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RED > Testicular function > Flashcards

Testicular function Flashcards

1
Q

Until what gestational week is the reproductive system indifferent in a fetus?

A

Week 7

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2
Q

When and where do primordial germ cells arise from?

A

During week 3, germ cells arise from the epiblast during gastrulation and then migrate to the gonadal ridges on the posterior wall.

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3
Q

What determines the development of testes?

A

The presence of the Y chromosome due to the SRY gene / TDF.

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4
Q

Why does the Y chromosome only contain an SRY gene?

A

Because the chromosome is too small to code for the whole of male development

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5
Q

How was SRY discovered?

A

Discovered in pts with mutations:
xy females with a deleted or mutated SRY = no male development occurs
xx male with a translocated SRY on to X chromosome = male development occurs..
Proven in mice, when females were presented with SRY they showed male development.

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6
Q

What is the function of SRY?

A

It is an indirect TF that bends the DNA to allow other TF to have an effect. It sets up a cascade of TF that will then turn on the genes for male development.

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7
Q

At week 7, which three types of cells arise in the genital ridges?

A 
PGCs
Sertoli cells (somatic)
Leydig cells (somatic)
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8
Q

Where do sertoli cells arise from?

A

Cells from coelomic epithelium form columns that proliferate and penetrate into the medullary mesenchyme of the developing testes, forming the primitive sex cords. In mature testes the sex cords form sertoli cells.

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9
Q

Where do leydig cells arise from?

A

Cells of mesonephric primordia form leydig and myoid cells and form the vasculature of the testes.

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10
Q

What forms the basic structural unit of the testes?

A

PGCs are surrounded by sex cords to form the unit known as seminiferous tubules.

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11
Q

Where do PGCs become prospermatogonia?

A

In the seminiferous tubules, surrounded by sertoli cells.

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12
Q

Where do the leydig cells lie?

A

Lie as groups along with the vasculature, in between the tubules of sertoli cells,

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13
Q

Which cells express SRY and when is expression stopped?

A

Sertoli cells express SRY until the testes begin to develop the hormone androgens and AMH for continuation of development

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14
Q

What is the function of the testes?

A

To produce spermatozoa and hormones

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15
Q

What is the blood-testis-barrier?

A

A barrier within the tubule formed by sertoli cells linking through adherens, gap and tight complexes.

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16
Q

Which two compartments are produced by the formation of the BTB?

A

Basal - lies outside the barrier next to the BM

Adluminal - lies next to the lumen

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17
Q

When does the BTB develop?

A

During puberty prior to spermatogenesis

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18
Q

What is the purpose of the BTB?

A

To protect sperm from the immune system as the sperm don’t develop until puberty and so would be viewed as foreign = immune privilege. To regulate selective transport of ions and small molecules to maintain an optimal environment for spermatogenesis.

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19
Q

What results from a disruption to BTB?

A

Trauma damaging the BTB will lead to the development of anti-sperm Igs that will cause AI orchitis and subfertility.

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20
Q

What are the 3 phases of spermatogenesis?

A

1) Proliferation
2) Division / meiosis
3) Differentiation

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21
Q

When does spermatogenesis begin?

A

At puberty

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22
Q

What happens during the proliferation phase of spermatogenesis?

A

At puberty the dormant prospermatogonia are reactivated and undergo mitosis within the basal compartment of the tubule.
As the gametes mature they move towards the lumen.

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23
Q

What is a reactivated prospermatogonia called and what is their function?

A

As Spermatogonia - stem cell that provide the self renewing reservoir throughout life. Each time they divide by mitosis they produce new SC for the pool.

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24
Q

Other than SC, what else is produced by mitosis in an As spermatogonia?

A

A spermatogonia. These are used for spermatogenesis.

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25
Q

What happens during spermatogenesis?

A

1) A spermatogonia undergoes mitosis = B spermatogonia
2) B spermatogonia undergoes mitosis = primary spermatocyte
Within 16 days

26
Q

What happens after the 2 mitotic divisions?

A

The primary spermatocyte moves through the BTB into the adluminal compartment as the junctions disrupt and rejoin.
Undergo 1st meiotic divison.

27
Q

What happens during the 1st meiotic divison?

A

Recombination and genetic diversity

28
Q

What does the 1st meiotic divison produce and how long does it take?

A

= secondary spermatocyte.

Takes 24 days, during which the sperm are sensitive to damage

29
Q

Describe the 2nd meiotic division.

A

Secondary spermatocyte divides quickly to from round HAPLOID SPERMATIDS

30
Q

What happens during the differentiation phase?

A

The round spermatids elongate to form a flagellum and mature into SPERMATOZOA. During maturation they form the acrosome and key changes occur in the organelles (centrioles, mitochondria, nucleus, cytoplasm). Takes 24 days.

31
Q

What is the acrosome?

A

A structure that lies over the nucleus at the sperm head, produced by golgi apparatus. It contains hydrolytic enzymes for the acrosome reaction.

32
Q

What happens during the acrosome reaction?

A

On binding to the zona pellucida, the plasma and outer acrosomal membrane fuse to release the enzymes for digesting through to the egg for fusion. The reaction exposes the receptor on the spermatozoa for fusion with the egg.

33
Q

What is the function of a flagellum?

A

A tail to assist movement through the female tract and to thrust through the egg. Both use different movements.

34
Q

How is the flagellum formed?

A

Formed from centrioles as they migrate to opposite sides of the nucleus fromt the golgi. The distal centriole forms the axoneme of the flagellum.

35
Q

What is the function of the proximal centriole?

A

The proximal centriole remains for post fertilistion to provide the egg with a spindle for its first embyronic mitotic division as an egg has no centrioles.

36
Q

Where are the mitochondria located and what is their function?

A

Lie in the midpiece around the top of the flagellum to provide energy for movement

37
Q

What are the characteristics of the specialised sperm nucleus?

A

Contains either x or y chromosome as sex determining. Sperm are small and streamline so DNA is highly condensed into the head by replacing histones with PROTAMINES.

38
Q

What happens to the cytoplasm in mature sperm?

A

Mature sperm lose their cytoplasm during the final stages of differentiation, and is released as a residual body. Sertoli cells phagocytose the droplet.

39
Q

Why are mature sperm transcriptionally and translationally inactive?

A

The tightly packed DNA means gene expression and transcription cannot occur and the lack of cytoplasm means proteins cannot be translated.

40
Q

What is spermiation?

A

The release of sperm from sertoli cells into the lumen of the seminiferous tubules.

41
Q

How long does the process of spermatogenesis take?

A

64 days

42
Q

What controls spermatogenesis?

A

Germ cells not endocrine. Rat sperm SC in a mouse will still produce rat sperm despite mouse testicular environment

43
Q

How is continuous production of spermatozoa ensured?

A

Different areas of the tubule enter spermatogenesis at different times to stagger the starting points.

44
Q

What hormones are produced by the testes?

A

Androgens - mainly testosterone for embryonic development and reproductive function.
Oestrogens - in small amounts
Cytokines e.g. inhibin and AMH for embryonic development

45
Q

Where are androgens produced?

A

Leydig cells

46
Q

Where dose the testosterone produced end up?

A

Enters blood and lymph to travel to accessory sex glands and some remains within the tubule for supporting spermatogenesis.

47
Q

What happens to the testosterone within the tubule?

A

Converted to DHT in sertoli cells by 5alpha reductase.

48
Q

Where does DHT bind and what does this result in?

A

It is a more biologically active form that can bind to androgen receptors in sertoli cells to stimulate spermatogenesis.
Binds to ABP to be carried in the testicular fluid and maintain a high concentration and to supply the rest of the tract as sperm moves out.

49
Q

What is the function of inhibin and where is it produced?

A

Produced by sertoli cells to regulate HPG axis by suppressing FSH production

50
Q

What is the function of AMH and where is it produced?

A

Produced by sertoli cells for embryonic development.

51
Q

What happens to the hormone levels at puberty?

A

Hypothalamus is activated to release GnRH and stimulate release of LH and FSH from anterior pituitary.
LH binds to LHCGR on LEYDIG for testosterone production.
FSH binds to FSHR on SERTOLI cells to activate genes and induce expression of androgen R, for increased sensitivity to androgens. Stimulates AMH and inhibin release.

52
Q

When sperm leave the testis they are immobile and unable to bind to an egg. What must happen to the sperm as it passes through the tract?

A

The sperm must undergo MATURATION. As the sperm passes through the epididymus cells in the tube act to modify the sperm to acquire the ability to fertilise and move. This is ANDROGEN dependent.

53
Q

Other than maturation, what happens as the sperm pass through the epididymus?

A

As the sperm travel for 2 weeks, OESTROGEN regulates the ABSORPTION of fluid to concentrate the sperm.

54
Q

What must happen to the sperm once within the female reproductive tract?

A

CAPACITATION - final stage of maturaton to give the sperm the capacity to fertilise. It causes hyperactivation for increased motility and allow the acrosome reaction to occur.

55
Q

What are the 3 sections of epididymus and their functions?

A

Caput / head - acquire motility
Corpus / body - fertilising ability
Cauda / tail - storage

56
Q

What is the vas deferens?

A

It follows the epididymus and is the main storage reservoir, densely packed with little fluid.

57
Q

What happens on ejaculation?

A

Sperm mixes with seminal plasma to form semen = 3ml of highly concentrated semen.

58
Q

Where is seminal plasma produced?

A

Secreted by the accessory sex glands prostate and seminal vesicles

59
Q

What is the purpose of seminal plasma?

A

Aid transport, provide fructose for nutrition, buffering / alkaline solution to protect from acidic vagina and antioxidants to prevent DNA damage. Depending on the stage of ejaculation the source of fluid will vary, starting with prostate to vas deferens to seminal vesicles.

60
Q

What does the seminal vesicle produce?

A

Empties on ejaculation to provide the majority of the volume. It contains fibrinogen like substance to clot the sperm post ejaculation and hold it in the vagina to act against gravity

61
Q

What does the fluid contain that is produced by the prostate gland?

A

Alkaline and high in zinc for sperm function. Contains enzymes that will form and then liquefy the clot after 30 minutes.

62
Q

What does the bulbourethral / Cowper’s gland produce?

A

Secretes pre-ejaculate for lubrication and to neutralise the urethra from acidic urine. Pre-ejaculate may contain sperm if left behind from previous ejaculation.

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