6 - Puberty and the HPG Axis Flashcards
What is puberty and what are some processes that occur during this?
Preparation for sexual maturity to enable us to reproduce, creates distinct differences between sexes.
What factors affect the start of puberty?
- Age variable but once starts sequence of changes constant
- Pineal gland* has some influence with light as issues e.g tumours, with this lead to precocious puberty
- In girls body weight, nutrition and leptin, critical weight being 47kg
How do you assess what level of puberty an adolescent is at?
Tanner Scale
What is the difference between primary and secondary sexual characteristics?
Primary - At birth, internal and external genitalia
Secondary - Those that develop after puberty, e.g pubic hair, breat development, menstruation
What is the sequence of events in female puberty?
Starts around 8-13
1. Thelarche
2. Pubic hair (testosterone)
3. Growth spurt (GH and oestrogen ending)
4. Menarche
5. Coarser pubic hair and anatomical spread
6. Breast development
What is the sequence of events in male puberty?
Starts around 10-14
- Testicular enlargement
2. Pubic hair growth (testosterone)
3. Spermatogenesis
4. Growth spurt (later than girls)
5. Testes and penis growth
6. Pubic hair coarser and anatomical spread
Why do boys grow taller than girls even though they have a growth spurt at a later stage?
- Boys have less oestrogen and it is oestrogen that causes epiphyseal growth plates to fuse
- Growth depends on IGF, GH and oestrogen
Complete the following table.
What can be the consequence of precocious puberty?
- Short stature as the levels of oestrogen rise earlier
- More common in obese adolescents, girls and Afro-Caribbeans
What process occurs endogenously in the body to signal the start of puberty?
- GnRH produced in hypothalamus, stimulated by leptin
- Pulsatile release, mainly nocturnal
- GnRH causes release of LH and FSH from anterior pituitary
- Final hormones from gonads drive secondary characteristics
What parts of the gonads to FSH and LH work on?
What is the relationship between the hypothalamus and the anterior pituitary gland?
Connected by superior hypophyseal artery
Why is sleep important in children at puberty age?
- GnRH released every 1-3hrs mainly at night into hypophyseal portal system
- Ensures there is sufficient LH and FSH levels to initiate gonadal development
How does negative feedback occur in the HPG axis?
- GnRH feedsback on itself along with every other hormone
- When follicles (gametes) stimulated they release inhibin to negatively feedback on FSH to stop further production and maturation
What effect does FSH and LH on male gonads?
LH:
- Stimulates Leydig cells to produce testosterone
FSH:
- Increases sperm production on Sertoli (support) cells. This cause inhibin release to stop FSH
When looking histologically where would you find sertoli and leydig cells?
- Sertoli cells have large nucleus
- Leydig cells in interstitium
What effect does FSH and LH on female gonads?
- Act via Gs receptors and stimulate oestrogen, inhibin and progesterone release
Where is inhibin released from in females and what does it cause?
- From granulosa cells of corpus luteum
- Inhibts secretion of FSH
- Tiny inhibitory effect on LH
What are the hormonal changes that occur in the HPG that lead to a growth spurt?
What effect does leptin have on the reproductive system?
- Derived from adipocytes and signals to CNS about energy stores in body
- Pulsatile release similar to LH
- Can regulate GnRH secretion. (critical weight 47kg, without will stop menstruation)
Fill in the following table with range ages in girls:
What feedback is occuring on the HPG during ovulation?
- Raised oestrogen is raising LH levels but not FSH as inhibin is present
