Puberty and the HPG Axis Flashcards
Define puberty
Stage of human development when sexual maturation and growth are completed and result in ability to reproduce
What is the critical weight for puberty in girls
- Critical weight = 47 kg
- Menstruation will not start below this
- Significant weight loss = reproductive cycles cease
State the age ranges of the different developments during female puberty
- 9-13
- Growth spurt - 10-14
- Breast bud and breast enlargement - 10-13 (first developed)
- Pubic hair growth due to testosterone - 11-13
- Menarche occurs at 12-13
What is adrenarche and menarche
Adrenarche - beginning of puberty where adrenal glands secrete androgens
Menarche - first occurrence of menstruation
State the age ranges of the different developments during male puberty
- 10-14 years
- Pubic hair growth - 12-14
- Spermatogenesis - beginning at 11
- Genital development - 11-14
- Growth spurt begins later and ends later than girls - 11-16
What is the tanner scale
Measurement of progression of puberty
Explain the mechanism of accelerated somatic growth
- Occurs in both sexes - depends on growth hormones and sex steroids in both sexes
- Earlier and shorter in girls
- Men larger growth because growth spurt longer and slightly faster
- Genital development in boys depends on testosterone levels
- Ended in both sexes by epiphyseal fusion
- Oestrogen closes epiphyses earlier in girls
Explain the hormonal change that occur in puberty
- Hormonal changes precede physical changes
- Increased stimulation of hypothalamo-pituitary-gonadal axis
- Gradual activation of the gonadotrophin-releasing hormone (GnRH)
- Increases frequency and amplitude of LH pulses
- Gonadotropins stimulate secretion of sexual steroids (oestrogen and androgen)
- Extragonadal hormonal changes (elevation of IGF-1 and adrenal steroids)
- Gonadotrophin-releasing hormone
- GnRH-1 gene responsible for puberty
- GnRH released from hypothalamus
- Lack of gonadotrophin synthesis and secretion and reproductive development occurs if
- GnRH is blocked
Describe precocious puberty
- Physical signs of sexual maturation before 8 years or menarche before 10 years old
- Could be caused by early GnRH production
- Shorter overall growth as high oestrogen level exposure early in life causes epiphyseal growth plates to fuse earlier
- Can be caused by meningitis
Explain delayed puberty and constitutional delay
- Present as primary amenorrhoea - failure to menstruate by 16
- Low leptin, underweight, problem with hypophyseal pathway
- Constitutional delay - most common cause of delayed puberty where delay in skeletal growth creates a short stature
- Gonads not receiving stimulus to produce testosterone from the hypothalamus and anterior pituitary
What is Kallman syndrome
Abnormal development of GnRH producing neurons
What is Klinfelter’s syndrome
(XXY) causes infertility but not delayed onset of puberty
Outline the hypothalamo-pituitary-gonadal axis
- Puberty initiated by the brain - hypothalamus
- Hypothalamus releases GnRH which goes to anterior pituitary
- Anterior pituitary releases FSH and LH which travels to the gonad
- Gonad produce androgens and oestrogen
Outline the role of leptin in HPO axis
- Adipocyte-derived protein hormone
- Regulate energy balance by inhibiting hunger
- Important in regulating neuroendocrine function
- Reproductive dysfunction associated with leptin deficiency
- Leptin can accelerate the onset of reproductive function
- Decreased weight = decreased leptin - may not sustain reproductive body
- Leptin has pulsatile release pattern significantly associated with the variations in LH
- Leptin can regulate GnRH levels
Describe which cell types in the anterior pituitary gland produce which hormones
- Lactotropes produce prolactin
- Somatotropes produce growth hormone
- Thyrotropes produce thyroid stimulating hormone (TSH)
- Corticotropes produce adrenocorticotropic hormone (ACTH)
- Gonadotropes produce Follicle stimulating hormone (FSH) and luteinizing hormone (LH)
