Physiology of the stomach and duodenum Flashcards
What is the function of the stomach?
Holds ingested food
Degrades this food both physically and chemically
Dellivers chyme to the small intestine
Enzymatically digests proteins with pepsin
Secretes intrinsic factor required for absorption of vitamin B12
Which secretory cells can be found in the gastric glands
Mucous neck cells: Secrete Acid mucus
Parietal cells: Secrete HCl and intrinsic factor
Cheif cells: Secrete pepsinogen
Enteroendocrine cells: Secrete Gastrin, histamine, endorphins, serotonin, cholecystokinin (CCK), somatostatin
What are the 3 phases regarding gastric secretion
Stimulatory and inhibitory events occur in 3 phases:
- Cephalic: Prior to food entry
- Gastric phase: Once food enters the stomach
- Intestinal phase: Partially digested food enters the duodenum
What are the exitatory and inhibitory events in the cephalic phase of gastric secretion
Excitatory: Sight or thought of food, Stimulation of taste and smell receptors
Inhibitory: Loss of appetite, depression, decrease in stimulation of the parasympathetic division
What are the excitatory and inhibitory events of the gastric phase
Excitatory: Stomach distention, Activation of stretch receptors, Activation of chemoreceptors, release of gastrin
Inhibitory: pH lower that 2, emotional upset overrides parasympathetic stimulation
What are the excitatory and inhibitory events in the intestinal phase
Excitatory: low pH, partially digested food enters the duodenum encourages gastric gland activity
Inhibitory: Distention of the duodenum, presence of fatty, acidic or hypertonic chyme, irritants
Explain the reflex mediated events involved in gastric filling
Recpetive relaxation: Food travels in the oesophagus, stomach muscles relax
Adaptive relaxation: the stomach dilates in response to gastric filling
Explain the formation of peristaltic waves in the stomach
The basal electrical rhythm is initiated by pacemaker cells, the cells of Cajal, which results in peristaltic waves at a rate of 3/min.
What is gatsric emptying regulated by
The neural enterogastric reflex
Hormonal (enterogastrone) mechanisms
These mechanisms inhibit gastric secretion and duodenal filling
Which factors affect the rate of gastric emptying
- fluidity of chyme
- Volume of gastric contents
- Osmolality of chime
- Caloric density
- Acidity of chime
- Body position
- Hormones - cholecystokinin, secretin, somatostatin, motilin, T3, insulin
Explain vomiting
Forceful expulsion of gastric and intestinal contents through mouth usually preceded by nausea.
It is controlled by the vomiting center in the medulla, efferent impulses go to diaphragm and abdominal muscles followign irritation
What are the functions of the duodenum
Movement of contents by peristalsis
Secretion of intestinal juice
Completion of chemical digestion of carbs, protein, fats
Protection against infections by microbes
Secretion of hormones cholecystokinin and secretin
Absorption of nutrients
