Senin, 25 Maret 2013

Hormones can be chemically classified into four groups:

Hormones can be chemically classified into four groups:
  1. Amino acid-derived: Hormones that are modified amino acids.
  2. Polypeptide and proteins: Hormones that are chains of amino acids of less than or more than about 100 amino acids, respectively. Some protein hormones are actually glycoproteins, containing glucose or other carbohydrate groups.
  3. Steroids: Hormones that are lipids synthesized from cholesterol. Steroids are characterized by four interlocking carbohydrate rings.
  4. Eicosanoids: Are lipids synthesized from the fatty acid chains of phospholipids found in plasma membrane.

Endocrine glands release hormones in response to one or more of the following stimuli:
  1. Hormones from other endocrine glands.
  2. Chemical characteristics of the blood (other than hormones).
  3. Neural stimulation.

Most hormone production is managed by a negative feedback system

     The nervous system and certain endocrine tissues monitor various internal conditions of the body. If action is required to maintain homeostasis, hormones are released, either directly by an endocrine gland or indirectly through the action of the hypothalamus of the brain, which stimulates other endocrine glands to release hormones.

     The hormones activate target cells, which initiate physiological changes that adjust the body conditions. When normal conditions have been recovered, the corrective action - the production of hormones - is discontinued.
   Thus, in negative feedback, when the original (abnormal) condition has been repaired, or negated, corrective actions decrease or discontinue. For example, the amount of glucose in the blood controls the secretion of insulin and glucagons via negative feedback.

Sumber : Bpk. Dr. Iskandar Zulkarnain

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