L11 Sex Hormones Flashcards
(33 cards)
Describe the hypothalamic-pituitary-gonadal axis
Human reproduction begins with secretion of GnRH from hypothalamus. GnRH stimulates FSH and LH release from pituitary. FSH and LH stimulate production of steroid hormones and gametes by the ovary and testes.
3 categories of steroids secreted by the gonads
- Oestrogens: oestradiol, estrone, estriol
- Progestins: progesterone
- Androgens: testosterone
Which enzyme is involved in the conversion of testosterone to dihydrotestosterone?
5α-reductase
Which enzyme is responsible for the conversion of testosterone to estradiol?
CYP19A1/aromatase
What is the main hormone in males?
total testosterone
What percentage of testosterone is produced by the testes?
95%
How does dihydrotestosterone affect external genitalia?
Dihydrotestosterone is responsible for differentiation during gestation, maturation during puberty, and adulthood prostatic diseases
How does testosterone affect internal genitalia?
Testosterone is responsible for Wolffian development during gestation
How does estradiol affect bone?
Estradiol significantly impacts bone density - why menopausal women experience changes in bone density, brittle bones, and increased risk of osteoporosis
The consequences of androgen deficiency depend on…
The stage of life during which the deficiency first occurs and the degree of the deficiency
Effect of androgen deficiency during foetal development
- incomplete sexual differentiation
- results only from testicular disease e.g. 17α-hydroxylase deficiency
- complete deficiency results in entirely female external genitalia
Effect of androgen deficiency before completion of puberty
- failure to complete puberty
- pubertal changes impaired to a degree proportionate to the abnormality of testosterone secretion
- if GH is normal when testosterone secretion is subnormal, long bones continue to lengthen (eunuchoid)
Effect of androgen deficiency after completion of puberty
i.e. after castration or anti-androgenic treatment
- regression of the pubertal effects of testosterone
- libido and energy decrease within a week or two, but other testosterone-dependent characteristics decline more slowly
Alkylated forms of testosterone
- methyltestosterone
- oxymetholone
- fluoxymesterone
Disadvantages of oral alkylated forms of testosterone
- associated with hepatopathy
- have erratic absorption
- decreased effectiveness compared to the intramuscular preparations
What oral testosterone therapy has a very short half-life and requires administration 2-3 times daily?
oral testosterone undecanoate (Andriol)
Why are buccal testosterone tablets rarely used?
because they require twice daily usage and 5-10% of men experience significant gingival irritation
What is oral testosterone/androgen therapy used for?
male hypogonadism
4 intramuscular testosterone esters that are used clinically
- testosterone propionate
- testosterone enanthate
- testosterone cypionate
- testosterone undecanoate
Classification of causes of male hypogonadism
- Hypothalamic-pituitary disorders e.g. panhypopituitarism
- Primary testicular abnormalities e.g. Klinefelter syndrome (XXY)
- Defects in androgen action e.g. complete/incomplete androgen insensitivity
Causes of male infertility
- Endocrine e.g. hypothalamic-pituitary disorders, primary testicular disorders
- Defects in spermatogenesis e.g. idiopathic, drug-induced
- Sperm transportation defects e.g. ductal obstruction, retrograde ejaculation (often occurs in BPH)
- Sexual function disorders e.g. erectile dysfunction
- Miscellaneous e.g. varicocele
Effect of GnRH agonists
promote follicle maturation
Effect of GnRH antagonists
suppress LH surge
What is Menotrophin?
A GnRH agonist that is used to treat infertility by providing LH and FSH to stimulate the ovaries
