REB 14. Biochemistry of the Main Gonadal Hormones Flashcards by Jennita Ariaratnam

What are the gonads?

Gonads: bifunctional organs that produce germ cells and the sex hormones
e.g. ovaries and testes

How well did you know this?

Not at all

Perfectly

What are the 2 types of gonadal hormones that are present in females?

[1] Oestrogens
[2] Progestogens
- progesterone is the most common progestogen

How well did you know this?

Not at all

Perfectly

How are the female gonadal hormones released?

monthly cycle of hormone levels
all germ cells present at birth (around 1 to 2 mllion)
no new ovums are produced
around 400 ova are ovulated in the span of a woman’s life

How well did you know this?

Not at all

Perfectly

What are the gonadal hormones that are present in males?

Androgens - testosterone + DHT (dihydrotestosterone)

How well did you know this?

Not at all

Perfectly

What is DHT?

Dihydrotestosterone - a potent metabolite of testosterone

How well did you know this?

Not at all

Perfectly

How are the male gonadal hormones released?

constant levels of hormones

- continuous production of sperm

How well did you know this?

Not at all

Perfectly

What produces ova?

Ovaries

How well did you know this?

Not at all

Perfectly

What produces spermatozoa?

Testes

How well did you know this?

Not at all

Perfectly

What hormone contains an aromatic ring?

Estrogens are the only hormones that contain an aromatic ring

How well did you know this?

Not at all

Perfectly

What is the name of the axis that controls the hormones that controls the female reproductive system?

Hypothalamic-Pituitary-Gonado Axis

How well did you know this?

Not at all

Perfectly

What are the 4 stages of the menstraul cycle?

[1] Menses (day 1 to day 5)
- shedding of endometrium

[2] Follicular Phase (day 5 to day 13)

ovum maturation + proliferation endometrium
estrogen levels gradually increase

[3] Ovulation (day 14)
- surge in LH

[4] Luteal Phase (day 15 to day 28)

increase in progesterone
decrease in LH and FSH
if no implantation, progesterone secretion stops, inducing menses
if fertilization (implantation), corpus luteum secretes progesterone

How well did you know this?

Not at all

Perfectly

What does the corpus luteum secrete?

progesterone

How well did you know this?

Not at all

Perfectly

What is Inhibin? What is its role?

a hormone that is secreted by the granulosa cells (in ovary)

- inhibits secretion of FSH by anterior pituitary gland

How well did you know this?

Not at all

Perfectly

Where is estrogen synthesized?

[1] ovary
[2] placenta
[3] testes (small amount)

How well did you know this?

Not at all

Perfectly

What is the primary roles of estrogen?

[1] development + maintenance of secondary sex characteristics
[2] control the reproductive cycle
[3] stimulate the linear bone growth - puberty

How well did you know this?

Not at all

Perfectly

What are the secondary sex characteristics that are developed and maintained in females?

enlargement of breasts
growth of body hair
greater development of thigh muscles behind femur
widening of hips
secretions of oil and sweat glands
changed distribution in weight and fat

How well did you know this?

Not at all

Perfectly

What are the 3 main endogenous estrogens?

[1] Estrone (E1)
[2] Estradiol (E2/17beta-estradiol)
[3] Estriol (E3)

What is the most common endogenous estrogen? Where is is synthesized and what is it regulated by?

Estradiol (E2) - 80%

synthesized by ovary (non-pregnant)
regulated by FSH
can also be made peripherally (aromatization)!

What is aromatization?

It is the creation of estrogen peripherally

What 2 processes is the aromatase enzyme responsible for (crucial part of)?

[1] conversion of testosterone to estradiol in the ovary in premenopausal women

[2] conversion of androstenedione to estrone on peripheral adipose tissue in postmenopausal

Why are aromatase inhibitors used?

they are frequently used as estrogens may promote some cancers
- e.g. anastrozole + letrozole

What hormone controls the timing of the follicular phase?

Estradiol (E2)

What are the actions of Estrogen? (on other hormones, metabolic actions, lipids…)

refer to slide 14

From what things is progesterone secreted from?

[1] corpus luteum
[2] placenta during pregnancy
[3] small amounts by testes and adrenal cortex (both sexs

What are the hormonal effects that progesterone has? [2]

[1] maturation of the endometrium | [2] supports gestation and embryogenesis

What are the gonadotrophins?

[1] FSH [2] LH [3] bonus: Human Chorionic Gonadotropin (HCG)

Where are the gonadotropins produced and secreted?

[1] Anterior Pituitary | [2] Chorion + Placenta

Describe the structure of the gonadotrophic hormones (the subunits).

All the gonadotropins have an alpha and beta subunit (they are dimeric) - alpha subunits are all the same - beta subunit differs between the 3 (biological activity resides here) *side note: the HCG and LH beta subunit is very similar (same target tissue + same cellular response)

What hormone does the hypothalamus secrete to stimulate the gonadotrophic hormones? In what type of manner?

hypothalamus secreted GnRH in a pulsatile manner

What characteristics of GnRH pulses alters the FSH and LH synthesis and secretion?

[1] Size [2] Frequency of the GnRH pulses

If there are low-frequency GnRH pulses, this leads to...

FSH release

If there are high-frequency GnRH pulses, this leads to...

LH release

Compare and contrast the GnRH pulse frequency in women, men and children.

WOMEN: - pulse frequency varies during the menstrual cycle - large surge before ovulation MEN: - GnRH is secreted in pulses at a constant frequency CHILDREN: - GnRH activity is very low - activated at puberty

What is ICSH? What is it a "replacement" hormone of?

ICSH = Interstitial Cell Stimulating Hormone | - older version of LH

What is Dihydrotestosterone (DHT)?

Testosterone is a precursor to this - DHT | - it is a very potent androgen

What specific/special cells produces testosterone, a major testicular androgen?

Interstitial Cells of Leydig

Explain the process of how testosterone is converted to Dihydrotestosterone (DHT). (enzymes and other molecules)

converted by the 5alpha-reductase enzyme + in the presence of NADPH - occurs in certain tissues (prostate gland, seminal vesicles, epididymides, skin, hair follicles, liver + brain)

What are the 3 major things testosterone is converted to?

[1] 10% DHT [2] 0.3% Estradiol (via aromatase) [3] 90% Inactive Metabolites

What is Androstenedione? Where is it produced?

- produced by Adrenal Cortex - far less potent than testosterone - major source of androgenic activity in females

List the male secondary sex characteristics.

[1] growth of facial + body hair [2] greater mass of thigh muscles in front of femur (in females it is behind it) [3] enlargement of larynx (deepening of voice) [4] increased stature [5] heavier skull and bone structure [6] increased muscle mass and bone structure [7] broadening of shoulders and chest [8] increased secretion of oils + sweat glands [9] higher waist to hip ratio

Explain what happens when there is an inherited deficiency of 5alpha-reductase?

- important enzyme converting testosterone to DHT - during embryogenesis, DHT plays an important role in formation of male external genitalia - the affected boys are born with ambiguous external genitalia - BUT, testes and internal Wolffian ducts structures are present and fine - full virilization takes place at puberty!

What are the deficiencies that lead to Congenital Adrenal Hyperplasia (CAH)?

[1] 21-alpha-Hydroxylase [2] 11beta-Hydroxylase - corticosteroid synthesis is blocked, the progestogens are overproduced and diverted into androgen synthesis (a) life-threatening electrolyte imbalance (sodium and water balance) (b) ambiguous external genitalia in girls, precocious puberty in boys --- e.g. enlarged clitoris (may look like penis)