e. Negative Feedback. Negative feedback enables the endocrine glands to
regulate themselves. Negative feedback means that once the normal physiological
function of the hormones has been achieved, information is transmitted back to the
glands in some way and the producing glands stops or slows the production of that
particular hormone. The presence of increased amounts of a hormone will depress the
endocrine gland responsible for the production of this hormone and cause less of this
hormone to be produced. Conversely, a decrease in the blood levels of a hormone will
cause the endocrine gland to produce more of this hormone.
a. Control "Systems" of the Human Body. The structure and function of the
human body is controlled and organized by several different "systems."
(1) Heredity/environment. The interaction of heredity and environment is
the fundamental control "system." Genes determine the range of potentiality and
environment develops it. For example, good nutrition will allow a person to attain his full
body height and weight within the limits of his genetic determination. Genetics is the
study of heredity.
(2) Hormones. The hormones of the endocrine system serve to control the
tissues and organs In general. (Vitamins have a similar role.) Both the hormones and
vitamins are chemical substances required only in small amounts.
(3) Nervous system. More precise and immediate control of the structures
of the body is carried out by the nervous system.
b. The Endocrine System. In the human body, the endocrine system consists
of a number of ductless glands that produce their specific hormones. Because these
hormones are carried to their target organs by the bloodstream, the endocrine glands
are richly supplied with blood vessels.
c. Better Known Endocrine Organs of Humans. The better known endocrine
glands are the:
Pancreatic islets (Islets of Langerhans).
Suprarenal (adrenal) glands.