Hormonal Regulation of Puberty

Question 1

What is puberty?

Answer 1

Transient, endpoint is the production of viable gametes. Orderly sequence of physiological, anatomical and social landmarks.
Occurs at different ages - affected by external factors.

Question 2

What 4 changes occur?

Answer 2

1) Adolescent growth spurt - skeleton, muscle, viscera.
2) Sex specific increase in growth rate - phenotypic sexual dimorphism
3) Changes in body composition - especially muscle and fat.
4) Development of reproductive function - gonadal activity, secondary sexual characteristics.

Question 3

Tanner scale?

Answer 3

5 stages of physical development - based on measurements of primary and secondary sexual characteristic - breasts/genital development, pubic hair.

Question 4

Androgens?

Answer 4

Steroid hormones that stimulate MALE physical and reproductive characteristics.
Testosterone - primary biological androgen from testes and adrenal gland.
Can be converted to oestrogens.

Question 5

Oestrogens?

Answer 5

Steroid hormone. Primary reproductive FEMALE hormone.
In non pregnant females - primary oestrogen is oestradiol.
Synthesised from androgens - released by ovaries.

Question 6

What are the 2 main events that can cause an increase in reproductive hormones and subsequent pubertal changes?

Answer 6

Adrenarche and the HPG axis.

Question 7

Adrenarche?

Answer 7

Increased adrogens from…
…adrenal cortex (zona reticularis), release weak androgens - DHEA, DHEA sulphate and androsterledione.
Peripheral conversion to testosterone = pubic and axillary hair, sweat and BO, increase oiliness of skin.
…from testis - facial hair.

Question 8

Explain the HPG axis.

Answer 8

Hypothalamus, pituitary, gonadal axis!

Hypothalamus (+) GnHR to the AP, (+ve) LH and FSH to the ovary testes - eggs/sperm.

-ve feedback to AP and hypothalamus.

Steroids.

Question 9

Kisspeptin?

Answer 9

GnRH stimulated by kisspeptin (can trigger early puberty), kisspeptin (kiss1 gene) binds to GPR54.

Question 10

Hypogonadotropic hypogonadism?

Answer 10

Impaired pubertal maturation therefore lack of reproductive function.

Question 11

LH?

Answer 11

males - stimulates production of testosterone.

Females - controls ovarian cycle and ovulation - stimulates oestrogens.

Question 12

FSH?

Answer 12

Males: Stimulates growth and maturation of testes and spermatogenesis.
Females: stimulates growth and maturation of follicles.

Question 13

Explain LH levels at different stages through puberty.

Answer 13

Pre: low
Mid: night time increased in LH
late: regular pulses of LH throughout the day and night.

Question 14

What is testis volume proportional to?

Answer 14

[plasma testosterone]

Question 15

Menarche?

Answer 15

1st ovarian cycle - frequent post menarcheal variations.
Anovulatory.
Missing luteal phase.
Varying [oestrogen] from follicles.

Take several years for regular cycling.

Question 16

Growth spurts?

Answer 16

Growth plates generates new bone longditundially and extend in length rapidly.
At the end, the epiphyseal growth plastes fuses into the bone to prevent extension in adulthood.

Question 17

Role of oestrogen in growth?

Answer 17

Oestrogen stimulates it but the concentration is critical.

If oestrogen receptor deficient - tall, unfused epiphyses, continued growht and osteoporosis.

Question 18

How does sexual dimorphism develop?

Answer 18

From changes in body composition.
Levels of oestrogen/testosterone in females/males causes changes in structures - hips/jaws.

Boys - increase muscle mass.
Girls - increase body fat (sensitivity of fat cells).