Match each term with the correct description below:

a. Fertilization
b. Zygote
c. Cleavage
d. Acrosomal reaction
e. Blastocyst
f. Human chorionic gonadotropin (hCG)
g. Inner cell mass
h. Ectoderm
i. Endoderm
j. Mesoderm
k. Chorionic villi
l. Placenta
m. Amnion
n. Umbilical cord
o. Relaxin
p. Parturition
q. False labor
r. Cesarean (C) section
s. Afterbirth
t. Menarche
u. Blastocyst cavity
v. Labor

Pairs

1. a - Event marking the moment the genetic material of a sperm joins with that of an ovum to form a fertilized egg.
2. b - Single cell containing 46 chromosomes formed from the union of an ovum and sperm.
3. c - Early stage of embryonic development in which the zygote undergoes rapid mitotic divisions.
4. d - Event in which sperm release enzymes and proteases when they are near an oocyte.
5. e - Hollow, sphere-shaped ball of cells with an inner cell mass.
6. f - Hormone produced by cells surrounding a developing embryo which causes the corpus luteum of the ovary to continue to produce other hormones that sustain pregnancy.
7. g - Small cluster of cells inside of a blastocyst.
8. h - Germ layer which becomes the nervous system and the epidermis of the skin.
9. i - Germ layer which forms mucosa and associated glands.
10. j - Germ layer which gives rise to the digestive tract, the heart and skeletal muscles, red blood cells, and the tubules of the kidneys, as well as a type of connective tissue called mesenchyme.
11. k - Embryonic tissue projections that will combine with tissue from the uterine lining to form the placenta.
12. l - Temporary organ that provides nutrients and oxygen to the developing fetus, carries away wastes, and produces the hormones of pregnancy.
13. m - Thin, tough, membranous sac that encloses the embryo or fetus.
14. n - Stalk of tissue containing blood vessels attached to the placenta.
15. o - Hormone that causes ligaments of the pelvis and pubic symphysis to relax.
16. p - Childbirth.
17. q - Weak, irregular uterine contractions that do not lead to delivery of a baby.
18. r - Delivery of an infant through surgical incision.
19. s - Placenta and attached fetal membranes expelled following delivery of the baby.
20. t - Event represented by the occurrence of the first menstrual period.
21. u - Large fluid-filled sphere inside of a blastocyst.
22. v - Series of events that expel the baby from the uterus.

Fertilization initiates human embryonic development with the formation of a zygote, which undergoes cleavage to become a blastocyst, implants in the uterus, and develops further through gastrulation into three germ layers. Hormones like hCG support early pregnancy, with key structures like the placenta, umbilical cord, and amniotic sac forming to sustain the embryo and fetus until parturition, possibly culminating in a natural birth or a surgical cesarean section.

The process of human development begins with fertilization, where a sperm and an egg fuse to create a zygote, a single cell with 46 chromosomes. Through a process known as cleavage, the zygote rapidly divides to form a multi-cellular structure. As this structure travels toward the uterus, it becomes a morula and then a blastocyst, which is characterized by an inner cell mass and the blastocyst cavity, surrounded by trophoblast cells.

The blastocyst implants into the uterine wall where embryonic development continues with the forming of the chorionic villi, leading to the development of the placenta, crucial for providing the embryo with nutrients and oxygen, and eliminating waste.

Gastrulation follows, where three germ layers form: the ectoderm (which will develop into the nervous system and skin), the mesoderm (which will become muscle, connective tissues, and more), and the endoderm (which forms internal organs). Hormonal regulation is vital throughout pregnancy, with human chorionic gonadotropin (hCG) playing a role in maintaining the pregnancy in its early stages.

Other key features include the formation of the amnion (a protective sac around the embryo), the growth of the umbilical cord (connecting the fetus to the placenta), and the hormone relaxin, which helps prepare the pelvis for parturition (childbirth). Childbirth can end naturally or, in some cases, through cesarean (C) section, which is a surgical incision to deliver the baby. Afterbirth refers to the expulsion of the placenta post-delivery, and irregular uterine contractions may indicate false labor rather than the onset of true labor.