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FHB Block 4 > Reproduction 2- Male reproduction > Flashcards

Reproduction 2- Male reproduction Flashcards

1
Q

What is the HPG axis?

A

Hypothalamic-pituitary-gonadal

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2
Q

What are the major hormones of the HPG axis that regulate male reproductive physiology?

A

H: Gonadotropin releasing hormone (GnRH)
P: LH and FSH
G: testosterone –> DHT and E2, progesterone

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3
Q

Which nuclei of the hypothalamus is responsible for releasing GnRH?

A

Preoptic area (POA)

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4
Q

Describe how the release of GhRH affects the hormones released by the pitutiary

A

GnRH must be released in a pulsatile manner.

Fast pulses increase the release of LH
Slow pulses increase the release of FSH

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5
Q

What is LH responsible for?

A

Stimulates steroidogenesis in the ovaries and testes

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6
Q

What is FSH responsible for?

A

Stimulates gametogenesis (egg and sperm maturation) in ovaries and testes

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7
Q

What is the importance of kisspeptin?

A

Presumed signal for pubertal onset -required to initiate increased GnRH release at the time of puberty

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8
Q

What results from mutations in the KISS1 receptor?

A

Hypogonadotropic hypogonadism

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9
Q

Describe the regulation GnRH

A

Gonadal steroid hormones (androgens/estrogens) along with many others (GnIH, prolactin, GABA, cortisol, stress, growth factors etc) all inhibit GnRH

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10
Q

What is the effect of inhibins in the pituitary?

A

Inhibins inhibit FSH specifically

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11
Q

What is the effect of activins in the pituitary?

A

Activin stimulates FSH and LH in the pituitary

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12
Q

Which form of inhibin is expressed in the testes and ovary?

A

Inhibin B

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13
Q

Which cell type forms the blood-testes barrier?

A

Sertoli cells

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14
Q

Which cells have high-affinity FSH receptors

A

Sertoli cells

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15
Q

What are the general effects of FSH on the sertoli cells?

A

Stimulates spermatogenesis/increase sperm motility
Stimulates growth of seminiferous tubules- primary determinant of testes size
Stimulates ABP
Stimulates aromatase, inhibit and growth factors

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16
Q

What is the purpose of ABP?

A

Androgen binding protein stays local in the testes and provides a way to maintain high local concentrations of testosterone

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17
Q

Which cells have high affinity LH receptors?

A

Leydig cells

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18
Q

What is the general action of LH on leydig cells?

A

Stimulates steroidogenesis from cholesterol, including stimulation of StAR protein –> increased androgen production
Stimulates leydig cell growth

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19
Q

Where is DHEA produced?

A

The adrenal cortex (zona reticularis)

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20
Q

What is DHEA converted into?

A

Androstendione- converted in the zona reticularis by 3beta-HSD

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21
Q

What is the precursor to testosterone? What else can it be converted into?

A

Androstendione- converted to testosterone by 17beta-HSD

Can also be converted to estrone

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22
Q

How does testosterone travel through the blood?

A

Bound tightly to SHBG. There is very little free testosterone in circulation.

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23
Q

What is the enzyme responsible for the conversion of testosterone to DHT?

A

5alpha-reductase

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24
Q

What other hormone is derived from testosterone that can bind to ER?

A

3beta-diol

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25
Q

How much testosterone is excreted as free testosterone? What happens to the rest?

A

less than 2% is excreted as free testosterone. The rest is converted to 17-ketosteroids and DHT –> conjugated to water soluble forms and excreted

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26
Q

Testosterone drives the development of what during fetal development.

A

Fetal development: Epididymis, Vas Deferens, Seminal Vesicles

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27
Q

Testosterone drives the growth/development of what structures during puberty?

A

Penis, Seminal Vesicles, Musculature, Voice, Skeleton, Spermatogenesis

28
Q

DHT drives the development of what structures during fetal development?

A

Penis, penile urethra, scrotum and prostate

29
Q

DHT drives the growth/maturation of what structures during puberty?

A

Scrotum, prostate, male pattern hair distribution (beard, balding, diamond-shaped pubic escutcheon) and sebaceous glands

30
Q

What is the most common abnormality of the male UG tract ?

A

Cryptorchidism- “hidden testes”- failure of testes to descend due to various pathologies

31
Q

What is it pertinent for testes to descend?

A

Testes must descend in order to maintain a lower temperature (1-2 degrees below core temperature). Lower temperature is critical for spermatogenesis

32
Q

What blood-flow pattern allows for cooler temperature in the testes (for better spermatogenesis)?

A

Countercurrent exchange –> transfer of heat from the venous blood in the pampiniform plexus to the blood in the testicular artery.

33
Q

What is the relative composition of the testes?

A

80%- germinal tissue

20%- supportive connective tissue with Leydig cells

34
Q

What is in the peritubular vs intratubular space of the testes?

A

Peritubular: leydig cells, myoid cells and vascular supply

Intratubular: sertoli cells, developing germ cells, lumen where mature sperm is released

35
Q

What occurs at the Sertoli-Leydig cellular junction?

A

Progenitor spermatogonia–> the leydig cells make lots of testosterone to keep cells healthy

Spermatogonia are separate from the blood supply to keep them protected from the immune system

36
Q

What forms the blood-testes barrier?

A

Tight junctions in between Sertoli cells

37
Q

What stimulates the production of testosterone in the Leydig cells?

A

LH.

LH stimulates testosterone production in the Leydig cells. Testosterone acts on neighboring Sertoli cells to increase local testosterone levels, which supports spermatogenesis.

38
Q

Why is testosterone converted to E2 in Sertoli cells? Why doesn’t this occur in the Leydig cells?

A

E2 is used in the Leydig cells to promote steroidogenesis.

Leydig cells do not have aromatase.

39
Q

What is the paracrine action of inhibin in Leydig cells?

A

Inhibin augments LH-induced testosterone production in Leydig cells

THis is opposite of their action in the pituitary

40
Q

What is the paracrine action of activin in Leydig cells?

A

Activin inhibits testosterone production in Leydig cells.

This is opposite of their action in the pituitary

41
Q

Define spermatogenesis

A

The process by which spermatogonia become 4 haploid spermatids

42
Q

Define spermiogenesis

A

Maturation of spermatids into spermatozoa-spermatids differentiate into flagellated spermatozoa. Nuclear condensation, shrinkage of the cytoplasm, formation of the acrosome, development of the tail.

43
Q

Define spermeation

A

release of spermatozoa from Sertoli cells into the lumen. Most remaining cytoplasm is removed and “residual body” is formed

44
Q

Where does all sperm development/maturation occur?

A

In the seminiferous tubules

45
Q

Where do spermatozoa mature?

A

Spermatozoa mature along the single tubule of the epididymis.

46
Q

What is the purpose of the epididymis?

A

The epididymis acts as a reservoir for sperm and is important for sperm maturation.

While stored in the epididymis, sperm gain motility and lose most of their cytoplasm.

47
Q

What is the acrosome of sperm?

A

The sperm “cap” containing hydrolyzing enzymes required to penetrate the ovum.

48
Q

When is the maturation of sperm complete?

A

When the sperm enters the vagina, when it finally reaches the ovum

49
Q

What are the main components of semen?

A

70%- fluid from seminal vesicles
10%- sperm
10%- fluid from epididymis

50
Q

What accessory gland comes together to form the ejaculatory duct?

A

The seminal vesicles

51
Q

What are the three main functions of the seminal vesicles?

A

1) Nutrients- fructose, citric acid and other nutrients keep sperm alive in the female reproductive tract
2) Prostaglandins- induce contractions of the uterus and fallopian tubes to facilitate sperm transport
3) Buffer- keep optimal pH for sperm survival and motility

52
Q

What are the two main functions of prostate secretions?

A

Alkaline secretions: neutralize vaginal secretions (which are acidic)

Proteolytic enzymes: important for the liquefaction of semen (which would clot otherwise)

53
Q

What is the purpose of the bulbourethral glands (Cowper’s glands)?

A

The bulbourethral gland sits immediately below the prostate. They secrete mucus into the urethra upon arousal. These secretions can contain some sperm and are secreted prior to ejaculation

54
Q

What does PSA measure?

A

Increased prostate growth.

Increase is normal with age as the prostate enlarges, but higher than normal can indicate prostate cancer.

55
Q

The flaccid state is regulated by what branch of the ANS?

A

Sympathetic- helicine arteries are constricted, inhibiting blood flow

56
Q

The erected state is regulated by what branch of the ANS?

A

Parasympathetic

57
Q

Describe the chain of events that causes an erection, starting with release of ACh from post-synaptic parasympathetic nerves

A

Ach binds to muscarinic receptors –> activates PLC (via G-alpha-q). This increases calcium and activates NO synthase. NO activates guanylyl cyclase –> GTP to cGMP –> relaxation

58
Q

How does Viagra work?

A

Viagra inhibits phosphodiesterases that would normally decrease cGMP. This leads to a chronic state of vasodilation/erection.

59
Q

Does viagra require CNS arousal?

A

Yes

60
Q

What muscle movements control emission?

A

Peristaltic rhythmic contractions via smooth muscle portions of vas deferens, seminal vesicles and the prostate

61
Q

Differentiate primary from secondary/tertiary pre-testicular disorders

A

Primary: Hypergonadotropic hypogonadism – (high FSH/LH, low T/DHT)

Secondary: Hypogonadotropic hypogonadism – (low GnRH, low FH/LSH, low T/DHT)

62
Q

Give examples of primary pre-testicular disorders

A

Klinefelter’s, enzyme deficiencies

63
Q

Give examples of secondary/tertiary pre-testicular disorders

A

Kallman syndrome, panhypopituitarism

Hyperprolactinemia is the most common

64
Q

Give three examples of testicular disorders

A

Klinefelter’s syndrome, cryptorchidism

Most common cause of subfertility in men is varicocele (no proper counter current exchange)

65
Q

Name three post-testicular disorders

A

Ductal obstructions, premature ejaculation, impotence

FHB Block 4 (15 decks)

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