2. What do we study in embryology?
• Intrauterine life- 9 months- Prenatal
development
• First two months- Embryo
• After that till birth- Foetus
• Postnatal development
4. • Gametes develop from Primordial germ cells
present in gonads at birth
• In 2nd wk of IU life- PMGCs develop from
epiblast—migrate to wall of yolk sac – during
4th-5th wk migrate to developing gonads
5. Oogenesis
• Primordial germ cells in ovary- oogonia
• Under go mitotic division- to increase number
• 5th month of IUL- 7 million
• 7th 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 oocyte arrested 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
10. Oogenesis (contd…)
• First meiotic division is completed in pre-ovulatory
growth phase
• Secondary oocyte and first polar body formed
• First polar body lies between zona pellucida and cell
membrane of secondary oocyte
• Secondary oocyte immediately enters into second
meiotic division
• At ovulation oocyte in metaphase stage in which it
remains arrested until fertilization
• At the time of fertilization 2nd meiotic division
completes and second polar body formed
• If fertilization does not take place-2nd meiotic division
not completes- oocyte degenerate in 24 hrs.
11.
12. Spermatogenesis
• From puberty till old
age
• Occurs in seminiferous
tubule
• From spermatogonia-
mature sperm- 74 days
• Approximately 300
million sperms are
produced daily
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, cytokinesis incomplete
Cells joined by cytoplasmic bridges
16.
17. • Sertoli cells support, protect, nourish & assist
in release of mature sperm
• LH (from pituitary)– receptor on leydig cells–
stimulate testosterone production– binds to
sertoli cells– promote spermatogenesis
• FSH– binds to sertoli cells– 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 epididymis by contractile
elements in wall of seminiferous
tubule
• 74 days includes spermiogenesis
19. Mature Sperm
• In Spermatozoa (60micron)-
– Head- Nucleus
– Acrosomal cap- 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 axila filament
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 seminiferous tubule- 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 ejaculataion when get
mixed with secretions of prostate gland and
seminal vesicle
