Fertilization to Implantation

Study Notes

Ovulation: Release of the egg.
Fertilization: Occurs in the fallopian tube. Sperm's acrosome penetrates egg's protective layers. Only sperm's nucleus enters the egg to form a zygote.
Capacitated Sperm: Sperm release enzymes to penetrate the cells surrounding the egg (corona radiata) and zona pellucida.
Zygote: A fertilized egg, formed from the fusion of sperm and egg nuclei.
Cleavage: Cell division without cell growth. The dividing cells proceed to the uterus.
Morula: A ball of cells formed during cleavage.
Blastocyst: A structure formed during cleavage, with an outer layer (trophoblast) and inner cell mass (ICM).
Implantation: The blastocyst attaches to the uterine wall (endometrium). Occurs around day 7.

Chorion: The outer layer of the blastocyst, that forms finger-like projections (chorionic villi) that penetrate the endometrium. It contributes to the placenta. Chorionic villi create a large surface area for the exchange of nutrients and waste products between the mother and the fetus.
Amnion: Amnion is a protective sac that surrounds the fetus. It's filled with amniotic fluid, acting as a cushion and regulating temperature.
Cellular Differentiation: Cells within the ICM start to specialize to form various tissues and organs.

A structure containing maternal blood filled sinuses and fetal tissue with fetal arterioles and venules.
Maternal and fetal blood do not mix. Material exchange occurs through diffusion.
The boundary between maternal and fetal tissues is important.
Placenta: This is a specialized organ that facilitates the exchange between maternal and fetal blood, providing nutrients and removing waste products.

HCG (Human Chorionic Gonadotropin): Produced by the developing embryo. Maintains corpus luteum. Its presence in urine is often used to detect pregnancy.
Corpus Luteum: Maintains hormone levels for the first 3 months of pregnancy.
Progesterone and Estrogen: Produced by the corpus luteum for the first 3 months. These hormones are crucial for maintaining the uterine lining and supporting fetal development.

Occurs around day 15. The inner cell mass differentiates into three germ layers: ectoderm, mesoderm, and endoderm.

Ectoderm: Forms skin, hair, nails, sweat glands, nervous system, eyes, ears, teeth, and mouth lining.
Mesoderm: Forms muscles, blood vessels, blood, kidneys, reproductive structures, connective tissue, cartilage, and bone.
Endoderm: Forms liver, pancreas, thyroid, bladder, and lining of the digestive and respiratory tracts.

Substances that may cause birth defects.
Includes Cigarette smoke, alcohol, prescription medications (antibiotics, acne medications, anti-thyroid drugs, anti-cancer drugs, thalidomide).
These substances interfere with the processes of fetal development.