Endocrine-Disrupting Pesticides - Pesticides: Evaluation of Environmental Pollution - page 610

Langerhans, producing insulin. Insulin is an aid in the metabolism of carbo-
hydrates. Its failure results in diabetes.
• Pituitary : The pituitary is a small oval-shaped gland at the base of the brain
secreting different hormones. It is the master gland as it controls the other endo-
crine glands and influences growth and metabolism. The hormones secreted
by it control mental, sexual, and physical growth of the body. Deficiency may
cause dwarfism and an excess result in much increased body growth called
acromegaly.
• Hypothalamus : The hypothalamus is a part of the brain and is involved in all
aspects of the emotional, reproductive, vegetative (including circulatory, diges-
tive, and respiratory), endocrine, hormonal, visceral (intestine), and autonomic
functions, and has a predominantly regulatory function.
20.2.1 Axes Within the Endocrine System
The hypothalamic-pituitary-thyroid axis (HPT axis) is a part of the endocrine system and
is responsible for the regulation of metabolism. The hypothalamus measures low levels
of thyroid hormone and reacts with the release of thyrotropin-releasing hormone (TRH).
TRH stimulates the pituitary to produce thyroid stimulating hormone (TSH). TSH in turn
stimulates the thyroid to make thyroid hormones until normal levels in the blood are
found. At high levels of thyroid hormone, the negative feedback starts.
The hypothalamic-pituitary-adrenal axis (HPA or HPTA axis) is a complex set of con-
trol and feedback between the hypothalamus, pituitary, and adrenal glands. They are an
important part of the neuroendocrine system that regulates not only stress responses but
also digestion, immune system, mood, sexuality, and energy consumption. When needed,
the production of corticotropin is stimulated in the pituitary via corticotropin-releasing
hormone in the hypothalamus. Negative feedback mechanisms come into effect at high
concentrations of glucocorticoids, such as cortisol and corticosterone, in a reduced produc-
tion of corticotropin by the pituitary.
The hypothalamic-pituitary-gonadal axis (HPG axis) consists of hypothalamus, pitu-
itary, and gonads. This system plays an important role in the development and regulation
of certain body functions such as reproduction and immune system.
The hypothalamus secretes gonadotropin-releasing hormone (GnRH). This stimulates
the pituitary to manufacture luteinizing hormone (LH) and follicle-stimulating hormone
(FSH). Both LH and FSH act on the gonads to release sex hormones. (Too) high levels of
androgens and estrogens are put into effect as a negative feedback to slow down the pitu-
itary and hypothalamus.
20.3 Secretion from Glands: Hormones
All hormones have regulating functions and are part of sometimes simple, but sometimes
complex, regulating systems. The body controls the quantities of hormones to release by
negative feedback. One part of the brain involved in that system is the hypothalamus. The
pituitary is regulated by the hypothalamus. Endocrine glands are controlled by the releas-
ing factors of the pituitary. Between endocrine glands and pituitary, feedback systems
exist. The hypothalamus registers quantities of different hormones in the blood and reacts