Endocrine Regulation of Puberty and Normal Pubertal Development Flashcards
What is puberty?
The process through which a child passes to achieve sexual maturity and reproductive capacity
What is pubertal onset precipitated by?
The secretion of hypothalamic pulses of gonadotrophin-releasing hormone (GnRH)
What does pulses of GnRH release cause?
Stimulates pulses of LH
What regulates the release of GnRH?
Unclear, but GnRH neurones are under control of excitatory and inhibitory neurones
What is the neurotransmitter in the excitatory neurones controlling GnRH neurons?
Glutamate
What neurotransmitter is in the inhibitory neurones controlling GnRH neurones?
GABA
What factors influence the onset of puberty?
- Genetic influences
- Nutritional effects
- Environmental influences
What shows that there are genetic influences in the onset of puberty?
The inherited pattern of the timing of onset of puberty
What mediates the nutritional effect on puberty onset?
Leptin
In which gender have environmental influences been shown to affect the onset of puberty?
Girls
What does increasing LH stimulate in boys?
Secretion of testosterone from tetiscular Leydig cells
What does the secretion of testosterone from testicular Leydig cells promote?
Development of secondary sexual characteristics
What secondary sexual characteristics are developed as a result of testosterone secretion?
- Enlargement and maturation of penis and scrotum
- Increased musculature
- Facial and other body hair
- Deepening of the voice
What stimulates the pubertal growth spurt in boys?
Rise in GH and IGF-1 levels
How does a rise in GH and IGF-1 levels stimulate the pubertal growth spurt in boys?
It leads to increased resistance to insulin-mediated glucose metabolism, which in turn causes increased insulin secretion to help fuel anabolism during the growth spurt
What effect does the increase in testosterone have on LH secretion?
It feeds back to modulate LH secretion
What effect does FSH have in boys?
It binds to Sertoli cells to enhance spermatogenesis
What do Sertoli cells produce?
Inhibin B
What is the role of Inhibin B?
It exerts a negative feedback on pituitary FSH release
What does an increase in LH levels stimulate in girls?
- Proliferation of the follicular and thecal cells
- Androgen secretion during the follicular phase of the menstrual cycle
What effect does increased FSH have in girls?
- Stimulates proliferation of granulose cells
- Supports aromatisation of androstenedione to oestradiol
- Stimulates progesterone production n
What effect does an increase in oestrogen levels have in girls?
- Stimulates secondary sexual charateristics
- Stimulates growth spurt
- Causes proliferation of follicular cells
How does oestrogen cause the proliferation of follicular cells?
Acts on FSH receptors on granulosa cells to cause proliferation of follicular cells
What is inhibin A produced by in girls?
- Large antral follicles
- Corpus lutem
What is inhibin B produced by in girls?
Small antral follicles
What effect do inhibins have in girls?
- Feed back on FSH secretion
- Involved in dominant follicle selection
How long does the follicular phase of the menstrual cycle last?
Variable, but typically 14 days
What develops during the follicular phase of the menstrual cycle?
15-20 primordial follicles
What happens to the primordial follicles developed during each menstrual cycle?
Most become atretic, but one dominant Graafian follicle remains
How good is this explanation of the menstrual cycle?
Pretty bad, maybe learn it elsewhere
What happens to FSH from the first day of the menstrual cycle?
It increases
What is the result of FSH increasing on the first day of the menstrual cycle?
It stimulates follicular production of estradiol
What is the effect of the follicular production of oestradiol which was stimulated by the rise in FSH?
Feedback inhibition of LH and FSH
What happens after oestriadiol has inhibited LH and FSH?
Oestradiol feedback to the pituitary switches from negative to positive, causing a preovulatory LH surge
What happens in the day 14 luteal phase of the menstrual cycle?
LH stimulation causes the ovum to enter the final phase of the first meiotic division
What is produced when the ovum enters the final phase of the first meiotic division?
It becomes a secondary oocyte
What happens to the follicle once the secondary oocyte has been formed?
The follicle swells, ruptures, and releases the ovum into the Fallopian tube
What is formed from the ruptured follicle?
The corpus lute
What does the formation of the corpus luteum result in?
Progesterone mediated swelling and secretion of the endometrium
When does progesterone peak in the menstrual cycle?
5-7 days post-ovulation
What is the effect of the peak in progesterone in the menstrual cycle?
It exerts a negative feedback on GnRH-regulated LH and FSH secretion n
What is the result of the negative feedback on GnRH-regulated LH and FSH secretion caused by the progesterone peak?
It causes the corpus luteum to lose its receptors and become atretic
What happens once the corpus luteum has become atretic?
A new cycle starts
What is the mean age of the onset of puberty in boys?
12
What is regarded as a normal age for boys to start puberty?
10-14
What is the first stage of normal puberty in boys?
The development of 4ml testicular volumes
What shortly follows the formation of 4ml testicular volumes?
Development of pubic hair and genital changes
How can the pubertal changes be document?
Tanner staging
What is the mean age for onset of puberty in girls?
11
What is considered a normal age to start puberty in girls?
8-13
What is the first sign of puberty in girls?
Breast bud development
What shortly follows breast bud development in girls?
Pubic hair growth
How does the timing of the pubertal growth spurt differ between girls and boys?
It occurs earlier in girls
How long does progression through puberty take?
Typically 3 years
