Physiology of Parturition Flashcards Preview

Life Cycles: Unit 2 > Physiology of Parturition > Flashcards

Flashcards in Physiology of Parturition Deck (14)
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Hormonal mechanisms to maintain myometrial queiscence during pregnancy

  • Myometrial inhibitor is progesterone, a smooth muscle relaxant, pro-gestation hormone. Blocks MLCK and thus the action of prostaglandins, promoting quiescence.
  • Progestin uses NO → cGMP to inhibit myosin, actin, and calcium interaction.  
  • CRH interacts through cAMP and PKA to inhibit these interactions, and stimulates NO as well.


Types of proteins that contribute to myometrial contractility

  • proteins that promote contractility of actin and myosin
  • proteins that increase myocyte excitability
  • proteins that promote intracell connectivity


Characteristics of proteins that promote contractility of actin and myosin

  • Calmodulin and increased calcium → activate myosin light chain kinase (MLCK) → MLCK activates myosin via phosphorylation.
  • Following myocyte depolarization there is an influx of [Ca2+]E through voltage-regulated calcium channels and the release of calcium from intracellular stores results in an increased [Ca2+]I, thereby promoting myosin-actin interactions and, consequently, contractions


Characteristics of proteins that increase myocyte excitability

  • ↓ Na+/K+ exchange pumps → At the time of labor, the function and distribution of these channels are altered so that a lower intensity stimulus is required to depolarize myocytes and produce the associated influx of calcium that generates contraction
  • ↓ β2 and β3 - sympathomimetic receptors. These normally ↑ the opening of potassium channels, which reduces the excitability of the cell


Characteristics of proteins that promote intracell connectivity

  • As parturition progresses → ↑synchronization of the electrical activity of the uterus
  • This is achieved via connecting myofibrils and through the production of prostaglandins, which act in a paracrine fashion to depolarize neighboring myocytes → increased recruitment into contraction
  • Multimers of connexin 43 connect myocytes, permitting function in concert


Phases of myometrial activation

0 - Quiescence

1 - Activation → it is unclear what signals the switch from quiescence to activation

2 - Stimulation → encompasses labor phases 1 - 3 (next LO)

3 - Involution → corresponds to phase 4 of labor; the six hours post delivery


Define: 4 clinical stages of labor

  1. Onset of effective contractions to complete dilation of the cervix
    1. Latent phase → Cervix closed
    2. Active phase → Cervix thinned out
  2. Complete dilation of the cervix to delivery of the fetus
  3. Delivery of the fetus to delivery of the placenta
  4. First 6 hours after delivery. After this, mom is usually by this time in the clear, ↓ risk of complication


Mechanisms of increased calcium near term

  • Put simply, prostaglandins (PGE) and oxytocin (OT) binding stimulate ligand-gated calcium receptors.
  • PGE and OT also promote Ca2+ release from SR
  • All of this intracellular Ca2+ triggers the opening of voltage gated Ca2+ channels and depolarization of the cell.
  • And then....
    • Calcium enters the depolarizing cell and combines with calmodulin to form calmodulin–calcium complexes that activate myosin light-chain kinase, which in turn phosphorylates the myosin light chain.
    • ==>  generation of ATPase activity ==>  sliding of myosin over the actin filaments  = contraction


Role of CRH and cortisol in initiation of parturition

  • CRH
    • Stimulates labor
    • Induces fetal cortisol secretion which → fetal pulmonary maturity,
    • ↑ rapidly before delivery and peaks at delivery
  • Fetal cortisol induces fetal pulmonary maturity


Role of estrogens in initiation of parturition

  • Induce contraction.
  • Increases in inflammatory factors such as COX-2 and IL-8 which are early events in the progression to active labor.
  • These increases precede changes in progesterone receptors, which cause changes in estrogen receptors and, as a consequence, expression of connexin 43 and the oxytocin receptor


Role of oxytocin and PGs in initiation of parturition

  • Oxytocin
    • Stimulates contractions
    • Activates MLCK,
    • ↑ intracellular Ca2+
    • Activates prostaglandins
  • Prostaglandins
    • Stimulate myometrial contractions
    • ↑ intracellular Ca2+


Role of fetal hypothalamic-pituitary axis in parturition

  • As term approaches, there is an ↑corticotropin by the fetal pituitary and ↑steriodogensis in the fetal adrenal glands.
  • ↑ fetal cortisol → maturation of fetal lungs → maturing fetal lungs ↑ surfactant production.
  • Amniotic fluid surfactant proteins stimulate the inflammation that is observed in the adjacent fetal membranes, cervix and underlying myometrium at the time of labor.
  • This inflammatory process is one element that leads to the onset of labor.


Maternal conditions assoc. w/preterm birth

  • Chronic HTN / HTN disorders of pregnancy
  • SLE
  • Restrictive lung disease
  • Hyperthyroidism
  • Pre-gestational DM
  • GDM
  • Maternal cardiac disease
  • Asthma
  • Pre-gestational renal disorders


Fetal/infant conditions assoc. w/preterm birth

  • Cerebral palsy: Swedish study → 50% of children with cerebral palsy had been born prematurely
  • Hypothermia
  • Hypoglycemia
  • RDS
  • Neonatal jaundice
  • Respiratory illnesses
  • Necrotosing enteritis
  • Intraventricular brain hemorrhage
  • Hearing impairments, retinopathy of prematurity
  • Higher incidence of motor impairment, ADHD