INDIFFERENT GONADS
sex is determinated at …
fertilization
INDIFFERENT GONADS
What is the indifferent stage of gonads?
there are no specific ovarian or testicular characteristics ⇒ longitudinal elevation or ridge of intermediate mesoderm
⇒
urogenital ridge
(weeks 4-7)
INDIFFERENT GONADS
The components of urogenital ridge are…
- primodial germ cells
- primary sex cords
- mesonephric (wolffian) and paramesonephric (mullerian) ducts
INDIFFERENT GONADS
Primordial Germ Cells
critical indutive influence
+
migrate to urogenital ridge at week 4
+
from lining cells in the wall of yolk sac
INDIFFERENT GONADS
Primary Sex Cords
finger-like extensions
+
epithelium which grows into gonad
+
populated by migrate primordial germ cells
INDIFFERENT GONADS
Mesonephric Duct
(Wolffian)
Male Genital Tract
INDIFFERENT GONADS
Paramesonephric Duct
(Mullerian)
Female Genital Tract
TESTIS AND OVARY
Testis development is directed by …
- SRY gene (short arm of the Y chromossome) → Testis-Determining Factor (TDF)
- Testosterone - Leidig Cells (aromatase)
- Mullerian-inhibiting Factor (MIF) - Sertoli Cells
- Dihydrotestosterone (DHT) - External Genitalia
TESTIS AND OVARY
Ovary development requires …
Estrogen
+
absence os SRY gene
+
WNT4 gene
MEIOSIS
Meiosis I
- synapsis (pairing 46 chromossomes)
- crossing over
- disjunction (no centromere-splitting)
MEIOSIS
Meiosis II
synapsis + crossing over = don’t occur
disjunction is centromere-splitting
MEIOSIS
Spermatogenesis
- primordial cells are dormant until puberty
- type A spermatogonia = stem cell to adult life
- type B spermatogonia = enter in meiosis
- meiosis I → primary spermatocyte
- primary → secondary (before meiosis II)
- meiosis II → spermatid
- spermatid → spermiogenisis (morphological changes)
- spermatozoa
MEIOSIS
Oogenesis
- primordial germ cells → oogonia (at week 4)
- meiosis I → primary oocyte (month 5 at fetal life - in diplotene of prophase I)
- puberty → primary oocyte completes meiosis I (monthly) → secondary oocyte + polar body
- ovulation → secondary oocyte stops at meiosis II (metaphase)
- fertilization → secondary oocyte completes meiosis II (mature oocyte + polar body)
