DEVELOPMENT 1
Dr. Farhat Aamir
At the end of session, student should able
to
• Define and classify gametogenesis.
• Identify and discuss the stages of gametogenesis.
• Discuss morphological changes during maturation of
gametes.
• Identify clinical application i.e., formation of abnormal
gametes.
Gametogenesis
• Gametes: derives from
primordial germ cells.
• Formed in epiblast during
second week.
• During fourth week, germ
cells migrate towards
developing gonads.
• Germ cell undergo meiosis
to reduce chromosome
number.
Gametogenesis
• Definition: the process
of forming gametes
• Two types
• Oogenesis in females
Start dividing to form
oogonia
Divides to form
primary oocyte
• Spermatogenesis in
males
Oogenesis
• Oogenesis is the
process of formation of
mature oocyte (or
ovum).
• Oogonia increase in
number by rapid
division.
• By fifth month of
prenatal life, it reach
up to 7 million
Oogenesis
• By seven month,
majority of oogonia
degenerates.
• The surviving primary
oocyte enters in
prophase of meiosis I
• Primordial follicle:
are primary oocyte
surrounded by layer of
flat epithelial cells
Oogenesis
• Primordial follicle remain
arrested in prophase and
do not finish their first
meiotic division before
puberty is reached.
• Controlled by oocyte
maturation inhibitor
secreted by follicular cells.
• At birth number of primary
oocyte are 600,000800,000.
• 500 oocyte reach up to
puberty.
Oogenesis
• Primary follicle:
conversion of
squamous granulosa
cells to cuboidal cells
More than one layer
Zona pellucida: layer
of glycoprotein
surrounding oocyte.
Oogenesis
• Antral/vesicular follicle:
Theca externa
Outer layer
Fibrous capsule
Theca interna
Inner layer
Secretory cells
Appearance of fluid filled
spaces
All these spaces join
together to form antral cavity
Mature vesicular/Graffian follicle
• Corona radiata: Granulosa
cells surrounding oocyte
• Cumulus oophorus
• 25mm or more in diameter
• Well developed theca
externa and interna
Oogenesis
• A surge in LH hormone
induce preovulatory growth
• Meiosis I is completed
Formation of two daughter
cells
Secondary oocyte and
polar body
Cell arrested in metaphase
of meiosis 2
It will complete at the time
of fertilization
Spermatogenesis
• It starts at puberty
• Events in which
spermatogonia are
transformed into
spermatozoa.
• During puberty, PGC
give rise to
spermatogonial stem
cells
• Further, they form type A
spermatogonia
• Sertoli cells are
supporting cells
Spermatogenesis
• Spermatocytes and
spermatid remain
inside sertoli cells
• Sertoli cells supports,
protect and help in
releasing mature
spermatozoa
• FSH and LH help in
spermatogeneis
Spermiogenesis
• Defined as series of
changes resulting in the
transformation of
spermatids into
spermatozoa
1. Formation of acrosome
2. Condensation of
nucleus
3. Formation of neck,
middle piece and tail
4. Shedding of cytoplasm
by sertoli cells
• Time span of 74 days
Clinical correlations
• Teratoma are tumors
having bone, hair,
muscle, tooth and
epithelia
• PGC may choose
irregular path can give
rise to teratoma
Clinical correlations
• Abnormal germ cells
• Primordial follicle with two
oocyte
• Some times, primary
oocyte contain two or three
nucleus
• These binucleated or
trinucleated oocyte dies
before maturity
Clinical correlations
• 10 % of spermatozoa
usually have defects.
• Head and tail may be
abnormal.
• Sometimes, gaint and
dwarf.
• It lacks normal mobility
and do not fertilize with
oocyte
References
• Langman’s: A text book of medical embryology.