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Repro > 4. Puberty And The -HPG Axis > Flashcards

4. Puberty And The -HPG Axis Flashcards

1
Q

What is puberty?

A

A stage of human development when sexual maturation and growth are completed and result in ability to reproduce.

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2
Q

What type of tumours can influence puberty in humans?

A

Pineal tumours.

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3
Q

What is the critical weight for puberty to begin in girls?

A

47kg.

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4
Q

In what order do secondary sexual characteristics develop in females?

A

9-13 years - breast but and pubic hair growth, growth spurt and onset of menstruation, pubic hair adult and breasts adult.

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5
Q

Under the influence of what hormones do girls start to develop secondary sexual characteristics?

A

Oestrogen and testosterone (increased oestrogen in puberty).

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6
Q

Under the influence of what hormone do boys begin to develop secondary sexual characteristics?

A

Testosterone anabolic androgenic steroid.

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7
Q

In what order do secondary sexual characteristics develop in boys?

A

10-14 years - genital development, pubic hair growth and spermatogenesis, growth spurt, genitalia adult and pubic hair adult.

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8
Q

What scale is used to measure how far into puberty boys and girls are?

A

Tanner scale (I-V).

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9
Q

What hormones does accelerated somatic growth depend on in both sexes?

A

Growth hormone and sex steroids.

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10
Q

What differences are seen in accelerated somatic growth between girls and boys?

A

Earlier and shorter in girls.

Growth spurt longer and slightly faster resulting in men being larger.

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11
Q

What is accelerated somatic growth ended by in both sexes?

A

Epiphyseal fusion.

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12
Q

Why is accelerated somatic growth ended earlier in females?

A

Oestrogen closes the epiphysis earlier in girls.

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13
Q

Does the duration of puberty tend to be shorter in girls or boys?

A

Girls.

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14
Q

What happens in increased stimulation of the hypothalamus-pituitary-gonadal axis at the onset of puberty?

A

Gradual activation of GnRH, increases the frequency and amplitude of LH and FSH pulses, stimulates secretion of sexual steroids (oestrogen and androgens), causes extragonadal hormone changes (elevation of IGF-1 and adrenal steroids).

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15
Q

What cells in the anterior pituitary produce both LH and FSH?

A

Gonadotrophs.

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16
Q

What interacts with the hypothalamus and affects the release of GnRH at the start of puberty?

A

Leptin.

Photoperiod.

17
Q

How do hormonal changes in puberty lead to a growth spurt?

A

Growth hormone secretion from the pituitary, increases TSH, increasing metabolic rate. This promotes tissue growth and increased androgens leads to the retention of minerals in the body to support bone and muscle growth.

18
Q

How does GnRH travel from the hypothalamus to the pituitary?

A

In the hypophysial portal system.

19
Q

What is the function of leptin?

A

Is an adipocyte-derived protein hormone that signals information bout energy stores to the CNS.

20
Q

What 3 hormones are produced by the anterior pituitary and are most significant for reproduction?

A

Prolactin.
LH.
FSH.

21
Q

What stimulates a nocturnal rise of testosterone in boys, and oestrogen in girls?

A

Sleep related LH increase.

22
Q

In humans, what precedes the phenotypic changes of puberty by several years?

A

Nocturnal GnRH pulsatility (and LH secretion).

23
Q

Most parts of the reproductive system can work before normal age, so by don’t they?

A

Hormone levels are too low due to low GnRH secretion.

24
Q

What type of feedback loop in the hypothalamic-pituitary-gonadal axis ensures GnRH and therefore LH and FSH production is pulsatile?

A

Negative feedback from androgens and oestrogen on the hypothalamus.

25
Q

What cells does LH stimulate in males? What do they produce?

A

Leydig cells in the interstitial tissue of the testis to produce testosterone.

26
Q

Once production of testosterone starts in males, the medium long term testosterone levels remain constant, but what 2 things have a slight affect?

A

Circadian rhythm - highest in the early morning.

Environmental stimuli - driven by the brain.

27
Q

The seminiferous tubule cells of the testis need what to function?

A

Functioning leydig cells.

28
Q

What cells in the testis are sensitive to FSH and secrete inhibit to have a negative feedback affect on the HPG axis and FSH production?

A

Sertoli cells in the seminiferous tubules.

29
Q

What is the role of Sertoli cells in the seminiferous tubule of the testis?

A

Provide nutrition and hormonal support to germ cells allowing sperm formation.

30
Q

Where in the seminiferous tubules of the testis are Sertoli cells and germ cells found?

A

Epithelium.

31
Q

What cells provide the tight testis blood barrier to stop sperm entering the blood?

A

Sertoli cells.

32
Q

Via what enzyme do FSH and LH act on the ovaries?

A

Galpha s PCR - adenylate cyclase.

33
Q

What are the target cells of FSH and LH in females?

A

Ovarian granuloma cells and theca interna.

34
Q

What is the action of LH and FSH on their target cells in the ovary?

A

Stimulate oestrogen, progesterone and inhibit synthesis.

Control gamete production (folliculogenesis and ovulation).

35
Q

Where in the ovary is the site of progesterone release?

A

Degenerating follicle.

36
Q

What affect do moderate titres of oestrogen have on GnRH secretion? What affect does progesterone have on this?

A

Negative feedback.

Progesterone increases the inhibitory affects of the moderate oestrogen.

37
Q

What affect do high titres of oestrogen have on GnRH secretion? What affect does progesterone have on this?

A

Positive feedback, leading to an LH surge.

Progesterone prevents the positive feedback of high oestrogen, to block the LH surge.

38
Q

From what cells in the ovary is inhibin released?

A

Granuloma cells of the corpus luteum of degenerating follicles.

39
Q

What affect does inhibin have on LH and FHS in females?

A

Inhibits FSH secretion (same as in males).

Also has a small inhibitory effect on LH.

Repro (18 decks)

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