Puberty
Puberty
Puberty is the period during which an individual will experience two changes that mark the
transformation of children into mature adults:
- Dramatic increases in height, weight & body fat distribution.
- Changes in the reproductive organs that mark sexual maturity, as well as acquisition of
secondary sexual characteristics such as body & facial hair, and the growth of breasts.
In other wards it is defined as It is the transitional period of development during which an individual mature from childhood to sexual & reproductive maturity
GONADOSTAT
Concept & definition of the GONADOSTAT:
The hypothalamic neurons releasing GnRH (gonadotropin releasing hormone) and associated
neurons concerned with stimulation or inhibition of GnRH neurons are collectively called the"GONADOSTAT"
Infantile & Early Childhood Periods
Infantile period:[GnRH] plasma increase.
In the early juvenile period, Gonadostat develops an extremely robust negative feedback
loop for any release of GnRH plus attendant FSH, LH (especially), estradiole &
testosterone. Very low plasma concentrations result.
LATER JUVENILE PERIOD
The gonadostat becomes a bit more sensitive to other stimuli such as leptin, IGF-1 etc.
The increases of [GnRH, FSH & LH] plasma remain relatively very small.
THE SEQUENCE OF MATURATION
- At the onset of puberty GnRH pulses occur during sleep leads to increase in LH pulses
- Concurrently, there is a slight & gradual decrease in sensitivity of the negative feedback
loop for hypothalmic GnRH. So, The frequency of LH pulses increases with further
maturation
- LH pulses appear during day time & increase in amplitude
- As menarche approaches, the pulses are detected all the time (no diurnal variation)
- Similar changes occur in FSH pulses
- LH/FSH ratio increases
BREAST DEVELOPMENT (THELARCHE)
The first visible change of puberty. Thelarche is induced by estrogen. Thelarche Starts at 10.6 Years old. Breast development should has completed in about 3 years,
Effects of estrogen on the breast
- Ductal proliferation
- Site spicific adipose deposition
- Enlargement of the areola & nipple
Breast development may be unilateral for several months. Other hormones that play
a role in breast development could be prolactin, glucocoricoids & insulin.
Breast development passes by 5 stages (Tanner Stages).
ADRENARCHE OCCURS DURING LATER CHILDHOOD & EARLY PUBERTY Adrenarche involves increased activation of the Hypothalamic-Adrenocortical Axis:
*Important! Adrenarche is independent of [GnRH] plasma.
- Adrenarche initiates phenotypic events in boys & girls. Begins around age 6 to 7 in girls;
around age 8 to 9 in boys.
- Fairly common that adrenarche either precedes gonadarche (marks the beginning of
puberty) or is coincident with the onset of gonadarche. Adrenarche is NOT the triggering
event for puberty
- Adrenarche is initiated by maturation of zona reticularis of adrenal cortex. Zona
reticularis matures in later childhood under the influence of HGH, IGF-1 & insulin (and
maybe leptin, the fat pad-satiety hormone). *Maturing adrenal zona reticularis results in
synthesis of androgens. Initially DHEA (dihydroxyepiandrosterone) & DHEA-S. Followed in
1-2 years by androstendione. Androgens circulate to target organs.
Effects of DHEA
DHEA & DHEA-S enter target cells. Within the target cells, DHEA & DHEA-S synthesized into testosterone & dihydrotestosterone.
- DHEA is synthesized into testosterone & dihydrotestosterone within target cells.
Stimulates axillary & pubic hair growth.
- DHEA conversion also leads to development of apocrine glands in these regions.
Also growth of pubic hair passes by 5 stages as in breast development.
GROWTH SPURT:
- A global process involving increasing skeletal growth rate, increase in muscle and
growth of all internal organs
- Dependent on mainly on estrogen & growth hormone however adrenal androgens
also play a role
- Estrogen has :
➢ A direct anabolic effect
➢ increases growth hormone
➢ increases insulin like growth factors
Peak Height Velocity
- 8.1 cm/year (before puberty 3-6 cm/y) -by the time PHV is achieved
- 90% of adult height has been achieved. the average increase in height
from the onset of growth spurt to cessation of growth 25 cm.
Girls who start the growth spurt early will have a shorter adult height.
Bone age is more closely correlated with pubertal events than chronological age
Growth Hormone (GH) plays role in pubertal development. Amplifies ovarian response to
gonadotrophins. IGF-1 enhances gonadotrophin effect on granulosa cells.
GONADARCHE:
- The onset of pubertal gonadal activity due to reactivation of HPO axis resulting in
increase in estrogen (E2)
- The process of ovarian follicular growth & atresia is initiated in utero & continues from
birth to puberty. It is independent of gonadotropin secretion & results in only minimal
estrogen secretion
- Reactivation of HPO axis results in increase in gonadotropin pulses
- sustained
follicular development to antral stage
- significant estrogen production
- There is direct relationship between follicular size & estrogen secretion
MENARCHE:
defined as the age of the first menstruation.
When there is sufficient gonadotropin stimulation of the ovaries will cause a follicular
growth (~16mm) leading to more increase in estrogen. Estrogen in turn will lead to
proliferation of the endometrium until it outgrows the estrogen capacity to maintain it
so menstruation (menarche).
Or, the follicle undergo atresia causing a drop in the level of estrogen menstruation (MENARCHE).
• NB: Anovulatory cycles will occur during the first 6-18 months of menarche as the
“endometrium is not exposed to progestrone”.
• NB: Anovulatory periods often are irregular unpredictable menstrual flow.
• The last stage in puberty is menarche immediately preceded by a growth spurt. The
announcement of puberty is the appearance of a breast bud followed by the
appearance of axillary and pubic hairs.
Abnormal puberty:
1. Early or Precocious Puberty 2. Delayed Puberty and primary amenorrehae
Precocious Puberty:
Onset of secondary sexual characteristics before age of 8 yrs in girls
Five times more common in girls. It is usually benign central process – girls
Premature thelarche / pubarche:
Thelarche – beginning of breast development. While pubarche (or) adrenalche – first
appearance of pubic hair (more common in certain populations e.g Asian / Afro-Caribbean),
Adrenalche is More common than true precocious puberty. It is a benign variants.
Precocious Puberty may be due to increase in GnRh or gonadotrophin (FSH & LH) i,e, central precocious puberty.
Examples of central ( causes presents in hypothalamous anterior pituitary or brains ) precocious puberty:
1. Idiopathic (sporadic / familial)
2. Congenital (Hydrocephalus)
3. Acquired (irradiation/surgery/infection)
4. Tumours (hamartomas/gliomas)
5. Neurofibrosis (Mc Cune Albright Syndrome)
Table 1 Important elements in the diagnosis of central precocious puberty in girls
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History
Onset of breast development, menarche, behavioral changes, concomitant disease or complaints, family history
Physical examination
Pubertal staging according to Tanner, height and weight, growth acceleration, signs of primary disease
X-ray left hand
Bone age and height prediction
Ultrasonography
Size of ovaries and uterus
Magnetic resonance imaging
Hypothalamic region, pituitary, optic nerves
Laboratory
GnRH stimulation test: Luteinizing hormone and Follicle-Stimulating hormone response to GnRH (agonist)administration
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