The Endocrine System

The Endocrine System - The Endocrine System Hormone- a...

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The Endocrine System Hormone - a chemical messenger secreted by a cell or group of cells (including neurons) into the blood for transport to a distant target, where it exerts its effects at very low concentrations. All hormones exert their effects by acting through receptors Alter membrane permeability and/or electrical state by activating 2 nd messenger pathways Regulate the transport of molecules across membranes Activate genes for transcription Stimulate the synthesis of proteins or other regulatory molecules Activate or deactivate enzymes Induce exocytosis (secretory activity) o Chemical Classes of Hormones: Amines - Derived from Tyrosine; Fast acting; Lipophobic; Made in advance, stored in secretory vesicles; exocytosed from parent cell; dissolves in plasma; short half-life; Receptors located on cell membranes; Activates second-messenger system; Modifies existing proteins Epinephrine, Norepinephrine, dopamine, and thyroid hormones Peptides - Derived from amino acids; fast acting (minutes to an hour); lipophobic; Uses G-Protein Coupled pathways and Tyrosine Kinase pathways; Made in advance, stored in secretory vesicles; exocytosed from parent cell; dissolves in plasma, short half-life; Activates second-messenger system; Receptors located on cell membranes; modifies existing protein, or induces new protein synthesis Insulin, ADH, Angiotensin II, ANF (atrial natriuretic factor) ACTH (Adrenocorticotropic hormone) Steroids - derived from cholesterol; Slow acting (hours or days); Lipophillic; Synthesized on demand from precursors; Diffuses through parent cell; Bound to protein carriers for transport; long half-life; Receptors located in cytoplasm or nucleus; activates genes for transcription or translation; Induces new protein synthesis Cortisol, Aldosterone o Humoral Stimuli (Ions or nutrients) for hormone release: ↑ Glucose = Insulin Cell of origin: Beta cells of Pancreas Biosynthesis: Typical Peptide Factors Affecting Release: Plasma [Glucose]> 100mg/dL. ↑ Blood amino acids; GI Hormones [feedforward reflex] and parasympathetic amplify. Sympathetic inhibits Target Cells: Liver, Muscle, Adipose Tissue Target Receptor: Membrane receptor with Tyrosine Kinase activity; Pathway with insulin-receptor substrates Whole Body or Tissue Action: ↓Plasma [Glucose] by ↑ transport into cells or ↑ metabolic use of glucose Action at cellular level: ↑ Glycogen synthesis; ↑ aerobic metabolism of glucose; ↑ Protein and triglyceride synthesis Action at Molecular Level: Inserts GLUT transporters in muscle and adipose cells; Alters enzyme activity. Complex signal transduction pathway Feedback Regulation: ↓ Plasma [Glucose] Shuts off insulin release Growth Hormone and Cortisol are antagonistic ↓ Glucose = Glucagon Cell of Origin: Alpha cells of Pancreas Biosynthesis: Typical Peptide
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Factors Affecting Release: Stimulated by plasma [glucose] < 200mg/dL, with
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The Endocrine System - The Endocrine System Hormone- a...

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