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Medical Physiology > Male reproduction > Flashcards

Male reproduction Flashcards

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USMLE® Step 1 flashcards
1
Q

What peripheral actions does DHT have in males?

A

DHT is involved in secondary sex characteristics such as changes in sebaceous glands and hair growth patterns

*DHT, just like in utero, play a role in secondary sex characteristcs (ex where you have hair).

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2
Q

Constriction of the internal sphincter of the bladder is also under sympathetic control. What is the purpose of this?

A

It prevents retrograde ejaculation of sperm into urinary bladder.

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3
Q

What is the path of sperm?

A

Lumen of seminiferous tubule ->
Rete testes (moving forces here include fluid currents & muscle contraction) ->
Epididymis (storage in tail region until ejaculation) ->
Vas deferens ->
Ampulla of ductus deferens->
Urethra (where it passes by seminal vesicles, prostate gland, and bulbourethral glands) ->
Penile urethra ->
Ejaculation!

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4
Q

The Bulburethral (Cowper’s) gland secretes an alkaline mucus-like fluid. What is its role?

A
  • neutralizes the acidity of the urine residue in the urethra
  • helps to neutralize the acidity of the vagina
  • provides some lubrication for the tip of the penis during intercourse
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5
Q

What peripheral actions does testosterone have in males?

A
  • It effects the lipid profile ( ↑VLDL, ↑LDL, ↓HDL)
  • changes in the larynx
  • increase in lean muscle mass, GH, hematocrit, and visceral abdominal fat.
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6
Q

When it comes to the role of LH and FSH on testicular cells, which cells express the LH receptors and which express the FSH receptors?

A

Leydig express LH receptors. (Think L and L)

Sertoli express FSH receptors.

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7
Q

Reminder: conversion of testosterone to DHT requires……………………..

A

5a-reductase

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8
Q

What are the anabolic 2° Secondary sex characteristics?

A
  • Growth promoting effects on somatic tissue

- Muscle development and growth

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9
Q

Erection, Emission, and Ejaculation are under the control of what?

A

ANS and somatic!
ANS has control of testes, vas deferens, male accessory glands and erectile tissue of penis.
In addition, the penis receives both somatic afferent and efferent innervation via the pudendal nerve.

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10
Q

Sperm and seminal fluid mix in the ejaculatory duct yielding a final pH of………………….

A

7.3-7.7.

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11
Q

What are the roles of sertoli cells?

A

Sertoli cells are considered the “nurse cells.” They produce anit-mullerian hormone (AMH), which is also called mullerian inhibiting substance (MIS).
They also do aromatization of testosterone to estradiol-17b (this has a local effect, not only endocrine).

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12
Q

Only low levels of circulating testosterone are required for function of the HPT axis. For sperm development, intra-testicular levels of testosterone are maintained at a concentration of over 100 times greater than in the blood. This is required to maintain spermatogenesis! How is there Interruption of the Hypothalamic-Pituitary Testicular axis when exogenous steroids are taken?

A

Administration of exogenous testosterone leads to inhibition of GnRH (from hypothalamus) and inhibition of pituitary gonadotrophs, specifically decreasing LH production. With long term exogenous steroid use, leydig cells no longer make testosterone (or any exogenous steroids, any androgens).

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13
Q

What are the 4 sections of spermatozoa?

A

1) head (Hapliod # of chromosomes, and the acrosomal cap which contains hydrolytic and proteolytic enzymes)
2) middle piece (filled with mito for ATP required for motility)
3) principle piece (stores the ATP)
4) end piece or tail: flagellum

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14
Q

So, in total, how many days does it take to produce mature spermatozoa?

A

74!
seminiferous tubule: 50 days
maturation in the epididymis: 24 days

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15
Q

Note that testosterone, DHT and estrogen selectively inhibit………. more than…………

A

LH

FSH

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16
Q

60% of circulating testosterone is bound to…………….., 38% is bound to……… and 2% is “free,”

A
  • androgen binding protein (ABP) or sex hormone binding globulin (SHBG)
  • albumin
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17
Q

Leydig cells have two roles, cholesterol production/acquisition and testosterone production. Describe how they do both.

A

They either do de novo synthesis of cholesterol and/or acquisition via expression of LDL and HDL receptors.

They convert progesterone to androstenedione, which they then make into testosterone via the enzyme 17b-hydroxysteriod dehydrogenase (17b-HSD).

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18
Q

Testosterone and its metabolites are excreted in………..

A

urine

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19
Q

Erection (engorgement, tumescence) is primarily a…………………. neurovascular event.

A

parasympathetic

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20
Q

During the final month in-utero, testes descend into scrotum thru inguinal canals due to action of…………
The Inguinal canals are sealed off shortly after birth.
Testes must be maintained at 1-2°C lower than body temp for normal spermatogenesis.

A

testosterone

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21
Q

Testosterone feeds back on………………. while Inhibin feeds back on……………..

A

the HPA axis

FSH

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22
Q

What is emission?

A

movement of ejaculate into the prostatic or proximal part of the urethra.

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23
Q

Spermatogonia are the earliest germ cells. When do they first appear?

A

6-7 wks gestation

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24
Q

Regulation of male reproduction is done by the Hypothalamic-Pituitary Testicular axis.

  • Production of male gametes in the seminiferous tubules is under the influence of what?
  • Androgen biosynthesis in Leydig cells is under the influence of what?

Inhibin directly inhibits FSH (doesn’t influence hypothalamus, only ant pit)

A

FSH and testosterone

LH

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25
Q

How is testicular temp regulated?

A
  • The scrotum
  • Double muscular action of the external cremster and tunica dartos.
  • In cold weather testes are drawn closer to body in warm weather fall away from body
26
Q

Erection (engorgement, tumescence) is primarily a…………………. neurovascular event.
Vasodilation of penile blood vessels causes blood flow to cavernous tissue, leading to engorgement.

A

parasympathetic

27
Q

What produces FSH and LH?

A

The anterior pituitary.

28
Q

What effect does FSH have on Sertoli cells?

A

Stimulates protein synthesis of “nursing” function of cell, and also stimulates the synthesis of inhibin (Inhibin B exerts negative feedback on FSH production. It is made EXCLUSIVELY by the sertoli cells).

29
Q

Maturation in the epididymis consists of what?

A
  • Progressive increase in forward motility
  • Maturation of acrosome
  • Molecular reorganization of plasma membrane
  • Ability to bind zone pellucida via acquisition of protein receptors for the zona pellucida
  • Decreased cytoplasm and cell volume
30
Q

In adults, only low levels of LH and FSH are required for spermatogenesis as long as there is adequate what?

A

Testosterone

31
Q

What is spermeation?

A

Release of spermatozoa into the seminiferous tubule lumen (At this time sperm are still immature).

32
Q

Testosterone has negative feedback on release of what?

A

GnRH release and LH release

33
Q

So, there are some skeletal muscle fibers in the penis, while the prostate is made of…………… muscle. The prostate tends to be individually innervated, instead of all innervated by the same thing. So, lots of nerves here!

A

SMOOTH

34
Q

1 spermatogonium gives rise to how many spermatids?

A

4

35
Q

This is the details on how engorgement actually occurs: AcH binds the…………….. receptor on endothelial cells. This leads to activation of…….. synthase and release of………, which diffuses to vascular smooth muscle and stimulates cGMP to cause vasodilation. Compression of veins decreases venous drainage.
* Sympathetic tone contributes to flaccidity (vasoconstriction).

A

M3 muscarinic
NO
NO

36
Q

Seminal vesicles secrete a yellowish viscous alkaline fluid containing what?

A
  • Fructose (fuel)

- Prostaglandins (help decrease viscosity of cervical mucus)

37
Q

Ejaculation is the forceful expulsion of semen from the urethra. It is a…………. reflex triggered when semen from the prostatic urethra enters the…………. urethra

A

spinal
bulbous

  • so, if ejaculate reaches the prostate gland, you will have ejaculation. It can’t be controlled at this point.
38
Q

Where is testosterone concentrated in an attempt to keep it in the testes?

A

Testosterone is concentrated in the adluminal compartment in the seminiferous tubules. Androgen binding protein is what holds it here.

39
Q

When it comes to peripheral actions of androgens, testosterone and DHT bind androgen receptor (AR) in the………….. of cells. This results in nuclear translocation of the androgen-AR complex, and dimerization and binding to the androgen-response element. This results in transcription.

A

cytoplasm

40
Q

Prior to puberty HPT axis still immature, so there is very low plasma testosterone levels. As puberty approaches………….secretion becomes more pulsatile.
Early and middle puberty has the nocturnal peak in……… which leads to ↑testosterone.

A

GnRH

LH

41
Q

Results from rhythmic contractions of ampullary portion of vas deferens, seminal vesicles and prostatic smooth muscles:

  • Unlike other visceral organs, the gonadal smooth muscle cells are not in close contact with limited electrical coupling.
  • In male accessory glands, individual smooth muscle cells are directly innervated. Release of…………. allows for fast, powerful and coordinated responses to neural stimulation.
A

norepinephrine

42
Q

Spermiogenesis is the maturation process, which occurs where?
How long does this maturation take?

A

epididymis

24 days

43
Q

Before sperm are completely mature, what move them forward?

A

Seminiferous tubule fluid and muscle contraction of the epididymis move spermatazoa forward.

44
Q

What are the 1° sex characteristics in males?

A
  • ↑ LH and hence testosterone
  • ↑ FSH leads to an increase in the release of inhibin from Sertoli cells
  • Testicular size ↑ due to growth of seminiferous tubules and Leydig cell proliferation
  • Sperm production begins
45
Q

Spermatogenisis occurs in the lumen of the seminiferous tubules. It proceeds from the………. to the………….

A

Basement membrane into the lumen

46
Q

Estrogen is produced peripherally via testosterone’s conversion where?

A

in adipose and liver.

47
Q

The prostate gland secretion enters the prostatic urethra when prostatic smooth muscle contracts during ejaculation. It is a milky, slightly alkaline fluid that plays a role in “……………..” sperm. What is in this fluid?

A

activating

  • Citrate: a nutrient source
  • Prostate specific antigen (a protease): participates in the dissolution of the seminal fluid coagulum.
  • Phosphate and bicarbonate: serve as buffers
48
Q

2° Secondary sex characteristics can be androgenic or anabolic (anabolic is more so in men than in women). Androgenic in men is due to what hormones?
What are these characteristics?

A

Due to both testosterone and adrenal androgens

  • Pubertal growth spurt (androgens plus additional GH)
  • Penile growth and pubic hair
  • Growth of beard, lowering of voice etc…
49
Q

What are the parts of the male urethra?

A

Prostatic urethra
Bulbous urethra
Penile urethra

Note that there is normally a membranous part (before the bulbous part) but that she did not mention this in the slides.

50
Q

Erection also has a somatic (voluntary) component. The motor branch of the pudendal nerve innervates striated penile muscle fibers. Contraction of ischiocavernosus muscle in the final phase of erection increases pressure inside the corpora………………. to values greater than systemic arterial pressure.

A

cavernosa

51
Q

inhibin has negative feedback on the release of what?

A

FSH

52
Q

Sperm are only ………..% of seminal fluid (semen). Ejaculate content is between 150 -600 million sperm. The remainder of seminal fluid is seminal plasma derived from the accessory glands. The male accessory glands are what?

A

10

the seminal vesicles, prostate and bulburethral glands.

53
Q

Describe the hormonal link between growth and reproduction in males.

A
  • The products of the GH (growth hormone)-IGF-1 (insulin growth factor-1) axis stimulate reproductive function in the hypothalamic-pituitary-testicular axis. GH and IGF both have an influence on gonadal function! They help grow the testes internal tract (along with FSH and LH).
  • Testosterone and estradiol stimulate the GH axis to secrete GH and IGF-1 to help with bone and muscle growth. They DONT effect the hypothalamus (so they dont stimulate GnRH release) and instead act SPECIFICALLY on the ANT PITUITARY SOMATOTROPHS.
54
Q

Normal onset of puberty in males extends from……………yrs of age and lasts for around………… yrs.

A

9-14

2-4.5 years

55
Q

Emission is primarily under what control?

A

Sympathetic

56
Q

What are the two main receptors sertoli cells express?

A

androgen receptor (AR) and follicle stimulating hormone (FSH) receptor

57
Q

Estrogen in men plays a role in what?

Lack of estrogen would……

A

bone maturation! It is required for bone growth.
Lack of estrogen or its receptors results in TALL stature due to a delay in epiphyseal plate closure, and also leads to osteoporosis.

58
Q

What effect does LH have on Leydig cells?

A

hydrolysis of cholesterol esters and expression of StAR (a protein that transfers cholesterol to inner mito membrane), and an overall increase in testosterone.

59
Q

Testosterone, via its conversion to DHT, is responsible for what?

A

EXTERNAL GENITALIA DIFFERENTIATION AND DEVELOPMENT!

During puberty, testosterone has an effect on internal and external genitalia.

60
Q

How much volume of semen is from each of the accessory glands?

A

60% is from seminal vesicles

30% is epididymal fluid and secretions from the bulburethral glands and prostate glands.

Medical Physiology (21 decks)

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