Pregnancy – Conceptus – Gestation period – Preembryo – Embryo – From Egg to Embryo Pregnancy – Conceptus – Gestation period – Preembryo – Embryo – Fetus –

Relative Size of Human Conceptus Figure 28.1

Accomplishing Fertilization The oocyte is viable for 12 to 24 hours Sperm is viable 24 to 72 hours For fertilization to occur, coitus must occur no more than: Three days before ovulation 24 hours after ovulation Fertilization – when a sperm fuses with an egg to form a zygote

Only one sperm is allowed to penetrate the oocyte Blocks to Polyspermy Only one sperm is allowed to penetrate the oocyte Two mechanisms ensure monospermy Fast block to polyspermy - Slow block to polyspermy – zonal inhibiting proteins (ZIPs):

Events Immediately Following Sperm Penetration Figure 28.3

Cleavage: From Zygote to Blastocyst Figure 28.4

Implantation of the Blastocyst Figure 28.5a

Implantation of the Blastocyst Figure 28.5b

Placentation Figure 28.7a-c

Placentation Figure 28.7d

Placentation Figure 28.7f

When embryonic mass implants someplace other than endometrium Ectopic Pregnancy When embryonic mass implants someplace other than endometrium Most often is tubular In abdominal cavity must be delivered by cesarean section

Maternal Serum Screen and Amniocentesis Done after 16 – 17 weeks to detect fetal chromosomal abnormalities Serum screen – looks for protein markers Amniocentesis – more invasive

Hormonal Changes During Pregnancy Figure 28.6

Parturition: Initiation of Labor Estrogen reaches a peak during the last weeks of pregnancy causing myometrial weakness and irritability Weak Braxton Hicks contractions may take place As birth nears, oxytocin and prostaglandins cause uterine contractions Emotional and physical stress: Activates the hypothalamus Sets up a positive feedback mechanism, releasing more oxytocin

ACTH acts on fetus adrenal cortex to produce cortisol, Parturition Fetus becomes too large for uterus, triggers fetus anterior pituitary to release ACTH ACTH acts on fetus adrenal cortex to produce cortisol, Cortisol targets placenta Inhibits its production of progesterone Stimulates production of estrogen Increases release of prostaglandins

Parturition: Initiation of Labor Figure 28.16