glucose solution (Gatorade)
- Moderate: Protein solution
- SLOWEST: Solid meal
What are the intestinal influences on gastric motility?
- Gastric contractions and gastric emptying are inhibited by:
- acid in the duodenum via neural (enteric and vagal) and hormonal (secretin and somatostatin) mechanisms
- fat in the duodenum via hormonal (CCK) mechanisms and via enteric neural mechanisms
- osmolality of the duodenal contents via enteric neural mechanisms and perhaps hormonal mechanisms (GIP)
- Lower pH => slower emptying
- large particles decrease
- greater the peristalsis and pressure => faster the emptying
What are the three phases of the Migrating Motor Complex?
- Phase I: Quiescence
- 20-60 minutes
- Phase II: Irregular, Peristaltic Contractions
- 10-30 minutes
- Increase in gastric, pancreatic juices to eliminate bacteria
- Phase III: Intense Contractions
- 5-10 minutes
- Pylorus opens fully
- Stimulated by some prokinetic drugs- macrolides
What housekeeping mechanism functions to remove indigestible material during fasting and is induced by motilin?
Migrating Motor Complex
MMC an be noisy often source of growling- How might you suppress?
Eating!
What is Pyloric Stenosis?
- Congenital condition where pylorus fails to relax after a meal leading to malnutrition and dehydration.
- Treated with surgical myotomy
What is Gastroparesis?
- Reduced gastric emptying often due to diabetic neuropathy involving the vagus and enteric nerves in the stomach such that the stomach fails to generate enough force to empty the stomach.
- Other causes include drugs and cancer treatments.
- Results in nausea, vomiting, bloating, poor digestion, weight loss, malnutrition, impaired absorption of medications, and impaired glycemic control.
- Treat with prokinetic drugs.
What is Dumping Syndrome?
- Rapid gastric emptying often resulting from gastric bypass surgery, vagotomy, and high sugar-containing meals.
- Rapid entry of gastric contents into the duodenum represents an osmotic challenge, water moves into the lumen resulting in hypovolemia and reduced blood pressure.
- Results in nausea, weakness, dizziness, sweating, shakiness, diarrhea, heart palpitations
What is Peptic ulcer disease?
- Scarring and ulcers near the pylorus can delay emptying or in duodenal ulcers can lead to rapid gastric emptying due to loss of duodenal negative feedback mechanisms.
What is the definition of vomiting/emesis?
expulsion of contents of one’s stomach and intestinal contents through reverse peristalsis in the intestine
What are the possible causes of vomiting?
- gastritis
- poisoning
- brain tumors
- increased intracranial pressure
- migraine
- vestibular problems
- bowel obstruction
- appendicitis
- pain
- stimulation of the pharynx
- sensory input from higher centers
- vestibular information
- irritants or blockage in the GI tract
- blood-borne emetics
How are vomiting/emesis mechanisms coordinated?
By vomiting center in brainstem medulla
Why do you get increased salivation prior to vomiting?
to protect the enamel of teeth from dental erosion
What is the mechanism of vomiting?
- Retro-peristalsis, starting from the middle of the small intestine (why bile is present in vomit), sweeping up the contents of the digestive tract into the stomach, through the relaxed pyloric sphincter.
- Retching includes contraction of abdominal muscles, relaxation of esophagus but no vomiting
- Epiglottis closes off larynx to prevent aspiration of vomitus, hyoid moves upward and forward opening upper esophageal sphincter, soft palate drawn upwards, and contract diaphragm and abdominal muscles propelling stomach contents into the esophagus.
- The neurotransmitters that regulate vomiting are poorly understood, but inhibitors of dopamine, histamine, and serotonin are all used to suppress vomiting.
What are the consequences of vomiting?
- Consequences of vomiting include:
- dehydration
- hypokalemia
- hyponatremia
- In inebriated or unconscious individuals protective mechanisms may fail causing aspiration of vomitus leading to pneumonia.
