Puberty Flashcards
D: puberty
The transition phase that takes a person from being a sexually immature child to a sexually mature, reproductively fertile adult.
first signs of puberty?
do they show fertility?
- In females, menarche (first menstruation) is the most definitive sign.
- In males, first ejaculation (often nocturnal) is a sign of similar degree of maturity.
• These do NOT signify fertility, more a sign that the gonads have awakened and are beginning to assume adult levels of activity
- First menstrual cycles - anovulatory
- First ejaculate - small quantities of seminal plasma and no sperm
do boys have their growth spurt 2 years later than girls?
yes - hence taller
T or F
Lean body mass and body fat are virtually identical in prepubescent boys and girls
T
tanner stages female
tanner stages male
describe Cryptorchid testes
• Testicular descent occurs during fetal development
- 3-4% of males
- Impaired spermatogenesis
Puberty involves _____ activation of the reproductive axis
Puberty involves central activation of the reproductive axis
T or F
Puberty in primates involves re-awakening of the HPG axis
T
Puberty in primates involves re-awakening of the HPG axis
elaborate.
High gonadotrophic hormone levels in Rhesus monkeys during first 20 weeks of life.
HPG axis suppressed by GABAergic inhibition of GnRH release
At puberty, GABA inhibition removed and stimulatory inputs onto GnRH neurons.
This pattern observed in gonadectomized monkeys so not dependent on sex steroids
Puberty in primates involves re-awakening of the HPG axis
is it dependantn on hte sex steriods?
no
GnRH pulsatility ______ at puberty
GnRH pulsatility increases at puberty
Amplitude and frequency of GnRH pulses regulates LH and FSH levels
How?
does GnRH fluctuate more in adults?
no - mcuh less fluctuations
LH, FSH and oestradiol levels rise
Early cycles not associated with
……
LH, FSH and oestradiol levels rise
Early cycles not associated with
ovulation
Rise in ……..causes onset of spermatogenesis and rise in testosterone from testes.
Rise in FSH and LH causes onset of spermatogenesis and rise in testosterone from testes.
in males what causes growth of accessory sex glands and secondary sex characteristics
Androgens cause growth of accessory sex glands and secondary sex characteristics
Describe Growth hormone
- • Secreted from anterior pituitary in greater amounts near to puberty
- • Responsible (along with androgens) for growth of long bones and tissues
- • Major effect on protein synthesis and glucose homeostasis
- • GH deficiency => short stature, delayed sexual maturation
describe thyroid hormones near puberty
- Increase in secretion from thyroid gland, secondary to increased thyroid stimulating hormone (TSH) from anterior pituitary
- May account for rise in metabolic rate in both sexes
- Also essential for body growth
4 factors which can affect the onset of puberty
- Genetic
- Metabolic
- Social
- Environmental
how can GWAS be used to identigy genes associated with puberty ?
how else can we identify genes involved in puberty?
Genes affecting puberty can be identified by genetic association studies looking for regions of the genome that segregate with reproductive phenotype (eg precocious puberty in girls) – eg MKRN3.
Genes can also be identified by studying individuals that do not go through puberty and identifying the causative mutation eg. Kisspeptin, Neurokinin B pathways.
what do yo uknwo about MKRN3
normally Delays puberty:
• MKRN3 mutations cause early puberty.
Protein – big
Binds Zinc
Involved in protein degredation thorugh ubiquitin pathway
Cannot degrade GnRN = more GnRH released
how are Kisspeptins involved in puberty?
- kisspeptins encoded by the Kiss1 gene
- signal through Kiss1 receptors (G protein) Expressed by GnRH neurons
- Kisspeptin binding causes GnRH depolarisation and GnRH release
*
how can mutations in Kiss1 or the Kiss1R gene affect puberty?
- Hypogonadotrophic + hypogonadism
- lack of puberty / developement
- smal testicle size
- Absence of secondary sexual development (for example, pubic, facial, and underarm hair)
how do mutations in the neurokinin B gene / receptor gene affect puberty?
family in turkey - didnt go through puberty.
Severe congenital hypogonadotrophic hypogonadism
Neurokinin B, a member of the substance P–related tachykinin family, is highly expressed in arcuate KISS1 hypothalamic neurons.
mutation = no puberty
why is the age at which puberty is onset decereasing?
Body weight is a critical determinant of the age of puberty
Puberty begins around 47 kg for girls and 55 kg for boys
people get bigger faster - diet
Puberty begins around ___ kg for girls and __ kg for boys
Puberty begins around 47 kg for girls and 55 kg for boys
Overweight childerne enter puberty ______ than skinny ones
Overweight childerne enter puberty earlier than skinny ones
Some human genetic disorders in Leptin pathway result in ______ of puberty
Some human genetic disorders in Leptin pathway result in failure of puberty
injecting leptin to ob/ob mouse can ______ fertility
injecting leptin to ob/ob mouse can restore fertility
In animals, _____ can delay sexual maturity.
In animals, stress can delay sexual maturity.
info:
controversial
Controversial, but some stressors (emotional or physical) can delay puberty in humans.
Opposite also proposed – stress during infancy and childhood can accelerate puberty (e.g. family stress)
Evidence? Girls who grow up in the absence of biological father, especially with stepfather present, tend to enter puberty earlier
environment al factors affecting puberty
Pollutants
- Some chemicals in industrial synthesis of plastics act as weak oestrogens,
- Controversial, but exposure to some of these “xenoestrogens” may accelerate puberty.
- Phytoestrogens in various plants – high in soya.
- Some pollutants (dioxins, polychlorinated biphenyls) may delay male puberty.
Altitude
- For every 100m increase in altitude, puberty delayed by 3 months.
fat
mamba
