20. Physiology of puberty Flashcards
Disorders and syndromes of puberty
Disorders of Puberty
Premature Puberty
Delayed Puberty
Syndromes
Klinefelter Syndrome
Turner Syndrome
Definition of puberty
Definition:
The stage of physical maturation in which an individual becomes physiologically capable of pro-creation (sexual reproduction)
Physical changes in puberty
Physical changes:
- Growth spurt
- Secondary sex characteristics
- Menarche/spermatogenesis
Physical changes in girls
GROWTH SPURT 8 - 14 yrs
6 - 10 cm / yr peak
2.5 yrs duration
BREAST GROWTH 8 - 13 yrs ( 11 yrs )
(Thelarche) Usually the first sign
PUBIC HAIR 9 - 13 yrs
(Pubarche) 1st Pubertal Sign in 25%
AXILLARY HAIR 9.5 - 15 yrs
(Adrenarche) May follow menarche
MENSTRUATION 10 - 16 yrs ( 13 yrs )
(Menarche)
Signs of puberty in boys
In boys, first sign of puberty is testicular size - testicular volume of 4 is about start of puberty
Growth spurt later in boys than girls, can grow 12-14cm in a year.
Axillary or pubic hair is not true puberty until see testicular volume of 4ml or above.
Endocrine changes in puberty - prepuberty
H-P-G synchrony – established in fetal life
Until puberty – neural mechanisms suppress GnRH release
At 6-9 yrs – pulsatile nocturnal GnRH release
Mini-puberty in babies - HPG axis becomes synchronous, gets ready for later maturation
Need LHRH test
How does FSH and LH change in puberty and what are the conseuqences
Pulsatile GnRH release (nocturnal) every 90-120 min - 6 to 9 y
increase in GnRH leads to increase in FSH and increase in LH
Ovaries/testes become sensitized to the effects of FSH and LH
Final phase: development of positive/negative feedback mechanism
What results in hair growth at puberty?
ACTH stimulates the adrenals – Pubic & Axillary hair
What is the role of the testes?
Production of gametes (sperms)
Sertoli cells under FSH control
Production of androgens (Testosterone)
Leydig cells under LH control
95% from testes, 5% from adrenals
Testosterone in blood – converted to DHT in the target organs
Testosterone is converted to oestrogen which acts on the long bones resulting in bone growth
The ovarian cycle
Follicular phase
Initially E rises (FSH) with LH surge in mid cycle
Ovulation occurs
Luteal phase
Negative feedback after ovulation
No further ovulation in the same cycle
Age of menarche
Related to general health, genetic and nutritional factors
Mean age is falling at a rate of 4 months per decade
- Mean age in 1840 = 16.5 y; 1990 = 12.8 y
One in 8 girls now reaches menarche while at primary school
Body weight and % fat is also important
- Mean weight at menarche is 47.8kg
- 16-24% fat
- Athletes, patients with anorexia – late onset
What is adrenarche?
Adrenal androgens – responsible for axillary and pubic hair
ACTH stimulates zona reticularis of adrenal cortex
DHEAS & Androstenedione:
Girls – starts by 6, adequate levels by 8
Boys – starts by 8, adequate levels by 10
Test with urine steroid profile test
Chronological order of puberty in girls
Growth spurt Breast development Pubic hair Axillary hair Menarche
Chronological order of puberty in boys
Testicular volume Penile length Pubic hair Growth spurt Axillary / Facial hair Deep voice
When is puberty considered early or precocious?
Girls – under 8 yrs
Boys – under 9 yrs
When is puberty considered delayed?
Girls – over 14 yrs
Boys – over 14 yrs
But if there is no breast budding at all by 13 then investigate for treatment because it means androgens aren’t working
Precocious puberty
Early or Premature puberty
Presence of true pubertal features at an young & inappropriate age
Central or True precocious puberty
Gonadotrophin dependent
Peripheral or Pseudo-precocious puberty
Gonadotrophin independent
Normal variants
Premature Thelarche
Premature Adrenarche
Central or true precocious puberty
Gonadotrophin dependent
Peripheral or pseudo-precocious puberty
gonadotrophin independent
Concerns raised by early onset
Possible underlying sinister cause
- Boys – upto 80%
Emotional & pyscho-social upheaval at an inappropriately young age
Early cessation of growth leading to decreased final adult height
Central precocious puberty
Long acting LHRH analog therapy
- Sustained supra-physiological LHRH levels
- Paradoxical cessation of gonadotrophin release
- Stops further pubertal progression
Pubertal progression resumes when treatment stopped (at 10-12 yrs)
Normal variants
Premature thelarche
Isolated breast development
Usually seen in children <2-3 yrs of age
Premature adrenarche
Isolated pubic hair development
Caution: first sign of puberty in some
And . . .
Pseudo-precocious puberty in males
Iso-sexual or masculinising
CAH, Adrenal/Leydig cell tumor
Hetero-sexual or feminising
Adrenal
Pseudo-precocious puberty in females
Iso-sexual or feminising
MAS, Ovarian/Adrenal
Hetero-sexual or masculinising
CAH, Ovarian/Adrenal
