The Physiology of
conception
Yasser Orief M.D.
Lecturer of Obstetrics & Gynecology, Alexandria University
Fellow, Lϋbeck University, Germany
DGOL, Auvergné University, France
Hypothalamo – Pituitary – Gonadal axis
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
Testes
Male Reproductive System
Processes of Spermatogenesis
Female Reproductive System
Female Reproductive System
Ovaries
Oogenesis
Folliculogenesis
• 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.)
Folliculogenesis, starting from pre-antral (late
secondary) stage.
The Hormonal Regulation of Ovarian
Activity
The 2 cell 2 gonadotropin theory
The Hormonal Regulation of the Female
Reproductive Cycle
Hormonal Control of the Ovarian and
Uterine Cycles
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
The Hormonal Regulation of the Female
Reproductive Cycle
Hormonal Control of the Ovarian and
Uterine Cycles
Stages of Pregnancy and
Development
 Fertilization
 Embryonic development
 Fetal development
 Childbirth
Fertilization
 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
Fertilization
• 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
Let the Division Begin!
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
Development from Ovulation to
Implantation
Gastrulation
• 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
Gastrulation
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
• The gestation period lasts 266 days from
fertilization to birth
• Organogenesis (development of the
organs and organ systems) begins with
the nervous system
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