Enzymes in Digestion Flashcards
What is the enteric nervous system?
It completes a neural circuit (independent from the CNS) that responds to a range of stimuli. It allows for coordination of the gut. It is modulated by the CNS via the para and sympathetic nervous pathways (autonomic nervous system).
Where are neurones located in the enteric nervous system?
Myenteric plexus - between longitudinal and circular muscle layers in the muscularis externa, controls peristalsis.
Submucosa plexus - in the submucosa. controlling mucosal, secretion, blood flow and barrier function.
In the muscularis externa, what are the two types of motor neurone?
Excitatory (contracting) - synthesise acetylcholine and act on the M3 receptors.
Inhibitory (relaxation) - synthesise nitric oxide to vasoactivate intestinal peptide of ATP. Inhibit P2Y receptors. In sphincter regions.
What are sensory neurones?
They are activated by stretch and chemical stimuli caused when the bolus moves along the GI tract.
What are secretomotor neurones?
Cause vasodilation of submucosal blood vessels - opening the lumen so more blood can flow.
What are gastriointestinal afferent neurones?
Convey sensory information from the gut to the CNS, very hypersensitive. Regulate satiety (fullness), anorexia, bloating, nausea and discomfort. Sensory info is conveyed through spinal afferents.
What is the vagus nerve?
Main sensory neurone. Found in serosa and mucosa. Respond to distension which causes abdominal pain via mechanoreceptors.
What is sympathetic innervation?
Fight or flight. Inhibits gut function by releasing noradrenaline to contract sphincteric muscles to slow propulsion of the contents.
What is parasympathetic innervation?
Operated by the vagus nerve. Main neurotransmitter is acetylcholine which acts on enteric nerves, facilitating digestion, opposing the sympathetic nervous system. Ensures peristalsis, therefore regulates the excitability of the enteric nervous system.
What causes hormones to be secreted?
Hormones are only secreted in response to a stimuli, if the stimuli is no longer present, they will top being signalled to be secreted.
What is endocrine regulation?
The gut contains a lot of enteroendocrine hormones which sample the chemical contents in the lumen of the GI tract. Some have villi to sense the content. They don’t release hormones into the lumen, but instead into the blood across the basal lateral membrane.
What is Histamine?
Secreted by enterochromaffin-like cells in the stomach and mast cells in lamina propria. It binds to H2 receptors on parietal cells, stimulating release of gastric acid.
What is gastrin?
It is stimulated by the vagal nerve and histamine. It secreted gastric acid from parietal cells and pepsinogen from chief cells.
What is somatostatin?
Stimulus - food intake (glucose and AAs)
Secreted from epithelial cells in the pyloric antrum, duodenum and pancreas. It inhibits release of gastric acid, gastrin, histamine.
What is Cholecystokinin CCK?
Stimulus - presence of fatty acids or AAs in chyme entering duodenum, and, Ach released from vagus nerve. Secreted from enteroendocrine cells. Stimulates contraction of gall bladder, and the release of digestive enzymes. It is a hunger suppressant.
