Updated: 9/9/2020

Pregnancy

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Overview 
  • Fertilization and implantation 
    • ovum is fertilized in ampulla of Fallopian tube several hours after ovulation
    • blastocyst implants in endometrium 6 to 7 days after ovulation
      • syncytiotrophoblast cells secrete hCG that rescues corpus luteum
    • hCG
      • in first trimester,hCG sustains corpus luteum in presence of falling LH levels
        • corpus luteum produces progesterone
          • progresterone is necessary for maintenance of pregnancy
      • hCG levels detectable in blood (1 week post-conception)
      • hCG levels detectable in urine (2 weeks post-conception)
        • e.g., home pregnancy test
    • in second and third trimesters, placenta produces estrogen and progesterone
      • corpus luteum degenerates
    • hCG levels elevated in certain pathologies
      • hydatidiform moles
      • choriocarcinoma
  • Lactation 
    • post-delivery, ↓ progesterone levels, prolactin promotes lactation
      • initiation of milk production by alveolar cells
  • Suckling
    • stimulates sensory nerves that carry suckling signal from breast to hypothalamus via spinal cord, a process that mediates prolactin and oxytocin release
  • Prolactin
    • suckling sends signal from breast (nipple) to hypothalamus
      • suckling input in arcuate nucleus of hypothalamus inhibits dopamine release
        • dopamine travels via hypothalamic-portal system to anterior pituitary to inhibit prolactin (PRL) release by lactotrophs
        • suckling inhibits release of dopamine and causes ↑ PRL
    • prolactin promotes lactation and maintains lactation once established
    • prolactin → (-) hypothalamus → ↓ GnRH → ↓ FSH and ↓ LH
      • prolactin inhibits reproductive function 
  • Oxytocin
    • suckling sends signal from breast (nipple) to hypothalamus
      • suckling input in supraoptic and paraventricular nuclei of hypothalamus triggers oxytocin release via posterior pituitary
    • oxytocin promotes contraction of myoepithelial cells promotes milk letdown
    • oxytocin may promote uterine contractions in childbirth 
  • Physiologic changes   
    • increased red blood cell mass
    • increased plasma volume
    • increased cardiac output
    • decreased vascular resistance
    • mild respiratory alkalosis due to increased tidal volume
    • hypercoagulability
    • increased glomerular filtration rate
 
 

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