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REPRO > Spermatogenesis > Flashcards

Spermatogenesis Flashcards

1
Q

What is spermatogenesis?

A

The process whereby spermatozoa are formed

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2
Q

What are the 3 phases of spermatogenesis?

A
  • Proliferation (mitosis)
  • Meiosis
  • Differentiation
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3
Q

Where does spermatogenesis take place?

A

In the seminiferous tubules

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4
Q

What happens in the proliferation phase of spermatogenesis?

A
  • Mitotic divisions of spermatogonia
  • Large number of B spermatogonia produced from A spermatogonia
  • Start as A up against basement membrane, A1-4
  • Push between Sertoli cells towards lumen
  • then form intemediate spermatogonia
  • Final mitotic division from I to B-spermatogonia
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5
Q

Describe the I-spermatogonia

A
  • Linked by intercellular bridges
  • Allows cohorts to develop in synchornicity
  • Some are not joined and will go back to replenish stem cell pool and start again at A1
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6
Q

How long does spermatogenesis take?

A

5-9 weeks depending on species

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7
Q

Describe the meiosis stage of spermatogenesis

A
  • Mitotic division from B-spermatogonia to primary spermatocytes
  • Then meiotic division from primary to secondary spermatocytes
  • DNA repication adn crossing over occurs
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8
Q

Why is crossing over in spermatogenesis meiosis important?

A

Ensures genetic heterogeneity

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9
Q

Describe the differentiation phase of spermatogenesis

A
  • Spermatids from secondary spermatocytes via meiosis

- Spermatids differentate into spermatozoa (no division in this phase)

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10
Q

What stage of spermatogenesis has the longest life span and why?

A
  • Primary spermatocyte

- Prophase of meiosis I is long process

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11
Q

What stages can differentiation be split into?

A
  • Golgi
  • Cap
  • Acrosomal
  • Maturation phase
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12
Q

Describe the golgi phase of differentiation

A
  • Active golgi in spermatid
  • Forms golgi vesicles that fuse to form acrosomic vesicles
  • Centrioles migrate to base of nucleus
  • Proximal centriole anchors tail to nucleus, distal forms central part of flagellum
  • Dense acrosomic granules as important enzymes are being produced
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13
Q

Describe the cap phase of differentiation

A
  • Acrosome forms cap
  • Golgi apparatus migrates and disappears
  • Primitive flagellum forms (axoneme)
  • Change in morphology
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14
Q

Describe the acrosomal phase of differentiation

A
  • Sperm start to take on familiar shape
  • Acrosome spreads out, nucleus longates
  • Acrosome ocvers 2/3rds of nucleus
  • Manchette tubules form
  • Neck and annulus formed
  • Proximal tubule lodged at base of nucleus
  • More elongation, mitochondria appearing
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15
Q

Describe the maturation phase of differentiation

A
  • Manchette tubules formm postnuclear cap, pick up where acrosomal cap stops
  • mitochondria form spiral assembly in middl epiece of sperm
  • Annulus forms junction between middle and principle piece of sperm
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16
Q

What is meant by the cycle of the seminiferous epithelium?

A
  • Progression through a complete series of stages (cellular associations) ato one location along the serminiferous tubule
  • At any onne time, different sections will be at different stages of development
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17
Q

What is the importance of he seminiferous tubule having different stages of development?

A

Different sections at different stages so not all sections will be releasing sperm at any one time

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18
Q

In what direction do spermatozoa develop

A
  • Start close to basement membrane

- Move towards lumen as develop

19
Q

In the cycle of the seminiferous tubules, what is meant by a stage?

A

Specific cellular associations at any cross section at any moment in time e.g. stage 1, which contains A’gonia, 1’cyte, 2’cyte and spermatids
- Go up to stage 8

20
Q

What is meant by stage duration?

A

The time taken to progress from one stage to the next

21
Q

What is meant by cycle duration?

A

The time taken to complete any one cycle (i.e. to go through all stages)

22
Q

Explain why the time to complete spermatogenesis in the bull is 61 days, or 4.5 cycles

A
  • Each cycle is 13.5 days, and this contains each stage once
  • Each cell has to pass through each stage more than once as it develops through its different forms, each time going through the stage in a different form of development
  • In the bull, each cycle lasts 13.5 days, and each cel has to go through the cycel 4.5 times
  • the half cycle is because the earliest A-spermatogonia start their development in the middle of stage III
  • The duration of each stage and length of cycle varies between species
23
Q

What is the spermatogenic wave?

A
  • Different stages along each section of the tubule
  • Some sections will be releasing sperm while others will not
  • Allows steady trickle of sperm to avoid overload
24
Q

Where do the stem cells for the earliest A-spermatogonia come from?

A

are from A4-spermatogonia that do not develop into the linked I-spermatogonia and instead go back to form stem cells. This occurs half way through stage III

25
Q

What morphological changes occur in the head of sperm in the differentiation to spermatozoa?

A
  • Nucleus, acrosome and post-nuclear cap develop

- Shape varies across species

26
Q

What is contained in the acrosome?

A

Hydrolytic enzymes

27
Q

What is the function of the acrosome?

A

release hydrolytic enzymes for the penetration of the zona pellucida

28
Q

describe the morphological features in the tail of the sperm during differentiation to spermatozoa

A
  • Self powered flagellum composed of 4 parts
  • Capitulum (part of middle piece that fits into the posterior nucleus)
  • Middle piece (containing mitochondria)
  • Principle piece
  • Terminal piece
29
Q

What hormones is spermatogenesis dependent on?

A
  • GnRH to stimulate secretion of FSH and LH

- Testosterone and oestrogen from gonad

30
Q

describe the hypothalamic-pituitary-gonadal axis

A
  • Hypothalamus secrete GnRH
  • Stimulates FSH and LH release from anterior pituitary
  • LH stimulates testosterone from the Leydig cells
  • FSH stimulates conversion of testosterone to oestradiol in the Sertoli cells, also stimulates release of inhibin
31
Q

Describe the nature of GnRH release

A

Pulsatile, every 4-8 hours

32
Q

Describe the action of LH

A
  • Binds to Leydig cells
  • Stimulates testosterone production
  • Prolonged LH secretion shuts down expression of own receptors on Leydig cells, stops production of testosterone (negative feedback)
33
Q

What is the importance of the pulsatile secretion of GnRH

A
  • Leads to pulsatile secretion of LH

- In order to continue production of testosterone, need pulsatile secretion of LH (more would shut dpwn receptors)

34
Q

Describe the next steps for testosterone following release from the Leydig cells

A
  • Back to GnRH to inhibit release (if too high)

- Crosses to Sertoli cells for conversion to oestradiol

35
Q

What is the action of FSH?

A
  • Binds to receptors on Sertoli cells
  • Enables conversion of testosterone to oestradiol and dihydrotestosterone
  • Also stimulates inhibin
36
Q

What is the action of dihydrotestosterone?

A
  • Inhibit GnRH release from hypothalamus

- More potent than testosterone alone

37
Q

What is the action of inhibin?

A

Inhibits action of FSH and LH

38
Q

What is the effect of the oestradiol produced in the Sertoli cells?

A

Negative feedback to stop production of GnRH

39
Q

Outline the synthetic pathway for androgen production

A
  • All from cholesterol
  • Series of enzymatic conversions
  • Cholesterol to progesterone to androstenedione to testosterone to dihydrotestosterone
40
Q

What is the function of the epididymis?

A

Maturation and storage of spermatozoa

41
Q

How long is the epididymis in

a. cats
b. bulls

A

A: 2m long
B: 60m long

42
Q

Define spermiogenesis

A

The final stage of spermatogenesis

43
Q

Define spermiation

A

The process by which mature spermatocytes are released into the seminiferous tubules

44
Q

How does frequent ejaculation affect semen quality?

A
  • Production occurs at a fixed rate (although may decrease)
  • If the stores are used up, then replacement takes time
  • very frequent ejaculation will decrease semen quality by decreasing the sperm density

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