Early developmental events

1
Early developmental events

• Nuclei come together, chromosomes replicate
• Cell divides (36 hrs. post-fertilization)
• Cleavage continues gt cells form morula
• 5-6 days post-fert., conceptus enters uterus

2
Early events

• Enters uterus as blastocyst
• fluid-filled sphere
• single layer of flat cells (trophoblasts)
• inner cell mass
• surrounded by zona pellucida
• Day 6, uterine protease dissolves zona
• Day 7-14, implantation

3
Function of placenta

• allows implantation in uterine wall
• delivers important substances (oxygen, glucose)
  to fetus
• eliminates toxic substances (CO2, wastes)
• secretes hormones, growth factors to maintain
  pregnancy (hCG, estrogen, progesterone)

4
Implantation

• trophoblasts adhere to endometrium secrete
  digestive enzymes
• trophoblasts proliferate and form villi
• uterine blood vessels degraded (lacunae form)
• endometrial cells cover blastocyst

5
Implantation

• implantation complete by day 14
• placenta begins to produce human chorionic
  gonadotropin (hCG)
• placenta fully functional by end of 2nd month
• maintains corpus luteum until 3rd month

6
Umbilical cord

• connects fetus to placenta
• has 3 main blood vessels 1 vein, 2 arteries
• umbilical vein carries oxygenated blood from
  mother to fetus
• fetal waste products carried by umbilical
  arteries back to maternal circulation

7
Pregnancy 1st Trimester

• nausea, vomiting
• loss of appetite
• fatigue
• breast tenderness
• great individual variability

8
2nd Trimester

• fetal movements felt
• uterus reaches umbilicus of mother
• relief from morning sickness
• breasts increase in size (25 larger by end of
  pregnancy)
• colostrum produced

9
3rd Trimester

• breathing, walking, sleeping difficult
• Braxton Hicks contractions (20-30 sec.)
• increased need to urinate
• 2-3 wks before labor, lightening occurs

10
3rd Trimester

• engagement occurs a few hours or 1 week before
  labor (head moves into pelvic girdle)
• Weight gain during pregnancy
• recommended gain 25-35 lbs.
• only 8 lbs. of weight gain is contributed by
  fetus

11
Think, pair, share

• Mifepristone (RU486) is a progesterone receptor
  antagonist that is used along with
  prostaglandins to induce 1st trimester abortions.
  Why does this drug combination terminate
  pregnancy?

12
Weight gain during pregnancy

• full term baby 7.7 lbs.
• placenta 1.4 lbs.
• amniotic fluid 1.8 lbs.
• enlarged uterus 2.0 lbs.

13
Weight gain, contd.

• breast growth 0.9 lbs.
• blood volume 4.0 lbs.
• fluid retention 2.7 lbs.
• fat stores 3.5 lbs.
• TOTAL 24 lbs.

14
Sex differences in pelvic structure

• female has wider pubic symphysis (connective
  tissue between pubic bones)
• relaxin released from placenta and corpus luteum
  causes relaxation of p.s.
• female has wider pubic arch
• ischial tuberosities point outward in female