3. Monoamines: Monoamines are derived from the aromatic amino acids like tyrosine, tryptophan and phenylalanine by the action of aromatic amino acid decarboxylase enzymes. Examples of monoamines are epinephrine, norepinephrine etc.

Endrocrine system and function: The endocrine system consists of the system of glands. Each gland secretes different types of hormone directly into the bloodstream to regulate the body.

Hormones of the pituitary gland: The pituitary is a small, pea-sized gland situated at the base of the brain. It sends signals to the thyroid and adrenal glands and the ovaries and testes, directing them to produce thyroid hormone, cortisol, estrogen, testosterone, and other hormones. These hormones have an effect on the metabolism, blood pressure, sexuality, reproduction and other essential functions of the body. In humans, the pituitary gland consists of three lobes:

• Anterior Lobe (Adenohypophysis)
• Posterior Lobe (Neurohypophysis)
• Intermediate lobe

1. Anterior Lobe : The anterior lobe contains six types of secretory cells. All of them secrete their hormone in response to hormones reaching them from the hypothalamus of the brain.The anterior pituitary gland secretes the following vital endocrine hormones:

(a) Thyroid stimulating hormone (TSH): Thyroid-stimulating hormone (thyrotropin) is a glycoprotein consisting of an alpha chain of 92 amino acids and a beta chain of 118 amino acids. TSH is synthesized and secreted by thyrotrope cells in the anterior pituitary gland. Thyroid stimulating hormone stimulates the thyroid gland to secrete the hormone thyroxine (T₄). T₄ is converted to triiodothyronine (T₃), which is the active hormone that stimulates metabolism. The TSH receptor is found mainly on thyroid follicular cells. A deficiency of TSH causes hypo thyroidism. TSH deficiency has also been implicated as a cause of osteoporosis.