Puberty Flashcards
What is puberty?
The transition phase that take a person from being a sexually immature child to a sexually mature, reproductively fertile adult
What is the definitive sign of puberty in females?
Menarche
What is menarche?
First period
What is the definitive sign of puberty in males?
First ejaculation (often nocturnal)
What is the main feature of the first few menstrual periods?
Anovulatory
What is the main feature of the first ejaculations?
Small quantities of seminal plasma
No spermatozoa
What causes the 10cm mean height difference between men and women?
Boys have their growth spurt later so are taller at point of take-off
Why is average strength of adult men greater?
Greater number of muscle cells due to androgens
When is the first ovulation?
Some months - two years after menarche
What causes spontaneous erections?
Stressful or emotionally-charged stimuli
Often not sexual matters
What do ovarian oestrogens cause?
Growth of breasts and female genitalia
What do ovarian and adrenal androgens do?
Growth of female pubic and axillary hair
What do testicular androgens do?
Development of male genitalia and body hair
Enlarging of larynx and laryngeal muscles
How many ovarian follicles are there in the newborn?
~500,000
How many follicles remain at puberty?
~83,000
At what stage of development do testes descend from the abdominal cavity?
7th or 8th month of fetal life
What controls descent of testes?
MIS and testosterone
What is the gubernaculum?
Ligament attached to testes and scrotum that pulls testes down
At what age does spermatogenesis begin?
9 years
At what age are mature spermatogonia produced?
14/15 years
What is cryptorchidism?
Testes that fail to descend
3-4% fail to descend by birth
- 8% fail to descend by 1 year
- 3% fail to descend by onset of spermatogenesis
How is cryptorchidism treated?
- Surgery
2. Treatment with gonadotrophins or GnRH to cause descent before damage is done
How do gonadotrophin levels change in life?
LH and FSH pulses in first 20 weeks are the same as in adult life
Secretion then ceases and levels are low during childhood
First change is rise in FSH
Then increasingly pulsatile LH
How do hormone levels change at menarche?
Sudden surge of LH and FSH sufficient for menstruation but not ovulation
What type of hormone pulses are needed for puberty to occur?
LH pulses every 1 to 3 hours at relatively high amplitude
Where is oestradiol released from?
Large growing follicles in ovary
Where is oestrone released from?
Body fat
What kind of androgens are released from the adrenal gland?
Weak androgens to maintain low circulating androgen level
Converted to testosterone at target tissues
What is the first endocrine change in puberty?
Rise in DHEA
Adrenarche
What is the source of oestrogens in males?
Sertoli cells
What is gynaecomastia?
Slight growth of mammary glands in males
Usually goes away within two years
What causes acne?
Androgens increase secretions of sebum from sebaceous glands
Glands become clogged and infected
What are the treatments for acne?
- Antibiotics
- Salicylic acid
- Oral contraceptive
- Benzoyl peroxide
What is the role of growth hormone?
Growth of long bones and tissues
Major effect on protein synthesis and glucose homeostasis
What is the role of thyroid hormones?
Rise in metabolic rate in both sexes
Essential for body growth
What causes childhood suppression of sexual maturation?
Androgens/oestrogens exert negative feedback
Hypothalamus very sensitive to steroidal inhibition during childhood
Sensitivity of hypothalamus decreases as puberty approaches
Central inhibition of GnRH pulse generator
What does TAC3 code for?
Neurokinin B
What is TACR?
TAC3 receptor
What is neurokinin B
Member of substance B-related tachykinin family
Highly expressed in hypothalamic neurons that also express kisspeptin
What is kisspeptin?
Regulator of GnRH secretion
At what weight does puberty begin?
47kg in girls
55kg in boys
How is weight sensed?
Leptin
Receptors in hypothalamus
What inhibits reproductive function?
Melatonin
Pineal gland secretions
What is the result of sensory deprivation on puberty?
Acceleration of sexual maturity
What is the effect of excess stress and parental conflict in girls?
Passed through puberty more rapidly
Earlier puberty onset
What are xeno-oestrogens?
Chemicals in industrial synthesis of plastics that mimic oestrogens
What is the effect of altitude on puberty?
Every 100m increase in altitude delays puberty by 3 months
What is the effect of CYP3A4 gene?
Produces liver enzyme that degrades testosterone, increasing oestrogen ratio
Homozygous leads to breast development before age 9.5 in 90%
Heterozygous - 56%
No copies - 40%
