Pregnancy

Fertilization

1. The sperm reaches the zona pellucida surrounding the egg. The first sperm to the center wins!
2. Once the sperm makes contact, the acrosome reaction triggered
3. The head of the sperm fuses with the plasma membrane of the egg which causes a reaction to block polyspermy
4. The head of the sperm enters into the cytoplasm - at this point the "zygote" has 2 nuclei
5. The two nuclei fuse to form a true zygote

Beginning Steps Of Pregnancy

1. egg (oocyte) leaves ovary and enters fallopian tube
2. oocyte meets sperm in the fallopian tube, they join together and become a zygote with 46 chromosomes (gamete + gamete = zygote)
3. zygote travels down fallopian tube, dividing and growing all the way
4. once in the uterus, it is called a blastocyst.
5. the blastocyst implants into the side of the uterus
6. endometrium (inner lining of uterus) and the blastocyst itself secrete a wack-load of hormones

• blastocyst enters the uterus and has two cell types at this point
• inner cell mass - will become the fetus
• trophoblasts - will become the placenta
• requires cooperation between the endometrial lining of the uterus and the blastocyst

1. endometrium cells proliferate around the blastocyst and secrete hormones to stimulate placenta formation
2. trophoblasts respond to endomedtrium stimulation and some of them become syncitiotrophobasts (fused trophoblasts) that go on to become the placenta.

Important Hormones

• Estrogen
• Progesterone
• human chorionic gonadotropin (hCG)
• human placental lactogen

• hCG is made by the placenta and is released for the first 3 months of pregnancy. Its main role is to maintain the corpus luteum
• through maintaining corpus luteum, it indirectly increases estrogen and progesterone levels
• through maintaining corpus luteum, it indirectly maintains uterine wall thickness
• Estrogen has higher and higher levels as pregnancy goes on
• Progesterone has higher and higher levels as pregnancy goes on
• human placental lactogen is made by the placenta
• decreases a mothers glucose intake into her cells so there is more available for fetal development.

End Of Pregnancy

• regulated by a positive feedback system
• stretching of the cervix starts the process
• progesterone levels go down ––> induce contractions
• estrogen and oxytocin (from posterior pituitary) also induce contractions

• oxytocin
• prolactin
• INHIBITORS
• estrogen
• progesterone