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ESA 3 - Reproductive System > The neuroendocrine timing of puberty > Flashcards

The neuroendocrine timing of puberty Flashcards

1
Q

What is puberty?

A

A stage of human development when sexual maturation and growth are completed and result in the ability to reproduce.
These are morphological, physiological and behavioural development.

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2
Q

When does puberty start?

A

NOT at same age but, same weight - 47kg for women

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3
Q

When does breast bud and pubic har start to grow?

A

9-13 years.

A small growth spurt also occurs

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4
Q

What chances occur in girls during puberty?

A

Breast buds (thelarch)
Pubic hair growth (T) Growth spurt
Onset of menstruation (menarche)

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5
Q

When do boys enter pubity?

A

10-14 years

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6
Q

What is the first sign of puberty in boys?

A

Genital development - increase in penis length

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7
Q

What puberty changes occur in boys?

A 
Genital development
Pubic hair growth
Spermatogenesis
Growth spurt
Genitalia adult 
Pubic hair adult
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8
Q

Why do boys grow for longer?

A

More testosterone.

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9
Q

What causes the fusing of the growth plates and end in growing?

A

Oestrogen.

Girls have more oestrogen so closes sooner so girls are shorter.

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10
Q

Why does puberty happen earlier now?

A

Better diet, reach 47kg earlier, less significant weight loss.
Leptin may be involved in signalling.

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11
Q

What is the average age puberty start in boys?

A

12.5yrs old (10-14)

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12
Q

What is the average age puberty start in girls?

A

11.5yrs old (9-13)

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13
Q

How does puberty occur?

A

Hypothalamus releases GnRH
Causes pituitary to release LH and FSH
This results in the gonads secreting androgens and oestrogen’s.

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14
Q

What are the characteristics of GnRH?

A
  • Secretion in pulses tied to internal biological clock
  • Act on specific membrane receptors
  • Transduce signals via second messengers
  • Stimulate release of stored pituitary hormones
  • Stimulates hyperplasia and hypertrophy of target cells
  • Regulates its own receptor.
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15
Q

What environmental influences trigger GnRH?

A

Sensitive to light. GnRH is always first released at night.

Pineal tumours can influence puberty in humans. (pineal gland produces melatonin)

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16
Q

What gene responsible for puberty?

A

GnRH-1 gene. This is primarily responsible for mammalian GnRH.

17
Q

Describe pulsitility of GnRH

A
  • Released every 1-3 hours
  • -Intensity of GnRH stimulus is affected by
  • -Frequency of release
  • -Intensity of release
  • GnRH travels to pituitary in hypophyseal portal system.
18
Q

When does LH increase in males?

A

At night. This stimulates a nocturnal rise of Testosterone.
This androgen levels increase could account for some of the early pubertal changes seen in males.
(similar in females with oestrogen)

19
Q

What type of feedback loop is the HPG axis

A

Negative.
Androgen and Oestrogen production inhibit GnRH which then inhibits the other hormones. But, then levels are low so GnRH is stipulated.

20
Q

In males, what does LH do?

A

LH stimulates Leydig cells in testes.
Produce stored hormone (from cholesterol) Testosterone.
The greatest amount of testosterone is produced in the testes.
Once production starts, the long term levels of testosterone remain constant.

21
Q

What changes the levels of testosterone?

A
  • Circadian rhythm - highest in early morning

- Environmental stimuli - driven by brain.

22
Q

What effect does oestrogen have on GnRH secretion?

A

High oestrogen = more GnRH = LH ‘surge’ - Positive feedback

If moderate oestrogen - reduced GnRH secretion - negative feedback

23
Q

What influences when the growth spurt starts?

A

It depends on growth hormone + IGF-1 snd sex steroids in both sexes.

24
Q

What hormones are produced by the anterior pituitary?

A
  • Prolactin
  • Growth hormone (GH)
  • Thyroid stimulating hormone (TSH)
  • Adenocorticotropic hormone (ACTH)
  • FSH
  • LH
25
Q

What is the structure of the testes?

A

Each lobule contains 1-4 seminiferous tubules (ST) which are about 60cm long and make up about 90% of the testicular volume. These tubules are also the location for spermatogenesis.
In between, loose CT and Blood vessels. This contains Leydig cells that produce testosterone.
The Leydig cells function independently of ST but, ST needs functioning Leydig cells.

26
Q

What is cells are the seminiferous tubules made from?

A

Lined by complex epithelium made of Sertoli cells and germ cells.

27
Q

What are the roles of Sertoli cells?

A

Nutrition and hormonal support to germ cells - sperm formation
Sensitive to FSH which increases sperm production
Secreted inhibit feedback on AP FSH.
Sertoli cells are connected by tight functions to ensure they are sealed/

28
Q

What do FSH and LH do in females?

A

Act primarily on gonads via G Alpha S -> PCR -> adenylate cyclase.

Target ovarian granulose cells, theca interna.

  • Stimulate sex hormone synthesis (steroidgenesis)
  • Control gamete production (folliculogenesis and ovulation)
29
Q

What do granulosa cells respond to?

A

FSH

30
Q

What do Theca cells respond to?

A

LH

31
Q

What effect does progesterone have on FSH and LH?

A

Progesterone increase inhibitory effect of moderate oestrogen.

It also prevents the positive feedback of high oestrogen so there is no LH surge.

32
Q

How do oestrogen and progesterone affect GnRH?

A

Oestrogen reduces the amount of GnRH per pulse and progesterone increases the frequency of pulses.

33
Q

What effect does inhibin have on FSH?

A

Inhibin comes from the granulosa cells of the corpus letup and inhibits the secretion of FSH (just like in males).
It also has a small inhibitory effect on LH.

34
Q

How does a growth spurt occur?

A

GH secretion from pituitary:

  • Increases TSH
  • Increases metabolic rate
  • Promotes tissue growth
  • Increases androgens (retention of minerals in the body to support bone and muscle growth)

This causes a growth spurt

35
Q

What is leptin?

A

An adipocyte-derived protein hormone.

It has a pulsatile release pattern significantly associated with the variations in LH

36
Q

What does leptin do?

A

Signals information about energy stores to the CNS.

It has an important role in regulating neuroendocrine function:

  • -There is reproductive dysfunction associated with leptin deficiency
    • Leptin can accelerate the onset of reproductive function

Can regulate GnRH levels - its secretions may be influenced by gonadal steroids but appear independent of LH control.

ESA 3 - Reproductive System (20 decks)

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