Notes Anatomy & Physiology II Endocrine System 4 Circulating and Local Hormones

Notes Anatomy & Physiology II Endocrine System 4 Circulating and Local Hormones

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Anatomy & Physiology II AHS 132 Chapter 18 The Endocrine System Circulating & Local Hormones • Circulating hormones – act on distant targets – travel in blood • Local hormones – paracrines act on neighboring cells – autocrines act on same cell that secreted them Lipid-soluble Hormones • Steroids – lipids derived from cholesterol – different functional groups attached to core of structure provide uniqueness • Thyroid hormones – tyrosine ring plus attached iodines are lipid soluble Water-soluble Hormones • Amine, peptide and protein hormones – modified amino acids or amino acids put together – serotonin, melatonin, histamine, epinephrine – some glycoproteins • Eicosanoids – derived from arachidonic acid (fatty acid) – prostaglandins or leukotrienes Interaction of hormones and receptors at the cellular level. Lipid Soluble : Steroid hormones are hydrophobic and can cross the cell membrane
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Unformatted text preview: to find receptors inside the cell. Water Soluble : Amine and polypeptide hormones are hydrophilic and, because they cannot cross the cell membrane , act via second messengers. Hormone Transport in Blood • Protein hormones circulate in free form in blood • Steroid (lipid) & thyroid hormones must attach to transport proteins synthesized by liver – improve transport by making them water-soluble – slow loss of hormone by filtration within kidney – create reserve of hormone General Mechanisms of Hormone Action • Hormone binds to cell surface or receptor inside target cell • Cell may then – synthesize new molecules – change permeability of membrane – alter rates of reactions • Each target cell responds to hormone differently – liver cells---insulin stimulates glycogen synthesis – adipose---insulin stimulates triglyceride synthesis...
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