Birth to puberty Flashcards
When do the tesis descend in the bull?
3.5-4 months of gestation
When do the stallion testis descend?
late pregnancy or a few days after birth
When do the canine testis descend?
up to 8 days after birth
Explain the process of testis descent
Transabdominal phase - testes lie in retroperitoneal position and are attached caudally to ligamentous gubernaculum
- as fetus grows testes are pushed against peritoneum which causes peritoneal cells to wrap around gubernaculum Inguinal-scrotal phase - the gubernaculum then undergoes a rapid period of expansion, pulling the testes down through the inguinal canal
- the gubernaculum then regresses
What is puberty?
a developmental process in which endocrine and morphologic changes transform the animal into an individual capable of reproducing
What stimulates puberty?
Secretion of GnRH from the hypothalamus at the appropriate frequency and quantity to stimulate gonadotropin release by the anterior pituitary
What is the difference between the hypothalamus in males and females in relation to puberty and what is the effect of this?
Males have no surge centre - post puberty -> small LH surges followed by testosterone
Females have a surge centre - high ampliture preovulatory episodes with basal low amplitude pulsatile episodes between the surges
Why does the female hypothalamus have a surge centre but not the male?
Oestrogen complex is too big to cross BBB -> development of surge centre
Testosterone small enough to cross BBB -> converted to oestrogen in brain (via aromatase)
Describe the control of GnRH secretion in females after puberty
Tonic centre controls basal levels
Surge centre controls pre-ovulatory surge in GnRH -> pre-ovulatory LH surge
What controls the onset of puberty?
GnRH levels from hypothalamus too lovw to stimulate FSH/LH release
Describe GnRH pulses in the pre-puberty female
Tonic centre stimulates LH pulses
Low frequency of GnRH pulses - stimulus not enough for LH and FSH release
- oestrodiol secretion by ovarian follicles very low
- below minimum threshold needed to stimulate GnrH neurons in surge centre
What changes in the tonic centre in females at the beginning of puberty and what is the cause of this?
Pre-puberty the tonic centre has an inhibitory effect of GnRH and therefore LH/FSH production
This inhibitory effect reduces so oestradiol levels increase and stimualte the surge centre leading to increased GnRH, LH and FSGH production -> puberty
Describe the onset of puberty in the male
inhibitory effect of oestradiol/testosterone decreases
GnRH neurones become less sensitive to -ve feedback
Increased GnRH
increased LH/FSH
pubert
indices of male puberty onset
Why is the amount of fat and body maturation important in the onset of female puberty?
GnRH neurones are sensitive to metabolic status
3 main pre-synaptic neurones: glucose sensitive, fatty acid sensitive, leptin sensitive
Leptin, fatty acids and glucose promote activity in ‘kisspeptin neurones’ which produce a hormone that acts on GnRH neurones
