Gametogenesis and Infertility

1. GAMETOGENESIS AND
INFERTILITY
CHOYTOO Shiksha
17

2. OVERVIEW
• GAMETOGENESIS
Formation of gametes ( ovum and sperm) from gonads (testes
and ovaries)
• Males: Spermatogenesis
SPERMATOGONIA
PRIMARY
SPERMATOCYTE
SECONDARY
SPERMATOCYTE
SPERMATIDS
SPERMS

3. • Females: oogenesis
• Note:
Meiosis is the 1st stage of gametogenesis
(separation of homologous chromosomes into haploid daughter cells)
Meiosis generates tremendous genetic diversity.
How many different types of gametes can be generated
by an individual (male or female) with 23 different
chromosomes?
More than 223 or 8,000,000 different gametes
OOGONIA
PRIMARY
OOCYTE
SECONDARY
OOCYTE
OVUM ( if
fertilization
occurs)

4. • The time of meiosis differs in males and females.
• In males
Spermatogonia enters meiosis at puberty and continues
till death
• In females
The process is more complex.
- The first meiotic division starts before birth but stops at
diplotene stage of prophase I.
- About one month before ovulation, the 1st meiosis is
completed and the secondary oocyte is arrested in the
metaphase state of meiosis II unless fertilization occurs

6. SPERMATOGENESIS
• Spermatogenesis can be
discussed into 3 stages
-spermatocytogenesis
-meiosis I and II
-spermiogenesis
(there is metamorphosis)

7. SPERMATOCYTOGENESIS
• There are 3 types of
spermatogonia
-Dark type A (Ad)
- Pale type A (Ap)
- Type B
• At puberty, Ad cells starts to divide
by mitosis (stimulation of
androgen). Ad cells produce more
Ad cells.
However, some division gives rise
to Ap cells (divides mitotic ally)

8. • Ap cells is the
precursor for type B
cells which divides
mitotically to give
primary
spermatocytes

9. MEIOSIS I AND II

11. SPERMIOGENESIS
• It is the process whereby the
spermatid undergoes
metamorphosis to become
sperm cells
• First, during golgi phase the
hydrolytic enzymes
accumulates in golgi vesicles
subsequently coalesce into a
single large acrosomal vesicle
close to the nucleus.

12. • The pair of centrioles
migrates to the
opposite posterior pole.
The distal centriole
begins to generate a
circular arrangement of
nine microtubule
doublets surrounding a
central pair.

13. • In the cap phase, the acrosomal vesicle flattens and
envelops the anterior half of the nucleus to form an
acrosomal cap.
• The axonemal complex continues to extend into the
developing tail region

15. CAPACITATION
• When sperms are first expelled in the semen, they are
unable to perform their duties in fertilizing the ovum.
• On coming in contact with the fluids of the female genital
tract, multiple changes occur that activate the sperm for
the final processes of fertilization.
• These collective changes are called capacitation of the
spermatozoa.

16. ACROSOMAL REACTION
• Stored in the acrosome of the sperm are large
quantities of hyaluronidase and proteolytic
enzymes
• When the ovum is expelled from the ovarian
follicle into the fallopian tube, it still carries
with it multiple layers of granulosa cells.
• Before a sperm can fertilize the ovum, it must
dissolute these granulosa cell layers,and then
it must penetrate though the the zona
pellucida.
• It does so by releasing the enzymes that
creates a pathway for the sperm head to
penetrate the ovum.

17. OOGENESIS
• The formation of secondary oocyte from oogania
• The process starts before birth.
• Oogenesis can also be described into 3 phases:
1. follicular phase
2. ovulation
3. Luteal phase

18. FOLLICULAR PHASE
Month 4 :
Oogonia is grouped in clusters
in the cortical part of the
ovaries (SOME of the oogonia
differentiate into primary
oocyte enters prophase I)
Month 7:
Most oogonia are transformed
into primary oocyte. They
enters the diplotene state of
prophase I in which they
remain until birth
At Birth:
Oogonia are absent. The
primary oocyte is surrounded
by a single layer of follicular
cells forming primodial follicles

19. Oogonia grouped in
clusters
Primary oocyte ( in prophase)
Primordial follicle (single
layer of follicular cells)

20. • At birth:
Primary oocyte have primodial follicle- throughout childhood
provides nourishment and secretes oocyte maturation
inhibiting factors
• At pubery:
- Few days before female sexual cycle,
FSH and LH (ant pituitary) is secreted
- proliferation of granulosa cells
-spindle cells derived from interstitium
of the ovary forms a layer – theca
-Theca-two layers: Interna- secretes estrogen
Externa- capsule of granulosa cells

21. • Granulosa cells starts
secreting follicular fluid
(estrogen)
• The accumulation of fluid
forms the atrum within the
granulosa cell mass.
• The enlarge follicular cells
continues to grow and
becomes vesicular follicle
• The ovum also grows in
size.

22. • At the same time
Primary oocyte undergo meiosis to become
seconday oocyte.

23. SECONDARY OOCYTE

24. OVULATION
• The process whereby a secondary
oocyte is discharged from the ovary.
• The outer wall of the follicle swells
rapidly and a small area of the
capsule protrudes outside – stigma
• Fluid starts to ooze from the stigma
causing it to rupture
• The secondary oocyte moves
outside carried by the viscous fluid
and is surrounded by corona
radiata.

25. LUTEAL PHASE
• Remaining theca and granulosa cells
in the ovary are converted to luteal
cells- becomes enlarged and filled
with yellowish fluid
• Mass is called corpus luteum- well
developed vascular supply and
secretes progesteron
• 12 days after ovulation ( if there is no
fetilisation)
corpus luteum looses secretory
functions and yellowish lipid
characteristics
• Now called corpus albicans (white). –
replaced by connective tissue.

27. Male Infertility
• Inflamation of testes – bilateral orchitis
Caused by mumps and it results in sterility
• Effect of temperature
Inc. in temp cause degradation of most of cells
of seminiferous tubules (excpt spermatogonia)

28. • Cryptorchidism
Failure of testes to
descend from the
abdomen to the scrotum
during fetal life.
Degeneration of tubular
epithelium due to high
temp
• Loss of sperm count
normal: 120 million
sperm in 3.5 ml of
semen

29. • Effect of sperm morphology and motility on
fertility
The sperm count may be normal but about half
of the cells are physically abnormal.
Loose motility

30. Female Infertility
• Fallopian tube may not be patent. ( Damage due to
pelvic infections, surgeries, endometriosis..)
Normal Abnormal

31. • Failure to ovulate due to hormonal disturbances
• Cervical problems
Abnormal mucous secretion in cervix- sperm
cannot pass and fertilisation does not occur
• Uterine causes
Abnormal anatomy of the uterus; the presence of
polyps and fibroids

32. • Endometriosis
A condition whereby
the endometrium grows
in different regions and
the tissues respond the
same way to hormones
as the endometrial
lining.
The symptoms are pain
and infertility

33. THANK YOU