Lecture 10: Spermatogenesis Flashcards

1
Q

Male reproductive anatomy

A
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2
Q

Process of ejaculation

A

1 - Contraction in epidydemis & vas defers -> propels sperm (& epididymal fluid)up and out through vas deferens
2- This fluid travels through vas deferens; at seminal vesicle, seminal vesicle fluid added.
3- At ejaculatory duct, secretions from prostate & Cowper’s gland added
4- fluid ejected

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3
Q

What makes up ejaculatory fluid?

A
  • Sperm
  • Epididymal fluid
  • Seminal vesicle secretions
  • Prostate secretions
  • Cowper’s gland secretions
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4
Q

Characteristics & function of testes

A
  • Produce sperm and store it.
  • Produce hormones (T) which regulate spermatogenesis.
  • Lie in scrotum outside body cavity
  • Well-vascularised, well-innervated.
  • Normal volume of testes approximately 15-25ml.
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5
Q

How can the volume of testes be measured?

A
  • Orchidometer
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6
Q

What will happen if testes overheat?

A
  • Reduced sperm count
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7
Q

What is the optimum temperature for sperm production

A
  • 1.5-2.5C below body temp. (approx. 35C)
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8
Q

Is there an evolutionary benefit to testes laying outside body cavity?

A
  • School of thought which believes there is a benefit.
  • Ejaculation of sperm into vagina -> activation of sperm to fertilise
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9
Q

Testicular anatomical structure and through which structures do sperm travel?

A

Seminiferous tubules -> rete testis -> epididymis -> vas deferens

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10
Q

What is the testis 90% made up of?

A
  • Seminiferous tubules

(600m ST in each testis- tubules are tightly coiled)

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11
Q

Approx how many lobes filled with seminiferous tubules in one testis?

A

300

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12
Q

Seminiferous epithelium structure

A
  • brown outer lining = basal lamina/membrane
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13
Q

Process of spermatogenesis

A
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14
Q

What is the function of Sertoli cells in the seminiferous epithelium?

A
  • Respond to T
  • Function to regulate the process of spermatogenesis
  • Provide sustenance for spermatogenic cells
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15
Q

Where do we find tight junctions in the male gonad?

A
  • Seminiferous epithelium
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16
Q

What are the characteristics and function of tight junctions?

A
  • Exist between Sertoli cells forming blood-testis barrier.
  • Open to allow passage of spermatogonia prior to completion of meiosis.
  • Divides into basal and adluminal compartments.
  • Protects the spermatogonia from immune attack.
  • Allows specific enclosed environment for spermatogenesis which is filled with secretions from Sertoli cells.
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17
Q

How is spermatogenesis regulated in the testes?

A

Leydig cells -> produce T -> T passes Basal L. to Sertoli cells -> S. cells respond to T = regulate spermatogenesis

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17
Q

How is spermatogenesis regulated in the testes?

A

Leydig cells -> produce T -> T passes Basal L. to Sertoli cells -> S. cells respond to T = regulate spermatogenesis

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18
Q

What is the importance of the blood-testis barrier created by the tight junctions? And what may happen during a vasectomy reversal failure?

A
  • Prevents AB production against spermatogenic/germ cells
  • Protects spermatogenic cells from a lot of toxins – most toxins cannot pass through the blood-testis barrier
  • vasectomy reversal procedure -> vas deferrers reattached -> may lead to sperm leaking out healing vas deferens, passing barrier & entering blood system -> anti-sperm ABs produced
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19
Q

What are the names of the different stages of spermatogenesis?

A
  • Spermatogonia
    -> Primary spermatocyte
    -> Secondary spermatocytes
    -> Spermatids
    => Spermatozoa
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20
Q

Describe spermatogonia

A
  • Germ cell on basement membrane,
  • Capable of mitotic or meiotic division to produce primary spermatocytes or more spermatogonia by mitosis.
  • They are diploid.
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21
Q

Describe primary spermatocyte

A
  • Cell committed to differentiative pathway,
  • 46XY diploid.
  • They move into the adluminal compartment
  • duplicate their DNA to produce sister chromatids which exchange genetic material & enter meiosis I.
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22
Q

Describe secondary spermatocytes

A
  • Undergone meiosis I
    = 23X + 23Y haploid number of chromosomes (arranged as sister chromatids).
23
Q

Describe spermatids

A
  • Meiosis II occurs to give 4 haploid spermatids.
  • Round spermatid -> elongated spermatid differentiation.
24
Q

Describe spermatozoa

A
  • Mature sperm extruded into the lumen
25
Q

What is spermiogenesis?

A
  • Spermatids differentiate into mature spermatozoa
  • Removal of extra cytoplasm & tail
  • Acrosome formation
  • condensation of sperm nuclear chromatin characterised by the replacement of spermatogonial histones with sperm-specific protamines. This results in transcriptional inactivity in spermatozoa.
26
Q

What is the difference between Ad, Ap and B?

A

Ad: can copy itself & differentiate into Ap
Ap: undergoes further differentiation into spermatogonia
B: At this point, the cells are committed to differentiated pathway for spermatogenesis

27
Q

What does meiosis I arise and what does meiosis II arise?

A

MI: Secondary spermatocytes
MII: Spermatids

28
Q

What does spermiogenesis produce?

A
  • Spermatozoa
29
Q

Why do men always have a supply of spermatogonia?

A
  • Due to dark spermatogonia
  • diploid
  • undergo mitotic divisions
30
Q

Summarise spermatogenesis (process & length of time) & what is the importance of Sertoli cells?

A
  1. Mitotic proliferation of spermatogonia.
  2. Meiosis and development of spermatocytes.
  3. Spermiogenesis, elongation, loss of cytoplasm, movement of cellular contents.
  4. Movement into lumen controlled by Sertoli cell secretions.
  • Factors produced by sertoli cells are required for development.
  • New cycle every 16 days, entire process takes approximately 74 days.
31
Q

HPO vs HPT axis

A
32
Q

How is testosterone produced in the testes?/ function of LH in spermatogenesis

A

A. pituitary -> LH -> LHR on Leydig cells -> conversion of cholesterol to T in Leydig cells -> cross over to and stimulate Sertoli cell function

= initiation, maintenance & regulation of spermatogenesis

33
Q

What does FSH do and its function in spermatogenesis?

A

A.pituitary -> FSH -> FSHR on Sertoli cells -> conversion of androgens to E2

Function:
- regulation of Sertoli cell population;
- allows Sertoli cells to act on their sustentacular role;
- PRODUCTION OF ABP -> binds to T = concentrates T in epithelium

34
Q

Significance of inhibin in spermatogenesis

A
  • InhibinB is produced primarily by Sertoli cells in response to FSH
  • Inhibin B reduces FSH production by the anterior pituitary (negative feedback).
  • Germ cells appear to be required for Inhibin B production.
  • FSH & Inhibin B in combination have been correlated with testicular volume & spermatogenic activity but this hasn’t proved clinically useful as yet.
35
Q

How to test for male fertility?

A
  • Semen analysis
36
Q

Spermatozoon ~5uM structure

A
37
Q

How many sperm produced per day on average and how many ejaculated?

A
  • 300 million
  • approximately 120 million in average ejaculate
38
Q

What is the normal ejaculate volume?

A
  • 1.4ml - 6ml
39
Q

How much of the ejaculate volume contain spermatozoa?

A
  • 1-5%
40
Q

Where is sperm most rich in the ejaculate?

A

Initial portion of the ejaculate

41
Q

What is the amount of sperm present at each section of the female reproductive tract?

A
  • 99.9% lost before reaching ampulla of the uterine tube
  • around 120,000 sperm get near to egg,
  • only one enters
42
Q

What does the seminal fluid consist of?

A

secretions from:
- seminal vesicles,
- prostate,
- bulbo-urethral gland (Cowper’s gland)
- combined with epididymal fluid

43
Q

What is the function of the seminal fluid?

A
  • Transport of sperm through the male reproductive tract.
  • Coagulation of the ejaculate and creating a sperm deposit in the vagina.
  • Creation of a neutral to slightly alkaline buffered milieu in the vagina to protect spermatozoa from the acidic vaginal milieu.
  • Activation and augmenting the motility of the sperm cells.
  • Coating the sperm cells with capacitation inhibitors.
  • Supplying nutrients for the sperm cells.
44
Q

Describe the motility of sperm in the male reproductive tract

A
  • non-motile
  • seminal fluid aids in activation of motility
45
Q

What is capacitation simply?

A
  • Process that sperm cells undergo in order to fertilise
  • capacitation before cervix = too early
  • capacitation should ideally take place closer to site of fertilisation
46
Q

What are the semen analysis limits set by WHO 2021?

A
47
Q

What do the semen analysis limits by WHO 2021 measure?

A
  • male fertility
48
Q

What is a more expensive test for male fertility?

A
  • Sperm DNA fragmentation
49
Q

How long goes spermatogenesis last in ones lifetime?

A
  • continuous from puberty, never stops.
50
Q

Is spermatogenesis a short process and free of errors?

A
  • NO
  • Process is long and complex with many errors
    => high quantity, low quality
51
Q

what is the objective of spermatogenesis?

A
  • to produce high numbers.
52
Q

What drives spermatogenesis?

A
  • FSH
  • Testosterone
53
Q

Are sperm specialised for its function?

A
  • Yes, highly specialised for function
54
Q

What is the process of meiosis?

A