4. Puberty And The HPG Axis

Question 1

What generally happens during puberty?

Answer 1

Accelerated somatic growth
Maturation of primary sexual characteristics
Appearance of secondary sexual characteristics
Menstruation and spermatogenesis begin

Question 2

What is thelarche?

Answer 2

The onset of breast development occurring near the beginning of puberty in girls

Question 3

What is adrenarche?

Answer 3

Maturation and increased activity of the adrenal glands prior to puberty

Question 4

What is gonadarche?

Answer 4

Activation of reproductive glands by the pituitary hormones FSH and LH

Question 5

What is menarche?

Answer 5

The onset of menstruation in puberty

Question 6

What can impact on timing of puberty?

Answer 6

Disorders of pineal gland can cause early onset puberty
Body weight in girls (released from adipose tissue)
Low body weight can cause cessation of menstruation
Varies in different areas of globe

Question 7

What is the order of female secondary sexual characteristics development?

Answer 7

9-13 years
Starts with breast bus (thelarche) and pubic hair growth
Leads to adenarche - growth spurt, onset of menstrual
Menstrual cycle begin (menarche) - pubic hair adult, breasts adult

Question 8

What is the order of male secondary sexual characteristics development?

Answer 8

10-14 years
Starts with genital development
Progresses to pubic hair growth and spermatogenesis
Completed by growth spurt, genitalia adult, pubic hair adult

Question 9

What does accelerate somatic growth depend on?

Answer 9

Growth hormone and IGF-1 and sex steroids

Question 10

What does the hypothalamus and pituitary control in terms of reproduction?

Answer 10

Reproductive glands (hypothalamic-pituitary-gonadal axis HPG)
Also control somatic growth, lactation, milk secretion and water metabolism

Question 11

What does the HPG axis control?

Answer 11

Puberty initatied by the brain
Nocturnal GnRH pulsatility (LH secretion) precedes phenotypic changes by several years
Phenotypic changes
Onset of puberty associated with steady rise in FSH and LH secretion

Question 12

What does GnRH regulate?

Answer 12

Puberty onset, sexual development and ovulatory cycles

Question 13

What does GnRH secretion stimulate?

Answer 13

Anterior pituitary gland gonadotrophs to secrete FSH and LH

Question 14

What is the negative feedback in puberty?

Answer 14

Hypothalamus releases GnRH
Stimulates pituitary to release LH and FSH
Stimulates gonads to produce androgens and oestrogen
Which negatively feedback to hypothalamus to stop produces GnRH

Question 15

What does LH stimulate in males?

Answer 15

Stimulates leydig cells in testis
Produce steroid hormone testosterone
Once production starts in the medium long-term testosterone levels remain constant

Question 16

What does FSH stimulate in males?

Answer 16

Sertoli cells for spermatogenesis

Question 17

Where are leydig cells located?

Answer 17

In interstitial tissue of testis

Question 18

What are seminiferous tubule cells lined by?

Answer 18

Complex epithelium made of 2 cell types - supporting cells (Sertoli cells) and spermatogenic cells/germ cells

Question 19

What does FSH stimulate in females?

Answer 19

Granulosa cells

Question 20

What are granulosa cells function?

Answer 20

Follicular development

• releases inhibin, specifically inhibits FSH only
• granulosa cells convert androgens to oestrogen

Question 21

What does LH stimulate in females?

Answer 21

Theca interna cells

Question 22

What do theca interna cells do?

Answer 22

Releases androgens, converted to oestrogen by granulosa cells

Question 23

What does LH maintain?

Answer 23

Corpus luteum after ovulation
Releases progesterone and oestrogen
Lasts 12-14 days unless further stimulated by pregnancy hormone beta-hCG

Question 24

What do moderate amounts of oestrogen do to GnRH secretion?

Answer 24

Reduce GnRH secretion - negative feedback

Question 25

What do high amounts of oestrogen do to GnRH secretion?

Answer 25

Promotes GnRH secretion - positive feedback, LH surge

Question 26

What effects does progesterone have on oestrogen?

Answer 26

Increases inhibitory effects of moderate oestrogen
Prevents positive feedback of high oestrogen
No LH surge

Question 27

What is the role of inhibin on FSH in females?

Answer 27

From granulosa cells of corpus luteum
Inhibits secretion of FSH
Has a small inhibitory effect on LH

Question 28

What does growth hormone secretion from pituitary do?

Answer 28

Increases TSH
Increases metabolic rate
Promotes tissue growth
Increase androgens - retention of minerals in body to support bone and muscle growth

Question 29

What is the role of leptin?

Answer 29

Signal information about energy stores to CNS

Can accelerate onset of reproductive function

Question 30

What is central precocious puberty?

Answer 30

Precocious puberty with elevated GnRH levels

Question 31

What are the causes of central precocious puberty?

Answer 31

Idiopathic or constitutional
CNS lesions
Pituitary gonadotropin secreting tumours
System conditions - tuberous sclerosis, neurofibromatosis
Obesity related

Question 32

What is the pathophysiology of central precocious puberty?

Answer 32

Premature activation of the hypothalamo-hypophyseal axis
Leads to abnormally early initiation of pubertal changes
Leads to early development of secondary sexual characteristics and gonadarche

Question 33

What is peripheral precocious puberty?

Answer 33

Precocious puberty without elevated GnRH levels

Question 34

What causes peripheral precocious puberty?

Answer 34

Increased androgen production (ovarian cyst, adrenal hyperplasia, leydig-cell tumour)
Increased oestrogen production (HCG secreting germ cell tumours)
Increased beta-HCG production
Primary hypothyroidism
Obesity

Question 35

What is delayed onset of puberty?

Answer 35

Absent or incomplete development of secondary sex characteristics by the age of 14 in boys or 13 in girls

Question 36

What can cause delayed onset of puberty?

Answer 36

Constitutional growth delay
Malnutrition and other chronic diseases
Hypogonadism