Oogenesis and spermatogenesis Flashcards
How long does oogenesis take to complete?
Years
When does oogenesis begin?
In utero then suspended until puberty
When does oogenesis stop?
Menopause
How is oogenesis completed?
Fertilization
What is a primordial germ cell?
The earliest mitotic precursor of gametes
Where do primordial germ cells migrate?
Genital ridge
What are oogonia?
The mitotic precursor of oocytes
What are oocytes?
Female germ cells capable of meiosis
What are primary and secondary oocytes?
Primary - first meiotic division
Secondary - seconda meiotic division
What is a polar body?
Small cellular structures containing minimal cytoplasm
What does the presence of two polar bodies indicate?
Fertilization (completion of second meiotic division)
What happens to germ cell numbers during birth and development?
They massively decline due to the limited number of mitotic divisions they are capable of
How long does the ovulation cycle last?
Roughly 28 days
What are the two phases of the ovulation cycle?
Follicular phase
Luteal phase
What is the follicular phase?
Maturation of the egg
Ovulation
What signals the end of the follicular phase?
Ovulation
What is the luteal phase?
Development of corpus luteum & preparation of the reductive tract for pregnancy
What is a primary follicle?
A single layer of granulosa cells which surrounds an oocyte
How many ovum does each primary follicle produce?
One
When do primary follicles degenerate to scar tissue?
Before the onset of puberty
What is a secondary follicle?
The expanded, differentiated follicle with grows around an ovum under hormonal influence
Which hormone is secreted in the follicular phase?
Oestrogen
What is lutenisation?
Transformation of follicular cells into corpus luteum
What is secreted in the luteal phase and by what?
Progesterone by the corpus luteum
What signals the end of the luteal phase?
Degeneration of the corpus luteum (i.e menstruation)
What happens to the corpus luteum if fetilisation occurs?
It persists and produces increasing quantities of oestrogen and progesterone
What is the extra-ovarian hormonal axis?
Hypothalamus secretes GnRH
Anterior pituitary secretes FSH and LH in response
What do FSH and LH act on in females respectively?
Ovaries
What effect does FSH have on a female?
Stimulates follicular development
What effect does LH have on a female?
Stimulates follicular maturation, ovulation and corpus luteum development
What combined effect do FSH and LH have on a female?
Secretion of oestradiol and ovulation
How does the extra-ovarian hormonal axis work during the follicular phase?
Hypothalamus secretes GnRH
Anterior pituitary secretes much FSH and little LH
FSH causes the granulosa and theca cells of a dozen follicles to develop
What do theca cells do?
Produce androgen
What do the granulosa cells do?
Convert androgen to oestradiol by secreted aromatase
What effect does oestradiol have?
Thickens endometrium and thins cervical mucus
Supresses FSH production by the anterior pituitary
What does the granulosa of the dominant follicle express?
LH receptors
What do high oestrogen levels mid cycle cause?
Hypothalamic release of GnRH in turn causing a surge of FSH and LH to be released from the anterior pituitary
What happens during ovulation?
Increased follicular fluid and granulosa
Cumulus oophorus loosens
Follicular wall weakens
Cumulus-oocyte complex (COC) picked up by oviduct
What stimulates ovulation?
Surge of FSH and LH
What happens to hormone levels after ovulation?
FSH and LH fall
How do we test for ovulation?
LH levels in urine (high –> low)
Increased temperature
High progesterone levels
What happens if there is no hCG production from an embyro 12 days after ovulation?
Corpus luteum degenerates to corpus albicans
What is hCG and what is it secreted by?
Human corionic gonadotrophin. Implanted embryos
What happens to progesterone and oestrogen levels if there is no fertilisation in the luteal phase?
They fall
What function does hCG have?
Maintains corpus luteum
What does progesterone do to ovulation?
Suppresses it
What happens around 6 weeks after fertilisation to the corpus luteum?
It degenerates to corpus albicans as the placenta takes over its role
When is surgical sperm aspiration indicated?
Azoospermia
Which hormones stimulate spermatogenesis?
FSH
Testosterone
Which hormones decrease the secretion of FSH in men?
Inhibin
What hormones decrease the secretion of GnRH and LH?
Testosterone
What does LH stimulate in males?
Testosterone secretion
