The neuroendocrine timing of puberty

Question 1

What is puberty?

Answer 1

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.

Question 2

When does puberty start?

Answer 2

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

Question 3

When does breast bud and pubic har start to grow?

Answer 3

9-13 years.

A small growth spurt also occurs

Question 4

What chances occur in girls during puberty?

Answer 4

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

Question 5

When do boys enter pubity?

Answer 5

10-14 years

Question 6

What is the first sign of puberty in boys?

Answer 6

Genital development - increase in penis length

Question 7

What puberty changes occur in boys?

Answer 7

Genital development
Pubic hair growth
Spermatogenesis
Growth spurt
Genitalia adult 
Pubic hair adult

Question 8

Why do boys grow for longer?

Answer 8

More testosterone.

Question 9

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

Answer 9

Oestrogen.

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

Question 10

Why does puberty happen earlier now?

Answer 10

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

Question 11

What is the average age puberty start in boys?

Answer 11

12.5yrs old (10-14)

Question 12

What is the average age puberty start in girls?

Answer 12

11.5yrs old (9-13)

Question 13

How does puberty occur?

Answer 13

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

Question 14

What are the characteristics of GnRH?

Answer 14

• 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.

Question 15

What environmental influences trigger GnRH?

Answer 15

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

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

Question 16

What gene responsible for puberty?

Answer 16

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

Question 17

Describe pulsitility of GnRH

Answer 17

• 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.

Question 18

When does LH increase in males?

Answer 18

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)

Question 19

What type of feedback loop is the HPG axis

Answer 19

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

Question 20

In males, what does LH do?

Answer 20

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.

Question 21

What changes the levels of testosterone?

Answer 21

• Circadian rhythm - highest in early morning

- Environmental stimuli - driven by brain.

Question 22

What effect does oestrogen have on GnRH secretion?

Answer 22

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

If moderate oestrogen - reduced GnRH secretion - negative feedback

Question 23

What influences when the growth spurt starts?

Answer 23

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

Question 24

What hormones are produced by the anterior pituitary?

Answer 24

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

Question 25

What is the structure of the testes?

Answer 25

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.

Question 26

What is cells are the seminiferous tubules made from?

Answer 26

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

Question 27

What are the roles of Sertoli cells?

Answer 27

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/

Question 28

What do FSH and LH do in females?

Answer 28

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)

Question 29

What do granulosa cells respond to?

Answer 29

FSH

Question 30

What do Theca cells respond to?

Answer 30

LH

Question 31

What effect does progesterone have on FSH and LH?

Answer 31

Progesterone increase inhibitory effect of moderate oestrogen. It also prevents the positive feedback of high oestrogen so there is no LH surge.

Question 32

How do oestrogen and progesterone affect GnRH?

Answer 32

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

Question 33

What effect does inhibin have on FSH?

Answer 33

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.

Question 34

How does a growth spurt occur?

Answer 34

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

Question 35

What is leptin?

Answer 35

An adipocyte-derived protein hormone. | It has a pulsatile release pattern significantly associated with the variations in LH

Question 36

What does leptin do?

Answer 36

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.