Gametogenesis Flashcards
Gametogenesis
process by which haploid or diploid cells give rise to haploid cells
process to obtain gametes via meiosis
2 forms of gametogenesis
spermatogenesis and oogenesis
end product of meiosis produces a cell with
half the chromosomes as a diploid cell (haploid)
Meiosis involves
one round of chromosomal duplication and 2 rounds of nuclear division
The human cycle
meiosis
formation of gametes
fertilisation
mitosis
form the new individual
spermatogenesis length
70 days
spermatogenesis
in the seminiferous tubules
diploid germ cell undergoes mitosis
forms type A and Type B cells
differentiates into primary spermatocytes
Primary spermatocyte
undergoes the first
round of meiosis (meiosis I)
forms 2 haploid secondary spermatocytes
these divide meiotically into 4 haploid spermatids by meiosis II
Sertoli cells
nurse cells that aid spermatogenesis by providing nourishment
their junctions form the blood-testis barrier
Spermatogenesis requires
cooler temperature than the core body temperature thus the testicles hang lower in the male body
Sperm produced
when they reach puberty, usually from 10-16 years old
large quantities (~200 million a day) to maximise the likelihood of sperm reaching the egg
continually produce
Sperm production occurs in
the testes of the male, seminiferous tubules
tubules are kept separate from the systemic circulation by the blood-testis barrier
After formation of the spermatids
cells undergo spermiation where they are released into the lumen of the seminiferous tubules prior to their transport to the epididymis
In the epididymis, sperm is stored and undergoes the final stages of maturation
Semen which is produced during male ejaculation contains
sperm and secretions from the prostate, seminal vesicles and bulbourethral glands which aids the sperm cell to overcome the unique environment of the female reproductive tract
capacitation occurs
once semen is introduced into the female reproductive tract
allows the sperm to fertilise the egg cell
Oogenesis
meiosis leads to the formation of an egg cell (gamete)
Oogenesis process
primary oocytes are arrested in prophase I until the female reaches puberty
begins in a developing female embryo
During each month, one oocyte resumes meiosis (ovulation)
secondary oocyte which receives the majority of the cytoplasm and a polar body forms
haploid secondary oocyte initiates meiosis II
this halted at metaphase II until fertilization
if the egg is not fertilized the cell never becomes an ovum and its shed via menstruation
fertilization occurs then meiosis II commences forming an ootid and another polar body
ootid eventually matures into an ovum
Polar bodies form to discard extra sets of chromosomes ensuring the final egg cell is haploid
Fertilization
union between the egg and sperm cell nucleus
produces a zygote which is the initial cell of the foetus/baby which eventually divides via mitosis to form an embryo
Capacitation
process whereby the membrane over the sperm’s acrosome is weakened due to chemical changes
enzymes are released from the capacitated sperm which then clears a path through the zona pellucida of the egg cell
prevent more sperm entry
rapid chemical changes take place across the cell membrane of the oocyte
Fusion with sperm allows
maturation of oocyte into an ovum and a polar body
The formed zygote has
46 chromosomes, 23 from each parent
Infertility
disease of the reproductive system defined by the failure to achieve a clinical pregnancy after 12 months or more of regular unprotected sexual intercourse
