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Endocrinology and Reproduction > Male Reproductive Endocrinology I > Flashcards

Male Reproductive Endocrinology I Flashcards

1
Q

The normal male has a chromosome complement of 44 autosomes and the two sex chromosomes

A

X and Y

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2
Q

The Y chromosome contains a 14-kilobase region termed the

A

Sex-determining region of the Y chromosome (SRY)

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3
Q

The SRY encodes the

A

Testis-determining factor (TDF)

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4
Q

A sequence specific transcription factor that regulates the expression of genes that are critical for male gonadal development

A

TDF

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5
Q

Although TDF and other loci on the Y chromosome are essential for testicular development and masculinization, they are not sufficient for

A

Complete maleness

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6
Q

Other autosomal- and X-chromosome genes are also important for maleness, such as the gene for the

A

Androgen Receptor (AR)

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7
Q

Sensitizes the genitsal ducts and external genitalia to the masculinizing effects of androgens

-located on the X chromosome

A

AR

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8
Q

The genes for SOX-9 and steroidogenic factor-1, both essential for gonad development and steroidogenesis, are which types of chromosomes?

A

Autosomal

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9
Q

During the first 4-7 weeks of development, the gonadal tissue of male and female embryos are

A

Indistinguishable

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10
Q

This indistinguishable gonadal tissue is organized into an

A

Outer cortex and inner medulla

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11
Q

In the normal male embryo, when do we see the formation of

  1. ) Sertoli cells
  2. ) Leydig cells
A
  1. ) 7 weeks

2. ) 8-9 weeks

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12
Q

At 9 weeks, the primordial germ cells become enclosed within the medulla forming

A

Spermatogonia

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13
Q

At this point, there is a recognizable testes that initiates the secretion of

A

Testosterone

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14
Q

In the normal XX female embryo (and thus in the absence of the SRY gene), differentiation of the indifferent gonad into the ovaries starts at

A

Week 9

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15
Q

During the sexual indifferent stage (4-7 weeks of development), two different genital ducts develop on each side of the embryo termed the

A

Wolffian and Mullerian ducts

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16
Q

In males, at about 8-9 weeks, testosterone acts to trigger Wolffian duct to differentiate into the internal male genitalia, including the

A

Epididymis, vas deferens, and seminal vesicles

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17
Q

The leydig cells secrete

A

Testosterone

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18
Q

The sertoli cells secret

A

Anti-Mullerian Hormone (AMH)

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19
Q

In males, at about 8-9 weeks, the Mullerian ducts atrophy and regress under the influence of

A

AMH

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20
Q

Belongs to a family of growth regulating factors (e.g., activin and inhibin)

A

AMH

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21
Q

In the absence of testosterone or AMH secretion, the Wolffian ducts regress and the Müllerian ducts will differentiate into the

A

Female genitalia

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22
Q

Starting at around week 10 of development, male external genitalia differentiates into the masculine format via testosterone secretion and conversion into

A

Dihydrotestosterone (DHT)

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23
Q

With DHT stimulation, the genital tubercle grows into the

A

Glans penis

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24
Q

With DHT stimulation, the genital swellings form the

A

Scrotum

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25
Q

With DHT stimulation, the urogenital sinus gives rise to the

A

Prostate

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26
Q

The male reproductive system comprises not only male-specific genitalia, but also the

A

Hypothalamus and pituitary gland

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27
Q

Sperm generated in the testis empties into the

A

Epididymus

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28
Q

This in turn leads into a long, straight tube called the

A

Vas deferens

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29
Q

The vas deferens from each testis rises up through the scrotum and inguinal canal and descends along the posterior end of the bladder. Here each vas deferens widens into an ampulla, which is attached to a

A

Seminal vesicle

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30
Q

Generate roughly 60% of the fluid volume of the semen, including the secretion of fructose that serves to nourish sperm

A

Seminal Vesicles

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31
Q

The contents of the ampullae and seminal vesicle pass into the prostate gland via an

A

Ejaculatory duct

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32
Q

Generates roughly 30% of the fluid volume of semen

A

Prostate

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33
Q

Along with simple sugars and proteolytic enzymes, the prostate gland secretes a slightly alkaline, milky white fluid that helps neutralize the acidity of the

A

Vaginal Tract

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34
Q

The urethra is supplied with lubricating mucus via the bilateral

A

Bulbourethral glands (Cowper’s glands)

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35
Q

The predominant source of testosterone in males and the exclusive site of male gamete maturation

A

Testes

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36
Q

Situated in the scrotum where they are maintained at a temperature 1 to 2 degrees C below the core body temperature

A

Testes

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37
Q

The testes receive blood from the spermatic arteries which originate directly from the

A

Aorta

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38
Q

About 80% of the testes is made up of

A

Seminiferous tubules

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39
Q

The remaining 20% of the testes is comprised of connective tissue containing

A

Leydig Cells

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40
Q

A coiled mass of loops, lead into the epididymis, a maturation and storage site for spermatozoa

A

Spermatogenic Tubules

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41
Q

Each spermatogenic tubule is bounded by a basement membrane that separates it from the

A

Leydig cells, Peritubular (myoid) cells, and the adjacent capillaries

42
Q

Just below this membrane are the

A

Sertoli Cells and spermatogonia

43
Q

As the spermatogonia divide and differentiate into spermatocytes and then spermatids, columns of maturing germ cells span from the basement membrane to the lumen of the tubule where it culminates in the formation of

A

Spermatozoa

44
Q

Each column lies between the cytoplasm of two adjoining

A

Sertoli Cells

45
Q

Nurture the germ cells and directly facilitate their differentiation from spermatogonia to spermatozoa

A

Sertoli Cells

46
Q

Two adjoining Sertoli cells fuse at defined areas called

A

Tight Junctions

47
Q

This creates two compartments of intercellular space between the basement membrane and the tubule lumen. The spermatogonia reside in the

A

Basal compartment

48
Q

Where as the spermatozoa reside in the

A

Adluminal compartment

49
Q

This compartmentalization of the intercellular space forms a

A

Blood-testes barrier

50
Q

This barrier also prevents developing sperm from reaching the blood stream where they may initiate an

A

Autoimmune response

51
Q

Also, this compartmentalization maintains a high local concentration of

A

Testosterone

52
Q

It is the expression of 17β hydroxysteroid dehydrogenase that converts androstenedione into

A

Testosterone

53
Q

Cholesterol, derived either from low-density lipoproteins circulating in the blood, or synthesized in situ from acetyl coenzyme A, is the

A

Starting substrate for this conversion

54
Q

The rate-limiting step in testosterone biosynthesis is the conversion of cholesterol into pregnenolone, which is catalyzed by

A

CYP11A

55
Q

Within the testes, a small amount of testosterone undergoes 5-α-reduction to

-Androgen w/ much higher potency

A

Dihydrotestosterone (DHT)

56
Q

Importantly, a much larger conversion of testosterone to DHT occurs at target tissues via the enzyme

A

5α-reductase

57
Q

For both males and female, androgens are the obligate precursors of

A

Estrogens

58
Q 
The P-450 enzyme 
complex CYP19 (also termed aromatase) converts androstenedione and testosterone into
A

Estrone and estradiol respectively

59
Q

The majority of circulating estradiol in males comes from testosterone conversion in

A

Adipose tissue

60
Q

What are three peptide hormones secreted by Sertoli cells?

A

Activin, inhibin, and anti-Mullerian hormone (AMH)

61
Q

The primary source of circulating inhibin in males are

A

Sertoli Cells

62
Q

In contrast is produced by many tissues including the hypothalamus, anterior pituitary, liver, and placenta and acts in an autocrine paracrine manner

A

Activin

63
Q

Acts in an endocrine manner to inhibit follicle stimulting hormone (FSH) secretion from the pituitary

A

Inhibin

64
Q

Whereas activin secretion from pituitary gonadotropic cells acts in an autocrine-paracrine manner to stimulate

A

FSH secretion

65
Q

Can stimulate testosterone secretion from Leydig cells, while activin inhibits secretion

A

Inhibin

66
Q

Transforming growth factors α and β (TGF α and β) and insulin-like growth factor-1 (IGF-1) are also synthesized by both

A

Leydig and Sertoli Cells

67
Q

Serve to regulate cell growth and hormone responses in the testes in a paracrine manner

A

TGF α and β and IGF-I

68
Q

Finally, a number of trace metal binding proteins, steroid-binding proteins, proteases, cytokines, extracellular matrix factors, and proteoglycans are also synthesized predominantly in

A

Sertoli Cells

69
Q

These factors act locally to promote the development of spermatogonia in the seminiferous tubules and subsequently, to facilitate the release of mature sperm from the

A

Testes

70
Q

The two major endocrine activators of the testes, generally termed gonadotropins, are

A

Leutenizing hormone (LH) and FSH

71
Q

Heterodimeric glycoproteins that resemble thyroid stimulating hormone (TSH)

A

LH and FSH

72
Q

The α subunits of LH and FSH are

-β subunits are uniwue

A

Identical

73
Q

Both LH and FSH are synthesized in the anterior pituitary gland in

A

Gonadotrophic cells

74
Q

In turn, LH and FSH secretion from pituitary gonadotrophs is stimulted by

A

Gonadotropin-releasing Hormone (GnRH)

75
Q

A decapeptide synthesized from a much larger preprohormone, is synthesized in two clusters of neurons in the arcuate and preoptic nuclei of the hypothalamus

A

GnRH

76
Q

Under dopaminergic, serotonergic, noradrenergic, and endorphinergic influence

A

GnRH releasing Hormones

77
Q

GnRH is released from the hypothalamus into the pituitary portal veins in a pulsatile fashion. Normal men have

A

8-10 pulses per day

78
Q

GnRH binds to its receptor on the surface of gonadotroph cells and triggers an influx of extracellular calcium that acts as a secondary messenger to stimulate the simultaneous release of

A

LH and FSH

79
Q

Acts on Leydig cells to stimulate the synthesis and secretion of testosterone

A

LH

80
Q

A member of the G-protein coupled receptor superfamily that activates signal transduction via the cAMP secondary messenger cascade

A

LH receptor

81
Q

LH-induced cAMP production acts mainly to stimulate the conversion of cholesterol into

A

Pregnenolone

82
Q

Expressed primarily on Sertoli cells, and is also a member of the G protein coupled receptor superfamily that utilizes a cAMP secondary messenger cascade

A

FSH receptor

83
Q

Acts on Sertoli cells to stimulate the upregulation of a number of proteins including the gonadotropin-regulating factor inhibin

A

FSH

84
Q

FSH secretion from the pituitary, together with testosterone from Leydig cells, act in concert on Sertoli cells to promote

A

Sperm production from seminiferous vesicles

85
Q

Elevated serum levels of testosterone in men can negatively feedback on testosterone biosynthesis by inhibiting the secretion of

A

GnRH at the hypothalamus and LH at the anterior pituitary

86
Q

Feeds back negatively to block FSH release from the pituitary and possibly GnRH secretion from the hypothalamus

A

FSH induced secretion of inhibin from Sertoli cells

87
Q

This classical endocrine regulatory feedback circuit is termed the

A

HPT axis

88
Q

Fetal GnRH is detected in the hypothalamus at

A

4 weeks of gestation

89
Q

FSH and LH are detected in the pituitary at

A

10-12 weeks

90
Q

There is a surge of gonadotropin secretion in the fetal plasma at midgestation, a drop at birth, and then a transient rise during the first

A

6-18 months

91
Q

Then, for the rest of childhood, GnRH, FSH and LH levels remain low, despite the fact that serum levels of androgens, estrogens, and inhibins are

A

Very low

92
Q

Thus, during childhood, either the HPT negative feedback axis is inoperable, or the hypothalamus and/or pituitary are hypersensitized to very low levels of

A

Testosterone, estradiol, and inhibin

93
Q

When the child reaches the transition from a non reproductive to reproductive individual (i.e. puberty), their hypothalamic neurons mature and begin to gradually release increasing levels of

A

GnRH in a pulsatile manner

94
Q

Subsequently, a pulsatile pattern of LH and FSH secretion gradually appears with

A

LH levels being greater than FSH

95
Q

Also at puberty, the response of gonads to increasing levels of LH and FSH becomes amplified and hence there is a sharp increase in

A

Testosterone levels in males and estrogen levels in females

96
Q

Stimulated by the increase in sex hormone levels, we also see an increase in pituitary secretion of

A

GH

97
Q

When the adult pattern of gonadotropin secretion is established, the major distinguishing feature between males and females is that females exhibit a monthly cycle of gonadotropin secretion in which

A

LH pulsation is greater than FSH pulsation

98
Q

Around the fifth decade of life, despite normal serum levels of gonadotropins, there is a loss of responsiveness of the gonads to

A

LH and FSH

99
Q

The loss of estradiol/testosterone induced negative feedback leads to increased serum levels of gonadotropins with

A

FSH levels exceeding LH levels

100
Q

Each spermatagonia can give rise to

A

64 spermatozoa

Endocrinology and Reproduction (15 decks)

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