Uterine Motility Flashcards
Briefly identify and describe the main layers of the uterus.
1) Perimetrium (serosa)
– Single thin outer layer of epithelium, not evident clinically
2) Myometrium
– Thick middle layer of smooth muscle
3) Endometrium
– Inner layer with glands, blood vessels, lymphatics and epithelial cells
Describe the physiological control of uterine motility.
1) Uterine contractions depend on gap junctions for phasic propagation of depolarisation
– Connexin 43
2) Hormonally influenced
– Menstrual cycle
– Pregnancy
– Labour
3) Minimal influence of autonomic innervation on contractions under physiological conditions.
Define connexin 43.
“Component of gap junctions, which allow for gap junction intercellular communication (GJIC) between cells.” (important for function of uterus including muscle contraction)
Distinguish between the junctions found in the heart, in vascular/intestinal smooth muscle, and in uterine muscle.
Gap junctions:
1) Cardiac muscle
– Constitutively expressed
– Arranged in intercalated discs
2) Vascular/intestinal smooth muscle
– Constitutively expressed
– Not concentrated in specialised areas (exception of myenteric interstitial cell of Cajal)
3) Uterine smooth muscle
– Inducible (especially hormonally).
– Fundal dominance during labour may arise from anatomical arrangement of expressed gap junctions.
Describe the expression of connexin 43 in rates during pregnancy.
- Uterus of pregnant rats.
- Immunofluorescence is absent day 4, evident day 14 and prominent day 20 (term).
- Disappears postnatally.
Describe innervation of the uterus.
• Sympathetic, parasympathetic and sensory
• Innervation of vascular smooth muscle and
myometrium
• Sympathetic outflow effect depends on receptor type
– a-adrenoceptors - contraction
– b-adrenoceptors - relaxation
• Ratio of sympathetic receptor types influenced by hormonal status.
Identify the main posterior pituitary hormones. Where are they produced ? secreted ?
Oxytocin and ADH/vasopressin (both created in the hypothalamus and secreted from the posterior pituitary into the circulation)
Compare the structure of ADH, and Oxytocin.
ADH and oxytocin are both 9 amino acid peptides, 2 amino acids different.
What are the main actions of ADH and Oxytocin ?
Both stimulate contraction of the uterus
ADH primarily acts on kidneys
Oxytocin also acts on mammary glands
What is the primary factor influencing number of Oxytocin receptors ?
Oxytocin receptor numbers and effect on uterine contraction are influenced by sex hormone levels.
Describe the number of oxytocin receptors in pregnancy.
At the start, few oxytocin receptors. At term, much increased (need oxytocin to trigger uterine contractions)
Describe the nature of uterine contractions in labour.
Increasingly regular, co-ordinated contractions that travel from the fundus to the cervix (fundal dominance) (stimulated by oxytocin)
Uterus relaxes completely between contractions.
Why are uterine relaxations in between contractions important ?
Because otherwise fetus would not receive enough blood
Identify groups of drugs which may modulate physiological control of uterine motility.
1) Uterine stimulants (oxytocics) (stimulate uterine contractions)
2) Uterine relaxants (tocolytics)
Identify the main clinical uses of oxytocics.
– Induce abortion.
– Induce and accelerate labour.
– Contract the uterus after delivery to control postpartum
haemorrhage (PPH).
