Lecture 6 - Puberty and HPG axis Flashcards
Puberty
Sexual maturation and growth
Develop ability to reproduce
Factors affecting timing of puberty
Pineal gland - disorders can causes precocious puberty
Body weight - low body weight can cause cessation of menstruation
Nutrition
Leptin - released from adipose tissue
Secondary sexual characteristics in girls
9 - 13 yrs old :
- thelarche
- adult pubic hair growth
- adrenarche: growth spurt
- menarche : initiation of menstruation
thelarche
Breast buds develop - marks start of puberty
Adult pubic hair
Coarser
Wider distribution
Influenced by testosterone
Primary sexual characteristics
At birth before puberty
Anatomy of the internal and external genitalia
Male secondary sexual characteristics
10 - 14 yrs old
- adult genital development - testicular volume enlargement
- pubic hair growth (testosterone)
- spermatogenesis
- growth spurt
Why are boys normally taller?
Men have less oestrogen so growth spurt lasts longer and occurs later.
Oestrogen fuses the epiphyseal growth plates so less oestrogen means you grow taller.
What scale is used to measure puberty development?
Tanner
Growth spurt
Depends on:
- GH
- IGF1
- Sex steroid hormones (testosterone and oestrogen)
Aromatisation
Converting androgens to oestrogen.
If testosterone levels are high in females can be converted to oestrogen in tissues such as adipose therefore fuses epiphyseal growth plates quicker
Critical weight for menstruation
47kg
What initiates puberty
Hypothalamus externally stimulated by e.g. weight, leptins and light in the median eminence
Leptin
Causes the pulsatile release of GnRH form the hypothalamus
Located in adipose tissue
HPG axis
- Nocturnal pulsatile release of GnRH from hypothalamus
- Anterior pituitary released FSH and LH
- Acts on the ovaries to release oestrogen and progesterone
GnRH release
Related to internal body clock - light
Acts on specific membrane receptors to transduse second messengers
Stimulates:
- synthesis and release of FSH and LH
- stimulates hyperplasia and hypertophy of target cells
- regulates own receptor (negative feedback)
Triggers of puberty
Changes of day length
Pineal gland - secretion of melatonin
Anterior pituitary
No neural signalling
Synthesises and secretes substances e.g. FSH and LH
Anterior pituitary hormones (6)
- FSH
- LH
- GH
- Thyroid stimulating hormone
- Prolactin
- Adrenocorticotrophic hormone (ACTH)
How does GnRH travel to the pituitary gland?
Hypophyseal portal system
FSH and LH on gonadal development
In young children the FSH and LH concenrations are insufficient to stimulate gonadal development.
Between 9- 12 yrs old, blood FSH and LH levels rise as amplitude of GnRH pulses rise especially during sleep.
High FSH and LH levels initiate gonadal development.
Sleep
Increase pulsatile amplitude of GnRH release
Increases LH
Increases testosterone/oestrogen
Male androgen production
LH stimulates Leydig cells in testes to produce testosterone
Affected by:
- circadian rhythm (highest in early morning)
- environmental stimuli
Seminiferous tubule epithelial lining
2 cell types:
- Sertoli cells - support sperm formation
- Spermatogenic germ cells
