IB biology: topic 6: the reproductive system

what is the function of the SRY gene?

encodes for a protein - testis determining factor (TDF)

what is the function of the testis determining factor protein (TDF)

in the presence of TDF, the gonads become testis.

in the absence of TDF the gonads become ovaries.

what are gonards?

part of reproductive system that becomes either ovaries or testes

when do testes begin to develop in the embryo?

the 8th week (when the embryo is becoming a foetus)

Secretion increases at puberty, stimulating sperm production and the development of the male secondary sexual characteristics.

what is the role of the testes during foetal development?

secrete testosterone which causes the male genitalia to develop.

what is the role of the testes during puberty?

increases secretion of testosterone, causing:

sperm production in the testes (primary sexual characteristic)

enlargement of the penis, growth of pubic hair and deepening of the voice (secondary sexual characteristics)

how is oestrogen and progesterone initially released in foetal development?

at first they are secreted by the first by the mother’s ovaries and later by her placenta.

what causes the ovaries to develop?

the absence of foetal testosterone and the presence of maternal oestrogen and progesterone

what is the role of the ovaries during puberty?

secretion of oestrogen and progesterone increases causing:

egg release (primary sexual characteristic)

enlargement of the breasts and growth of pubic hair (secondary sexual characteristics)

what is the role of the uterus? (female reproductive system)

provides protection, nutrients and waste removal for the developing foetus,

muscular walls contract to aid birthing process

what is the role of the fallopian tube/oviduct? (female reproductive system)

collects eggs at ovulation, provide a site for fertilisation then move the embryo to the uterus

what is the role of the ovaries? (female reproductive system)

eggs stored, develop and mature,

produce oestrogen and progesterone

what is the role of the vulva? (female reproductive system)

protect internal parts of the female reproductive system

what is the role of the vagina? (female reproductive system)

stimulate penis to cause ejaculation and provide a birth canal

what is the role of the cervix? (female reproductive system)

protects the foetus during pregnancy and dilate to provide a birth canal

what is the role of the testis? (male reproductive system)

produce sperm and testosterone

what is the role of the scrotum? (male reproductive system)

hold testes at lower than core body temperature for sperm production

what is the role of the epididymis? (male reproductive system)

store sperm until ejaculation

what is the role of the sperm duct? (male reproductive system)

transfer sperm until ejaculation

what is the role of the seminal vesicle and prostate gland? (male reproductive system)

secrete fluid containing alkali, proteins and fructose that is added to sperm to make semen

what is the role of the urethra? (male reproductive system)

transfer semen during ejaculation and urine during urination

what is the role of the penis? (male reproductive system)

penetrate the vagina for ejaculation of semen near the cervix

what are the two phases of the menstrual cycle?

follicular phase and luteal phase

what takes place during the follicular phase of the menstrual cycle?

1. a group of follicles develops
2. in each follicle, an egg is stimulated to grow
3. endometrium is repaired and begins to thicken
4. most developed follicle ruptures releasing its egg
5. other follicles degenerate.

what takes place during the luteal phase of the menstrual cycle?

1. wall of ruptured follicle becomes corpus luteum
2. further thickening of endometrium prepares it for implantation of embryo
3. if fertilisation doesn’t occur, corpus luteum breaks down
4. endometrium also breaks down and menstruation occurs.

what is the role of follicle stimulating hormone (FSH) in the menstrual cycle?

binds to receptors in membrane of follicle cells,

rises to peak towards end of cycle,

stimulates development of follicles

stimulates secretion of oestrogen

where is FSH produced?

by pituitary gland

where is oestrogen produced?

by the wall of a follicle

what is the role of oestrogen in the menstrual cycle?

rises to a peak towards end of follicular phase,

stimulates repair and thickening of endometrium,

stimulates increase in FSH receptors, making follicles more receptive to FSH, boosting oestrogen production (positive feedback)

when reaches high levels, inhibits FSH secretion (negative feedback) and stimulates LH secretion

where is LH produced?

by pituitary gland

what is the role of LH in the menstrual cycle?

binds to receptors in membrane of follicle cells.

rises to sharp peak towards end of follicular phase.

stimulates partial digestion of follicle wall, allowing it to rupture at ovulation.

promotes development of corpus luteum which secretes oestrogen (positive feedback) and progesterone.

where is progesterone produced?

by corpus luteum

what is the role of progesterone in the menstrual cycle?

levels rise at start of luteal phase, reach a peak and then drop back to a low level by end of the phase.

promotes thickening & maintenance of endometrium.

inhibits FSH & LH secretion (negative feedback).

what is the process of IVF?

Stop normal menstrual cycle (with drugs)

Hormone treatments to promote super ovulation

Extract multiple eggs from the ovaries

Sperm collected, then prepared (via capacitation) and injected into egg

Fertilisation occurs externally under controlled conditions (in vitro)

Implantation of multiple embryos into uterus (either patient or surrogate)

Test for pregnancy after \~ two weeks