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3002 > 65 Spermatogenesis > Flashcards

65 Spermatogenesis Flashcards

1
Q

What are the two major compartments of the testes?

A
  1. Seminiferous tubules
  2. Interstitial spaces

• Both compartments separate: “blood-testis barrier”

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2
Q

What are the seminiferous tubules in testes?

A
  • ~ 250 m total length
  • Developing germ cells
  • Sertoli (sustentacular) cells
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3
Q

What are the interstitial spaces in testes?

A
  • Leydig cells (synthesise androgens

* Blood and lymph vessels

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4
Q

Role of blood-testis barrie?

A
  • Prevents immune reaction to spermatozoa

* Separates fluids of different composition

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5
Q

What is spermatogenesis?

A

Production of mature spermatozoa from undifferentiated germ cells (primordial germ cell)

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6
Q

What are the 3 stages of spermatogenesis?

A
  1. Mitotic proliferation
  2. Meiotic (reduction) division
  3. Cell modelling (spermiogenesis)
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7
Q

How long is the spermatogenic cycle?

A

~74 days (from 1st mitotic division to release of spermatozoa)

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8
Q

Spermatogenesis occurs in waves, how often is its initiated?

A

Every 16 days

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9
Q

Spermatogenic cycle stages (length of time)

A
  • Spermatogonium —> 1 ̊ spermatocytes = 25 days
  • Meiotic division 1 —> 2 ̊ spermatocytes = 9 days
  • Development —> spermatids = 19 days
  • Differentiation –> spermatozoa = 21 days

= ~ 74 days

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10
Q

Structure of sperm

A
  • Flagella: End piece, principal piece, middle piece

* Head (nucleus covered by acrosome)

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11
Q

How much sperm produced a day?

A

200 million/ day (~ 2300/sec)

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12
Q

What happens in spermiation at the end of differentiation?

A
  • Cytoplasmic links are broken
  • Spermatozoa released into tubule lumen
  • Sperm virtually immobile
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13
Q

Role of Sertoli cells in spermiation?

A

Fluid secreted by Sertoli cells flushes spermatozoa from seminiferous tubules, through the rete testis into the epididymis:

  • Capacity for motility by the time they reach the tail of the epididymis
  • Motility is suppressed by epididymal fluid
  • Instead movement through reproductive tract is aided by peristaltic muscle contractions
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14
Q

What is capacitation?

A
  • If ejaculated spermatozoa are placed with oocytes in vitro fertilisation doesn’t occur immediately
  • Need to undergo capacitation - occurs in female reproductive tract (2-6 h)
  • Glycoprotein coat gained in the epididymis is stripped
  • Results in 2 changes:
  1. Head acquires the capacity to initiate the acrosome reaction
  2. Hyperactivation (increased flagellar beats)
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15
Q

Human sperm quality?

A
  • Relatively poor

* ~ 30% show morphological abnormalities or abnormal function

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16
Q

Normal sperm count?

A

50-150 million/ml

17
Q

Sub fertility sperm count?

A

< 15 million/ml

18
Q

What is oligozoospermia?

A

Low sperm count (<15 million/ml)

19
Q

What is azoospermia?

A

Absence of sperm in the ejaculate

20
Q

What is asthenozoospermia?

A

Low sperm motility (< 50% moving)

21
Q

What is teratozoospermia?

A

High proportion of abnormally-shaped sperm

22
Q

What is antiserum antibodies?

A

Abnormal immune response to semen

23
Q

What stimulates the anterior pituitary gonadotrophs?

A

Pulsatile secretion of Gonadotrophin-releasing hormone (GnRH) from the hypothalamus

24
Q

What pituitary hormones control testicular functions?

A
  1. Gonadotrophins
  2. Luteinizing hormone (LH)
  3. Follicle stimulating hormone (FSH)
25
Q

Blood supply between hypothalamus and pituitary gland

A

Hypothalamo-hypophysial portal system - allows the hypothalamus to communicate with the anterior pituitary via the release of neurotransmitters into the bloodstream

26
Q

Control of gonadotrophin secretion

A
  • LH and FSH secretion is controlled by GnRH secreted by the hypothalamus
  • GnRH is released into the portal blood in pulses every hour
  • GnRH must be pulsatile or it’s ineffective
  • High GnRH pulse amplitude and frequency preferentially stimulates LH synthesis and secretion
  • Low GnRH pulse amplitude and frequency stimulates FSH synthesis and secretion
27
Q

Hormone production in the anterior pituitary gland

A
  1. Gonadotrophs
    • Secrete LH and FSH (glycoproteins)
    • Most cells secrete one or other, but some secrete both
  2. Lactotrophs
    • Secrete prolactin (protein)
28
Q

Hormone production in the posterior pituitary gland

A

Neurosecretory neurones

• Secrete arginine vasopressin (AVP) and oxytocin (peptides)

29
Q

Functions of LH and FSH

A
  • Leydig cells in the testes have receptors for LH - stimulates synthesis and secretion of testosterone
  • If LH secretion is too low, testosterone is low - spermatogenesis halts
  • However, LH and testosterone cannot maintain spermatogenesis at its normal level without FSH
  • FSH is required for maximum sperm production - acts on Sertoli cells
30
Q

Functions of FSH on Sertoli cells

A
  • ↑ RNA and protein synthesis
  • ↑ Energy metabolism
  • ↑ cAMP
  • ↑ Inhibit secretion
  • ↑ ABP secretion
  • ↑ Fluid secretion
  • ↑ Androgen receptors —> ↑ FSH receptors
31
Q

What hormones are produced by the testes?

A
  1. Testosterone (steroid) by Leydig cells
    • In some tissues do not exert direct effects, but are converted to dihydrotestosterone or oestrogens
  2. Oestrogens (steroid) by Sertoli and Leydig cells
  3. Inhibits (peptide hormone) by Sertoli cells
    • Feedback loop to control hormone levels
  4. Oxytocin (peptide hormone) by Leydig cells
    • Contraction of smooth muscle of the genital tract
32
Q

Steroid hormone biosynthesis

A

Acetate –> Cholesterol –> (Progesterone —> Testosterone) OR (Testosterone) —> Oestogens

33
Q

Role of testosterone

A

• Essential for spermatogenesis
– If production prevented spermatogenesis ceases
– Blocked when primary spermatocytes enter meiotic prophase

• If blood [testosterone] is low then fewer stem cells will begin cell division but the whole process will still take 74 days

34
Q

What does inhibin do?

A

Hormone secreted by Sertoli cells that inhibit the production of follicle-stimulating hormone (FSH) by anterior pituitary

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