Pharmacology of the Uterus Flashcards
What are the three layers making up the smooth muscle of the uterus?
β Outer longitudinal fibres
β Middle figure eight fibres
β Inner circular fibres
What are the three layers of the uterus?
β endometrium
β Myometrium
β perimetrium
What do uterine contractions do?
β Increase uterine pressure
β Forces content towards the cervix
β acts as a natural ligature to prevent blood loss
What is the activity of the myometrium like?
β Spontaneously active basal electrical activity
What kind of contractions are there in parturition?
β Rhythmic
What is the myometrium sensitive to?
β Neurotransmitters
β Hormones
What type of cells are in the myometrium?
β ICC pacemaker cells
How is synchronous contraction achieved?
β Electrical communication between gap junctions
β electrical activity is transmitted to adjacent cells
Where is electrical activity transmitted between in the myometrium?
β Between ICCs
β between ICC and smooth muscle
β between smooth muscle cell
How do the myometrium cells function as?
β A syncytium
Describe how contraction occurs?
β ICC periodic activation of inward currents
β depolarisations
β Ca2+ entry through VGCC
β Intracellular calcium leads to contraction
What are the slow waves of ICCs and smooth muscle responses modulated by?
β Neurotransmitters and hormones
Describe how calcium is increased inside the cell?
Slow wave of depolarisation β Ca2+ channels get activated β Ca2+ entry increases Ca2+ β Ca2+ binds to calmodulin β This phosphorylates myosin light chain kinase β actin interaction lead to contractions
Describe how oxytocin leads to increased Ca2+?
Oxytocin is Gq couples β Activation of phospholipase C β PIP2 β DAG + IP3 β IP3 binds to IP3 receptors in the SR β Causes Ca2+ from the store to be released into the cytosol β Ca2+ increases
What are smooth muscle cells joined by?
β Gap junctions
How can intracellular calcium be reduced?
β Na+/Ca2+ exchanger
β Ca2+ pump
β some Ca2+ gets taken into the mitochondria
What is the effect of low concentrations of stimulants on ICCs?
β Increase in slow wave frequency producing
β Increase in frequency of contractions
How is the myometrium similar to other smooth muscle tissues?
β There is a graded response - no threshold
β increases in Ca2+ lead to increases in force of contraction
What is the effect of higher concentrations of stimulants on ICCs?
β Increased frequency of action potentials on top of slow waves
β Increased frequency and force of contractions
What is the effect of even higher concentrations of stimulants on ICCs?
β plateau of slow wave producing prolonged sustained contractions
What is the effect of large concentrations of stimulants on ICCs?
β hypertonus (incomplete relaxation)
βCa2+ extrusion process is not as effective
β interferes with blood flow - fetal distress
What innervation does the myometrium have?
β Sympathetic
What receptors does the myometrium express?
β alpha and beta adrenoceptors
What is the effect of alpha 1 adrenoceptor agonist?
β contraction
What is the effect of beta 2 adrenoceptor agonist?
β relaxation
What are alpha 1 adrenoceptors coupled with?
β Gq
What are beta 2 adrenoceptors coupled with?
β Gs