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LR Endocrine > Reproductive Axis > Flashcards

Reproductive Axis Flashcards

1
Q

Which hormone does the hypothalamus secrete in control of the reproductive axis?

A

Gonadotropin releasing hormone (GnRH)

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2
Q

Name the two gonadotropic hormones secreted by the anterior pituitary in response to GnRH

A

Follicle stimulating hormone (FSH)

Luteinising hormone (LH)

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3
Q

What is the function of FSH and LH in males? (1 for each)

A

FSH: causes the testes to produce sperm (spermatogenesis)

LH: causes the testes to secrete testosterone

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4
Q

What is the function of FSH and LH in females? (2 for each)

A

FSH:

  • causes growth of ovarian follicles (oogenesis)
  • causes ovaries to secrete oestrogen

LH:

  • causes ovulation
  • causes progesterone production by the corpus luteum
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5
Q

Which cells in the hypothalamus secrete GnRH?

A

GnRH neurons

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6
Q 
Which of the following is true:
GnRH is released from GnRH neurons...
- diurnally
- in a pulsatile manner
- overnight
?
A

In a pulsatile manner

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7
Q

How is GnRH release regulated?

A

Oestrogen and progesterone act on kisspeptin neurons which act on GnRH neurons (both in the hypothalamus)

This regulates frequency of GnRH release

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8
Q

Oestrogen causes high/low frequency GnRH pulses

Progesterone causes high/low frequency GnRH pulses

A

Oestrogen causes high frequency GnRH pulses

Progesterone causes low frequency GnRH pulses

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9
Q

High frequency GnRH pulses cause FSH/LH release

Low frequency GnRH pulses cause FSH/LH release

A

High frequency GnRH pulses cause LH release

Low frequency GnRH pulses cause FSH release

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10
Q

How does frequency of GnRH pulses differ between males and females?

A

Males: GnRH pulses at constant frequency

Females: Frequency of GnRH pulses varies during menstrual cycle

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11
Q

Describe the two phases of the menstrual cycle

A

Follicular phase:

  • FSH causes follicles to grow and secrete oestrogen
  • Once threshold of oestrogen is crossed, LH surge at end of phase causes ovulation
  • Length of this phase can vary

Luteal phase:

  • LH causes the corpus luteum to produce progesterone
  • Length of this phase is fixed at ~14 days
  • Progesterone peak ~half way through
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12
Q

Describe GnRH pulse frequency in the follicular phase of the menstrual cycle

A
  • FSH release is high at first, stimulating follicle growth
  • Growing follicle produces oestrogen which increases frequency of GnRH pulses
  • Increased GnRH frequency increases LH secretion and reduces FSH secretion
  • LH surge causes ovulation
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13
Q

Describe GnRH pulse frequency in the luteal phase of the menstrual cycle

A
  • Corpus luteum produces progesterone

- This reduces GnRH pulse frequency which lowers LH and increases FSH secretion

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14
Q

How does FSH cause the follicle to grow? (2)

A
  • Increases number of follicular cells surrounding the oocyte
  • Increases accumulation of follicular fluid
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15
Q

How do oestrogen and progesterone affect the endometrium itself?

A

Follicular phase: Increased oestrogen thickens the endometrium

Luteal phase: Increased progesterone makes the endometrium a secretory tissue (important for egg implantation)

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16
Q

Name the specialised follicle cells surrounding an oocyte which LH and FSH act on

Which hormone acts on which cell?

A

LH acts on outer Theca cells

FSH acts on inner Granulosa cells

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17
Q

Describe the function of theca cells

A

Convert cholesterol to androgens under the influence of LH

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18
Q

Describe the function of granulosa cells

A

Convert the androgens from the theca cells to oestrogens under the influence of FSH

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19
Q

Which enzyme converts androgens to oestrogens in granulosa cells?

A

Aromatase

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20
Q

Number of follicles in the ovaries increases up until puberty. T/F

A

False

Primordial pool of follicles in each ovary forms before birth

The number of follicles decreases up to puberty -
Primordial pool: 7 million
Birth: 2 million
Puberty: 0.5 million

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21
Q

Early stages of follicle growth are gonadotropin-independent. When does follicle growth start the rely on FSH?

A

When it forms a fluid-filled antrum (when it’s ~2-5mm diameter)

22
Q

How many follicles grow under the influence of FSH per cycle?

A

~7

23
Q

Why does only 1 growing follicle take part in ovulation?

A

Dip in FSH at time of LH surge means that only the dominant follicle goes through ovulation as it can cope with the FSH decrease

24
Q

What features of the dominant follicle make it most likely to survive the FSH decrease? (3)

A
  • Largest
  • Most FSH receptors
  • Highest vascularity
25
Q

How can tracking the LH surge be helpful in IVF treatment?

A

LH surge precedes ovulation by ~34-36 hours

In IVF, the follicles should be removed after the LH surge but before release of the oocyte

26
Q

Formation of the corpus luteum occurs under the influence of LH/FSH?

A

LH

27
Q

What happens to granulosa and theca cells during the luteal phase?

A

They lose their specialisation and all become luteal cells

28
Q

What is the function of luteal cells?

A

Convert cholesterol to progesterone

29
Q

How does LH increase progesterone secretion from the corpus luteum? (2)

A
  • Stimulates angiogenesis which diverts cholesterol to the corpus luteum (to be used as a substrate for progesterone synthesis)
  • Stimulates enzymes involved in conversion of cholesterol to progesterone
30
Q

When LH drops once the egg has implanted, which hormone takes over control of progesterone production from the corpus luteum?

A

hCG produced by the embryo

hCG = human chorionic gonadotropin

31
Q

List 4 functions of oestrogens in females

A
  • Increases thickness of vaginal wall (to support implantation)
  • Regulates LH surge
  • Reduces vaginal pH through increased lactic acid production
  • Decreases viscosity of cervical mucous to facilitate sperm penetration
32
Q

List 3 functions of progesterone in females

hint: “pro-gestation”

A
  • Maintains thickness of endometrium
  • Responsible for infertile, thick mucous (to prevent sperm transport and prevent infection)
  • Relaxes the myometrium (smooth muscle of the uterus)
33
Q

How is progesterone thought to regulate birth?

A

Functional withdrawal of progesterone is thought to regulate smooth muscle contractions of the myometrium

34
Q

How is rigidity (i.e., width) of the cervical canal determined?

A

By collagen in the cervical wall

35
Q

Which cells of the cervical canal produce cervical mucus?

A

Columnar epithelium cells

36
Q

A sperm’s ability to penetrate cervical mucus is regulated by… (4)

A
  • Thickness of mucus (hormonal control)
  • Motility of sperm (less mobile sperm will get stuck)
  • Interaction with reactive oxygen species produced by leukocytes in the mucus
  • Interactions with mucins
37
Q

The cervix also contains primary and secondary grooves which do not lead to the uterus. Why might this help select the best sperm for reproduction?

A

Weaker sperm will swim into the grooves to avoid the thick mucus and immune cells in the cervical canal

38
Q

Which hormones are involved in spermatogenesis?

A

LH, FSH and testosterone

39
Q

How many days does it take to complete spermatogenesis?

A

~70 days

40
Q

Spermatogenesis begins in the womb and continues for 60+ years. T/F

A

False

Spermatogenesis first occurs at puberty and continues for 60+ years

41
Q 
Humans produce ~1000 sperm per...
- Heartbeat
- Minute
- Hour
- Day
?
A

Heartbeat

42
Q

Describe the structure of the seminiferous tubules in the testes

A

Seminiferous tubules contain Sertoli cells and maturing germ cells

Surrounded by an extra tubular compartment of interstitial tissue i.e., Leydig cells, blood vessels, immune cells

43
Q

As the spermatocytes undergo spermatogenesis, they move from the outside/inside to the inside/outside of the tubule

A

As the spermatocytes undergo spermatogenesis, they move from the outside to the inside of the tubule

44
Q

How does FSH influence spermatogenesis?

A

FSH stimulates sertoli cells in the seminiferous tubules to drive spermatogenesis and produce androgen binding globulin (ABG)

(fSh, Sertoli cells, Spermatogenesis)

45
Q

How does LH influence spermatogenesis?

A

LH stimulates Leydig cells in the interstitium to produce testosterone

46
Q

How does the testosterone produced by Leydig cells influence spermatogenesis?

A

It crosses the blood-testes barrier, enters the seminiferous tubules and is taken up by sertoli cells for spermatogenesis (90%)

It also maintains the integrity of the blood-testes barrier

The other 10% of testosterone is released into circulation

47
Q

Why is testosterone content in the testes 25-125x greater than in the serum?

A

Testosterone binds to androgen binding globulin (ABG) produced by sertoli cells

48
Q

What is meant by ‘the blood-testes barrier’?

A

A layer of peritubular myoid cells that separate the seminiferous tubules from the interstitium

49
Q

What is the function of the blood-testes barrier?

A

It separates sperm from immune cells in the blood stream

50
Q

Why should immune cells be separated from the sperm?

A

Sperm are not produced till puberty so may be recognised as foreign cells, resulting in inflammation of the testes

LR Endocrine (12 decks)

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