Ch. 23

1
Ch. 23

• Pregnancy and Development

2
Gestation

• Pregnancy lasts an average of 266 days
• Measured from last day of menstrual period (LMP)
• Birth is predicted to occur 280 days (40 weeks)
  from LMP
• Pregnancy is divided into trimesters
• Fertilization is when a sperm reaches a secondary
  oocyte, invades the follicular cells, and binds
  to cell membrane
• The sperm head penetrates and a fertilization
  membrane prevents additional sperm from entering
• See figure 23.3

3
Prenatal development

• Fertilization occurs in the distal half of the
  uterine tube
• Developing individual is a blastocyst for most of
  the first 2 weeks
• Blastocyst attaches to endometrium about 4 days
  after arrival (implantation)
• It becomes an embryo from 3-8 weeks
• It becomes a fetus from 9 weeks to birth
• After birth the fetus becomes a neonate for the
  first 6 weeks

4
Hormones

• Corpus luteum is important source of hormones in
  the first 7-12 weeks
• Placenta takes over after corpus luteum
  degenerates
• Hormones include estrogens, progesterone, HCG,
  and human chorionic somatomammotropin

5
Human chorionic gonadotropin

• Detected in home pregnancy tests as early as 8 or
  9 days
• Peaks at 10-12 weeks then falls
• Stimulates corpus luteum growth which is
  necessary to maintain the pregnancy in the early
  stages

6
Estrogens

• Increases to about 30 times normal by end of
  gestation
• Secreted by corpus luteum in early pregnancy
• Androgens converted to estrogen by placenta for
  remainder of pregnancy
• Estrogen stimulates tissue growth in fetus,
  increases size of uterus, breasts, and external
  genitalia
• Also makes joints more limber and cartilage more
  flexible (preparing for birth)

7
progesterone

• Secreted by placenta and corpus luteum
• Works along with estrogen to suppress FSH and LH
  so additional follicles dont mature during
  pregnancy
• Progesterone suppresses uterine contraction to
  prevent early birth
• Promotes proliferation of decidual cells of the
  endometrium on which the blastocyst feeds
• Also plays a role in development of secretory
  acini (lactation)

8
Human Chorionic Somatomammotropin

• HCS secretion begins around the 5th week and it
  increases steadily until term
• Less understood than others hormones, mother
  secreted more of this than any of the others
• Seems to play a role in reducing mothers insulin
  sensitivity so the baby gets more glucose

9
Primary Germ layers-a cells fate is determined by
which layer it is in

• Ectoderm-develops into nervous system, sensory,
  hair, epidermis, linings of mouth and anal canal,
  nails, glands of skin
• Mesoderm-develops into muscle, bone, blood, blood
  vessels, kidneys, internal reproductive organs
• Endoderm-develops into epithelial linings of
  digestive tract, respiratory, urinary bladder,
  urethra

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Miscellaneous

• By full term, the placenta requires 625 ml of
  blood per minute
• Moms blood volume increases about 30 during
  pregnancy
• Stretching of the skin during pregnancy leaves
  striae or stretch marks
• Melanocyte activity increases and nipple, areola,
  and linea alba darken (racing stripe)

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Interesting note

• Oxytocin may play a role in the bonding that
  occurs between mother and child!
• Zygote is the name used to describe the ovum
  immediately after fertilization
• At 35 days the heart is beating and the embryo is
  3.8 inches long

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Disorders in pregnancy and early development

• Tubal pregnancy-fertilized egg implants in
  uterine tube
• Placenta previa-blastocyst implants too low and
  too close to cervical opening, causes placenta to
  detach there and causes hemorrhaging
• Abruptio placenta-separation of the placenta in a
  pregnancy of 20 weeks or more, can cause
  immediate death of fetus and mother

13
Continued

• Preeclampsia- acute hypertension after 24th week,
  with proteinuria and edema and may progress to
  eclampia (life threatening)
• Miscarriage-loss of embryo or fetus before the
  20th week (spontaneous abortion)
• Most common cause is a structural or functional
  defect
• Problems with mom like hormone imbalances can
  cause this too
• Stillbirth-loss after 20 weeks

14
Childbirth-parturition

• Braxton Hicks contractions are practice
• Declining progesterone levels stimulate a
  prostaglandin that promotes uterine contractions
• Labor contractions increase in response to
  oxytocin (may give pitocin to speed things up)
• Fetus is usually positioned head down

15
continued

• May require an episiotomy-incision in vulva to
  widen the vaginal canal and prevent tearing
• Multiple births-twinning can result from 2
  different processes
• Identical twins -develop from the same fertilized
  egg and have the same genetic code
• Fraternal twins -develop from two separate eggs
  (can have 2 biological fathers) HOW?

16
Stages of Labor

• Primipara-giving birth for first time
• Multipara- previously given birth
• Dilation is first stage-lasts 8-24 hours
  (usually) in first pregnancy, much quicker in
  subsequent pregnancies
• Marked by dilation and effacement (thinning of
  cervix)
• Membranes usually rupture here (doc may have to
  do this)

17
Stages continued

• Second stage-expulsion-usually 30 minutes in
  primipara, 1 minute in multipara
• Begins when babys head enters the vagina and
  lasts until the baby is expelled
• Crowning is when they can see the head
• Valsalva maneuver helps push baby out (hold
  breath, contract abs, push)
• Clamp cord in two places when baby is out

18
Stages continued

• Third stage is placental stage
• Uterus contracts and expels the placenta
• Doctors/nurses check it to make sure it is all
  out
• Also called afterbirth
• About 350 ml of blood is usually lost at this
  stage too
• Postpartum period-6 weeks-is puerperium and mom
  gets back to normal
• Uterus shrinks by a process called involution
• Can save cord blood or donate it for stem cells

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Neonatal period

• Newborns first breath must be forceful because
  its lungs are collapsed and the airways are small
  
• Surfactant is secreted by the lungs of a full
  term infant to reduce surface tension which holds
  the moist membranes of the lungs together
• First breath is stimulated by rising CO2 and
  decreasing pH, low oxygen, drop in body temp

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Neonate continued

• Once placenta stops functioning the
  cardiovascular system changes quickly
• Umbilical vessels constrict (Umbilical arteries
  close first)
• If umbilical cord isnt clamped for a minute or
  so the umbilical vein continues to add to the
  newborns blood volume
• The foramen ovale closes as a result of changes
  in blood pressure in the left and right atria
  (becomes fossa ovalis)

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First stage of labor is?

• Placental stage
• Dilation
• expulsion

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Disorders and/or birth defects

• Progeria-mutations occur in DNA that cause
  changes associated with aging
• Conjoined twins-1 in 50,000 births and 40 are
  stillborn
• Thalidomide-used to ease morning sickness
  prevented limb development

23
Birth defects continued

• Rubella-exposure in first trimester may cause
  heart defects, deafness, cataracts
• Fetal alcohol syndrome-small head, facial
  deformity, mental impairment, small size (3rd
  most common cause of mental defects in newborns)
• Malnutrition during pregnancy causes IUGR
  (intrauterine growth retardation), causes small
  infant but older child has problems with obesity

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Interesting facts

• Respiratory and digestive systems mature last,
  which is why premature infants often have
  difficulty digesting milk and breathing
• Fetal hemoglobin can carry 20-30 more oxygen
  than the adult hemoglobin

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Readings

• Table 23.1-assisted reproductive technology
• Dont forget the clinical applications and boxes!