Gametogenesis

Dr Jyoti Chopra

1. Gametogenesis
DrJyoti Chopra
Professor
Department of Anatomy
KGMU, Lucknow

2. What do we study in embryology?
•Intrauterine life-9 months-Prenatal
development
•First two months-Embryo
•After that till birth-Foetus
•Postnatal development

3. Gametogenesis
Spermatogenesis
Testis
Sperms
(n)
Oogenesis
Ovary
Oocyte
(n)

4. •Gametes develop from Primordial germ cells
present in gonads at birth
•In 2
nd
wk of IU life-PMGCs develop from
epiblast—migrate to wall of yolk sac –during
4
th
-5
th
wk migrate to developing gonads

5. Oogenesis
•Primordial germ cells in ovary-oogonia
•Under go mitotic division-to increase number
•5
th
month of IUL-7 million
•7
th
month of IUL-start degenerating
•Oogonia-Primary oocyte(mitotic division)
•Primary oocyte-first meiotic division-arrest in
prophase
•Surrounded by flat epithelial cell-primordial
follicle

6. •At birth-600,000-800,000 primordial follicle have
primary oocytearrested in prophase
•During childhood-most oocyte-atretic
•At puberty-40,000 oocyte
•During reproductive life not more than 500 oocyte
ovulate
•In each cycle-15-20 follicles grow
•One ovulate
•Fertilization in late maternal age-primary oocyte
vulnerable to damage

7. Membranagranulosa

8. Cumulus oophoricus
Discus Proligerus

10. Oogenesis(contd…)
•First meiotic division is completed in pre-ovulatory
growth phase
•Secondary oocyteand first polar body formed
•First polar body lies between zonapellucidaand cell
membrane of secondary oocyte
•Secondary oocyteimmediately enters into second
meiotic division
•At ovulation oocytein metaphase stage in which it
remains arrested until fertilization
•At the time of fertilization 2
nd
meiotic division
completes and second polar body formed
•If fertilization does not take place-2
nd
meiotic division
not completes-oocytedegenerate in 24 hrs.

12. Spermatogenesis
•From puberty till old
age
•Occurs in seminiferous
tubule
•From spermatogonia-
mature sperm-74 days
•Approximately 300
million sperms are
produced daily

13. Prepubertalstage
After Puberty

14. Type A Spermatogonia
(2n)
Type B Spermatogonia(2n)
Primary spermatocyte(2n)
Secondary Spermatocyte(n)
Spermatids(n)
Spermatocyte
Spermatids(n)
Spermatocyte
Secondary Spermatocyte(n)
Spermatids(n)
Spermatocyte
Spermatids(n)
Spermatocyte
Type A Spermatogonia
(2n)

15. Type A–Spermatid, cytokinesisincomplete
Cells joined by cytoplasmicbridges

17. •Sertolicells support, protect, nourish & assist
in release of mature sperm
•LH (from pituitary)–receptor on leydigcells–
stimulate testosterone production–binds to
sertolicells–promote spermatogenesis
•FSH–binds to sertolicells–stimulate testicular
fluid production & androgen receptor protien

18. Spermiogenesis/ Spermateleosis
•Process of formation of spermatozoa
from spermatid
•Changes include-
–Condensation of Nucleus
–Formation of Acrosome–contains
enzyme-to penetrate egg and
surrounding layers
–Formation of neck, middle piece and
tail
–Residual cytoplasm shed off
•Pushed to epididymisby contractile
elements in wall of seminiferous
tubule
•74 days includes spermiogenesis

19. Mature Sperm
•In Spermatozoa (60micron)-
–Head-Nucleus
–Acrosomalcap-Golgi apparatus
–Neck-Proximal centriole, basal
body (nine segmented rod like
structure)
–Middle piece-axial filament
surrounded by mitochondria
–Annulus-distal centriole-at base of
middle piece
–Tail-remaining axilafilament

20. Structure of mature sperm

21. Structure of
mature sperm
(Basal body)
Axial Filament
-Pair of central fibril
-Surrounded by 9 pairs of
doublets
-9 coarse petal shaped fibrils
-Fibrous sheath
-Mitochondrial sheath
-Plasma membrane

22. •In seminiferoustubule-sperm immature, non-
motile, incapable of fertilizing ovum
•Maturation-Occurs in epididymis. Changes in
glycoprotein of plasma membrane covering
head. Also acquires some motility
•Fully motile only after ejaculataionwhen get
mixed with secretions of prostate gland and
seminal vesicle