Anatomy and Physiology II essays

Anatomy and Physiology II essays - Anatomy and Physiology...

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Anatomy and Physiology II Essays for Exam I 2. Give the chemical classification of hormones and explain the mechanism of hormone action Lipid-soluble Hormones- include steroid hormones, thyroid hormones, and nitric oxide. Steroid Hormones are derived from cholesterol. Each steroid hormone is unique due to the presence of different chemical groups attached at various sites on the four rings at the core of its structure. These small differences allow for a large diversity of functions. Two thyroid hormones (T 3 and T 4 ) are synthesized by attaching iodine to the amino acid tyrosine. The benzene ring of tyrosine plus the attached iodines make T 3 and T 4 very lipid soluble. The gas nitric oxide (NO) is both a hormone and a neurotransmitter. Its synthesis is catalyzed by the enzyme nitric acid synthase. Action of Lipid-soluble hormones 1. A free lipid-soluble hormone molecule diffuses from the blood, through interstitial fluid, and through the lipid bilayer of the plasma membrane into a cell. 2. If the cell is a target cell, the hormone binds to and activates receptors located within the cytosol or nucleus. The activated receptor-hormone complex then alters gene expression: It turns specific genes of the nuclear DNA on or off. 3. As the DNA is transcribed, new messenger RNA (mRNA) forms, leaves the nucleus, and enters the cytosol. There, it directs synthesis of a new protein, often an enzyme, on the ribosomes. 4. The new proteins alter the cell’s activity and cause the responses typical of that hormone. Water-soluble Hormones- include amine hormones, peptide and protein hormones, and eicosanoid hormones. Amine Hormones are synthesized by decarboxylating (removing a molecule of CO 2 ) and otherwise modifying certain amino acids. They are called amines because they retain an amino group (-----NH 3 + ). The catecholamines----epinephrine, norepinephrine, and dopamine---are synthesized by modifying the amino acid tyrosine. Histamine is synthesized from the amino acid histidine by mast cells and platelets. Serotonin and Melatonin are derived from tryptophan. Peptide Hormones and protein hormones are amino acid polymers. The smaller peptide hormones consist of chains of 3 to 49 amino acid; the larger protein hormones include 50 to 200 amino acids. Examples of peptide hormones are antidiuretic hormones and oxytocin. Several of the protein hormones, such as thyroid-stimulating hormone, have attached carbohydrate groups and thus are glycoprotein hormones. The eicosanoid hormones are derived from arachidonic acid, a 20-carbon fatty acid. The major two types of eicosanoids are prostaglandins and leukotrienes. The eicosanoids are important local hormones, and they may act as circulating hormones as well. Action of Water-soluble Hormones
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This note was uploaded on 04/18/2008 for the course BIO 3040 taught by Professor Carr during the Spring '08 term at Palm Beach Atlantic University.

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Anatomy and Physiology II essays - Anatomy and Physiology...

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