Endocrine-Disrupting Pesticides - Pesticides: Evaluation of Environmental Pollution - page 611

with hormonal or neural messages to the endocrine glands, especially to the pituitary. The
messages indicate if the production of hormones has to be stimulated or inhibited.
Hormones are chemical substances formed in an endocrine gland and conveyed by the
bloodstream to a specific organ or tissue elsewhere (sites remote from that of its produc-
tion) whose function they modify by means of chemical activity. Hormones are produced
in extremely small quantities, but their action is very rapid. They control growth and vari-
ous life processes of the body. For example, in the ovaries and testes, female and male
hormones are produced, respectively, which are responsible for female and male charac-
teristics such as voice, facial and body hair, stature, appearance, etc.
Homeostasis is a regulation within a body to achieve or maintain a balance. The body
comes into action when this balance is compromised, think of body temperature and
blood sugar level. Homeostasis is set within certain limits. Setting and recording of those
boundaries occur during fetal and neonatal periods.
To learn more about endocrine systems and hormones, see Henry and Norman (2003),
Norman et al. (2011), and Neal and Sompayrac (2001).
20.4 Endocrine System and Hormones of Insects
In insects, the endocrine system comprises four main organs, namely neurosecretory cells,
corpora cardiaca, corpora allata, and prothoracic glands, which are described in the fol-
lowing paragraphs.
Neurosecretory cells : The neurosecretory cells (NSC) are neurons in the central nervous
system that are specialized to secret hormones. Typically, two groups of such cells are
located in the protocerebral lobes of the brain: a pair of median groups and a pair of lateral
groups present respectively in the pars medialis and pars lateralis . Whereas the axons of the
median groups make a cross before emerging from the brain as the Nervi corporis cardiaci
I (NCC 1), those of the lateral groups pass out without decussating as the Nervi corporis
cardiaci II (NCC II). In most insects, the two NCCs enter the corpus cardiacum of their side
to unload the hormone brought from NSC for storage and release into circulation (hemo-
lymph) as and when needed.
Corpora cardiaca : The corpora cardiaca (CC) are small paired bodies situated immediately
behind the brain and are believed to be modified ganglia. They are made up of their own
intrinsic secretary cells and nerve fibers received from the brain through the NCCs. They
function as storage and release organs for the hormone synthesized in the NSC and since
the hormone is released in the hemolymph, they are called neurohemal organs. While the
storage and release of hormone constitute their main function, they are also believed to
produce their own (indigenous) hormone/hormones.
Corpora allata : The corpora allata (CA) are also paired organs though they may fuse into
one in some insects. They lie immediately behind the CC with which they are connected
by Nervi corporis allati (NCA) not conspicuous in many cases. They are ectodermal in ori-
gin and clearly glandular.
Prothoracic glands : The prothoracic glands (PTG) are again paired and flattened organs
lying close to the prothoracic spiracles. They are ectodermal, glandular, and larval organs
being lost in the adult. They are innervated in some insects and noninnervated in others.
In the larvae of Cyclorrhaphous diptera , the CC, CA, and PTG are all fused into a single
structure called the ring gland or Weismann's ring after the name of the discoverer.