Hypothalamic pituitary gonadal axis 2 Flashcards
What is puberty?
Puberty is the transition from non-reproductive to reproductive state
In puberty, what are the gonads able produce?
Gonads produce mature gameres
- Testis–>Spermatozoa
- Ovaries –>Oocytes
What is puberty defined as?
Defines as breast development in females and increased testicular volume in males
What characteristics develop in puberty and what profound changes are there?
Secondary characteristics develop
Profound physiological and psychological changes
How many endocrine events of puberty are there?
Two endocrine events
What is the first endocrine event of puberty and what is it and what does it result in?
The first is adrenarche:
- It is the result of adrenal androgen secretion
- Results in the growth of pubic and axillary hair and growth in height
What is the second endocrine event of puberty and what is it and what does it result in?
The second is gonadarche:
- It is the reawakening of the HPG axis
- Results in the development in secondary sexual characteristics
What do both adrenarche and gonadarche result in?
Both of these events result in complete puberty
What is adrenarche and what secretion do we get?
Adrenarche is the change in adrenal androgen secretion due to cellular remodelling of adrenal
-Get secretion of DHEA and DHEAS
Is there any other change in steroids in adrenarche?
No other adrenal steroid change
Where are both DHEA and DHEAS secreted from?
DHEA and DHEAS are secreted from the zona reticularis of adrenal cortex
What is pubarche the result of?
Is the result of adrenarche
What does pubarche result in the appearance of?
Results in the appearance of pubic/axillary hair
What is pubarche associated with?
Associated with:
- Increase in sebum production=acne
- Infection, abnormal keratinization=acne
When is pubarche known as precocious?
If pubarche is before 8 yrs old in girls or 9 yrs old in boys, this is known as precocious
When does gonadarche occur?
Occurs several years after adrenarche
What is gonadarche?
Is the reactivation of hypothalamic GnRH
What do we see the activation of in gonadarche and what does this lead to?
We see the activation of gonadal steroid production which leads to the production of viable gametes and ability to reproduce
What is GnRH synthesized and secreted by?
Synthesised and secreted by specialist hypothalamic centres-GnRH neurons
When is HPG axis first activated?
HPG axis first activated at 16th gestational week
What secretion is there in a foetus and until when?
There’s pulsatile GnRH secretion in foetus until 1-2 years postnatally when it ceases
When are GnRH neurons restrained?
GnRH neurons restrained during postnatal period
What happens at puberty to the release of GnRH?
At puberty there’s a gradual rise in pulsatile release of GnRH
What does anorexia nervosa/intensive physical training result in in terms of reproduction?
-Reduced response to GnRH
-Decreased gonadotropin levels
-Amenorrhea
Restored when nourished/exercise stopped
What does inactivating mutations of KISS1R or the gene coding for KISSpeptin result in?
Results in:
- Hypogonadism
- Failure to enter puberty
- Hypogonadotropic hypogonadism
What does activating mutation of KISS1R result in?
Results in:
-Precocious puberty
What is consonance?
Consonance is smooth ordered progression of changes in puberty
What are the physical changes in girls during puberty?
- Breasts enlarge
- Pubic/axillary hair
- Uterus enlarges, cytology changes
- Uterine tubes
- Vagina
- Cervical changes
- Height increase
- Body shape
- HPG axis
- Increase in ovarian size and follicular growth
What are physical changes in boys during puberty?
- External genitalia
- Increase in testicular volume
- Growth in penis, scrotum, scrotal skin changes - Vas deferens
- Lumen increases - Seminal vesicles and prostate
- Facial/body hair
- Pubic/axillary hair
- Larynx - androgens –> enlarge larynx(adam’s apple)
- Height
- Body shape
- Onset of fertility
What is a growth spurt a complete interaction between?
Is a complete interaction between:
- Growth hormones
- Oestrogen
In what gender is growth spurts earlier in?
Earlier in girls
What is the biphasic effect of oestrogen on epiphyseal growth?(LOW LEVELS OF OESTROGEN)
-Linear growth and bone maturation
What is the biphasic effect of oestrogen on epiphyseal growth?(HIGH LEVELS OF OESTROGEN)
-Epiphyseal fusion
What are psychological changes due to puberty?
- Increasing need for independence
- Increasing sexual awareness/interest
- Development of sexual personality
What is precocious sexual development defined as?
Defined as the development of any secondary sexual characteristic before the age of 8 in girls and before the age of 9-10 in boys
What is precocious puberty?
Is when pubertal changes are early but in consonance
Premature activation of HPG axis
-Is gonadotropin dependent precocious puberty in consonance:
-Can result from excess GnRH secretion-idiopathic or
secondary
-Or result from excess gonadotropin secretion-pituitary
tumor
-Is also gonadotrophin independent precocious puberty-loss of consonance:
-Results from testotoxicosis where an activating mutation . of LH receptor results in premature maturation of
external genitalia.
-Also results from sex steroid secreting tumor or administration of exogenous steroids
What is Mccune albright syndrome the most common thing?
The most common gonadotrophin independent precocious puberty
What is Mccune albright syndrome caused by?
Caused by mutation in the GNAS1 gene
What does Mccune albright syndrome result in?
Results in café au lait skin pigmentation
What is there a hyperactivity of in Mccune albright syndrome?
Hyperactivity of signalling pathways and overproduction of hormones
What is pubertal delay?
Is the absence of secondary sexual maturation by 13 yrs in girls or 14 yrs in boys
What causes pubertal delay?
Delayed activation of HPG axis:
-Constitutional delay
-Affecting both growth and puberty
-Hypogonadotropic hypogonadism(Low LH and FSH)
-Rare but can occur due to kallman’s syndrome due to
impaired GnRH migration
-Can occur due to other mutations causing defects in
GnRH production
-Hypergonadotropic hypogonadism(High LH and FSH)
-Presents at gonadal dysgenesis and low sex steroid
levels
