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Male Reproduction Function & Dysfunction > Embryology & Physiology Review > Flashcards

Embryology & Physiology Review Flashcards

1
Q

What develops by week 4 (day 28 post fertilization) of gestation?

A

Indifferent gonads

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2
Q

From where do the indifferent gonads begin to develop and to where do these new cells migrate?

A

From germ cells in the endoderm of the yolk sac, which migrate to the T10 thoracic cells of the developing embryo.

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3
Q

What are three areas of interest superior to the primordial gonad in a 4 week embryo and what is one area of interest inferior to it, respectively?

A
  1. Degenerating pronephros
  2. Mesonephric duct
  3. Mesonephric tubule
    - PRIMORDIAL GONADS -
  4. Ureteric bud
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4
Q

What is a point of interest superior to and inferior to the 4 week embryo’s yolk sac, respectively?

A
  1. Developing liver
    - YOLK SAC -
  2. Allantis (?)
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5
Q

What forms supportive cells in the developing gonads of a 4 week embryo?

A

Coelomic epithelium (Sertoli cells)

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6
Q

What two things happen by week 6 after gestation (42 days post fertilization)?

A

Primary sex cords have developed & primordial germ cells have completed their migration from the yolk sac to the now developing gonad.

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7
Q

What are primary sex cords?

A

Projections that divide the gonad into a medulla and cortex section.

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8
Q

Primary sex cords later become what structure for male embryos?

A

Seminiferous tubules

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9
Q

What is the function of seminiferous tubules?

A

Sperm production site.

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10
Q

The extent to which the medulla and cortex develop is dependent on what?

A

SRY expression (or lack thereof).

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11
Q

What happens at the 7th week of gestation and what doesn’t happen with regards to gender?

A

Sexual differentiation occurs but external genitalia fully develops LATER.

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12
Q

Around when can external genitalia be viewed with ultrasound?

A

12th week or 3rd month of pregnancy.

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13
Q

Where is the SRY gene located exactly?

A

On the short arm f the Y chromosome in sperm (Yp11.31).

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14
Q

What differentiates into Sertoli cells and when?

A

Primordial cells in the cortex region of the gonads; in the presence of the expressed SRY gene.

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15
Q

Formation of external genitalia in a developing embryo is dependent on what?

A

Hormones (i.e. testosterone, antimullerian hormone, etc.)

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16
Q

What happens by day 12 post fertilization?

A

Amnionic and yolk sac (site of germ cell origination) cavities develop.

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17
Q

Cells that differentiate into Sertoli cells begin to secrete what and why?

A

Mullerian Inhibitory Factor (aka antimullerian hormone) to degenerate mullerian duct of female gonad.

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18
Q

What happens in the absence of SRY and the MIF secretions from the Sertoli cells?

A

Mullerian ducts will develop into uterus, vagina, and oviducts.

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19
Q

The SRY gene has been found to influence the developing human embryos as early as what week and day of embryonic development?

A

6th week; day 41.

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20
Q

The stage of development regarding the SRY gene expression begins after the formation of what two important regions in the brain and what two relevant and two interesting events, respectively?

A
  1. Hypothalamus
  2. Pituitary gland
  3. Migration of GnRH neurons to hypothalamus
  4. Appearance of leg buds
  5. Footplate begins to form
  6. Nasal pits move to their ventral position
    (Note: by day 41 above occurs)
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21
Q

What is the size of a 41 day human embryo?

A

A fifth of an inch in length

22
Q

Do human embryos possess heartbeats at day 41 post fertilization?

A

No

23
Q

Around when is a clinical pregnancy established and why?

A

Around day 41 when an ultrasound is performed on patients with high beta hCG (but external genitalia are still not visualized until 3rd or 4th month).

24
Q

Is it possible for an X chromosome to have an abnormally located SRY gene and, if yes, what would this result in?

A

Yes; were this to fertilize an oocyte, the result would be an individual with female external organs and male internal organs (XX male).

25
Q

The development of the penis was found in 1886-1898 to be similar to the development of what other body part?

A

Nose.

26
Q

What is Kallmann’s syndrome?

A

X-linked disease characterized by anosmia (no ability to smell), small genitalia, and sterile gonads.

27
Q

What causes the symptoms of Kallmann’s syndrome?

A
  1. Anosmia - due to lack of neurons in brain that receive input from the axons coming from nasal neurons.
  2. Small genitalia - due to lack of neurons responsible for secreting GnRH (which also means no FSH and LH) leading to the deficiency of testosterone and low/no dihydrotestosterone.
    NOTE - May be caused by mutations in the GnRH genes in these neurons as well.
28
Q

What are six clinical characteristics of Kallmann’s syndrome?

A
  1. Delay in puberty
  2. Low GnRH
  3. Low FSH & LH (as a result of #2)
  4. Low T (as a result)
  5. Sertoli cells are not supplied with FSH and T
  6. Spermatogenesis declines as a result
29
Q

What is the treatment for Kallmann’s syndrome?

A
  1. Give pulsatile GnRH or gonadotropins
  2. If no response to #1, it means that pituitary is also insufficient (cannot secrete FSH or LH) and you should also give gonadotropins, which the patient may respond to.
  3. If the patient doesn’t respond to #2, there may be a problem at the testis level (remember this).
30
Q

Describe the biochemical makeup, function, and characteristics of GnRH.

A
  1. 10 amino acid peptide.
  2. Secretion at onset of puberty triggers sexual development.
  3. Is essential for post-pubescent sexual physiology in males and females.
  4. In both sexes it occurs in periodic pulses.
  5. Frequency and amplitude of pulses determine gonadotropin subunit gene expression and therefore the secretion of pituitary LH and FSH.
  6. High frequency GnRH pulse = low FSH production
  7. High frequency GnRH pulse = favors LH secretion (beta subunit secretion).
31
Q

Describe the relationship between GnRH pulse frequency and FSH secretion.

A

Inverse proportional

32
Q

Describe the relationship between GnRH pulse frequency and LH secretion.

A

Proportional

33
Q

The formation of what structure then drives the subsequent development of male genitalia in human embryos?

A

Testes

34
Q

How do the testes drive the development of male genitalia in human embryos?

A

By secretion of testosterone from Leydig cells in the testes and the conversion of testosterone to dihydrotestosterone (DHT) via the function of 5-alpha reductase.

35
Q

Wolffian duct development is dependent on what hormone?

A

Testosterone (note: also the development is indirectly due to AMH because of the degeneration of the paramesonephric [Mullerian] ducts).

36
Q

What is the Wolffian duct also called?

A

Mesonephric duct.

37
Q

What four structures develop from the Wolffian duct in males?

A
  1. Efferent ductules
  2. Epididymis
  3. Ductus differens (vas deferens)
  4. Seminal vesicles
38
Q

What is one important thing to remember in clinical andrology about all male reproductive ducts/tubules/glands and why? Give an example

A

That they all come from the same origin embryologically (Wolffian duct) and therefore if one is defective or absent it is quite possible that others are affected/absent as well.
Example: congenital absence of vas deferens is often accompanied by the absence of seminal vesicles and this has a diagnostic value when semen samples from azoospermic men are evaluated.

39
Q

What is one male reproductive organ unrelated to the Wolffian duct origins and what does it develop from?

A

Prostate; formed from urogenital sinus.

40
Q

What are two primary functions of the testis?

A
  1. Produce hormones involved in the regulation of reproductive function and virilization.
  2. Produce spermatozoa with help from Leydig and Sertoli cells.
41
Q

The functions of the testes are regulated by what?

A

Pituitary gonadotropins FSH and LH.

42
Q

What is the half-life of plasma FSH and LH, respectively, and how do they travel in blood plasma?

A
  1. 1-3 hours
  2. 30 minutes
  3. Unbound (both)
43
Q

Which has higher variability in plasma levels, LH or FSH and what is the clinical significance of this difference?

A

Higher variability = LH

As a result, single measurements of FSH are more reliable/accurate.

44
Q

What three hormones are produced by the testes during reproductive life?

A
  1. Testosterone
  2. Inhibin
  3. Estradiol
45
Q

Describe the production of testosterone in six steps.

A
  1. Anterior pituitary secretes LH –> binds to receptor on Leydig cells in testes to stimulate synthesis of cholesterol via steroidogenic pathway:
  2. Within minutes of LH binding, steroidogenic acute regulatory protein initiate transfer of cholesterol from the outer mitochondrial membrane of Leydig cells –> inner membrane to be converted to pregnenolone.
  3. Pregnenolone diffuses out of the mitochondria –> the smooth endoplasmic reticulum.
  4. In SER, pregnenolone is then further metabolized by 3-beta hydroxysteroid dehydrogenase –> progesterone.
  5. Progesterone (by a 2 step process) –> androstenedione (by the action of 17-alpha hydroxylase).
  6. Androstenedionie –> testosterone by 17-beta hydroxysteroid dehydrogenase.
46
Q

All steps involved in the Leydig cell conversion of cholesterol to androstenedione (before the final step to testosterone) is identical to what happens where?

A

Adrenal cortex.

47
Q

What is the one enzyme unique to the testes (not involved in the adrenal cortex) and what is its function?

A

17-beta hydroxysteroid dehydrogenase; converts androsterone into testosterone.

48
Q

How can adrenal hyperplasia cause oligozoospermia?

A

By producing excess androgens in blood circulation which leads to a negative feedback loop and subsequent reduction of FSH/LH, which prevents the Leydig cells in the testes from producing sufficient testosterone in the absence of LH (which then impacts Sertoli cells and germ cell functions, and the cycle continues).

49
Q

What are three things that happen when testosterone diffuses out of Leydig cells?

A
  1. Impacts Sertoli and germ cell functions in the seminiferous tubules.
  2. Binds to sex hormone binding globulin (SHBG).
  3. Enters circulation and binds to both SHBG (44%) and albumin 54%).
50
Q

The inner cell mass (trophoblast) will then develop what three parts in a human embryo?

A
  1. Amnionic sac
  2. Epiblast
  3. Hypoblast
51
Q

From where does the yolk sac in a human embryo originate and what does it become?

A

Blastocystic cavity; umbilical vesicle.

Male Reproduction Function & Dysfunction (3 decks)

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