Spermatogenesis and fertilisation Flashcards
Is phase 4 of spermatogenesis more or less rapid than oogenesis
More rapid
Where does spermatogenesis begin?
Seminiferous tubules of testers after puberty
What are type A spermatogonia?
mitotically active throughout reproductive life
How are spermatogonia kept at edge of semiferous epithelium?
Interlocking sertoli cells connected by intercellular cytoplasmic bridges
What are type B spermatogonia termed as when they enter meiosis
Primary spermatocytes
How long do spermatocytes take to complete meiosis 1
24 days
What happens during meiosis 1
spend this time making mRNA for later protein production
What is the result of early translation into protein
Sterility
What is produced from meiosis 1
Secondary spermatocytes
What is produced from meiosis 2
Spermatids
How are spermatids converted to spermatozoa
Spermiogenesis
How does spermatid changes as it becomes spermatozoa
- Reduction in nuclear size
- Golgi apparatus condense
- Flagellum grows from centriole
- Cytoplasm streams away from nucleus
- Mitochondria in spiral arrangement around flagellum
- Head partitioned into domains
What is the final step of sperm maturation
Capacitation
Where does capacitation occur
Female genital tract (requires contact with secretions of the oviduct)
What does LH stimulate
Testosterone production by Leydig cells
What are the main targets of testosterones and FSH
Sertoli cells which secrete androgen binding fluids
What do androgen binding fluids do
Binds to testosterone and carries to seminiferous tubule: stimulates spermatogenesis
Where is sperm deposited?
Cervical ovarian sphincter
What propels the sperm up the uterine canal?
Uterine cilia
Sperms propulsion
Describe the steps of the acrosome reaction
- Sperm fuses with overlying plasma membrane
- Enzyme released allow passage through zona pellucida
- Finishes jounry between zp and oocyte (oolemma)
- Sperm becomes enveloped
- Fusion
- Large increase in intracellular cacium forms wave across the egg
How does fusion occur
- Binds with egg receptors once acrosome reaction complete
- Cortical vesicle fuses with plasma membrane undergo exocytosis
- Releases contents into peri-vitelline spae
- Modified fertilisation detaches and rises
- Sperm pulled into egg by fertilisation cone
- Microtubules from the centrosome associated w male pronucleus
- Fuses with female pro nucleus
How do mature egg and sperm finding each other
Chemotaxis
How do cells with each other in a species specific way
In mammals there is a glycoprotein called ZP3 found in zona pellucida
Capacitated sperm are species specific in their binding to ZP3
Binding triggers changes in calcium and pH in sperm
How is number of cell fusing restricted
Production of second messenger on sperm/ egg binding triggers blocking
Calcium wave triggers cortical release and activation of cell division
What happens at 16-32
Polarisation of 2 cell populations
Outer cells form trophoblast precursors and inner cell are pluriblast (morula)
What happens at 32-64 cell stage
This is blastocyst
Has to hatch off the hardened zona pellucida
What attach itself to uterine wall
7-9 days post ovulation
