Gastric Motility and Secretion Flashcards
(30 cards)
What are the main functions of the stomach?
- stores food
- mixes and digests food
- empties contents into the small intestine
What are the 3 main steps of gastric motility?
- Receptive relaxation
- mixing/peristalsis (contractions)
- gastric emptying
what are the two areas that the stomach is divided into?
- Orad region: receptive relaxation
- Caudad region: retropulsion, mixing
What is peristalsis?
the rhythmic contraction of smooth muscle in the walls of the GI tract that pushes contents forward, in the esophagus, stomach and intestines
What is receptive relaxation and what controls it?
when the upper stomach (orad region) relaxes to receive food bolus, controlled by the vagovagal reflex using VIP and nitric oxide
What are interstitial cells of Cajal (ICCs)?
gastric pacemaker cells that set the rhythm for stomach contractions and direct their flow toward the pylorus
What occurs during gastric mixing and Trituration?
- lower stomach contracts to mix and grind the food
- large particles undergo retropulsion to mix further until they’re small enough to pass
What stimulates gastric contractions during fasting?
Motilin stimulates periodic contractions called migrating myoelectric complexes to clear the stomach
What triggers Gastric secretion?
- Vagal stimulation (ACh & GRP)
- Gastrin from G-cells
- Histamine from ECL cells
- Food (especially protein) and stomach distension
What occurs once gastric secretion is triggered?
- parietal cells secrete HCl and intrinsic factor
- Chief cells release pepsinogen → activated to pepsin by HCl
- G-cells (in antrum) release gastrin → stimulates HCl via ECL cell → histamine release
What is the “alkaline tide”?
After eating, bicarbonate (HCO₃⁻) enters the blood as a result of HCl production, making venous blood temporarily alkaline
* H+/K+-ATPase pumps pump H+ into the lumen to form HCl
What occurs during gastric emptying?
well-mixed chyme moves toward the pylorus where particles <1 mm pass; larger ones are pushed back
What is the lower esophageal sphincter and what happens if it isnt functioning?
prevents acid from entering the esophagus
** If barrier is compromised, it can lead to esophagitis or possibly esophageal cancers
What inhibits acid secretion in the stomach and what medications block these inhiibitors?
Somatostatin and prostaglandins inhibit acid secretion through Gi-protein pathways
- NSAIDs, aspirin, ethanol inhibit PG formation
What two reflex pathways are triggered when stomach stretch receptors are activated?
- Short Reflex (ENS): oxyntic glands secrete HCl and Pepsinogen
- Long Reflex (Vagovagal Reflex): dorsal vagal complex → signals back down the vagus nerve to release gastrin-releasing peptide (GRP) → G-cells → gastrin into the bloodstream → oxyntic glands → more HCl and pepsinogen
what are the 3 phases of gastric secretion?
- Cephalic: smell, taste, conditioning
- Gastric: distension, small peptides, amino acids
- Intestinal: products of protein digestion
What slows gastric emptying?
- *fats (via CCK)
- *acid (via ENS reflexes)
- nerves (enterogastric reflex)
- high caloric/dense meal
- hyperosmolarity
- food particle size
- distension of duodenum
*main
What is gastroparesis?
abnormally slow gastric emptying, often linked to obesity or diabetes
What is amylin?
molecule co-secreted with insulin to
- Decreases pancreatic exocrine and bile acid secretions
- stimulate satiety
- Slows gastric emptying and glucagon secretion
What is intrinsic factor and where is it made?
made by parietal cells in the stomach and is needed to absorb vitamin B12 in the ileum
What are the 4 main components of gastric juice?
- HCl
- pepsinogen
- intrinsic factor
- mucus
What is Emesis?
stimulation of sensory afferent pathways to a higher center or chemoreceptor trigger zone (CTZ) to initiate the vomiting reflex
what happens during the expulsion phase of emesis?
- Inhibition of respiration, airway closure and diaphragm descent
- Increased salivation –> protect dentition
- Inhibition of gastric motility and inhibition of LES, UES, and pyloric motor activities
(i.e., opens these sphincters)
What is nausea and what are its triggers?
a conscious recognition that a food or toxin has been ingested
- GI tract or heart (mechanoreceptors or chemoreceptors) —-> CN IX or X —-> medulla oblongata
- cerebral cortex (food avoidance behaviors)
- change in the vestibular system (motion sickness)
