Smooth Muscle
No description yet. This curated deck is ready for daily study.
Card preview (20)
where in the GI tract is skeletal muscle found?
pharynx , top 1/3 of the oesophagus and the anal sphincter
what are the 2 types of smooth muscle present in the GI tract?
phasic and tonic
where is tonic muscle found?
sphincters e.g. lower oesophageal, ileocecal (between large and small intestine), internal anal and orad (upper stomach)
where is phasic muscle found?
rapid contraction and relaxation, this is present in the body of the oesophagus, stomach antrum and small/ large intestines (e.g. peristalsis)
what is the role of myenteric plexus?
Involved in tonic contractions, can increase their rhythm and intensity for peristalsis
what is the role of the submucosal plexus?
Submucosal plexus has more of a sensory function and it modulates intestinal absorption
Give an example of a GI reflex?
Gastro-colic reflex, when stretch is detected in the stomach motor activity increases in the colon to provide space for the new chyme
explain Hirschsprung’s disease
(causes megacolon)- congenital lack of nerve cells in the lower colon, this makes the area become aperistaltic and it becomes tightly wound leading to megacolon before the point where the nerves are missing
explain chagas disease
infectious disease of a parasitic nature, resulting in a reduction in the number of ganglionic cells
explain achalasia
dramatic reduction in the number of neuronal cells in the lower esophagus
what is the vago-vagal reflex?
The vago-vagal reflex relaxes the fundus (upper area of the stomach) when there is stretching in the oesophagus, this is known as receptive relaxation
how is stomach pressure prevented from greatly increasing during digestion?
highly folded structure that flattens out and relaxes in response to vagus stimulation
explain the cephalic phase of gastric motility?
Inhibitory fibres stimulated in vagus nerve to allow large volume to enter stomach
explain the gastric phase of gastric motility?
• Excitatory phase where the stomach empties at rate proportional to volume in it • Activation of pressure receptors and release of gastrin stimulates activity • Myogenic reflex - stretching smooth muscle causes reflex contraction
explain the intestinal phase of gastric motility?
• Mainly an inhibitory phase to prevent overloading of the small intestine • Hormones and paracrine systems regulate the phase • e.g. high levels of fat = release of CCK which inhibits gastric motility
what are the 3 main functions of gastric motility?
• Peristaltic contractions- propulsion allowing propagated movement of food to be absorbed and eliminate waste products at the end • Produces segmental contractions- not related to propulsion that increase churning / mixing of food to aid absorption of nutrients Allows organs such as the stomach and large intestine to act as revisors, made possible by the sphincters
how often does the MMC occur?
every 90-120mins
what is the function of the MMC?
• Has a nutritional and cleansing function • Removes undigested squamous cells (from desquamation), bile and pancreatic secretions and undigested food • It also keeps bacteria populations in check e.g. prevents the migration of colonic bacteria into the terminal ileum
what are the 2 types of motility in the colon?
colonic rhythmic phasic and giant migrating contractions