gonads Flashcards
sex hormones: explain the process and regulation of steroidogenesis in male and female gonads, recall the physiological actions of male and female gonadal steroids; recall the hypothalamo-pituitary gonadal axis and its regulation in males and females
steroid hormones in males
mainly androgens (some oestrogens, progesterones)
steroid hormones in females
mainly oestrogens and progesterones (some androgens)
steroidogenesis of androgens: precursor and location
cholesterol to small amount of androgens in adrenal cortex (zona reticularis) or in gonads (progesterones, androgens and oestrogens)
dihydrotestosterone synthesis pathway from androstenedione in testes
androstenedione → 17-OH-progesterone → testosterone → dihydrotestosterone
significance of dihydrotestosterone
most potent form responsible for puberty phenotypic appearances
17B-oestradiol synthesis pathway from androstenedione
androstenedione → 17-OH-progesterone → oestrone → 17B-oestradiol
significance of 17B-oestradiol
most common oestrogen; activated by FSH
testosterone transport
lipid-soluble so must be bound to sex hormone binding globulin in blood or androgen binding globulin in seminiferous fluid
what % of testosterone is unbound and bioactive
2%
2 effects of testosterone in fetus
development of male internal and external genitalia; fetal growth acting with other hormones
effects of testosterone in adults
needed for spermatogenesis; growth and development of male genitalia and secondary sex characteristics (e.g. facial hair); protein and bone anabolism (i.e. muscle, bone growth); behavioural (male sexual behaviour); pubertal growth spurt (with GH); some effects mediated by conversion to oestrogen
oestrogens definition
any substance which induces mitosis in the endometrium (causing womb to thicken)
examples of oestrogens
17B-oestradiol, oestrone (precursor), oestriol
17B-oestradiol effects in endometrium
stimulates proliferation (mitosis) causing womb thickening
17B-oestradiol effects in menstrual cycle
triggers LH surge resulting in ovulation
other 17B-oestradiol reproductive effects
vagina/cervix secretions; stimulation of growth of ductile system in breasts; decrease of sebaceous gland secretions in skin
other 17B-oestradiol effects unassociated with reproduction: GnRH, osteoblasts, metabolic actions, behaviour, salt and water reabsorption, plasma protein synthesis, release of other hormones
feedback regulation on GnRH (negative and positive), stimulates osteoblasts, metabolic actions (e.g. on lipids), behavioural effects, increases salt and water reabsorption, increases plasma protein synthesis, influences release of other hormones
define progestogens
any substance inducing secretory changes in endometrium
examples of progestens
progesterone, 17a-hydroxyprogesterone
effects of progestogens: secretory activity in endometrium, GnRH, body basal temperature, renal NaCl reabsorption, alveolar system in breasts
stimulates secretory activity in endometrium and cervix, negative feedback regulation on hypothalamic GnRH, increase body basal temperature, decrease renal NaCl reabsorption, stimulates growth of alveolar system in breast
hypothalamo-pituitary-testicular axis
GnRH released from hypothalamus pulse generator → stimulates release of LH and FSH from anterior pituitary → LH stimulates Leydig cells to make testosterone and FSH stimulates Sertoli cells to support spermatogenesis → testosterone feed backs negatively on (direct) anterior pituitary and (indirect) hypothalamus, and Sertoli cells produce inhibin which feeds back negatively on (direct) anterior pituitary and (indirect) hypothalamus
what does GnRH stand for
gonadotrophin releasing hormone
hypothalamo-pituitary-ovarian axis
GnRH released from hypothalamus pulse generator → stimulates release of LH and FSH from anterior pituitary → LH stimulates ovulation and FSH stimulates 17B-oestradiol and inhibin production → 17B-oestradiol and inhibin feed back negatively on (direct) anterior pituitary and (indirect) hypothalamus
