4. Puberty And The -HPG Axis

Question 1

What is puberty?

Answer 1

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

Question 2

What type of tumours can influence puberty in humans?

Answer 2

Pineal tumours.

Question 3

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

Answer 3

47kg.

Question 4

In what order do secondary sexual characteristics develop in females?

Answer 4

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

Question 5

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

Answer 5

Oestrogen and testosterone (increased oestrogen in puberty).

Question 6

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

Answer 6

Testosterone anabolic androgenic steroid.

Question 7

In what order do secondary sexual characteristics develop in boys?

Answer 7

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

Question 8

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

Answer 8

Tanner scale (I-V).

Question 9

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

Answer 9

Growth hormone and sex steroids.

Question 10

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

Answer 10

Earlier and shorter in girls.

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

Question 11

What is accelerated somatic growth ended by in both sexes?

Answer 11

Epiphyseal fusion.

Question 12

Why is accelerated somatic growth ended earlier in females?

Answer 12

Oestrogen closes the epiphysis earlier in girls.

Question 13

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

Answer 13

Girls.

Question 14

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

Answer 14

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).

Question 15

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

Answer 15

Gonadotrophs.

Question 16

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

Answer 16

Leptin.

Photoperiod.

Question 17

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

Answer 17

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.

Question 18

How does GnRH travel from the hypothalamus to the pituitary?

Answer 18

In the hypophysial portal system.

Question 19

What is the function of leptin?

Answer 19

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

Question 20

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

Answer 20

Prolactin.
LH.
FSH.

Question 21

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

Answer 21

Sleep related LH increase.

Question 22

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

Answer 22

Nocturnal GnRH pulsatility (and LH secretion).

Question 23

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

Answer 23

Hormone levels are too low due to low GnRH secretion.

Question 24

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

Answer 24

Negative feedback from androgens and oestrogen on the hypothalamus.

Question 25

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

Answer 25

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

Question 26

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

Answer 26

Circadian rhythm - highest in the early morning. | Environmental stimuli - driven by the brain.

Question 27

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

Answer 27

Functioning leydig cells.

Question 28

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?

Answer 28

Sertoli cells in the seminiferous tubules.

Question 29

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

Answer 29

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

Question 30

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

Answer 30

Epithelium.

Question 31

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

Answer 31

Sertoli cells.

Question 32

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

Answer 32

Galpha s PCR - adenylate cyclase.

Question 33

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

Answer 33

Ovarian granuloma cells and theca interna.

Question 34

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

Answer 34

Stimulate oestrogen, progesterone and inhibit synthesis. | Control gamete production (folliculogenesis and ovulation).

Question 35

Where in the ovary is the site of progesterone release?

Answer 35

Degenerating follicle.

Question 36

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

Answer 36

Negative feedback. | Progesterone increases the inhibitory affects of the moderate oestrogen.

Question 37

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

Answer 37

Positive feedback, leading to an LH surge. | Progesterone prevents the positive feedback of high oestrogen, to block the LH surge.

Question 38

From what cells in the ovary is inhibin released?

Answer 38

Granuloma cells of the corpus luteum of degenerating follicles.

Question 39

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

Answer 39

Inhibits FSH secretion (same as in males). | Also has a small inhibitory effect on LH.