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Testicular Function Flashcards

1
Q

At which point in development is the male reproductive system distinguishable from the female reproductive system?

A

Week 7.

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2
Q

Which cells are the precursors to the reproductive systems?

What ploidy are these cells?

A
  • Primordial germ cells.

- Diploid cells.

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3
Q

What is the role of the Y chromosome in the determination of male sex?

A
  • The Y chromosome has a control gene that triggers the male developmental pathway; it doesn’t code for the masculine traits.
  • This gene is the SRY gene, and it codes an architectural transcription factor.
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4
Q

What is an architectural transcription factor?

A

A transcription factor that alters the structure of DNA to allow other transcription factors to act upon it (rather than directly activating the DNA itself).

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5
Q

What is the cause of females with XY chromosomes and males with XX chromosomes?

A

Deletion or mutation of the SRY gene.

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6
Q

List the processes that occur from weeks 3-7 of reproductive development in a male.

A

1 - Coelomic epithelial cells arrive at the gonadal ridges of the embryonic dorsal wall.

2 - They penetrate deeply into the developing testis and proliferate.

3 - These are the cells that express SRY.

4 - They form the primitive sex cords.

5 - Primordial germ cells migrate to the primitive sex cords.

6 - The sex cords envelop the primordial germ cells.

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7
Q

From which cells are Sertoli cells derived?

A

Coelomic epithelial cells.

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8
Q

From which structures are seminiferous tubules formed?

A

Primitive sex cords that have enveloped the primordial germ cells.

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9
Q

Other than coelomic epithelial cells and primordial germ cells, which cells migrate to the developing testis from weeks 3-7 of male reproductive development?

What is the fate of these cells?

A
  • Cells from the mesonephric primordia.

- They form the vasculature, leydig cells and myoid cells.

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10
Q

What are primordial germ cells called once they become enveloped within seminiferous tubules?

A

Prospermatogonia.

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11
Q

What cellular event occurs in primordial germ cells once they become enveloped within seminiferous tubules?

A

Meiosis is inhibited.

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12
Q

List the structures / cells that exist between seminiferous tubules.

A

1 - Vasculature.

2 - Clusters of Leydig cells.

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13
Q

When does SRY stop being expressed?

What directs further development of the male reproductive system?

A
  • Once seminiferous tubules have formed.

- The testes direct further development via androgens and anti-Mullerian hormone (AMH).

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14
Q

At which point in development are the testes in their final pre-pubertal form?

At which point in development is the male reproductive system in its final pre-pubertal form?

A
  • The testes finish developing by ~week 8.

- The male reproductive system finishes developing by ~week 12.

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15
Q

List 2 roles of the male reproductive system at puberty.

A

1 - To produce sperm.

2 - To produce hormones.

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16
Q

List the two compartments of post-pubertal testis.

Which cells are present in these compartments?

A

1 - Intraseminferous compartments of the seminiferous tubules (Sertoli cells).

2 - Interseminiferous compartments (Leydig cells).

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17
Q

What is the function of the Sertoli cells in the seminiferous tubules of the post-pubertal testis?

A

To produce sperm.

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18
Q

What is the function of the Leydig cells in the seminiferous tubules of the post-pubertal testis?

A

To produce androgens.

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19
Q

List the 3 subcompartments of the intraseminiferous compartment.

Where are these compartments?

A

1 - The lumen in the centre of the seminiferous tubule.

2 - The adluminal compartment surrounding the lumen of the seminiferous tubule.

3 - The basal compartment by the outer basement membrane of the seminiferous tubule.

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20
Q

Where is the blood-testis barrier?

A

Between the adluminal and basal compartments of the seminiferous tubules.

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21
Q

List the junctions that form the blood-testis barrier.

Which cells are being linked together by these junctions?

A

1 - Adherens junctions.

2 - Gap junctions.

3 - Tight junctions.

  • These junctions are linking adjacent Sertoli cells.
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22
Q

When does the blood-testis barrier form?

Why is this important?

A
  • During puberty prior to the onset of spermatogenesis.

- This is important because the role of the blood-testis barrier is to keep mature sperm away from the immune system.

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23
Q

Other than separating the immune system from mature sperm, what is the other role of the blood-testis barrier?

A

To selectively transport ions and small molecules into the seminiferous tubule.

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24
Q

What is the rate of production of sperm?

A

100 million per day.

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25
Q

List the phases of spermatogenesis.

A

1 - Proliferation.

2 - Division by meiosis.

3 - Differentiation.

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26
Q

Describe the proliferation phase of spermatogenesis.

A

1 - At puberty, prospermatogonia are reactivated and are then known as ‘As spermatogonia’.

2 - As spermatogonia undergo mitosis in the basal compartment of the seminiferous tubule to produce another As spermatogonium (renewal) and an ‘A spermatogonium’.

3 -The A spermatogonia undergo mitosis to produce B spermatogonia.

4 - B spermatogonia undergo mitosis to produce primary spermatocytes.

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27
Q

Describe the division phase of spermatogenesis.

A

1 - The primary spermatocytes move from the basal compartment of the seminiferous tubule through the blood-testis barrier into the adluminal compartment.

2 - Here, they undergo the first meiotic division over the course of 24 days to form diploid secondary spermatocytes.

3 - They then undergo the second meiotic division over the course of 24 hours to form haploid round spermatids.

28
Q

Give an overview of the differentiation phase of spermatogenesis.

A

1 - Round spermatids elongate to form elongated spermatids.

2 - Elongated spermatids become mature spermatozoa.

  • The maturation process includes formation of specialised sperm structures:

1 - Acrosome.

2 - Flagella.

3 - Centrioles.

4 - Mitochondria.

5 - A nucleus.

6 - Cytoplasm.

29
Q

From which structure is the acrosome formed?

A

The golgi apparatus.

30
Q

What is contained within the acrosome?

A

Hydrolytic enzymes that facilitate the acrosome reaction.

31
Q

Where on the acrosome is the receptor for fusion with the egg cell found?

A

On the inner acrosomal membrane.

32
Q

From which structures do sperm flagella develop?

Briefly describe the process of flagellum development.

A
  • Centrioles
  • One centriole migrates to the opposite end of the cell to the nucleus, and one stays proximal to the nucleus.
  • The centriole distal to the nucleus elongates to form an axoneme, which becomes the main structural component of the flagellum.
33
Q

What is the importance of the proximal centriole of a sperm cell?

A

Upon entry of the sperm into an egg cell, the proximal centriole is donated to the egg to form the spindle for the first cell division of the embryo.

34
Q

What is the midpiece?

What is the function of the midpiece?

A
  • The helically arranged structure of mitochondria that forms around the first part of the flagellum.
  • It provides the flagellum with ATP.
35
Q

What is the function of protamines?

Why is this important?

A
  • They replace the function of histones in order to pack DNA more tightly into the sperm.
  • Sperm DNA therefore does not have nucleosomes (as these require histones).
  • This is important to ensure that the sperm is streamlined.
36
Q

What is a residual body?

What happens to it after it forms?

A
  • The superfluous cytoplasm released by a sperm in order to produce a more streamlined cell shape.
  • It is phagocytosed by Sertoli cells.
37
Q

Which process occurs after spermatogenesis?

What does this involve?

A
  • Spermiation.

- This is the release of sperm into the lumen of the testis.

38
Q

How long does spermiation take?

What controls the duration of spermation?

A
  • 64 days.

- The duration of spermiation is controlled by a process intrinsic to the germ cells themselves.

39
Q

What is the spermatogenic wave?

A

The phenomenon whereby different seminiferous tubules enter spermatogenesis at different times, ensuring that there is not a burst of sperm released into the lumen every 64 days, but rather a continuous flow.

40
Q

What is the main male androgen?

List 3 other hormonal products of the testis.

A
  • Testosterone.

1 - Oestrogens.

Cytokines:

2 - Inhibin.

3 - Anti-Mullerian hormone.

41
Q

Into which substance is testosterone converted in the seminiferous tubules?

Which cells mediate this process?

Which enzyme is necessary to do this?

A
  • Dihydrotestosterone.
  • Sertoli cells.
  • 5 alpha reductase.
42
Q

What is the fate of dihydrotestosterone?

A
  • Some binds to androgen receptors in Sertoli cells to stimulate spermatogenesis.
  • Some binds to androgen-binding protein (ABP), a carrier protein.
43
Q

List 2 functions of antigen binding protein.

A

1 - To form a store of testosterone within the testis.

2 - To carry testosterone to the cells lining the reproductive tract.

44
Q

Which cells produce inhibin?

A

Sertoli cells.

45
Q

What is the function of inhibin?

A

It suppresses FSH production by the anterior pituitary gland.

46
Q

Which cells produce anti-Mullerian hormone?

A

Sertoli cells.

47
Q

What is the function of anti-Mullerian hormone?

A

It has an embryonic role in the development of the reproductive system.

48
Q

Where in the testis does LH bind?

What is its effect?

A
  • To LHCG receptors on Leydig cells.
  • It induces testosterone production.
  • Testosterone moves to the tubules and binds to the androgen receptor on Sertoli cells to stimulate spermatogenesis.
49
Q

Where in the testis does FSH bind?

What is its effect?

A
  • To FSH receptors on sertoli cells.
  • It induces expression of androgen receptors.
  • It also stimulates production of inhibin and androgen-binding protein.
50
Q

List the feedback molecules produced by the effects of FSH and LH.

A
  • LH results in the production of testosterone, which feeds back to the hypothalamus.
  • FSH results in the production of inhibin, which feeds back to the hypothalamus.
51
Q

List the sperm maturation processes that occur between release of sperm from the testis and contact with an egg.

Where do these processes occur?

Why are these processes necessary?

A

1 - Maturation (in the epididymis).

2 - Capacitation (in the female tract).

  • These processes are necessary because sperm released from the testis are:

1 - Immotile.

2 - Unable to recognise / bind to an egg.

52
Q

What is the epididymis?

A

The tube through which all sperm pass after being released from the testis.

53
Q

How does the epididymis affect the composition of sperm?

Which hormone controls this?

A
  • Most of the fluid of the sperm is reabsorbed in the epididymis, making the sperm 100x more concentrated.
  • Fluid reabsorption is controlled by oestrogen.
54
Q

How long does sperm passage through the epididymis take?

A

10-14 days.

55
Q

Which cell lines the epididymis?

What is their role?

Which hormone drives the activity of these cells?

A
  • Pseudostratified columnar epithelium.
  • They modify the sperm passing through the epididymis by conjugating and modifying proteins to the sperm surface.
  • The activity of these cells is driven by androgens.
56
Q

List the segments of the epididymis.

List the functions that the epididymis confers on the sperm cells at each segment.

A

1 - Caput (head - motility).

2 - Corpus (body - fertilising ability).

3 - Cauda (tail - no functional change to the sperm. It is part of the storage of sperm).

57
Q

Into which structure do sperm pass after the epididymis?

What is the function of this structure?

A
  • The vas deferens.

- It is a storage reservoir for sperm.

58
Q

Which structure is the target of vasectomies?

A

The vas deferens.

59
Q

What is semen?

A

Sperm mixed with seminal plasma.

60
Q

What is the average concentration of sperm in ejaculated semen?

A

~200 million sperm per 2.5mls (average ejaculate volume).

61
Q

List 4 functions of seminal plasma.

A

1 - Transport.

2 - Nutrition.

3 - Buffering of pH.

4 - Antioxidants.

*Seminal plasma is also the means of transport of STIs.

62
Q

Where is seminal plasma produced?

A

1 - Seminal vesicles.

2 - Prostate.

3 - Bulbourethral glands.

  • These are sac-like accessory glands.
63
Q

What is semenogelin?

Why is this useful?

A
  • A fibrinogen-like substrate produced by seminal vesicles that cause ejaculate clotting.
  • This keeps the semen in the cervical mucus.
64
Q

What prevents ejaculate clotting in the male reproductive tract?

A

The presence of enzymes that break down semenogelin.

65
Q

List 2 components of the semen that are produced by the prostate.

A

1 - Alkaline secretions that are high in zinc.

2 - Enzymes for ejaculate clotting and liquefaction.

66
Q

List 2 functions of the bulbourethral glands.

A

1 - Lubrication.

2 - Neutralisation (important as urine also passes through the urethra).

67
Q

List the 2 components of capacitation.

A

1 - Hyperactivation of the tail.

2 - Acrosome reaction.

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