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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?

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
How can tracking the LH surge be helpful in IVF treatment?
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
Formation of the corpus luteum occurs under the influence of LH/FSH?
LH
27
What happens to granulosa and theca cells during the luteal phase?
They lose their specialisation and all become luteal cells
28
What is the function of luteal cells?
Convert cholesterol to progesterone
29
How does LH increase progesterone secretion from the corpus luteum? (2)
- 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
When LH drops once the egg has implanted, which hormone takes over control of progesterone production from the corpus luteum?
hCG produced by the embryo | hCG = human chorionic gonadotropin
31
List 4 functions of oestrogens in females
- 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
List 3 functions of progesterone in females | hint: "pro-gestation"
- 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
How is progesterone thought to regulate birth?
Functional withdrawal of progesterone is thought to regulate smooth muscle contractions of the myometrium
34
How is rigidity (i.e., width) of the cervical canal determined?
By collagen in the cervical wall
35
Which cells of the cervical canal produce cervical mucus?
Columnar epithelium cells
36
A sperm's ability to penetrate cervical mucus is regulated by... (4)
- 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
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?
Weaker sperm will swim into the grooves to avoid the thick mucus and immune cells in the cervical canal
38
Which hormones are involved in spermatogenesis?
LH, FSH and testosterone
39
How many days does it take to complete spermatogenesis?
~70 days
40
Spermatogenesis begins in the womb and continues for 60+ years. T/F
False Spermatogenesis first occurs at puberty and continues for 60+ years
41
``` Humans produce ~1000 sperm per... - Heartbeat - Minute - Hour - Day ? ```
Heartbeat
42
Describe the structure of the seminiferous tubules in the testes
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
As the spermatocytes undergo spermatogenesis, they move from the outside/inside to the inside/outside of the tubule
As the spermatocytes undergo spermatogenesis, they move from the outside to the inside of the tubule
44
How does FSH influence spermatogenesis?
FSH stimulates sertoli cells in the seminiferous tubules to drive spermatogenesis and produce androgen binding globulin (ABG) (fSh, Sertoli cells, Spermatogenesis)
45
How does LH influence spermatogenesis?
LH stimulates Leydig cells in the interstitium to produce testosterone
46
How does the testosterone produced by Leydig cells influence spermatogenesis?
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
Why is testosterone content in the testes 25-125x greater than in the serum?
Testosterone binds to androgen binding globulin (ABG) produced by sertoli cells
48
What is meant by 'the blood-testes barrier'?
A layer of peritubular myoid cells that separate the seminiferous tubules from the interstitium
49
What is the function of the blood-testes barrier?
It separates sperm from immune cells in the blood stream
50
Why should immune cells be separated from the sperm?
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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