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Repro 313 > Male reproductive tract. Lecture 6 > Flashcards

Male reproductive tract. Lecture 6 Flashcards

1
Q

What are the two functions of the testes?

A

Spermatogenesis

Hormone production

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2
Q

What hormones do the testis produce?

A

Androgens
Estrogens (low levels)
Inhibin / activin (homeostasis)
Relaxin-like factor

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3
Q

Describe the movement of sperm from production to ejaculation:

A 
Seminiferous Tubules
Rete Testis
Head of epididymis
Epididymis
Tail of epididymis
Vas defernes (then ejaculation)
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4
Q

What cells are found within the seminiferous tubules?

A

Sertoli cells

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5
Q

What cells are found between seminiferous tubules?

A

Leydig cells

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6
Q

How are the seminiferous tubules divided?

A

Into three compartments:

1) Basal compartment
2) Adluminal Compartment
3) Luminal Compartment

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7
Q

What separates the seminiferous tubules from the rest of the body?

A

A physical barrier formed by:

  • Tight Junctions
  • Adherens Junctions
  • Gap junctions between sertoli cells.

Basement membrane.

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8
Q

What is the physical barrier of the seminiferous tubule called?

A

The blood/testis barrier.

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9
Q

Why does the blood/testis barrier exist?

A

To prevent an immune attack on sperm as sperm are not considered self.

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10
Q

Where are sperm developed?

A

Sperm are developed in the seminiferous tubule wall and are released into the lumen.

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11
Q

When do testicles start to develop in the foetus?

A

Around 6 weeks of gestation before the pituitary gland.

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12
Q

What happens to the testis during late prepubertal development?

A

During later fetal life and early postnatal life the testis grow slowly and the seminiferous cords are solid.

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13
Q

Do pro-spermitgonial germ cells contribute to the growth of pre-pubertal testis?

A

Their contribution is insignificant to this slow growth.

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14
Q

What happens to leydig cells during pre-pubertal testicular development?

A

Leydig cells are sparsely distributed.
They are present in the first and second trimester and contribute to fetal testicular development. In the third trimester they die off and are replaced by another generation of leydig cells.

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15
Q

What happens to the testis during puberty?

A
  • At puberty there is a sudden testicular growth by all components of the testes.
  • The seminiferous tubules develop a lumen and the germ cells begin to proliferate again.
  • The synthetic activity activity of the sertoli and leydig cells increases sharply.
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16
Q

What are the steps of spermatogenesis?

A

1) Mitotic division
2) Meiotic division
3) Cytodifferentiation

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17
Q

Whats the rate of sperm production per a gram of teste?

A

300-600 sperm per second per gram of tissue.

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18
Q

Is mitosis a cycle?

A

Yes

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19
Q

Is meiosis a cycle?

A

No

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20
Q

What is mitosis?

A

One diploid cell produces two diploid daughter cells

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21
Q

What is meiosis?

A

One diploid cell produces four haploid daughter cells

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22
Q

Describe the genesis of sperm:

A 
Primordial Germ cell
- (mitosis)
Primary Spermatocyte
- First meiotic division
Secondary Spermatocyte
- Second mitotic divison
Spermatid
Cytodifferentiation
Sperm cell.
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23
Q

Describe the location of the various sperm lineage stages in the seminiferous tubule:

A

Primordial germ cell starts off near the basement membrane of the seminiferous tubule i.e near the blood teste barrier.

Sperm stages move towards the lumen and spermatids are ejected into the lumen.

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24
Q

How long does spermatogenesis take?

A

64 days

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25
Q

What is spermiogenesis?

A

The conversion of a spermatid into a sperm cell.

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26
Q

During spermiogenesis to the shape of the spermatid?

A

The spermatid forms a tail, a mid piece and a tail.

27
Q

The formation of a mid piece in the spermatid contains what?

A

Packed with mitochondria.

28
Q

What is in the formed head of the spermatid converting into the sperm?

A

The head contains condensed heterochromatic DNA and is covered by the acrosome - a compartment filled with enzymes that are required for egg penetration.

29
Q

What happens to the excess cytoplasm of the spermatid converting into the sperm?

A

The excess cytoplasm of the spermatid is also lost into a body called the residual body that is phagocytosed by the sertoli cells after the sperm leaves.

30
Q

Does each spermatocyte continually produce sperm?

A

No, each spermatocyte does not continually produce sperm but undergoes cycles of development called the spermatogenic cycle.

31
Q

How long is the spermatogenic cycle?

A

16 days

32
Q

What does spermatogenic cycle mean for sperm production?

A

At any point of time there must be more than one spermatogenic cycle underway.

33
Q

As happens at the end of each mitotic division?

A

At the end of each mitotic division a new one starts.

34
Q

What does a cross section of a seminiferous tubule reveal in terms of sperm development?

A

A cross section will reveal that sperm are all at the same stage of development within the tubule lumen.

Each segment of the seminiferous tubule contains a different stage of spermatogenic development that is either ahead or behind the consecutive segments.

35
Q

What is the cycle of the seminiferous epithelium?

A

This describes the synchronisation of sperm development within the cross section of the seminiferous tubule.

36
Q

What is the synchronisation of spermatogenesis along the length of the tubule called?

A

The Spermatogenic wave.

37
Q

What do the sertoli cells control during spermatogenesis?

A

Temporal and spatial organisation of spermatogenesis is controlled by the sertoli cells.

38
Q

How can sertoli cells regulate spermatogenesis?

A

Sertoli cells are able to communicate with each other via tight junctions and with spermatocytes and spermatids via gap junctions and ectoplasmic specialisations.

39
Q

What moves sperm through the testis?

A

Pressure from secretions and ciliated cells in the efferent ducts aid sperm movement.

40
Q

How many days does it take for sperm to move from the seminiferous tubule to the epididymis?

A

6 days

41
Q

Describe the fertility of sperm in the upper epididymis?

A

Not motile and not capable of fertilising eggs.

42
Q

What aids the maturation of sperm?

A

Sertoli cells and the epithelium of the epididymis secrete a fluid rich in nutrients and hormones that sperm are maintained i+ mature in.

43
Q

After 10-14 days what happens to the sperm?

A

After 10-14 days in the epididymis sperm mature and gain fertilising potential but the sperm remain immotile because of inhibitory proteins secreted by the epididymis.

44
Q

How much sperm are produced daily and where are they stored?

A

Around 120million per day and they are stored in the primarily in the vas deferens and ampulla of the vas deferens for up to a month.

45
Q

What happens if sperm are not ejaculated during their time in the van=s defernes and ampulla?

A

If they are not ejaculated during that time, they degenerate and are re-absorbed by the body.

46
Q

What is a general description of the vas deferens?

A

Muscular tube about 45cm long.

47
Q

What happens to the vas deferens during ejaculation?

A

It contracts during ejaculation resulting in the movement of spermatozoa out of the epididymis and into the ejaculatory duct.

48
Q

Describe the anatomy of the ejaculatory duct:

A

The ejaculatory duct enters the urethra as it passes through the prostate gland.

49
Q

Describe the prostate:

A

Walnut sized gland containing 70% glandular tissue and 30% muscle.

Lies just below the bladder.

50
Q

What happens to sperm as it passes through the prostate?

A

As sperm passes through the prostate it is there is sequential release of seminiferous fluid and prostate fluid, but they are not mixed as this would cause coagulation, so they mix after ejactulation.

51
Q

What is the importance of the seminal and prostatic fluids?

A

Glandular secretion from the seminal vesicles and prostate are important for sperm motility and survival in the female reproductive tract

52
Q

Describe the GnRH and LH pulse:

A

Every LH pulse released about once per hour has an GnRH pulse before it, but not every GnRH pulse is followed by an LH pulse.

53
Q

What does LH do?

A

It acts on Leydig cells to produce testosterone, which causes initiation of spermatogenesis.

54
Q

What does FSH act on and what is its function?

A

FSH acts on the sertoli cells and causes them to unregulated androgen receptors (so testosterone can diffuse into the seminiferous tubule and bind to the receptors and cause spermatogenesis.)

55
Q

What happens with experimental destruction of the hypothalamus?

A

No LH or FSH release. This results in regression of the male accessory glands and gonads.

56
Q

If GnRH was given continuously i.e because the hypothalamus is destroyed then what happens?

A

GnRH binds to its receptors on the pituitary and they receptor-protein complex is internalised. Leaving some un-occupied receptors on the surface.

However if continuous GnRH is given then all receptors are internalised and leads to leads to the cells being unresponsive.

57
Q

What does the removal of the pituitary gland lead to?

A
  1. Testicular shrinkage
  2. Leydig cells involute and testosterone production stops
  3. Arrest of spermatogenesis at primary spermatocyte stage.
58
Q

What happens if testosterone supplementation is given upon pituitary removal?

A
  • Leydig cells involute
  • Spermatogenesis continues.

This demonstrates that the pituitary regulates testosterone production by the leydig cells.

59
Q

What mediates pituitary control over the leydig cells?

A

LH

60
Q

What happens if LH is administered when the pituitary removed?

A

If LH is administered at pituitary removal

  • Leydig cells do not involute
  • Testosterone production is maintained
  • Spermatogenesis continues

Antibodies to exogenous LH cause symptoms similar to removing the pituitary gland.

61
Q

Can you delay LH administration after pituitary removal?

A

If there is a delay LH is not enough adequate to restore spermatogenesis.

IN this case FSH is also required.

62
Q

Describe the action of FSH:

A

FSH acts on sertoli cells to stimulate androgen receptors. Once the sertoli cells become sensitive to androgens the androgens then up regulate expression of FSH receptors by a positive feedback pathway.

63
Q

Describe the feedback loop of the endocrinology of the male reproductive tract:

A

Testosterone reduces GnRH secretion and therefore LH+ FSH release.

FSH is also regulated by inhibin, such that FSH and LH levels can be different.

64
Q

What produces inhibit?

A

Sertoli cells produce inhibit in response to stimulation by FSH.

Repro 313 (20 decks)

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