Puberty And The HPG Axis Flashcards
What is puberty
The preparation for sexual maturity
List 4 influences on puberty
- Pineal gland (thought to be an important influence)
- Body weight in girls
- Nutrition
- Leptin (from adipose tissue)
What effect can Pineal Gland disorders have puberty?
What about low body weight?
Pineal gland disorders can cause Precocious Puberty (early onset puberty)
Low body weight can cause cessation of menstruation, even after puberty has occurred
What is the Tanner Scale?
What is it based on in boys and girls?
A scale used to asses stage of puberty in boys and girls
Boys- Pubic hair and genitalia
Girls- Pubic hair and breast development
Compare Primary and Secondary Sexual characteristics
Primary;
- Sexual characteristics at birth
- Includes anatomy of internal and external genitalia
Secondary;
- Characteristics that develop after puberty (menstruation, pubic hair, breast/ genital development/ enlargement)
Define;
- Thelarche
- Adrenarche
- Gonadarche
- Menarche
- Thelarche: Onset of breast development near start of puberty
- Adrenarche: Maturation and increased activity of adrenal glands prior to puberty
- Gonadarche: Activation of reproductive glands by FSH and LH
- Menarche: Onset of menstruation at puberty
At what age range do girls start puberty?
What are the 6 sequence of events?
Age 9-13
- Thelarche
- Initial Pubic hair growth (under influence of testosterone)
- Growth Spurt
- Menarche
- Pubic Hair adult (Becomes coarser, further anatomical spread)
- Breast development adult (further growth)
In the Growth Spurt stage of puberty, what are the significance of Oestrogen and Growth Hormone (GH)?
Oestrogen: Important in fusion of Epiphyseal Growth Plate, stopping the growth spurt
GH: Key role in causing growth spurt to occur
At what age range do boys start puberty?
What are the sequence of events?
Age 10-14
- Genital development
- Initial Pubic Hair Growth (under influence of testosterone)
- Spermatogenesis
- Growth Spurt
- Genital Enlargement
- Pubic Hair Adult
What is the first sign of puberty in boys and girls
Boys- Testicular volume enlargement (Genital development stage)
Girls- Initial breast development(Thelarche)
The Growth Spurt stage of puberty occurs much later in boys.
Why do boys typically grow taller than girls?
Due to lower oestrogen levels, epiphyseal growth plates close more slowly
When is the HPG axis switched on?
Puberty
Explain what effect Precocious Puberty can have on stature
Can lead to Oestrogen levels rising earlier-> Shorter stature as Epiphyseal Growth Plates close sooner
What hormone triggers the start of puberty?
What hormone is thought to initially stimulate the Hypothalamus to produce this hormone?
GnRH
Leptin is thought to initially stimulate the Hypothalamus to produce GnRH
Describe the HPG Axis
- Hypothalamus releases GnRH to act on Ant. Pituitary Gland
- Ant. Pituitary Gland releases LH and FSH in BOTH males and females
- LH and FSH act on Gonads( Ovaries/ Testes) to release Oestrogen and Androgens
- Oestrogen and Androgens contribute to development of Secondary Sexual Characteristics
Describe the pattern of release of GnRH before and after puberty
Before;
- Released in low frequency pulses, especially at night
After;
- GnRH released every 2 hours in males
- GnRH release frequency depends on phase of menstrual cycle)
Why does GnRH release pattern change after puberty?
Before puberty, synapses are not fully matured
What cells of the Seminiferous Tubules are acted on by LH and FSH?
Sertoli cells- FSH
Leydig cells- LH
What will constant administration of artificial GnRH/ GnRH Receptor agonist lead to?
- Reduced sensitivity of GnRH Receptor on AP Gland
- Leads to reduced FSH and LH release
- Leads to loss of fertility
Is the HPG axis subject to Negative Feedback?
What cells of the developing follicle in ovaries respond to FSH and LH?
Yes
FSH- Granulosa cells
LH- Theca Interna cells
Sertoli and Granulosa cells respond to FSH
What chemical/ hormone do they produce when stimulated? Why?
Produce Inhibin, which causes negative feedback on FSH only
To prevent any further sperm production/ follicle maturation
What is Central Precocious Puberty? (Causes early activation of HPG Axis)
List 5 causes
Precocious Puberty with elevated GnRH
- Idiopathic/ Constitutional
- CNS Lesions
- Pituitary Gonadotrophin-secreting tumours
- Systemic conditions (TB)
- Obesity related precocious sexual development due to increased Leptin levels
What is Peripheral Precocious Puberty? (Causes early activation of HPG Axis)
List 5 causes
Precocious puberty without elevated GnRH
- Increased androgen production
- Increased oestrogen production
- Increased Beta-HCG production
- Primary hypothyroidism
- Obesity-related early sexual development due to compensatory hyper insulin anemia (due to obesity)
How do Oestrogen/ Testosterone and FSH/LH levels differ in Central and Peripheral Precocious Puberty?
Central;
- Raised oestrogen/ testosterone
- Raised LH and FSH
Peripheral;
- Raised oestrogen/ testosterone
- Decreased LH and FSH (Negative feedback on GnRH from Oestrogen and Testosterone)
