PREGNANCY

Pregnancy (gestation) – carrying of developing young within the female reproductive tract Fertilization to birth Humans = 266 days (38 weeks) –(actually doctors measure 40 weeks because they start from the last menstrual cycle)

About 1 week after conception, the embryo (blastocyst) implants in the endometrial wall of the uterus Stem cells – give rise to every type of cell in the body (inner cell mass) Trophoblast – outer cell layer, becomes part of the placenta Placenta – organ that provides nourishment and oxygen to the embryo, also gets rid of metabolic waste

After Implantation: 4 pieces of life support 1.Amnion – fluid filled sac that encloses and protects the embryo, breaks just before birth 2.Yolk Sac – contains no yolk, produces embryos first blood and germ cells (gamete forming cells) 3.Allantois – forms part of the urinary bladder and part of the umbilical cord (life-line between embryo and placenta) 4.Chorion – part of the placenta, maintains high levels of estrogen and progesterone in mom’s blood…why? No new follicles mature Prevents menstruation

Placenta… Contains chorionic villi – embryonic blood vessels that are in close contact with maternal blood supply Mom’s blood and embryo’s blood do not mix. By diffusion, nutrients, oxygen, antibodies, viruses (German measles), and drugs move from mom to embryo and waste moves from embryo to mom

First Trimester 5 week embryo ~ 1 month = 7 mm Brain and spinal cord 4 limb buds, short tail and gill pouches 9 week Fetus ~5.5 cm Placenta, umbilical cord, amnion All organs and body parts Can move

Second Trimester increase in size and refinement Ultrasound – 18 week fetus, can show sex or abnormalities 14 week fetus ~ 6 cm 20 week fetus ~ 19 cm ~ ½ kg (1 lb) Nails, eyelashes, covered with hair

Third Trimester rapid growth Premature babies 24 weeks may survive with medical care Circulatory and respiratory systems prepare for breathing air Rotates head toward cervix At birth ave = –50 cm (20 in) – kg (6-10 lb)

Childbirth Labor – strong rhythmic contractions of the uterus controlled by hormones 1.Estrogen - Induce oxytocin receptors 2.Oxytocin – causes uterus to contract, placenta to make prostaglandins (more contractions)

Childbirth… 1.Cervix dilates (0 to ~10 cm), ave hours 2.Full dilation of cervix to birth, strong contractions, ave. 20 – 60 minutes, clamp umbilical cord 3.Delivery of the placenta (afterbirth), ~ 15 minutes after birth

Hormones after birth… Estrogen and progesterone allow uterus to return to pre-pregnancy state Prolactin – promotes milk production in mammary glands –colostrum (protein and antibodies) before milk –Milk comes in ~2-3 days after birth