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Sex Steroids
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University of Edinburgh Lecture notes for Reproductive Biology 3 Lecture "Sex Steroids"
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Sex Steroids Steroids regulate endocrine function
o Steroids are lipid soluble meaning they can move across membranes
o They have an effect on many different parts of the body
Different types of steroid hormones
o Glucocorticoids- increase protein turnover and gluconeogenesis
o Mineralocorticoids- control sodium and potassium balance in the body
o Androgens- maintain functional activity of male reproductive system, anabolic
and sexual behaviour actions
o Progestagens- maintenance of pregnancy
o Oestrogens- maintain functional activity of female reproductive system, also
acts on cardiovascular system and bone
Steroids have effects on many tissues
Steroids are complex molecules
o Have multiple enzyme pathways
o Depend on the availability of substrates
o Depend on interconversion between active and inactive forms
o Have multiple signalling pathways
o They have multiple receptor types and distinct molecular pathways
o Bioavailability of the steroid for its receptor- actions of binding proteins
98% of steroid hormones are not available to bind to their cognate receptors
o Can synthesise steroids through different routes
Depends what enzymes are available
Steroids can be generated in different ways in different parts of the body
There are four key reproductive steroid hormones
o Progesterone
o Testosterone
o DHT
o And Oestradiol
Male sex hormones are needed to make female sex hormones
Progesterone is converted to 17α-hydroxy progesterone by 17α-
hydroxylase
17α-hydroxylase is converted to androstenedone by 17,20 lyase
Androstenedone is converted to testosterone by 17β-HSD
Testosterone is converted to oestrogens by aromatase
,
Control of the human menstrual cycle
o In first half of cycle follicles make steroids (oestrogen)
o In second half of cycle, corpus luteum makes steroids (progesterone)
o The receptive state is the period in the menstrual cycle where implantation can
occur
o Oestrogen stimulates the endometrium to develop
o
Thecal cells and granulosa cells work together to produce oestradiol
o Thecal cells are found outside the follicle
o Granulosa cells found on the inside of the follicle
o Need combination of enzymes from both cells to make oestradiol
Granulosa perform the most aromatisation
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