Puberty and Its Disorders Flashcards
What is puberty and what happens?
- Transition from non-reproductive to reproductive state
- Secondary characteristics develop (primary present at birth)
- Adolescent growth spurt
- Profound physiological + psychological changes
- Gonads produce mature gametes (spermatozoa + oocytes)
Name the two endocrine events of puberty
- Adrenarche
- Gonadarche
Both occur independently of each other
What is adrenarche?
- Change in adrenal androgen secretion (from zona reticularis), the two androgens are DHEA and DHEAS
- Occurs ages 6-8, peaks at 20-25
- Growth of pubic + axillary hair
- Growth in height
What is adrenopause?
The end of adrenarche - the decline in DHEA/DHEAS
What is pubarche?
- Appearance of pubic/axillary hair
- Induced by adrenal androgen secretion
- Associated with acne due to inc sebum prod, infection + abnormal keritinization
What is gonadarche?
- Several years after adrenarche (~11)
- Reactivation of hypothalamic GnRH
- Activation of gonadal steroid production -> prod of viable gametes + ability to reproduce
Where is GnRH released from and in what manner?
- Released from GnRH neurons (specialist hypothalamic centres)
- Pulsatile secretion essential for GnRH function
What is meant by ‘reactivation of GnRH’ during gonadarche?
The HPG axis is first activated at the 16th gestational week, pulsatile GnRH secretion in foetus until 1-2 years postnatally when it ceases.
Then re-activated at ~11 years - during gonadarche.
The GnRH neurones ‘restrained’ during postnatal period -> 10 years or more. At puberty a gradual rise in pulsatile release of GnRH.
How do we know GnRH rises during puberty?
- Early-mid puberty there is a nocturnal rise of GnRH secretion
- But we measure LH levels as GnRH cannot be easily measured (as it’s in hypophyseal circulation)
- LH secretion increases during pubertal development
What stimulates the onset of puberty?
Clear that it is a maturational event within the CNS
- Inherent (genetic) maturation of 1000-3000 GnRH synthesising neurones
- Environmental/genetic factors
- Body fat/nutrition
- Leptin
- Other gut hormones
- Kisspeptin
Frisch et al
Describe the link between fat metabolism and reproduction
Certain % fat:body weight necessary for menarche (17%) and required (22%) to maintain reproductive ability
What impact does anorexia nervosa (or intensive physical training) have on puberty?
- Reduced response to GnRH
- Decrease gonadotrophin levels
- Amenorrhea
- Restored when nourished/exercise stopped
What is the role of kisspeptin?
Gateway for puberty, kisspeptin receptors (GPR54) are expressd on GnRH neurones.
What can mutations of GPR54 or the gene coding for kisspeptin lead to?
- abnormal development of GnRH neurones -> hypogonadotrophic hypogonadism
- failure to enter puberty
- activating mutations of kisspeptin receptor -> precocious puberty
What is meant by ‘consonance’?
Consonance describes the smooth ordered progression of changes that occur during puberty.
- Age of onset, pace & duration of changes (these can be different between individuals)
- But the stages and order of the stages remain the same
What is the average age of menarche onset (UK)?
First menstrual period - ~ 12.5 (on the decline)
Briefly describe the Tanner stages of puberty
- 1 - prepubertal
- 2 - early puberty, breast-budding + inc in testicular vol (>4ml)
- 3/4 - mid-late stage of puberty
- 4 - adult phenotype, completion of puberty
What stimulates breast development?
Oestrogen
What stimulates penile and scrotal development?
Testosterone
What stimulates testicular enlargement as well as follicular development?
FSH
What are the physical changes in girls during puberty?
- Breasts enlarge (thelarche)
- Pubic/axillary hair
- Uterus enlarges
- Uterine tubes, vagina, cervical changes
- Height + body shape
- HPG axis
- Menarche (not = fertility)
- Fertility (after about a year)
What are the physical changes in boys during puberty?
- External genitalia: test vol >4ml, growth of penis, scrotum
- Vas deferens (lumen increases)
- Seminal vesicles + prostate
- Facial/body hair
- Pubic/axillary hair
- Larynx (enlarged via androgens), adams apple, deeper voice
- Height + body shape
- Onset of fertility from beginning of puberty
Describe growth spurt in boys and girls
- Girls - PHV (peak height velocity) = 9cm/y @ 12 years (earlier)
- Boys - PHV = 10.3cm/y @ 14 years
- Complex interaction between GH and oestrogen, oestrogen has a biphasic effect on epihyseal growth:
- Low levels -> linear growth + bone maturation
- High levels -> eipihyseal fusion
What is the Prader Orchidometer?
- Series of numbers on beads representing diff volumes in cms
- Used to measure testicular size in boys at diff ages
- Orchidometer in one hand, testicle in other hand and then measured against each other
