Session 4- Puberty and the HPG axis Flashcards
What is puberty
A stage of human development when sexual maturation adnd growth are completed and result in ability to reproduce
What is adenarche
Maturation and increase activity of the adrenal glands prior to puberty
Gonadarche
Activation of reproductive glands by the pituitary hormones FSH and LH
Thelarche
The onset of breast development occurring near the beginning of puberty in girls
Pubarche
Onset of the growth of pubic hair
Menarche
Teh onset of menstruation at puberty
What is thought to have an important influence on puberty
The pineal gland as disorders of this gland can cause early onset puberty
What is the SMR
Tanner developed a scale in 1962 that divides the sexual maturity ratings into 5 classes based on Pubic hair and breast in females and pubic and genitalia in males
What is the first sign f puberty
Testicular enlargement- males
Breast development - females
When does female puberty start
8-13
When does male puberty start
9-14
What does acccelerated somatic growth depend on
Growth hormone + IGF-1 and sex steroids in both sexes
How does accelerated somatic growth end in males
Fusion of epiphysis
Oestrogen closes epiphysis earlier in girls
What ones the HPG axis consist of
Hypothalamus
Pituitary
Gonad
Describe the HPG axis
Hypothalamus releases GnRH which acts on the pituitary to produce LH and FSH which acts on the gonads to produce androgen and Oestrogen
Where is teh GNRH receptor
Anterior pituitary
Why is GnRH released in pulsate
Teh receptors will become insensitive to teh GnRH if it is constantly secreted and the cascade will stop
When do LH nd FSH levels increase
9-12 years old
How does LH work in males
It stimulates Leydig cells in testis which produce testosterone which affects
The HPG axis in males
FSH stimulates Sertoli cells which initiate spermatogeneis and causes the developing gametes to produce inhibin. Negative feedback on anterior pituitary - FSH- and possible hypothalamus
LH stimulates Leydig cells
-testosterone released. Negative feedback on hypothalamus and anterior pituitary
What cells are present in seminiferous tubules
Supporting cells
Spermatogenic cels
Sertoli cells
-provide nutrition and hormonal support to germ cells allowing sperm formation
-sensitive to FSH
-secreted inhibin by developing gametes- negative feedback on AP FSH
The HPG axis- female
FSH stimulates granulosa cells
As follicles envelop get release inhibin which inhibit FSH only.
Granulosa cells a covert androgens to oestrogen
LH stimulates theca interna cells
- release androgens. Converted to oestrogen by granulosa cells
- LH surge is required for ovulation
- LH maintains corpus luteum after ovulation
How does oestrogen affect the release of GnRH i females
Moderate tires of oestrogen reduce GnRh secretion
-negative feedbacks
High titres of oestrogen alone promote GnRH secretion
- positive feedback
- LH surge
How does progesterone affect FSH nd LH
Increases inhibitory effects of moderate oestrogen
Progesterone prevents positive feedback of high oestrogen
Oestrigen reduces GnRH per pulse, progesterone frequency of pulses
