Puberty and Menopause Flashcards
1
Q
Puberty
A
- Transition from sexual immaturity to sexual maturity. It is composed of 2 main events:
- Gonadarche - activation of gonads by FHS and LH
- Adrenarche - increased production of androgens by the adrenal cortex
2
Q
What are the components of Puberty
A
- Thelarche - appearence of breast tissue due to presence of estradiol from the overies
- Menarche - first menustral bleed
- Spermarche - first sperm production (indicated by noctural emissions of presence of sperm in urine). Due to LH and FSH stimulating release of testoserone.
- Pubarche - appearance of pubic hair, due to effects of androgen from adrenal gland.
3
Q
Explain the hormones involved in initiation gonadarche
A
- Gonadarche is due to an increase in the pulsatile secretion of GnRH from the hypothalamus. This results in increased frequency and amplitude of FSH and LH secretion from the pituitary, which stimulates sex-steroidgenesis and eventually gametogenesis in the gonades.
4
Q
Gonadarche girls
A
LH stimulaes theca cell activity and results in the prodcution of androstenedione and progesterone. FSH stimulates growth of ovarian follicles and stimulates aromatase to convert androstenedione into estradiol. Estradiol stimulates breast development and skeletal growth (pubertal growth acceleration). Later, secretions of LH, FSH, and estradiol leads to ovulation and menstrual cycle. Estradiol induces skeletal maturation, and eventually causes fusion of growth plastes and end of lineral growth.
5
Q
Gonadarche boys
A
- LH stimulates leydig cells to produce testosterone, stimulating growth of seminiferous tubuls and increasing testicular size. FSH stimulates further growth of seminferous tubules, further increasing testicular size. Testosterone also leads to growth of the penis, deepening of the voice, growth of hair, and increases in musularity. Some testosterone is converted into estradiol resulting in skeletal growth.
6
Q
Adrenarche
A
- Andrenarche is due to changes in patterns of androgen secretion in response to ACTH. In preandrenarchal children, ACTH stimulates cortsiol release, but has a very limited effect on 17-ketosteroid secretion. However, during andrenarche, 17-ketosteroid becomes more responsive to ACTH (cortsiol responsivness does not change).
- Zona reticularis of adrenal cortex is a major source of adrenarchal steriods - and this area expands from ages 3-5.
- Adrenarche contributes to the appearence of pubic hair (pubarche), and sebaceous (oil gland) and aprocrine (sweat) gland development.
7
Q
Order of pubertal development in girls
A
- Breast budding (thelarche) ~8-10.5
- Pubic hair (pubarche)
- Maximal growth velocity ~12
- Menarche ~12.5-13
- Development of axillary hair
- Adult breast type
- Adult pubic hair development
- Completion of puberty ~13.5-14.5
8
Q
Hypothalamic pituitary-ovarian (HPO) axis
A
9
Q
Hypothalamic pituitary testicular axis
A
10
Q
Explain hormonal changes from birth to puberty
A
- At 10 weeks gestation, the hypothalamic-pituitary system begins to form and is completed by 19-20 weeks. At this point there is an increase in the gonadotropins and ovarian sex steriods that stimulate germ cell and follicular development.
- Soon after birth (after large amounts of maternal estrogen and progesterone wear off), we see the characteristic pulsatile pattern of GnRH. At this point, you can see levels of gonadotropins and ovarian steriods as high as in reproductive age female, until the negative feedback system becomes fully functional and levels drop. Suppression lasts until puberty.
- GnRH pulsatile secretion can still be seen in prepubertal children, but the frequency and amplitude are low, occur mainly during sleep, and don’t result in gonadal steroid production.
- At puberty, GnRH noctural pulses will become more pronounced and eventually GnRH pulses frequency increases and will obtain a daily pattern.
11
Q
What are the endocrine mediators of puberty
A
- At a certain time, noctural pulses of GnRH will become more pronounced and LH levels will start to be higher than FSH levels. This occurs about 1 year before breast budding (requries estradiol, which needs the increase in gonadotropin).
- GnRH pulse frequency increases and obtains a daily pattern.
- During puberty we see an increase in the responsiveness of the pituitary to GnRH due to regulations of gonadotrope receptors and increase synthesis of gonadotropins. As a result of this, LH secretions increase greatly (20-40) and FSH secretions increase, but less so (2-3 fold).
- The gonades also release inhibins that suppress FSH secretion.
- As ovaries mature, they become better able to respond to GnRH and release more steriod hormones. When estradiol and inhibin levels reach high enough levels to negatively feedback on gonadotropin secretion, a cycle will develop and menarche will occur.
- At same time as gonadal maturation occurs, we see andrenarche. Begins around 6 years, but like the HPO axis we also see a pattern of high activity in infancy and during puberty, wtih a period of inactivity inbetween.
- Follwing adrenarche, gonadarche and rise in steriod hormones, we see activation of GH and ILGF which are the main drivers of pubertal growth spurt (although the gonadal steriods also play an important role).
12
Q
Linear growth and puberty
A
- Before puberty, growth velocity slightly decelerates. With production of sex hormones at puberty (estrogen and testosterone) you see a pubertal growth spurt, due to the augmentation of GH production.
- Girls: Pubertal growth spurt starts at breast and pubic hair stage 2 and reaches a velocity of 8.23cm/y at breast and pubic hair stage 3 (~1 year before menarche). Growth slows after menarche, with girls gaining ~7cm more. (Growth is 99% complete at bone age 15)
- Boys: Pubertal growth spurt occurs about 2 years after it starts in girls. It starts at genital and pubic state 2, reaching a velocity of 9.5cm/y at genital and pubic stage 3 and 4. (Growth is 99% complete at bone age 17).
13
Q
Precocious Puberty
A
- The appearance of physical and hormonal signs of puberital development that occurs ealier than what is considered normal.
- Girls- precocious puberty can be considered if signs occur before 6-8
- Boys -precocious puberty can be considered if signs occur before 9
14
Q
Types of precocious puberty
A
- Central/dependent precocious puberty: gonadotropin-dependent. Early maturation of HPG axis. See full spectrum of physical and hormonal pubertal development. Characterized by sequtial maturation of breasts and pubic hair in girls, and testicular and penile enlargement and pubic hair in boys.
- Periperal/independent precocious puberty: Production of sex steriods indepdent of gonadotropins.
- Benign/non-progessive: Isolated breast development or isolated androgen mediated sexual characteristics due to early activation of HPA axis. This is a normal varient of puberty.
15
Q
Pathophysiology Central Precocious Puberty
A
- Gonadotropin dependent
- Due to premature pulse generation of GnRH leading to pulsatile gonadotropin (LH and FSH) secretion.
- May be due to CNS lesions, idopathic, activation of genes that code for kisspeptins (play a role in GnRH activation).
