Hormones - derived from the amino acid tyrosine and are...

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Hormones The endocrine system is a collection of glands that secrete chemical messages we call hormones . These signals are passed through the blood to arrive at a target organ, which has cells possessing the appropriate receptor. Exocrine glands (not part of the endocrine system) secrete products that are passed outside the body. Sweat glands, salivary glands, and digestive glands are examples of exocrine glands. Hormones are grouped into three classes based on their structure: 1. steroids 2. peptides 3. amines Steroids Steroids are lipids derived from cholesterol. Testosterone is the male sex hormone . Estradiol, similar in structure to testosterone, is responsible for many female sex characteristics. Steroid hormones are secreted by the gonads , adrenal cortex, and placenta .
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Peptides and Amines Peptides are short chains of amino acids ; most hormones are peptides. They are secreted by the pituitary , parathyroid, heart , stomach , liver, and kidneys. Amines are
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Unformatted text preview: derived from the amino acid tyrosine and are secreted from the thyroid and the adrenal medulla. Solubility of the various hormone classes varies. Synthesis, Storage, and Secretion Steroid hormones are derived from cholesterol by a biochemical reaction series. Defects along this series often lead to hormonal imbalances with serious consequences. Once synthesized, steroid hormones pass into the bloodstream; they are not stored by cells, and the rate of synthesis controls them. Peptide hormones are synthesized as precursor molecules and processed by the endoplasmic reticulum and Golgi where they are stored in secretory granules. When needed, the granules are dumped into the bloodstream. Different hormones can often be made from the same precursor molecule by cleaving it with a different enzyme. Amine hormones (notably epinephrine ) are stored as granules in the cytoplasm until needed....
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