 In this topic, we shall discuss the various chemical types of hormones and their functions. Based on their chemical structure and pathway of synthesis, hormones are classified into four chemical types. Number one, the peptide and protein hormones. Number two, amine hormones. Number three, steroid hormones. And number four, prostaglandins. First we shall discuss the peptide and protein hormones. They are composed of amino acids. They include very small peptides as well as large protein molecules. For example, the thyrotropin-reasing hormone, TRH, released from hypothalamus, has only three amino acids in it. It is a very small peptide. In comparison, growth hormone or prolectin, large protein molecules, in which the amino acids are approximately 200. The amine hormones are small molecules which are synthesized from a single amino acid tyrosine. The hormones which are derived from tyrosine include epinephrine, norepinephrine, thyroxine and triiodothyronine. Simply we can say that thyroid gland and adenyl gland, adenyl medulla hormones, they are amine hormones. Now we shall discuss the steroid hormones. Acid hormones are synthesized from cholesterol. Cholesterol is called steroid and all the hormones derived from it are called steroids. These hormones have four fused carbon rings. These four rings are combined into a single structure to form the cholesterol. And it is derivative hormones. The examples of steroid hormones include hormones of adrenal cortex, cortisol and aldosterone. Hormones of ovaries that is estrogen and progesterone and the male sex hormone produced by the testase that is testosterone. The prostaglandins are cyclic unsaturated hydroxy fatty acids. They are synthesized in cellular membranes from a 20 carbon fatty acid chain. Now we shall discuss the general functions of hormones. Hormones coordinate long term functions of animal tissues and organs. For example, they modulate growth and maintenance, sexual activity of the animal, reproductive cycles and modification of behaviors. They also perform many regulatory functions. For example, osmoregulation, regulation of blood sugar level and control of metabolic rate. Many rhythmic activities of the animals are also due to hormones. For example, insects may be molding, that is regulated by hormones, sleep, wake up cycles are affected by hormones. Similarly, hunger and hunger cycle and seasonal reproductive activities in many animals are because of hormonal regulation of these rhythms. Migration in birds seasonal basis and that is also because of the hormones. Moreover, hormones also maintain homeostasis. They also coordinate bodies responses to stress. They also mediate responses to many environmental stimuli. A very important function of hormones is the nervous system, which produces rapid acting short living responses. It complements its activities with its long term and slow chemical activity. The stage of complementarity has no systems key that results in the overall integration of the physiological and metabolic functions in the body.