I would say this way of defining family is by blood relationship ie sharing the same blood as the parents as opposed to say someone brought up by foster parents ie adopted and thus having a family by virtue of upbringing ie by who the child was brought up by.
The physical changes during puberty are due to <u>secondary sex characteristics</u>
Explanation:
Origin: Secondary sex characteristics in male typically originate at the onset and develop during puberty from 9-16 years.
Mechanism: The hypothalamus of the brain initiates the release of follicular stimulating and leutinizing hormones which trigger the Sertoli cells of the testes to begin spermatogenesis and the interstitial cells of Leydig to produce the male sex hormone testosterone.
It is this release of testosterone that leads to the development of secondary sexual characteristics like:
- Muscular and strong body
- Deepening of voice
- Growth of facial, axillary (underarm) and pubic hair
- Enlargement of reproductive organs like the scrotum, testes, etc; along with penis lengthening
- Spermatogenesis begins along with feelings of sexual drive during this adolescent period
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