Conception and fetal development – Chapter 12
Definitions and study questions:
Conception—union of a single egg and sperm
Fertilization: where does it occur? Fertilization takes place in the ampulla (outer third) of the uterine tube.
Meiosis: The process by which germ cells divide and decrease their chromosomal number by half, produces gametes (eggs and sperm).
Mitosis: Body cells replicate to yield two cells with the same genetic makeup as the parent cell. Mitotic division facilitates growth and development or cell replacement.
Gametogenesis is (accomplished through meiosis) production of gametes. When and where does each occur?
a. Spermatogenesis – occurs when a male reaches puberty. It is the process by which male spermatogonia develop into male gametes.

b. Oogenesis – is the process of egg (ovum) formation. It begins during fetal life in the female.

Which parent determines the sex of the infant? The male
Implantation-
How long after conception does this occur? Implantation occurs between 6 to 10 days after conception. What is the developing baby called at this stage? The developing baby is called a blastocyst.
List the stages of fetal development.
Ovum or pre-embryonic, embryo, and fetus.
How long does each last?
Ovum stage last from conception until day 14. This period covers cellular replication, blastocyst formation, initial development of the embryonic membranes, and establishment of the primary germ layer.
Embryo stage last from day 15 until approximately 8 weeks after conception, when the embryo measures 3cm from crown to rump.
Fetus stage last from 9 weeks (when the fetus becomes recognized as a human being) until the pregnancy ends.
What are the primary germ layers? The primary germ layers are the ectoderm, the mesoderm, and the endoderm or entoderm. All tissues and organs of the embryo develop from these three layers.
Name the systems that originate from each?
The ectoderm – the upper layer of the embryonic disk gives rise to the epidermis, the glands (anterior pituitary, cutaneous, and mammary), the nails and hair, the central and peripheral nervous systems, the lens of the eye, the tooth enamel, and the floor of the amniotic cavity.
The mesoderm – the middle layer develops into the bones and teeth, the muscles (skeletal, smooth, and cardiac), the dermis and connective tissue, the cardiovascular system and spleen, and the urogenital system.
The endoderm or entoderm – the lower layer gives rise to the epithelium lining the respiratory and digestive tracts, and the glandular cells of associated organs, including the oropharynx, the liver and pancreas, the urethra, the bladder, and the vagina. The endoderm forms the roof of the yolk sac.
What is the relationship of trophoblast to chorionic villa? Trophoblast is the outer layer of cells surrounding the blastocyst cavity. The trophoblast differentiates into villous and extravillous trophoblast. Chorionic villa is Finger-like projections develop out of the trophoblast and extend into the blood-filled spaces of the endometrium. These villi are vascular processes that obtain oxygen and nutrients from the maternal bloodstream and dispose of carbon dioxide and waste products into the maternal blood.
What is the endometrium called after implantation of the fertilized ovum? After implantation the endometrium is called the decidua.
Chorion: develops from the trophoblast and contains the chorionic villi on its surface. The Chorion becomes the covering of the fetal side of the placenta. It contains the major umbilical blood vessels as they branch out over the surface of the placenta.
Amnion: Is the inner cell membrane that develops from the interior cells of the blastocyst. As it grows larger, the amnion forms on the side opposite to the developing blastocyst.
What is the function of the amniotic fluid and where does the fluid come from?
The amniotic fluid helps to maintain a constant body temperature. It serves as a source ofluid and a repository