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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
How much testosterone is excreted as free testosterone? What happens to the rest?
less than 2% is excreted as free testosterone. The rest is converted to 17-ketosteroids and DHT --> conjugated to water soluble forms and excreted
26
Testosterone drives the development of what during fetal development.
Fetal development: Epididymis, Vas Deferens, Seminal Vesicles
27
Testosterone drives the growth/development of what structures during puberty?
Penis, Seminal Vesicles, Musculature, Voice, Skeleton, Spermatogenesis
28
DHT drives the development of what structures during fetal development?
Penis, penile urethra, scrotum and prostate
29
DHT drives the growth/maturation of what structures during puberty?
Scrotum, prostate, male pattern hair distribution (beard, balding, diamond-shaped pubic escutcheon) and sebaceous glands
30
What is the most common abnormality of the male UG tract ?
Cryptorchidism- "hidden testes"- failure of testes to descend due to various pathologies
31
What is it pertinent for testes to descend?
Testes must descend in order to maintain a lower temperature (1-2 degrees below core temperature). Lower temperature is critical for spermatogenesis
32
What blood-flow pattern allows for cooler temperature in the testes (for better spermatogenesis)?
Countercurrent exchange --> transfer of heat from the venous blood in the pampiniform plexus to the blood in the testicular artery.
33
What is the relative composition of the testes?
80%- germinal tissue | 20%- supportive connective tissue with Leydig cells
34
What is in the peritubular vs intratubular space of the testes?
Peritubular: leydig cells, myoid cells and vascular supply Intratubular: sertoli cells, developing germ cells, lumen where mature sperm is released
35
What occurs at the Sertoli-Leydig cellular junction?
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
What forms the blood-testes barrier?
Tight junctions in between Sertoli cells
37
What stimulates the production of testosterone in the Leydig cells?
LH. LH stimulates testosterone production in the Leydig cells. Testosterone acts on neighboring Sertoli cells to increase local testosterone levels, which supports spermatogenesis.
38
Why is testosterone converted to E2 in Sertoli cells? Why doesn't this occur in the Leydig cells?
E2 is used in the Leydig cells to promote steroidogenesis. Leydig cells do not have aromatase.
39
What is the paracrine action of inhibin in Leydig cells?
Inhibin augments LH-induced testosterone production in Leydig cells THis is opposite of their action in the pituitary
40
What is the paracrine action of activin in Leydig cells?
Activin inhibits testosterone production in Leydig cells. This is opposite of their action in the pituitary
41
Define spermatogenesis
The process by which spermatogonia become 4 haploid spermatids
42
Define spermiogenesis
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
Define spermeation
release of spermatozoa from Sertoli cells into the lumen. Most remaining cytoplasm is removed and "residual body" is formed
44
Where does all sperm development/maturation occur?
In the seminiferous tubules
45
Where do spermatozoa mature?
Spermatozoa mature along the single tubule of the epididymis.
46
What is the purpose of the epididymis?
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
What is the acrosome of sperm?
The sperm "cap" containing hydrolyzing enzymes required to penetrate the ovum.
48
When is the maturation of sperm complete?
When the sperm enters the vagina, when it finally reaches the ovum
49
What are the main components of semen?
70%- fluid from seminal vesicles 10%- sperm 10%- fluid from epididymis
50
What accessory gland comes together to form the ejaculatory duct?
The seminal vesicles
51
What are the three main functions of the seminal vesicles?
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
What are the two main functions of prostate secretions?
Alkaline secretions: neutralize vaginal secretions (which are acidic) Proteolytic enzymes: important for the liquefaction of semen (which would clot otherwise)
53
What is the purpose of the bulbourethral glands (Cowper's glands)?
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
What does PSA measure?
Increased prostate growth. Increase is normal with age as the prostate enlarges, but higher than normal can indicate prostate cancer.
55
The flaccid state is regulated by what branch of the ANS?
Sympathetic- helicine arteries are constricted, inhibiting blood flow
56
The erected state is regulated by what branch of the ANS?
Parasympathetic
57
Describe the chain of events that causes an erection, starting with release of ACh from post-synaptic parasympathetic nerves
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
How does Viagra work?
Viagra inhibits phosphodiesterases that would normally decrease cGMP. This leads to a chronic state of vasodilation/erection.
59
Does viagra require CNS arousal?
Yes
60
What muscle movements control emission?
Peristaltic rhythmic contractions via smooth muscle portions of vas deferens, seminal vesicles and the prostate
61
Differentiate primary from secondary/tertiary pre-testicular disorders
Primary: Hypergonadotropic hypogonadism -- (high FSH/LH, low T/DHT) Secondary: Hypogonadotropic hypogonadism -- (low GnRH, low FH/LSH, low T/DHT)
62
Give examples of primary pre-testicular disorders
Klinefelter's, enzyme deficiencies
63
Give examples of secondary/tertiary pre-testicular disorders
Kallman syndrome, panhypopituitarism | Hyperprolactinemia is the most common
64
Give three examples of testicular disorders
Klinefelter's syndrome, cryptorchidism Most common cause of subfertility in men is varicocele (no proper counter current exchange)
65
Name three post-testicular disorders
Ductal obstructions, premature ejaculation, impotence

FHB Block 4 (15 decks)

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