HUMAN REPRODUCTION BIOLOGY 269

1. HUMAN REPRODUCTIONBIOLOGY 269

2. Recall: Three Periods of Prenatal Development: Pre-embryonic = Fertilization to 2 weeks Embryonic = 2 weeks to 8 weeks Fetal = 8 weeks to 38 weeks (Birth)

4. Typical Pregnancy: Mother: Uterus reaches to ribcage Weight gain ~ 25 pounds Full-term fetus 8.0 lb Placenta 1.4 lb Amniotic fluid 2.0 lb Enlarged uterus 2.0 lb Enlarged breasts 1.0 lb Increased blood volume 4.0 lb Fluid retention 2.7 lb Maternal storage fat 3.5 lb 24.6 lb (From Mitchell et al, Nutrition in Health and Disease, 16th ed.)

5. (Mother): Fetal nutrition = Significant extra load on her system - Problems regulating nutrients - Increased risk of diabetes Fetal wastes = Significant extra load on her kidneys - Increased urination - Urine more concentrated - Increased risk of kidney failure Milk production stimulated by prolactin from pituitary - Breasts enlarged and tender - Expression of colostrum Joint between two pubic bones softens - Problems standing and walking

6. Fetus: Surrounded by amnion and chorion. Amniotic fluid ~ 1 liter/quart All organs mature, but: Lungs No food Temperature Vision Blood

7. Few weeks before birth: - Fetus rotates - Myometrium begins Stronger contractions Cervix

8. Triggering Events: - Adrenal glands of fetus stimulate placenta to produce chemicals called prostaglandins. - Prostaglandins cross placenta into mother’s blood; stimulate her pituitary gland to secrete oxytocin. - Prostaglandins also cause placenta to stop producing progesterone Myometrium (muscle layer) of uterus begins strong, coordinated, rhythmic contractions

9. Three Stages of Labor: (thinning) and 8-24 hrs (widening) of cervix 15-30 min 10-45 min

10. Stage 1: Effacement and dilation of cervix Contractions begin many minutes apart, relatively weak Gradually increase in strength and frequency Cervix thins, shortens due to pressure of fetal head – Cervical opening widens to about 10 cm - Amnion/chorion usually ruptures toward end of this stage

11. Stage 2: Expulsion of fetus Contractions of uterus strong, regular ~ 1-2 minutes apart. Mother may push with diaphragm and abdominal muscles. Head enters vagina, Stretches vagina & labia Head turns so top of head faces front Head = widest part, so rest of body follows easily Shoulders rotate as they pass through vagina, so baby faces right or left

12. Stage 3: Delivery of placenta Once breathing, baby no longer dependent on umbilical cord. Can be cut. Placenta still attached to endometrium of uterus. Ruptured amnion and chorion attached to placenta. Umbilical cord extends out vagina. Contractions of uterus continue, loosening placenta Placenta expelled through vagina

13. Adjustments after Birth: Mother: Uterus continues to contract for days to expell remaining functional layer of endometrium. Uterus becomes smaller over weeks / months Pubic joint (and other joints) tighten over over weeks / months Prolactin from pituitary gland continues to stimulate production of milk in breasts Oxytocin from pituitary gland stimulates expression of milk from breasts

14. Milk: First few days = High in fat, protein, mineral, antibodies Later:

15. Adjustments after Birth: Infant: As body cools,. As infant nurses,. Starts breathing, Blood starts flowing

16. Lots of things can go wrong during or after birth: 1) Labor & delivery begins too early or too late 2) Amnion/chorion ruptures too early or too late 3) Strong contractions can not develop 4) Fetus not head-down in uterus 5) Placenta over cervix 6) Placenta separates from uterus too early or too late 7) Fetus (or just head) too large to fit through cervix and vagina 8) Fetus (or just head) too large to fit through pelvic bones 9) Umbilical cord wrapped around fetus – gets constricted 10) Maternal hemorrhage x