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Endocrine > Biochemistry of the Main Gonadal Hormones > Flashcards

Biochemistry of the Main Gonadal Hormones Flashcards

1
Q

why are the gonads described as bifunctional organs?

A
  • produce germ cells
  • produce sex hormones
    *
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2
Q

What are the main gonadal hormones in males and females?

A

Female= oestrogens and progestogens

Males= androgens (testosterone and DHT)

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3
Q

Ovaries produce… ?

A

Ova

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4
Q

How many germ cells are present at birth in the female?

A

All of them -

there are 1-2 million germ cells present at birth in the female and no new ones are produced , you loose a lot of the immature germ cells over time - then 1 is ovulated every month for the entire fertile life cycle

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5
Q

Do men fluctuate in hormones - like a cycle?

A

no - they are rather constant in hormone levels

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6
Q

testes produce…?

A

spermatazoa

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7
Q

what are the 5 major classes of steroid hormones?

A

they are derived from cholesterol and pregnenolone

  • progestagens
  • glucocorticoids
  • mineralocorticoids
  • androgens
  • estrogens
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8
Q

what structure releases gonadotropin releasing hormone in a pulsatile secretion?

A

Hypothalamus

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9
Q

what hormone is responsible for the development of the graafian follicle?

A

FSH

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10
Q

What hormone is responsible for the rupture of the follicle and the release of the egg?

A

the LH

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11
Q

what importance does the corpus luteum ( remnant of the follicle) have in the ovarian cycle?

A

it can produce estrogen and progesterone - maintains a pregnancy

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12
Q

what is the rational for using estrogens and progesterones as birth control?

A

they have a negative feedback release which block the effects of the gonadotropin releasing hormone

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13
Q

when does the menstrual cycle start?

A

Day 1 of menses - shedding endometrium

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14
Q

What is the ‘follicular phase’ ?

A

phase in which the graafian follicle matures - and proliferation of the endometrium (FSH leads to development of the follicle and the follicle itself releases estrogen)

gradual increase in estrogen leads to the proliferation of the endometrium

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15
Q

What occurs on day 14 of the mestrual cycle?

A

Ovulation - surge in LH- ruptures the follicle and ovulation occurs as a result -

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16
Q

What is the ‘luteal phase’ how long does it last?

A

it lasts from day 15- 28

if no implantation - progesteron secretion stops and induces menses eventuallly

if fertilization- implantation- corpus luteum continues to secrete progesterone until the placenta is formed and functional and able to take over production of progesterone

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17
Q

the pulses of GnRH control what?

A

they control the peak of LH and FSH levels

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18
Q

what is the ‘secretory’ phase of the endothelium?

A

after the proliferative phase, the endometrium begins to prepare itself for implantation -

there is a slight increase in the body temperature during ovulation

19
Q

estrogens are produced where?

A

ovaries/placenta in women

testis in men

adrenal cortex in both sexes

20
Q

what are the primary roles of estrogens in the body?

A

Development and maintenance of secondary sex characteristics

–Enlargement of breasts

–Growth of body hair

–Greater development of thigh muscles behind the femur, rather than in front of it

–Widening of hips; lower waist to hip ratio than adult males, on average

–Increased secretions of oil and sweat glands

–Changed distribution in weight and fat; more subcutaneous fat and fat deposits mainly around the buttocks, thighs and hips

•Control the reproductive cycle

–Coordinate the ovarian and uterine cycles

•Stimulate linear bone growth – puberty

21
Q

what are the 3 main endogenous estrogens?

A

E1 = estrone = 10% - dominant estrogen in menopause

E2 = estradiol= 17beta estradiol = 80% - primary estrogen and the most potent one

E3= estriol = 10% produced by the placenta during pregnancy

* when we refer to estrogen in the medical context most of the time we’re referring to estradiol b/c it’s most potent and highest concentration

22
Q

what regulates the synthesis of estradiol?

A

regulated mainly by FSH

23
Q

estrogens produced peripherally are controlled by what process?

A

aromatisation

24
Q

What is Aromatase?

A

it is the enzyme responsible for the key steps in the biosynthesis of peripheral estrogens (primary source of estrogen in post-menopausal women)

  • this is why aromatase inhibitors are very effective in women post-menopause with estrogen receptor positive breast cancer
25
Q

aromatase converts what?

A
  1. converts testosterone to estradiol in the ovary = predominant source of estrogen in premenopausal women
  2. conversion of androstenedione to estrone in peripheral adipose tissue - predominant source of estrogen synthesis in postmenopausal women
26
Q

what does estrogen do?

A

•Fertility control - ovum maturation/ development of the ovum/follicular unit. Timing of follicular phase is controlled by Estradiol

•Preparation of uterus for implantation

–proliferation/vascularisation of endometrial cells

–induction of progesterone receptors to allow progesterone response during luteal phase

•Inhibit FSH release, negative feedback on AP - basic rational for using estrogen containing contraceptive

•Metabolic action

–Mineralocorticoid-like - retention of Na+ and water

•Lipids

–Increase [HDL] in plasma

–Decrease [LDL], [cholesterol]

•Increase coagulability of blood

–Increases production of a number of clotting factors (2,5,7 and 9)- this can lead to DVTs and PEs

•Maintains bone density and elasticity of skin & blood vessels

27
Q

what is the primary progesteren we see in females?

A

progesterone

28
Q

what produces progesterone in women ?

A

secreted by corpus luteum -and placenta during pregnancy

  • small amounts made by testes and adrenal cortex in both sexes
29
Q

what are the hormonal effects - of progesterone?

A
  • Hormonal effects:
  • maturation of the endometrium
  • supports gestation and embryogenesis
30
Q

Why do we give a combined estrogen/progesterone contraceptive?

A

b/c estrogen has profound endometrium proliferative effects, and progesterone counteracts this by inducing maturation of the endometrium

31
Q

where are gonadotropins produced/secreted?

A

Produced & secreted by anterior pituitary or chorion & placenta

–Follicle stimulating hormone (FSH)

–Luteinising hormone (LH)

–Human chorionic gonadotropin (HCG)

32
Q

what are the three gonadotrophic hormones? How do they differ?

A

All 3 hormones are dimeric► a & b subunits

  • a subunit is common
  • b subunit differs - biological activity resides
  • b subunit in HCG and LH very similar [90% homology]
  • same target tissue (corpus luteum) and cellular response (↑ progesterone)
33
Q

what is GnRH?

A

GnRH - gonadotrophic releasing hormone = peptide hormone, synthesized and released from neurons within the hypothalamus

GnRH secreted in a pulsatile manner from hypothalamus controls secretion of FSH and LH by AP in females

34
Q

What controls FSH and LH synthesis and secretion?

A

FSH & LH synthesis and secretion are controlled by the size and frequency of GnRH pulses, as well as by feedback from androgens and oestrogens:

–low-frequency GnRH pulses lead to FSH release

–high-frequency GnRH pulses stimulate LH release

35
Q

how does GnRH pulses change in the female cycle? men? during childhood?

A

In females, GnRH pulses frequency varies during the menstrual cycle, with large surge just before ovulation

  • In males, GnRH is secreted in pulses at a constant frequency
  • During childhood, GnRH activity very low, activated at puberty
36
Q

in men, what two hormones are controlled by GnRH?

A

GnRH increases production of FSH and interstitial cell stimulating hormone (AKA ICSH or sometines refered to as LH)

37
Q

what is the more potent metabolite of testosterone? what enzyme converts testosterone to this metabolite?

A

Dihydrotestosterone -

testosterone is converted to this by 5 alpha reductase

38
Q

what is the main androgen produced- where is it produced?

A

testosterone = major testicular androgen

produced by interstitial cells of leydig in testis

39
Q

how much Dihydrotestosterone is produced compared to testosterone concentration in men?

A

DHT is present at 1/10th concentration of testosterone in blood

40
Q

What is the major source of androgeneic activity in females?

A

androstenedione - produced by adrenal cortex - far less potent than testosterone but major source of androgenic activity in females

41
Q

what are the secondary sex characteristics of men?

A
  • Growth of facial & body hair
  • Greater mass of thigh muscles in front of the femur, rather than behind it
  • Enlargement of larynx and deepening of voice
  • Increased stature; adult males are taller than adult females, on average
  • Heavier skull and bone structure
  • Increased muscle mass and strength
  • Broadening of shoulders and chest; shoulders wider than hips
  • Increased secretions of oil and sweat glands
  • Higher waist to hip ratio than females or prepubescent males, on average
42
Q

What occurs in inherited deficiency of 5 alpha reductase?

A

prevents synthesis of DHT from testosterone - (very rare condition) - during embryogenesis DHT essential role in formation of male external genitalia - affected boys born with ambiguous external genitalia - although testes and internal wolffian ducts are present - full virilizaiton takes place at puberty (aka penis at twelve syndrome) - pretty rare condition

43
Q

what is congenital adrenal hyperplasia?

A

most common defiicency -

Deficiency of e.g. 21-a-hydroxylase or 11b-hydroxylase

–Enzymes required for synthesis of corticosteroids but not androgens

–Corticosteroid synthesis blocked, overproduced progestogens are diverted into androgen synthesis

  1. Life threatening electrolyte imbalance
  2. Ambiguous external genitalia in girls, precocious puberty in boys (early puberty as early as 9 yr. old)

Endocrine (16 decks)

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