1) Fertilization involves several sperm penetrating the corona radiata and zona pellucida to fuse with the egg nucleus to form a zygote, preventing additional sperm from entering. 2) The fertilized egg travels through the fallopian tubes to the uterus within 3-5 days, propelled by cilia and fluid currents. 3) The blastocyst implants in the uterine endometrium through enzymes secreted by trophoblast cells, forming the placenta which facilitates nutrient/gas exchange between mother and fetus and produces important hormones.

1. Fertilization, Anatomy &
Functions of Placenta
Dr. Sara Sadiq
(MBBS, M.Phil)

3. Steps of Fertilization
• Several sperm penetrate corona radiata.
• Several sperm attempt to penetrate zona pellucida.
• One sperm enters egg and nuclei fuse, producing a zygote.
• Egg’s plasma membrane and zona pellucida change to prevent
polyspermy.

6. Entry of Ovum into Fallopian Tube
• 3 to 5 days is normally required
• Transport is effected mainly by:
1. A feeble fluid current in the tube resulting from epithelial
secretion
2. Action of the ciliated epithelium that lines the tube; the cilia
always beat toward the uterus  activated by estrogen from the
ovaries
3. Weak contractions of the fallopian tube may also aid passage of
the ovum

8. Implantation of Blastocyst in Uterus
• Before implantation, the blastocyst obtains its nutrition from the
uterine endometrial secretions, called “uterine milk”
• Implantation results from the action of trophoblast cells that develop
over the surface of the blastocyst
• Trophoblast cells secrete proteolytic enzymes that digest and liquefy
the adjacent cells of the uterine endometrium
• Once implantation has taken place, the trophoblast cells and decidual
cells proliferate rapidly, forming the placenta

11. Placenta
• Site of metabolic and nutritional exchange
• Maternal side – decidua basalis
• Fetal side – amnion
• 15 – 20 cotyledons: contain the complex vascular system of villi

14. Functions of Placenta
1. Transfer gasses
2. Transport nutrients
3. Excretion of wastes
4. Hormone production – temporary endocrine organ  hCG, hPL,
estrogen and progesterone
5. Formation of a barrier – incomplete, nonselective – alcohol, steroids,
narcotics, anesthetics, some antibiotics and some organisms can
cross

15. Placental Transport
• Simple diffusion  water, oxygen, carbon dioxide, sodium and
chloride
• Facilitated transport  glucose and galactose
• Active transport  amino acids, calcium, iron, iodine and vitamins

16. Thank You