6.3 Reproductive Hormones
192 MHR • Unit 2 Homeostasis
Previously you learned that sexual reproduction is
the result of the combination of gametes, one from
a male and one from a female. On a biological level,
the process is necessary for the survival of the
species. Sexual reproduction produces the variations
necessary to maintain homeostasis as a species. As
the environment changes, natural selectionFigure 6.22As a species, Homo sapiensis characterized
by a relatively high degree of variation.determines which individuals will survive to breed
and pass on their variations to the next generation.
A species with few variations faces possible
extinction. The human species, with its reasonably
high degree of variation, has proven to be very
adaptable as it has populated the globe. In
fact, the incredible reproductive success of the
billions of Homo sapienswill be at the heart of
many of the challenges of the twenty-first century.
The biology of human reproduction is one of the
factors that has allowed us to inhabit almost every
part of Earth. In most mammals, reproductive
cycles are seasonal and mating occurs so that the
offspring are born when environmental conditions
are most favourable. Humans, along with some
non-human primates, elephants, and giraffes, are
examples of continuous breeders. That is, human
reproduction is not influenced by the seasons or
by location. However, as you will see, human
reproduction does have a cyclical component,
which is controlled by reproductive hormones.The Male Reproductive System
The male reproductive system begins to form when
the fetus is eight weeks old and becomes functional
at the end of puberty, when a boy is about 13 years
old. Pubertyin males is the stage of life during
which reproductive hormones are formed and
reproductive development begins, until the first
viable sperm are formed. From the end of puberty,
the male reproductive system is usually capable of
producing sperm 24 hours a day, seven days aEXPECTATIONSExplain the action of hormones in the female and male reproductive
systems, including the feedback mechanisms involved.
Compile and display, either by hand or computer, data and information about
homeostatic phenomena in a variety of formats.
Analyze how environmental factors (physical, chemical, emotional, and
microbial) and technological applications affect the maintenance of
homeostasis, and examine related societal issues.
Synthesize case study information about the effects of taking chemical
substances to enhance performance or improve health (for example, explain
the effect of steroids on health).
Present informed opinions about problems related to the health industry,
health legislation, and personal health.