Gametogenesis Flashcards
What is spermatogenesis?
Production of sperm cells from germ cells
What is spermiogenesis?
Maturation of spermatids
What process produces gametes?
Meiosis
How is genetic variation produced in gametogenesis?
Crossing-over - exchange of DNA between homologous chromosones
Independent assortment - random orientation during metaphase
Random segregation - random distribution of alleles
Where does spermatogenesis take place?
Sertoli cells in seminiferous tubules
Describe the phases of spermatogenesis
Spermatogonium - undergoes mitosis
- Ad spermatogonium
- Ap spermatogonium
Ap spermatogonium (primary spermatocyte) - undergoes meiosis 1
Secondary spermatocyte - undergoes meiosis 2
Spermatid - undergoes spermiogenesis
Mature sperm
What is an Ad spermatogonium?
‘Resting’ spermatogonium - reserve stock
What is an Ap spermatogonium?
‘Active’ spermatogonium - maintains stock + after puberty produces type B spermatogonia which are primary spermatocytes
What is a spermatogenic cycle?
Time taken for reappearance of the same stage within a given segment of tubule
How long is a spermatogenic cycle?
~16 days
What is a spermatic wave?
Distance between each stage
How does spermatogenesis occur in the tubules?
Occurs in waves migrating through tubule
What is spermiation?
Spermatids released into the lumen of seminiferous tubules
What happens during spermiogenesis?
Spermatids released into lumen
Remodel as they pass through into epididymis
- non motile until they reach the epididymis
- moved by peristaltic contraction
What is sperm capacitation?
Final maturation step required for sperm to become fertile - occurs in female genital tract
What happens in sperm capacitation?
Removal of glycoproteins and cholesterol from sperm membrane
Activation of sperm signalling pathways
Allow sperm to bind to zona pellucida
What is oogenesis?
Production of oocytes
What happens to the oocytes before birth?
Germ cells colonise gonadal cortex Differentiate into oogonia Proliferate End of 3rd month = arranged in clusters Some enter meiosis - stop in prophase 1 = primary oocytes Majority degenerate All surviving enter meiosis 1 Surrounded by follicular cells
What happens every month post puberty?
15-20 oocytes start to mature each month
What are the stages of oocyte maturation?
Preantral
Antral
Preovulatory
What happens in the preantral stage?
Primordial follicles grow
Follicular cells change from flat to cuboidal to produce stratified epithelium of granulosa cells
What happens in the antral stage?
Fluid filled spaces appear between granulosa cells
Spaces form the antrum
What happens in the preovulatory stage?
Induced by LH surge
Cell enters meiosis 2 - arrests in metaphase 2
How is ovulation stimulated?
FSH + LH stimulate rapid growth of the follicle
LH surge increase collagenase activity
Prostaglandins increase in response to LH - cause muscular contractions in ovarian wall
Oocyte released
What is the corpus luteum?
The remaining granulosa and theca cells
What happens to the corpus luteum?
Cells become vascularised and change into lutein cells
Secrete oestrogens and progesterone - stimulate uterine mucosa to enter secretory stage
Dies after 14 days if no fertilisation
How is the oocyte transported from the ovary?
Swept up by fimbriae
Propelled along fallopian tube by peristaltic contractions + cilia
What happens to the corpus luteum if no fertilisation occurs?
Corpus luteum degenerates into corpus albicans
Progesterone production decreases - menstrual bleeding
What happens to the corpus luteum if fertilisation occurs?
Degeneration prevented by HCG produced by embryo
Corpus luteum continues to grow and form the corpus luteum graviditatis
Continues to produce progesterone until 4th month
