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Yasser Orief M.D. Lecturer of Obstetrics & Gynecology, Alexandria University PowerPoint Presentation
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The Physiology of conception. Yasser Orief M.D. Lecturer of Obstetrics & Gynecology, Alexandria University Fellow, L ϋ beck University, Germany DGOL, Auvergné University, France. Hypothalamo – Pituitary – Gonadal axis. The Reproductive System. Gonads – primary sex organs

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The Physiology of conception

Yasser Orief M.D.

Lecturer of Obstetrics & Gynecology, Alexandria University

Fellow, Lϋbeck University, Germany

DGOL, Auvergné University, France


The Reproductive System

  • Gonads – primary sex organs
    • Testes in males
    • Ovaries in females
  • Gonads produce gametes (sex cells) and secrete hormones
    • Sperm – male gametes
    • Ova (eggs) – female gametes
  • It begins by the recruitment of a cohort of primordial follicles into a pool of growing follicles and ends by either ovulation or atresia.

It requires almost one year for a primordial follicle to grow and develop to the ovulatory stage.


Gougeon A: Dynamics of follicular growth in the human: A model from preliminary results. Hum Reprod 1:81, 1986. Reproduced with permission from Oxford University Press.)


Menstrual (Uterine) Cycle

  • Cyclic changes of the endometrium
  • Regulated by cyclic production of estrogens and progesterone
  • Stages of the menstrual cycle
    • Menses – functional layer of the endometrium is sloughed
    • Proliferative stage – regeneration of functional layer
    • Secretory stage – endometrium increases in size and readies for implantation

Stages of Pregnancy and Development

  • Fertilization
  • Embryonic development
  • Fetal development
  • Childbirth


  • The oocyte is viable for 12 to 24 hours after ovulation
  • Sperm are viable for 12 to 48 hours after ejaculation
  • Sperm cells must make their way to the uterine tube for fertilization to be possible
  • Divided into 4 steps:
  • 1. Contact and recognition (“Casual Introductions”)
  • Sperm undergo capacitation (further maturation) within the female reproductive tract
  • Recall that sperm were produced in the testes and matured in the epididymus until ejaculation
  • Sperm reach the egg in the oviduct where fertilization will occur
2. Sperm Entry
  • Only ONE sperm is allowed to enter
  • Fast block - electrical charge in egg plasma membrane prevents polyspermy
  • Slow block - depolarization of egg plasma membrane due to Ca++ release
3. Egg Activation
  • The release of calcium ions in egg plasma membrane also triggers protein synthesis
  • 4. Fusion
  • The sperm nucleus is propelled to the egg nucleus by microtubules
cleavage follows fertilization
Cleavage follows fertilization
  • Cleavage is a series of rapid mitotic divisions (without cell growth)
  • The two-celled zygote divides repeatedly until a ball of 32 cells is formed
  • This is the morula - 32 cells
Continued divisions make the hollow blastula
  • These few cells are pluripotent (have the potential to become ANY of the 220 types of cells in the human body).
  • These are embryonic stem cells
  • At the end of the cleavage stage, cells making up the blastula move about and surface proteins help cells recognize each other
  • The gastrula is formed, which consists of 3 “germ layers”
    • Endoderm
    • Mesoderm
    • Ectoderm
extraembryonic membranes
Extraembryonic Membranes
  • These membranes develop from the germ layers, but are NOT part of the embryo (they are lost at birth)
  • They lie outside of the embryo & provide protection and nourishment
  • Four exist in terrestrial vertebrates:
  • Chorion, amnion, allantois (stores nitrogenous waste in reptiles), & yolk sac (not found in humans, but yolk aids in formation of RBC
human development
Human Development
  • The gestation period lasts 266 days from fertilization to birth
  • Organogenesis (development of the organs and organ systems) begins with the nervous system