Pregnancy

  1. Overview

    1. Time from fertilization until birth
      1. 'gestation period' - 280 days from last menstrual period
      2. Embryonic (week 3 - 8)
      3. Fetus ( 9th week-->)
      4. pre-embryonic before 3rd week
    2. Genetic sex determined at time of fertilization
      (XX- female, XY- male)

  2. Fertilization

    1. Oocyte viable 12-48 hrs after ovulation
    2. Sperm viable 12-48 hrs after ejaculation
    3. Window of pregnancy 72 hrs before-24 hrs after ovulation
    4. Sperm hurdles:
      1. Vagina acidic (millions die)
      2. Cervical mucus barrier (unless E2 thins)
      3. Uterus - leukocytes (Phagocytize) at this point may only be 500-1,000 left
      4. Takes 24 hrs for sperm to have capacity to release hydrolytic enzymes
        1. cholesterol coating
        2. journey to uterine tube only takes mins
      5. Need 100s of acrosome to digest into oocyte
        1. hyaluronic acid, protease
    5. Sperm Entry
      1. Only 1 sperm enters egg (Na+ channel) in humans (monospermy)
      2. Na+ influx-> depolarization
      3. increase Ca+2 intracellularly
      4. cortical granules spill contents which bind H20 --swells (sperm detach zona pellucida)
      5. Once sperm enters into oocyte:
        1. completion of Meiosis II
        2. 2nd polar body ejected
        3. 2 pairs chromosomes combine--> zygote
        4. mitotic divisions begin (cleavage)
      6. Period of rapid cell division (pre-embryo) - no significant increase in size
        1. ovum - only source of nutrients
        2. after 3 days = Morula cluster of ~ 16 cells
        3. Blastocyst - lose outer layer and fluid fills
          1. 2 zones: inner cell mass (--> embryo)
            trophoblast (---> placenta)
      7. Still not implanted in uterus until 7-10 days after ovulation (complete in 14 days)

  3. Embryonic membrane development

    1. Amnion - transparent sac encircling embryon
      1. interrupted only by umbilical cord
      2. 'bag of waters'
        1. cushions
        2. maintains constant temp.
        3. allows free movement (mus/skel)
        4. amniotic fluid derived from maternal blood initially, later from fetal urine
        5. rapid turnover (~ 3 hrs)
    2. Yolk sac
      1. site of blood cell formation
      2. seeds of gonads
    3. Chorion-
      1. forms placenta
      2. outermost membrane later fuses tightly with amnion
    4. allantois-
      1. base for umbilical cord
      2. all organs develop from inner cell mass
      3. Germ Layers of embryonic disc:
        1. Endoderm: digestive, respiratory, some glands, urinary
        2. Mesoderm: muscle, blood, bone, reproductive
        3. Ectoderm: nervous, epidermis skin

  4. Placenta

    1. HcG - Human chorionic gonadotropin
      1. Hormone marker of pregnancy
      2. (LH - like) maintains Corpus Luteum
      3. Elevated after 3rd week--> 4th month
      4. is secreted by chorionic membrane and later by the placenta
    2. Placenta- is a temporary organ of fetal + maternal tissue formed after ~2nd month
      (corpus luteum degenerates)
      1. Produces Estrogen (E2), Progesterone thru birth
      2. fully formed by the 3rd month
        1. responsible for nutrition, respiration, excretion
      3. Produces other hormones:
        1. Lactogen (HPL) maturation of breasts growth of fetus, glucose sparing
        2. Chorionic thyrotropin (HCT)
          1. very similar to TSH
            Increase in metabolism
        3. Relaxin - pelvic ligaments, pubic symphysis allow widening (cervix relax)
      4. Placenta is- 'bridge' between mother, fetus
        1. no mixing of blood supply
        2. diffusion of nutrients, O2, ( & toxic substances)
    3. Fetal Circulation (HR ~3 1/2 wks)
      1. Unique features:
        1. Umbilical artery - Fetus to Placenta (waste)
        2. Umbilical Vein - Placenta to Fetus (O2, nutrients)
        3. 3 Vascular Shunts (close off at birth):
          1. ductus venosus - bypass liver
          2. foramen ovale - atrium
          3. ductus arteriosus - links pulmonary artery to aorta, bypass lungs (along with foramen ovale)

  5. Physiologic changes of pregnancy

    1. Adverse changes
      1. Nausea (increase in progesterone, estrogen)
      2. heartburn
      3. decreases motility of Large intestine (constipation)
      4. increases frequency of urination
      5. blood volume increases 25-40% -> (increases BP)
        1. Eclampsia (Toxemia)-edema, hypertensive
      6. decreased venous return (varicose veins)
    2. Labor (Parturition)
      1. Positive Feedback Mechanism
      2. Initiating events:
        1. increase in estrogens
          1. increased uterine receptors for oxytocin)
          2. works against progesterone (uterus activity)
        2. fetal & maternal oxytocin (muscle contract)
        3. prostaglandins (placenta) ( [inc] myometrium)
        4. emotional/ physical stressors --> hypothal.
      3. Dilation Stage
        1. Contractions cause infant against cervix (dilates): water breaks, longest stage
      4. Expulsion Stage -
        1. contractions ~2-3 min ( 1min duration)
        2. 'crowning' of infants head
        3. Episiotomy performed
      5. Placental Stage - ' afterbirth' or placenta
        1. exits ~ 15 min later
    3. Lactation - milk production
      1. Increase in Lactogen, Placental estrogen, progesterone stimulates PRH which stimulates Prolactin (Anterior Pituitary)
        1. milk comes in 2-3 days after birth:
          1. colostrum-yellow fluid
          2. Antibodies IgA
          3. Proteins
          4. mineral & vitamin rich
        2. Prolactin Stimulated by suckling
          1. no nursing decreases Prolactin, milk production
          2. hi prolactin inhibits gonadotropins
      2. Oxytocin --> milk letdown
        1. Positive feedback cycle
        2. pressoreceptos--> hypothal--> posterior pituitary --> myoepithelial cells (mammary gland)
          1. also stimulates uterus to contract (restore tone of uterus)