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Endo Test 2 > Male hormones in development and reproduction > Flashcards

Male hormones in development and reproduction Flashcards

1
Q

Case 1: A 17 y/o female presents to her pediatrician with complaint that she has not had a menstrual period yet. She reports breast development but scant axillary and pubic hair. On exam, she is noted to have a blind vaginal pouch with no evidence of a uterus or cervix.

A

46,XY.

- lack of cervix, utuers and tubes: AMH

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2
Q

What cells secrete AMH?

A

Sertoli cells of testes

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3
Q

what does AMH do?

A

causes regression of female mullerian structures

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4
Q

what promotes development of testes?

A

SRY gene causes transcription factor TDF (testis determining factor) to be expressed.
- SRY gene is located on Y chromosome

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5
Q

what promotes development of male external genitalia? what enzyme is required?

A

DHT (dihydrotestosterone)

- 5alpha- reductase-2

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6
Q

5-alpha reductase 2 deficincies

A

results in ambiguous or feminzed external genitalia with not internal female structures

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7
Q

what cells secrete testosterone

A

Leydig cells

- action stimulated by LH

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8
Q

Before fetal pituitary LH action is initiated, which hormone stimulates fetal Leydig cell production of T?

A

hCG
- Note: hCG can be substituted for LH in clinical attempts to stimulate spermatogenesis in oligospermic men due to its increased availability. hCG is structurally most similar to LH and binds LH receptors.

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9
Q

Androgen insensitivity?

A
  • patient does not develop a penis, scrotum or prostate but is secreting testosterone and has no 5alpha reductase 2 deficiency
  • DHT is required for external male genitalia and prostate
  • DHT binds same androgen receptor as testosterone, but with great afinity
  • if patient is missing androgen receptors then target tissues do not respond to DHT/T
  • this is an X-linked recessive trait
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10
Q

Do you expect a patient with androgen insensitivity to have seminal vesicles, ejaculatory ducts, and vas deferens/epididymis associated with the testes?

A

No, testosterone action required for these Wolffian duct structures to develop

Defective androgen receptors

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11
Q

What is required for formation of prostate gland and scrotum/penis?

A

DHT!!!!

Testosterone is converted to DHT via 5 alpha reductase 2

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11
Q

What is required for formation of prostate gland and scrotum/penis?

A

DHT!!!!

Testosterone is converted to DHT via 5 alpha reductase 2

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12
Q

What is required for formation of epididymis, Vas deferens, ejaculatory duct and seminal vesicle?

A

Just testosterone, secreted from Leydig cells

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12
Q

What is required for formation of epididymis, Vas deferens, ejaculatory duct and seminal vesicle?

A

Just testosterone, secreted from Leydig cells

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13
Q

What is required for development of Sertoli cells and Leydig cells?

A

SRY gene –> TDF –> development of testes –> development of these cell types –> secrete AMH and testosterone

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13
Q

What is required for development of Sertoli cells and Leydig cells?

A

SRY gene –> TDF –> development of testes –> development of these cell types –> secrete AMH and testosterone

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14
Q

when is SRY made?

A

6-8 weeks

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14
Q

when is SRY made?

A

6-8 weeks

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15
Q

When is testosterone/AMH made?

A

8 weeks

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15
Q

When is testosterone/AMH made?

A

8 weeks

16
Q

when is DHT made?

A

9-12 weeks

16
Q

when is DHT made?

A

9-12 weeks

17
Q

why would patient with 46 XY and androgen receptor insufficiency present with breast development?

A
  • production of testosterone still occurs, peripherally body converts the testosterone to estradiol via cyp19-aromatase
17
Q

why would patient with 46 XY and androgen receptor insufficiency present with breast development?

A
  • production of testosterone still occurs, peripherally body converts the testosterone to estradiol via cyp19-aromatase
18
Q

what is required for pubertal hair growth in males?

A

testosterone secretion –> DHT

- If have receptor insensitivity, then pubic hair will devleop

18
Q

what is required for pubertal hair growth in males?

A

testosterone secretion –> DHT

- If have receptor insensitivity, then pubic hair will devleop

19
Q

What hormone is thought to initiate puberty?

A
  • GnRH
  • Resurgence of pulsatile, sleep-associated GnRH secretion from the hypothalamus during adolescence
  • Initial increase during gestation, again within the first 2 years of life, and then inhibition of GnRH neurons by the CNS until puberty; lower hypothalamic and pituitary set-point
  • Increased pituitary gonadotrope sensitivity to GnRH
19
Q

What hormone is thought to initiate puberty?

A
  • GnRH
  • Resurgence of pulsatile, sleep-associated GnRH secretion from the hypothalamus during adolescence
  • Initial increase during gestation, again within the first 2 years of life, and then inhibition of GnRH neurons by the CNS until puberty; lower hypothalamic and pituitary set-point
  • Increased pituitary gonadotrope sensitivity to GnRH
20
Q

What promotes LH/FSH secretion and Testosterone secretion? where are the receptors?

A
  • pulsatile hypothalamic GnRH release stimulates anterior pituitary LH And FSH secretion
  • LH receptors on Leydig cells
  • FSH receptors are on Sertoli cells
20
Q

What are androgenic actions of testosterone?

A
  1. Fetal differentiation of male internal (T) and external genitalia (DHT)
  2. Growth, development of secondary sexual characteristics at puberty
  3. Maintenance of reproductive tract & production of semen
  4. Initiation and maintenance of spermatogenesis
21
Q

What are the anabolic actions of testosterone?

A
  1. Stimulation of erythropoietin synthesis
  2. Stimulation of sebaceous gland secretion
  3. Control of protein anabolic effects (nitrogen retention)
  4. Stimulation of linear body growth, bone growth and closure of the epiphyses
  5. Promotion of ABP synthesis
  6. Maintenance of secretions of sex glands
  7. Regulation of behavioral effects, including libido
21
Q

What are the anabolic actions of testosterone?

A
  1. Stimulation of erythropoietin synthesis
  2. Stimulation of sebaceous gland secretion
  3. Control of protein anabolic effects (nitrogen retention)
  4. Stimulation of linear body growth, bone growth and closure of the epiphyses
  5. Promotion of ABP synthesis
  6. Maintenance of secretions of sex glands
  7. Regulation of behavioral effects, including libido
22
Q

What are important hormonal factors that stimulate spermatogenesis?

A

Luteinizing hormone (LH): stimulates Leydig cells to secrete testosterone

Testosterone (T): essential for growth and division of testicular germinal cells, beginning of sperm formation

Follicle-stimulating hormone (FSH): stimulates the Sertoli cells which are essential for supporting spermatogenesis

Estradiol (T is converted by aromatase to E): ER expressed on sperm cells, some evidence for a role in optimizing spermatogenesis

Growth hormone (GH): necessary for controlling background metabolic functions of the testes. Promotes early division of sperm. (Pituitary dwarfs: spermatogenesis is severely deficient or absent rendering them infertile)

22
Q

know tanner stages

A
  1. Preadolescent: no pubic hair
  2. scrotum and testes enlarge and scrotal skin changes texture: sparse, long downy hair at base of penis
  3. growth of penis in length and further growth of testes/scrotum; darker coarser hair
  4. growth of penis in length; darkening of scrotal skin; adult type hair but less area
  5. adult-sized genitalia; adult texture and quantity of pubic hair
    * ** puberty of male starts around 10 years of age, and ends at 17 years.
23
Q

how is circulating testosterone bound?

A
  • SHBG (sex hormone-binding globulin): binds about 45-60% of testosterone
  • 38-55% bound to serum albumin
  • 2-5% is free
23
Q

how is circulating testosterone bound?

A
  • SHBG (sex hormone-binding globulin): binds about 45-60% of testosterone
  • 38-55% bound to serum albumin
  • 2-5% is free
24
Q

What protein is responsible for maintaining adquate testosterone concentration in testes?

A

ABP (androgen-binding protein)

25
Q

Why must Testosterone be concnetrated in testes?

A
  • Adequate concentration within the testes is essential for maintaining normal rate of spermatogenesis
  • 100 : 1 (intra-testicular : circulating)
26
Q

Case 2: 16 y/o male with no signs of puberty. lower in height and weight. no secondary sex characteristics. little muscle mass. high pitched voice. sparse pubic hair, underdeveloped testes.
LH: low
Testosterone: low
MRI: normal hypothalamus and pituitary

A

hypogonadotropic hypogonadism

  • testes are immature and have no sperm due to low LH, FSH and testosterone plasma levels
  • congenital disease
27
Q

Kallman syndrome

A

decreased or absence GhRH secretion

  • results in low LH/FSH and low testosterone
  • testes are immature and have no sperm
28
Q

hypogonadism

A

defects in spermatogenesis or steroidogenesis

- usually due to endocrine factors

29
Q

What promotes LH/FSH secretion and Testosterone secretion? where are the receptors?

A
  • pulsatile hypothalamic GnRH release stimulates anterior pituitary LH And FSH secretion
  • LH receptors on Leydig cells
  • FSH receptors are on Sertoli cells
30
Q

GnRH therapy?

A

given for prostate cancer

  • continuous high doses of GnRH will suppress gonadotropin secretion
  • inhibition of GnRH receptor replenishment –> results in decreased levels of LH/FSH and decreased Testosterone
31
Q

What are main functions of Sertoli Cells?

A 
- Supportive Function:  
  Maintaining blood-testis barrier
 Phagocytosis
 Transfer of nutrients to sperm 
 Receptors for hormones & paracrines
  • Exocrine Function:
    Fluid produced for sperm mobilization
    Production of ABP
    Spermination: release of sperm from seminiferous tubule
  • Endocrine Function:
    Expression of testosterone, ABP and FSH receptors
    Production of AMH
    CYP19 Aromatase: testosterone  estradiol-17β (local)
    Production of inhibin B to regulate FSH levels
32
Q

Which hormones are important for adequate spermatogenesis?

A
  • testosterone from Leydig cells (req. ABP from Sertoli cells for sufficient concentration)
  • FSH and LH (necessary for Leydig and sertoli fn.)
33
Q

What are important hormonal factors that stimulate spermatogenesis?

A

Luteinizing hormone (LH): stimulates Leydig cells to secrete testosterone

Testosterone (T): essential for growth and division of testicular germinal cells, beginning of sperm formation

Follicle-stimulating hormone (FSH): stimulates the Sertoli cells which are essential for supporting spermatogenesis

Estradiol (T is converted by aromatase to E): ER expressed on sperm cells, some evidence for a role in optimizing spermatogenesis

Growth hormone (GH): necessary for controlling background metabolic functions of the testes. Promotes early division of sperm. (Pituitary dwarfs: spermatogenesis is severely deficient or absent rendering them infertile)

34
Q

In patient with hypogonadic hypogonadism what would be the effect of administering exogenous testosterone?

A

Virilization of secondary male sex traits

  • would not promote fertility because testosterone feeds back negatively to decrease LH secretion which is already low in this patient
  • decreased LH –> decreased Testosterone production by Leydig cells –> decreased testicular concentration –> decreased spermatogenesis
35
Q

primary testicular failure

A

removes negative feedback from hypothalamic-pituitary axis
- see low levels of T, thus high levels of plasma gonadotropins

in contrast:
- decreased gonadotrpoin and steroid levels and reduced testicular size almost always accompany hypothalamic and pituitary failure

36
Q

gonad failure before puberty

A

results in absence of secondary sex characteristics (eunuchoidism)
- men with a postpubertal testicular failure retain masculine featues, but exhibit low sperm counts later in life

Endo Test 2 (10 decks)

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