1. Conception
Lecture 3

2. Conception Conception is when sperm and egg meet
and fertilization occurs
Conception occurs in the outer third of the
fallopian tube
Zygote - fertilized egg

3. Conception
The sperm reaches the caudal epididymis approximately 72 days after the initiation of spermatogenesis.
Preservation of optimal sperm function during storage requires adequate testosterone levels and maintenance of a normal scrotal temperature.

4. Stages of Fetal Development
Preembryonic stage: fertilization through 2nd week
Fertilization; cleavage; morula
Blastocyst and trophoblast
Implantation
Embryonic stage: end of 2nd week through 8th week
Basic structures of major body organs and main external features
Fetal stage: end of the 8th week until birth

5. Embryonic Layers
Ectoderm: forms the central nervous system, special senses, skin and glands
Mesoderm: forms skeletal, urinary, circulatory, and reproductive organs
Endoderm: forms respiratory system, liver, pancreas, and digestive system

6. Site of sperm formation
Seminiferous tubules of Testis

7. Seminiferous tubule under microscope

8. Conception
The alkaline pH of semen provides protection for the sperm from the acid environment of the vagina.
Of an average of 200 to 300 million sperm deposited in the vagina, at most only a few hundred achieve proximity to the egg.

9. Conception Capacitation is characterized by three accomplishments:
The ability to undergo the acrosome reaction.
The ability to bind to the zona pellucida.
The acquisition of hypermotility.

10. SPERMIOGENESIS Spermatids are rounded cells.
They modify to assume specific shape of the sperm.
This process is called Spermiogenesis. In it they elongate and reorganize internal structure to acquire the particular shape.

11. Accomplishing Fertilization
The oocyte is viable for 12 to 24 hours
Sperm is viable 24 to 72 hours
For fertilization to occur, coitus must occur no more than:
Three days before ovulation
24 hours after ovulation
Fertilization – when a sperm fuses with an egg to form a zygote

12. Sperm Transport and Capacitation
Fates of ejaculated sperm
Leak out of the vagina immediately after deposition
Destroyed by the acidic vaginal environment
Fail to make it through the cervix
Dispersed in the uterine cavity or destroyed by phagocytic leukocytes
Reach the uterine tubes
Sperm must undergo capacitation before they can penetrate the oocyte

13. Acrosomal Reaction and Sperm Penetration
An ovulated oocyte is encapsulated by:
The corona radiata and zona pellucida
Extracellular matrix
Sperm binds to the zona pellucida and undergoes the acrosomal reaction
Enzymes are released near the oocyte
Hundreds of acrosomes release their enzymes to digest the zona pellucida

14. Acrosomal Reaction and Sperm Penetration
Once a sperm makes contact with the oocyte’s membrane:
Beta protein finds and binds to receptors on the oocyte membrane
Alpha protein causes it to insert into the membrane

15. Acrosomal Reaction and Sperm Penetration
Figure 28.2a

17. Blocks to Polyspermy Only one sperm is allowed to penetrate the oocyte
Two mechanisms ensure monospermy
Fast block to polyspermy – membrane depolarization prevents sperm from fusing with the oocyte membrane
Slow block to polyspermy – zonal inhibiting proteins (ZIPs):
Destroy sperm receptors
Cause sperm already bound to receptors to detach

18. Implantation
Implantation is defined as the process by which an embryo attaches to the uterine wall and penetrates first the epithelium and then the circulatory system of the mother to form the placenta.
The human blastocyst remains in the uterine secretions for approximately 1 to 3 days and then hatches from its zona pellucida in preparation for attachment.

19. Implantation
Viability of the corpus luteum is maintained by human chorionic gonadotropin (hCG) secreted by the trophoblasts
hCG prompts the corpus luteum to continue to secrete progesterone and estrogen
Between the second and third month, the placenta:
Assumes the role of progesterone and estrogen production
Is providing nutrients and removing wastes

20. Implantation
The blastocyst loosely adheres to the endometrial epithelium, a process called apposition, which most commonly occurs on the endometrium of the upper posterior wall of the uterus.
The implantation occur in fundus of the uterus, which is rich blood supply.

22. Placental Hormones HUMAN CHORIONIC GONADOTROPIN
maintenance of function of the corpus luteum
Stimulation of the maternal thyroid gland
Promotion of relaxin secretion
Promote uterine vascular vasodilatation and myometrial smooth muscle relaxation

23. Student Practice 2 1. Fates of ejaculated sperm caused by:
2. Explain the process of implantation?

24. The END