birth to puberty Flashcards
how do the testis descend
Transabdominal Phase:
Testis within the transabdominal position pre inguinal ring descent.
Held in place above the inguinal ring via the gubernaculum ligament which is connected with the scrotum sac.
Gubernaculum comes into contact with peritoneal cells above the inguinal ring and fuse together (to become the tunica albugina and the other two layers)
Inguinal Scrotal Phase:
This pulls the testes down through the inguinal ring as the gubernaculum expands; ending up with peritoneal cells around the testis into the scrotum.
As testis passes through the gubernaculum then begins to regress to a knot at the base of the scrotum to pull the testes into the scrotal sac.
what is puberty
a developmental process in which endocrine and morpholigic changes transform the animal into an individual capable of reproducing
what event is required for puberty to occur
secretion of GnRH at the appropriate frequency ad quantity to stimulate gonadotrophin release by the anterior pituitary
do males have a surge centre in their hypothalamus
NO
Describe the key endocrinological and anatomical changes that occur from birth to puberty
Birth:
Female
Oestrogen enters circulation and binds to alpha fetoprotein (aFP)
Complex is too big to cross the BBB
Female surge centre develops in the hypothalamus as nothing is stopping it
Male
Testosterone produced in testes which does not bind aFP
Diffuses across BBB
Under influence of aromatase enzyme this is converted to oestrogen
This stops the surge centre from developing in the hypothalamus
Puberty:
Hypothalamus- GnRH released- stimulates anterior pituitary to stimulate gonadotrophins (FSH and LH) causes gametogenesis, steroidogenesis and reproductive tissue dev
Puberty Onset in Females:
PRE PUBERTY LOW LEVELS OESTORGEN: no effect on surge centre; inhibitory effect on tonic centre so GnRH is not produced so little FSH and LH in the blood
PUBERTY LOW LEVELS OESTROGEN: lifts inhibit effect on tonic centre so GnRH release is increased and FSH and LH release increased. This presence of FSH and LH increases oestradiol production which in turn stimulates more LH and FSH causing ovulation and puberty. The increased oestradiol levels also acts on the surge centre for increased kisspeptin neuron activity
The lifting of inhibition in the tonic centre is the trigger for puberty in the female
Puberty Onset in Males:
PRE PUBERTY OESTROGEN PRESENFCE: inhibits GnRH production so low levels of LH and FSH
PUBERTY LOW LEVELS OESTRADIOL: more GnRH produced, more lH and FSH produced, puberty triggered
discuss GnRH pulses in the pre puberty female
- pre puberty the tonic centre stimulates LH pulses
- frequency of the GnRH pulses is low, stimulus not enough for LH and FSH release at high levels
- oestradiol secretion by ovarian follicles very low
- below minimum threshold needed to stimulate GnRH neurones in surge cente
discuss puberty onset in the female
- pre puberty the tonic centre is inhibited, meaning there are low GnRH and FSH/LH secretions
- during transition to puberty inhibition of tonic centre is lifted –> increase in GnRH and as a result FSH/LH
- oestradiol levels then increase having positive effect on surge centre leading to positive feedback on GnRH leading to increased LH = ovulation and puberty
discuss puberty onset in the male
list indices of male puberty onset
- behaviour change
- age at first ejaculation
- age when sperm appear in ejaculate
- age when ejaculate contains a threshold number of sperm
how does body size influence female puberty
- amount of fat and body maturation important
- GnRH neurones sensitive to metabolic status
- three main types of pre-synaptic neurones (glucose sensitive, fatty acid sensitive, leptin sensitive)
- leptic, fatty acids and glucose thought to promote activity in kisspeptin neurones
how do kisspeptin work
- an intact kisspeptin signalling pathway is a prerequisite for the onset of puberty
- kisspeptin binds to its receptor on GnRH secreting neurones
- kisspeptin neurones express oestrogen receptor
- since rising concentrations of oestradiol stimulate the HPG axis it must involve kisspeptin neurones
what external factors effect female puberty
