1 of 16

�FERTILIZATION /CONCEPTION�

  • It is the fusion of the sperm with the secondary oocyte to form the zygote.
  • The process takes about 24 hours and it occurs in the ampulla of the uterine tubes.

​

2 of 16

3 of 16

PROCESS OF THE FERTILIZATION �

  • At intercourse about 300 million sperm are deposited in the posterior fornix of the vagina. Most of them are destroyed by the acid medium of the vagina only few are propelled into the uterine tubes.
  • Those inside the fallopian tubes undergo the process of capitation.
  • The acrosome layer of the sperm releases an enzyme Hyaluronidase which disperses the corona radiate to penetrate the oocyte.

​

4 of 16

�PROCESS OF THE FERTILIZATION CONT’D �

  • Oocyte after ovulation is 0.15mm in diameter.
  • The cervix under the influence of oestrogen secretes alkaline mucus that attracts spermatozoa.
  • The first sperm that reaches the zona pellucida penetrates it and a cortical reaction occurs making it impermeable to other sperms.
  • The oocyte at the completes its 2nd meiotic division and becomes mature.

​

5 of 16

�PROCESS OF THE FERTILIZATION CONT’D�

  • The pronucleus now has 23 chromosomes referred to as haploid.
  • The tail of the sperm degenerate as the sperm penetrate the oocyte and there is formation of male pronucleus.
  • The male and the female pronuclei fuse to form a new nuclueus that is the combination of the genetic material from both sperm and oocyte.

​

6 of 16

�ZYGOTE �

  • The new cell that is formed from the union of the sperm and the oocyte is called zygote.

DEVELOPMENT OF THE ZYGOTE

  • Pre-embryonic period- 1st to 2nd week after fertilization.
  • The zygote undergoes mitotic cellular replication and divides into 2 cells at day 1.
  • 4 at day 2,
  • 8 by 2.5days

7 of 16

 � DEVELOPMENT OF THE ZYGOTE CONT’D�

  • 16 by 3rd day and it is known as the morula.
  • Cavitations occurs and the outermost cells secrete fluid into the morula and becomes the blastocyte comprising of 58 cells by the process of blastulation by day 4.
  • Blastocyte enters the uterus by day 3-5days and possesses an inner cell mass or embryoblast and an outer cell mass or the throphoblast.

​

8 of 16

 � DEVELOPMENT OF THE ZYGOTE CONT’D�

  • The trophoplast becomes the placenta and chorion. The embroyoblast becomes the embryo, amnion and the umbilical cord.
  • The cells of the embroyoblast differentiate into 2 types of cells.
  • Epiblast
  • hypoblast

​

9 of 16

EPIBLAST

  • Each layer of the cells form particular part of the embryo first appearance of these layers are collectively known as the primitive streak by day 15th

HYPOBLAST

  • It is close to the blastocyte cavity.
  • The hypoblast layer give rise to extra embryonic structure s like yolk sac which serve primary nutritive function after birth the remains of the yolk sac becomes vitelline duct at base of umbilical cord. 

​

10 of 16

ECTODERM

  • It forms the skin, hair, nails and nervous system.
  • MESODERM - it forms the muscle, skeleton, dermis of the skin, connective tissue, uro- genital glands blood vessels, blood and lymph cells.
  • ENDODERM - it forms the epithelia linning of the digestive ,respiratory and urinary systems and glandular cells of organs example liver and pancreas.

 

​

11 of 16

�DEVELOPMENT OF THE PLACENTA�

  • Two weeks after fertilization the trophoblast proliferate and differentiate into two layers. Outer syncytiotrophoblast or synctium and the inner cytotrophoblast.
  • The trophoblast is then implanted into the decidua.
  • The syncytrophoblast layer invades the deciduas forming finger like projections called villi that make their way into the deciduas.

12 of 16

�DEVELOPMENT OF THE PLACENTA CONT’D�

  • The villi begin to branch and contain the blood vessels of the developing embryo allowing gaseous exchange between the mother and embryo.
  • Implantation of the trophoblast is assisted by hydrolytic enzymes secreted by the syncytiotrophoblast cells that erode the deciduas and assist with nutrition of the embryo.
  • Syncytiotrophoblast cells also produce human chorionic gonadotrophin(HCG) Hormones that prevent menstruation and maintain pregnancy.

13 of 16

�DEVELOPMENT OF THE PLACENTA CONT’D�

  • CHORIONIC VILLI formed 3 weeks after fertilization and multiply at the deciduas basalis area which is very rich in blood.
  • CHORION FRONDOSUM -The portion of the throphoblast with chorionic villi at the deciduas basalis and later developed into placenta.

​

14 of 16

 �DECIDUA CAPSULARIS�

  • The portion of the deciduas surrounding the blastocyst where it projects into the uterine cavity.
  • The villi under the capsularies degenerate to form the chorion lavae which becomes the chorion membranes.
  • DECIDUA PARIETALIS -is the remaining deciduas.
  • NUTRITIVE VILLI- they are the projections that absorb food and oxygen and excrete waste.

15 of 16

ANCHOING VILLI

  • The villi that embedded deep into the deciduas.
  • In the center of each chorionic villi is mesoderm and fetal blood vessels branches of the umbilical artery and vein.
  • Four layers of tissues separate maternal blood from the fetal blood making it impossible for the two blood to mix unless villi are damaged.

​

16 of 16

THANK YOU

​

​

​

ANY QUESTION