smooth muscle Flashcards
Location of smooth muscle and disease treatments that target it
Found in: vasculature, airways, GIT, urinary tract, eye.
Hypertension and angina (coronary artery) are targeted by relaxing the vasculature
Asthma targetted by relaxing bronchial SM
Constipation by stimulating GIT SM. Diarrhoea by inhibitng GIT SM contraction
Structure of SM and peristalsis
Not on structures - no tendons. Contains and supported by connective tissue.
Arranged in single (arterioles/airways) or multiple sheets (e.g., intestine)
Intestinal SM is in perpendicular sheets (circular and longitudonal) that contract synchronised and wave like. Nerve myenteric plexus is found between the layers to coordinated the SM tone.
SM contraction mechanism (+ varicosities)
Actin filaments anchored to dense bodies. Increase of cellular Ca (from VGCCs or IC Ca stores by IP3) binds to calmodulin which activates MLCK, which phospohrylates myosin light chain using ATP. This then binds to actin to form a cross-bridge, which drives the contraction. The myosin is then dephosphorylated by MLCP (which is regulated by the subunit MYPT1).
cAMP (from Gas-coupled) causes PKA to inhibit MLCK
Characteristics of SM tone
SM are electrically coupled by gap junctions. this enables IC communication (such as by Ca). Due to this the fibres will act in unison, to synchronise contraction/relaxation.
When SM is stretched, it slowly becomes used to the new tone, and it becomes baseline, e.g., when eating large amount of food. Accomodates variable amounts of content in hollow organs without increasing pressure on the lumen.
what are varicosities
The smooth muscle is innervated by varicosities, where NTs are released stimulating the contraction or relaxation of the SM.
