Hypothalamic-pituitary-gonadal axis II Flashcards
What is puberty?
the period of sexual maturation, during which a person becomes capable of reproducing
What is puberty defined as clinically?
increased breast development in females (thelarche)
increased testicular volume in male
What are the endocrine events of puberty?
Adrenarche
Gonadarche
What is Adrenarche (6/8-15 years)?
maturation of adrenal glands
- foetal zone shrinks and definitive zone grows once foetus is born
- definitive zone releases adrenal androgens DHEA&DHEAS that cause maturation of adrenal glands (6/8-15 years old)
Where are DHEA and DHEAS synthesized?
in zona reticularis of adrenal cortex
What is the consequence of adrenarche?
Pubarche
- growth of pubic and axillary hair
- growth in height
- increased sebum production causing acne
- infection and abnormal skin keratinisation, causing acne
What is Precocious Puberty?
a condition in which puberty begins before the age of 8 in girls and 9 in boys
What is Gonadarche (11 years)?
reactivation of HPG axis and GnRH secretion
- at 16th gestational week, HPG axis is activated for sexual differentiation
- HPG axis deactivated after birth
- HPG axis reactivated during puberty (11 years)
When are the pregnancy scans?
12-13 weeks
20 weeks
At what pregnancy scan can the baby’s sex be revealed and why?
not at the 12-13 week scan, but at the 20th week scan
this is because activation of HPG axis which results in sexual differentiation is at 16th gestational week
How can we study changes in pattern of GnRH secretion?
by observing changes in pattern of LH secretion because it mimics GnRH secretion and easier to obtain
-(GnRH secreted into hypophyseal portal vein)
What is the Effect of body fat on GnRH?
Individuals with anorexia nervosa or who undergo intensive training:
- reduced response to GnRH
- decreased gonadotrophin levels
- amenorrhoea in females (absence of menstrual periods)
Restored when nourished/exercise stopped
Describe the Stimulation of onset of puberty.
kisspeptin
environmental/genetic factors
body fat/nutrition
maturation of GnRH neurones
How can leptin and ghrelin mediate puberty regulation?
they feed into hypothalamus and regulate kisspeptin, which in turn regulates onset of puberty
Describe the Inactivating mutations of KISS1 receptor or Kisspeptin gene.
Hypogonadotrophic Hypogonadism (HH) -failure to enter puberty
What is the Activating mutations of KISS1 receptor?
Precocious puberty
What is consonance?
smooth ordered progression of changes that occur during puberty
- ORDER of pubertal changes is same in everyone
- AGE OF ONSET/PACE/DURATION of changes will vary
Describe the Tanner stages of puberty.
5 stages of physical measures of development used to clinically diagnose pubertal disorders in/out of consonance based on:
1) Pubic and Axillary Hair Growth
2) Testicular Volume and Penile Length in males
3) Breast Development in females
What is a growth spurt?
Biphasic effect of oestrogen on epiphyseal growth:
>first starts with low oestrogen levels- linear growth and bone maturation
>followed by high oestrogen levels- epiphyseal bone fusion
What is a pilosebaceous unit?
structure consisting of:
>hair+hair follicle+arrector pili muscle+sebaceous gland
What are the Main types of pilosebaceous units?
Sebaceous PSU
Vellus PSU
What are the Effect of Androgens on PSUs?
Sebaceous PSU
-androgens increase sebum production, resulting in acne
Vellus PSU
-androgens differentiate vellus PSUs into:
>terminal PSUs responsible for beard growth
>APO-PSU responsible for axillary and pubic hair
What are the Psychological changes in puberty?
- increasing need for independence
- increasing sexual awareness/interest
- development of sexual personality
*later maturation is associated with better adjustment because psychological and sexual behaviours are occuring in sync
What is Precocious Puberty?
a condition in which puberty begins before the age of 8 in girls and 9 in boys
What is a common cause of precocious puberty?
premature activation of HPG axis
What is the cause of Gonadotrophin Dependent Precocious Puberty?
Could be due to:
- excess GnRH secretion
- pituitary tumour causing excess gonadotrophin secretion
What is the cause of Gonadotrophin Independent Precocious Puberty?
Could be due to:
-testoxicosis (activating mutation of LH receptor in testis)
- sex steroid secreting tumour causing early gonadal maturation
- exogenous steroids causing early gonadal maturation
- McCune Albright Syndrome: activating mutation in GNAS1 gene encoding Gas subunit, causing hyperactivity and overproduction of hormone
What is Pubertal Delay?
absence of secondary sexual characteristics by 13 years old in girls (or absence of menarche by 18) or 14 years old in boys
What is a common cause of pubertal delay?
delayed HPG axis activation
What is Constitutional Pubertal Delay?
affects growth and puberty
secondary to chronic illnesses e.g. diabetes, cystic fibrosis
What is Hypogonadotropic hypogonadism?
FSH+LH are low due to:
-Kallman’s syndrome: X-linked KAL1 gene mutation, impaired GnRH neurone migration to hypothalamus during development
- Inactivating mutation of KISS1 receptor or kisspeptin gene
- other mutations causing defects in GnRH production
What is Hypergonadotropic hypogonadism?
FSH+ LH are elevated due to:
-gonadal dysgenesis and low sex steroid levels (no negative feedback)
-gonadal dysgenesis in those with normal karyotype caused by viral mutations e.g. mumps
-gonadal dysgenesis resulting from abnormal karyotype:
>Klinefelter’s syndrome (XXY) in males; characterised by feminine features such as breast development
>Turner’s syndrome (XO) in females; characterised by “streak ovaries” and being shorter than normal
