2. Human/Mammalian Fertilization
Human fertilization, or conception, is the biological process in which the human egg and sperm meet and fuse.
It occurs mostly in the fallopian tube.

3. After entering the female reproductive system, the sperms swim towards the oocyte (or egg) through flagellation.
The oocyte has several “defenses” to make sure that only one sperm reaches the nucleus.

4. Protective layers of the oocyte:
Corona radiata – two or three layers of follicle cells that supply vital proteins to the cell.
Zona pellucida – the glycoprotein membrane that surrounds the cell membrane of the oocyte.
Perivitelline space – space between zona pellucida and cell membrane
Vitelline membrane – attached to the cell membrane of the ovum

5. Two simultaneous processes occur when the sperm and egg meet.

6. Acrosomal Reaction – occurs in the sperm
The acrosomal reaction occurs in the sperm cells when it comes into contact with the corona radiata of the egg (also called the jelly layer).
The acrosome is found on the tip of the sperm’s head like a cap.
When it does reach the corona radiata, the acrosome dissolves so that the actin filament (in dark blue) can come into contact with the zona pellicuda. Then the plasma membrane of the sperm fuses with the plasma membrane of the egg. The cortical reaction then helps to bring the sperm nuclei inside and “close” the egg to other cells.

7. Cortical Reaction – occurs in the egg cell
The cortical reaction is the exocytosis of the cortical granules. When the plasma membranes of the two cells fuse, it causes calcium stored inside the egg cell to be released, causing a chain reaction that makes the cortical granules fuse with the cellular membrane.
Cortical Reaction – occurs in the egg cell
It is an exocytosis of the cortical granules.

8. Polyspermy
It is the condition wherein two or more sperms fertilize an egg.
Fast block to polyspermy – once the sperm binds to the vitelline layer, the plasma membrane depolarizes, disallowing entry of other sperm.
Slow block to polyspermy – after the plasma membrane depolarizes, the vitelline layer hardens into the fertilization membrane which ultimately disallows the entry of sperm.

9. Each pronuclei has 23 chromosomes.
Once the cell membranes fuse, the nucleus of both sperm and egg prepare to fuse.
At this point, the nuclei of the egg cell and sperm cell are now called the pronuclei.
Each pronuclei has 23 chromosomes.
The sperm's tail and mitochondria degenerate with the formation of the male pronucleus. This is why all mitochondria in humans are of maternal origin.

10. The zygote is still traveling down the Fallopian tube.
After the sperm and egg pronuclei fuse, it then proceeds to its first mitotic division resulting in the zygote.
The zygote is still traveling down the Fallopian tube.
After the first mitotic division, the process is now known as cleavage. This refers to the divisions that forms the blastula.
Zygote is the product of fusing the pronuclei.

11. After the cleavage forms over 100 cells, the zygote is now called a blastocyst. This occurs at the fifth day after conception.
After cleavage is completed, the blastocyst is now the blastula.

12. The trophoblast is the outer layer of the blastocyst
The trophoblast is the outer layer of the blastocyst. The blastocoel is the hollow space inside the blastocyst.
Once the blastocyst has formed, it attaches to the endometrium or the uterus lining. The blastocyst contains the inner cell mass, and the trophoblast.

13. The inner cell mass forms into the ectoderm, mesoderm and endoderm layers of the embryo.
The trophoblast eventually forms the placenta which will supply the nutrients for the embryo in the future.
The trophoblast is the part that connects the blastocyst to the endometrium.

14. At the moment of conception to about 12 weeks later is the first trimester.
Organogenesis is the process wherein the inner cell mass becomes the endoderm, ectoderm, and mesoderm then becomes the innner organs.
First Trimester

15. Human chorionic gonadotropin (HCG) - is the hormone made by the embryo that maintains the production of progesterone. Progesterone thickens the lining of the uterus to ensure safety for the fetus and to provide nutrients to the placenta.
First Trimester

16. Second Trimester This is the 4th month to the 6th month of pregnancy.
The zygote is past its embryonic stage and is now called a fetus.
The placenta is now developed and regulates nutrients in and out of the fetus.
Umbilical cord - connects the fetus to the placenta.
Second Trimester

17. First of all, the belly drops because the fetus is now upside down, to let the head go out first.
The baby is already fully developed but still needs heat for its homeostasis, that is why it cannot go out prematurely yet.
The pregnancy period or the gestation is nearing its end.
Third Trimester

18. Labor/Parturition Stage 1: Contractions Stage 2: Delivery
8 hour duration women’s first birth
4 hour duration for second birth and so on.
Stage 2: Delivery
The part of labor when the head of the baby is through the pelvis up to the time when the baby is fully outside.
The umbilical cord can be safely cut then.
Stage 3: Placenta
The female reproductive system will remove the placenta within 30 minutes of childbirth.
First of all, the belly drops because the fetus is now upside down, to let the head go out first.
Labor/Parturition

19. Post-Childbirth
Lactation – secretion of milk from the mammary glands. Also known as breastfeeding.
The hormones prolactin and oxytocin are produced. Prolactin stimulates milk production. Oxytocin stimulates milk ejection.
Prolactin makes the milk, oxytocin secretes the milk.

20. Pregnancy Complications
Placental Abruption
It is a condition wherein the placenta separates from the endometrium.
It is occurs most commonly after 20 weeks of gestation.

21. Ectopic Pregnancy
A condition where the embryo develops anywhere but the uterus.
A symptom may be hematosalpinx (fallopian tube bleeding).
The embryo looks for a blood supply so it can strain the tissues around it and cause tissue damage. It will then cause bleeding.
in most cases, the irritation due to hematosalpinx forces the embryo out of the tube and results in a miscarriage.
Ectopic pregnancy is most of the time fatal.

22. Mammalian Adaptations in Pregnancy
Attachment of infant to the mother.