Human Reproduction Overview Flashcards
What are the 4 endocrine glands controlling reproductive processes?
Hypothalamus
Pituitary gland
Adrenal gland
Gonads (testes and ovaries)
What reproductive hormones does the hypothalamus produce?
Gonadotropin-releasing hormone (GnRH), antidiuretic hormone, and oxytocin
What reproductive hormones does the hypothalamus RELEASE?
GnRH
Where are ADH and oxytocin 1. produced and 2. stored?
Produced by the hypothalamus and stored in the posterior pituitary.
How are hormones stored in the posterior pituitary?
In secretory vesicles which are triggered for release by the nerve impulses
What does ADH do?
Vasoconstriction
Increased BP and HR
What does oxytocin do?
Smooth muscle control (milk ejection and contraction of the uterus during childbirth)
Used to induce labour
What stimulates oxytocin secretion?
Nipple stimulation or uterine distension
How does the anterior pituitary contribute to the release/inhibition of gonadotropins?
Synthesizes releasing and inhibiting hormones which are stored in vesicles and are released in response to nerve impulse. The hormones then travel through the hypophyseal portal vessels where they act a specific clump of secretory cells and the termini of the portal blood vessel - e.g. gonadotrophs
What 2 hormones do gonadotrophs produce and release?
Follicle-stimulating hormone (FSH)
Luteinising hormone (LH)
What is the site of secretion of LH?
Anterior pituitary
What is the site of secretion of FSH?
Anterior pituitary
What is the site of secretion of Oxytocin?
Posterior pituitary
What is the site of secretion of ADH?
Posterior pituitary
What is the site of GnRH’s secretion?
Hypothalamus
What are the 3 sex steroid hormone classes?
Androgens
Oestrogens
Progestagens
What is the main androgen?
Testosterone
What is testosterone involved with (broadly speaking)?
Male sex development, spermatogenesis, sexual behaviour and muscle development
What is the more active form of testosterone called?
5-alpha dihydrotestosterone
How much less testosterone is produced in females compared with males?
10-100x less
What is Oestrogen responsible for (broad)?
Female sex development, regulation of menstrual cycle, growth of endometrium and bone growth
How much less oestrogen is produced in males compared with females?
10-100x less
What is the main production site for oestrogen?
Granulosa cells of the growing follicle
What are the 3 types of oestrogen? Describe their characteristics.
Oestrodial - most potent, made in granulosa cells, produced from puberty to menopause
Oestrone - always present, also made by men, important post menopause
Oestrial - made by placenta, softens cervix
What produces progestagens?
The corpus luteum and placenta
What is the role of progestagens?
Provide the best environment for the embryo to implant and its maintenance.
Is progestagen produced in males?
No
What chromosome is the sex-determining gene found on?
Y
What is the sex determining gene?
SRY
What does the SRY gene do?
Provide the pathway for testes to develop
What are the female chromosomes?
XX
What are the male chromosomes?
XY
What occurs in the absence of the SRY gene?
Embryo develops into female
What occurs in the presence of the SRY gene?
Embryo develops into male
What is sex differentiation?
Phenotypic development of genital structures due to the action of hormones produced by the gonad
Describe the pathway of male genitalia formation.
Mesoderm -> bipotential gonad –(SRY)-> Testis -> leydig cells (+ sertoli cells) -> testosterone -> wolffian duct development -> internal male genitals
Sertoli cells -> anti mullerian hormone (AMH) -> mullerian duct regression
Describe the pathway of female genitalia formation.
Mesoderm -> bipotential gonad –(no SRY)-> ovary -> Oestrogens + progestagens -> mullerian duct development & wolffian duct regression -> internal female genitals
At what stage in the embryo are the genitals undifferentiated (both Mullerian and Wolffian ducts present)?
5-6 weeks
At what stage in the embryo does the male internal genitalia develop?
Weeks 7-8
At what stage in the embryo does the female internal genitalia develop?
Weeks 8-9
What does the Wolffian duct develop into?
Epididymis
Vas deferens
Seminal vesicles
At what stage in pregnancy do the testes descend into the scrotum?
7th month
What maintains the Wollfian ducts?
Testosterone secreted from the Leydig cells in testis
What hormone is responsible for the regression of the Mullerian duct?
Anti-Mullerian hormone (AMH)
At what stage in a female embryo does the Wolffian duct begin to regress?
10 weeks
What do the Mullerian ducts give rise to?
Fallopian tubes
Uterus
Cervix
Upper vagina
What does the genital tubercle of an undifferentiated embryo develop into in a male?
Glans penis
What does the genital tubercle of an undifferentiated embryo develop into in a female?
Clitoris
What do the urethral folds of an undifferentiated embryo develop into in a female?
Labia minora
What does the labioscrotal swelling of an undifferentiated embryo develop into in a female?
Labia majora
What do the urethral folds of an undifferentiated embryo develop into in a male?
They enclose the urethral tube and form the shaft of the penis
What does the labioscrotal swelling of an undifferentiated embryo develop into in a male?
It fuses in the midline, forming the scrotum
What is androgen insensitivity syndrome?
Person is XY and has testes, but external genitalia is female. Due to a mutation in androgen receptor genes preventing androgen function and ‘normal’ female external genitalia development occurs
What is puberty?
Re-awakening of the reproductive system which leads to full secondary sexual maturation with capacity for reproduction
What is the first endocrine sign of puberty?
Increase in LH level (as a result of an increase in GnRH release)
What time of the day does GnRH release occur in early puberty?
At night during sleep
What follows the early puberty rise in LH?
Rise in sex steroids (androgens, oestrogen)
What is the first sign of secondary sexual maturation in females? What age does it tend to occur and why?
Breast development at age 10-11 in response to oestrogen secretions (breast bud followed by breast mound)
What is the second occurrence in female puberty?
Pubic hair, occurs ~6 months after breast bud appearance
When do females experience a growth spurt?
~ 12
What does the early appearance of pubic hair indicate?
Problems with androgens
When do males experience a growth spurt?
~ 13-15
How long after pubic hair growth does armpit hair occur?
~ 1 year
What is Menarche?
1st menstrual bleed (does not signal 1st ovulation)
When does 1st ovulation tend to occur?
6-9 months after 1st menstrual bleed.
What is the first sign of secondary sexual development in males?
Enlargement of the testicles
Why does ovulation occur after the 1st few menstrual bleeds?
Positive feedback mechanisms of oestrogen have not developed
What causes enlargement of the testicles when puberty begins?
Leydig cells enlarging and secreting testosterone
How far into puberty does elongation and enlargement of the penile begin?
1 year
How long after male pubic hair growth does armpit and facial hair grow?
18 months
How long after the testicular enlargement does sexual hair growth occur?
6 months
What is spermache?
Motile sperm seen in urine?
At what age does spermache first occur?
13-14 years
What are the ages for precocious puberty in males and females?
< 7 for girls
<9 for boys
What are the ages for delayed puberty in males and females?
> 13 in girls
14 in boys
What is the role of follicle-stimulating hormone (FSH) in both male and female gonads?
Acts on the ovaries to stimulate the growth and development of gametes.
Acts on the testes to stimulate the production of gametes.
What is the role of luteinising hormone (LH) in both male and female gonads?
Acts on the ovaries to trigger ovulation and promote the sythesis and release of ovarian hormones.
Acts on the testes to promote the synthesis of testosterone.
What is the sequence of key events in female puberty?
Breast budding, pubic hair, menarche, ovulation
What is the sequence of key events in male puberty?
Testes enlargement, pubic hair, penile enlargement
