Introduction to the reproductive axis Flashcards
Principle sources of sex steroids
gonads, the adrenal cortex, and the placenta
Who play key roles in the conversion and metabolism of sex steroids?
peripheral tissue (skin, liver and adipose tissues )
Major classes of steroids
- Glucocortocoids such as cortisol (C-21)
- Mineralocorticoids such as aldosterone (C-21)
- Sex steroids which include progestins (C-21), androgens (C-19), and estrogens (C-18)
How many carbons does cholesterol have?
27
What is the rate limiting step in steroid hormone synthesis from cholesterol?
The initial and rate-limiting step in these reactions is catalyzed by the cholesterol side chain cleavage enzyme located in the mitochondrial membrane.
This enzyme is also known as 20, 22 desmolase
Converts cholesterol to pregnenolone, which can then be converted into all other steroid hormones.
Progestins
21-carbon sex steroids derived from cholesterol
Pregnenolone, 17-alpha-hydroxy-pregnenolone, progesterone, and 17-alpha-hydroxy-progesterone (17-OH-P).
Act as sex steroids and precursors for the production of aldosterone and cortisol by the adrenal gland.
Affect almost all tissues in the body, most notably the uterus, the ovaries, and the breasts.
Key functions: growth and development of the tissues and organs related to ovulation, menses, pregnancy, and lactation.
Androgens
19-carbon sex steroids derived from cholesterol via pregnenolone
testosterone, dehydroepiandrosterone (DHEA), dehydroepiandrosterone-sulfate (DHEA-S), dihydrotestosterone (DHT), and androstenedione
Testosterone (95% made in testes, 5% adrenal cortex)
DHEA and DHEA-S (majority made in adrenal cortex)
Testosterone actions
Androgenic impacts include the growth and development of the internal and external genitalia, the development and maintenance of secondary sex characteristics, spermatogenesis, and sexual fantasies and libido. Sebum production is an androgen dependent process.
Anabolic effects can be summarized as the growth-promoting effects on somatic tissues such as bone and muscle. Within the hypothalamic – pituitary – testicular axis, testosterone acts as a key feedback inhibitor at the levels of hypothalamus and pituitary.
The levels of circulating testosterone in men are relatively stable throughout most of adulthood.
What is the rate limiting step in the production of sex hormones?
The conversion of cholesterol into Pregnenolone by 20-22 Desmolase, which is located in the mitochondrial membrane.
What are the two ways in which LH stimulates the conversion of cholesterol into pregnenolone?
LH increases the amount of 20,22 desmolase and also increases the affinity of desmolase for cholesterol.
What steps can granulosa cells not complete in the production of sex hormones?
Granulose cells cannot convert progesterone to androstenedione because they lack 17a-hydroxylase to produce 17a-OH-progesterone and 17, 20 desmolase to produce androstenedione. Thus 17a-OH-progesterone should not be present in granulosa cells.
What steps can theca cells not complete in the production of sex hormones?
Theca cells cannot convert testosterone into estradiol because they lack aromatase. This also prevents them from converting androstenedione into estrone, which also requires aromatase.
What enzyme and pathway to cells stimulated by FSH possess that cells stimulated by LH do not?
Cells stimulated by FSH (Sertoli and Granulosa cells) also possess Aromatase, and can convert testosterone and androstenedione into estradiol and estrone, respectively.
What are some of the key functions of progesterone?
Key functions of progesterone include the growth and development of the tissues and organs related to ovulation, menses, pregnancy, and lactation. Within the context of the hypothalamic – pituitary – ovarian axis, progesterone acts as a key feedback inhibitor at the levels of hypothalamus and pituitary.
What are some of the key functions of testosterone?
Testosterone affects almost all tissues in the body. The effects are classified into two major categories: androgenic and anabolic. Androgenic impacts include the growth and development of the internal and external genitalia, the development and maintenance of secondary sex characteristics, spermatogenesis, and sexual fantasies and libido. Sebum production is an androgen dependent process. Anabolic effects can be summarized as the growth-promoting effects on somatic tissues such as bone and muscle. Within the hypothalamic – pituitary – testicular axis, testosterone acts as a key feedback inhibitor at the levels of hypothalamus and pituitary.
