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UHD BIOL 1301 - Endocrine System

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Chapter 16: Endocrine System16.2: Introduction- The endocrine system is a collection of cells, tissues, and glands and serves as a central mechanism through which cells communicate with other cells and regulate physiological processes16.3: Anatomy Overview: Endocrine System16.4: Patterns of Organization- Endocrine cell: Releases chemical messengers into the bloodstream - General properties of hormones includeo Regulation of physiological processeso Released in very low quantitieso Movement solely through diffusiono Release in response to changes in homeostasis- Autocrine: cell releases a chemical messenger that activates itself- Paracrine: cell releases a chemical messenger that activates neighboring cells- Some chemical messengers can act as only a neurotransmitter, both a hormone and neurotransmitter, or only a hormone- Neurotransmitters have highly localized affects, while hormones can affect entire tissues or organ systems- Endocrine processes are most often regulated by negative feedback loops- Hormoneso Four main types of hormones based on chemical structure Amino acid derivatives  made of a single amino acid Peptide  chains of up to 40 amino acids Protein  chains greater than 40 amino acids Steroids  derivatives of cholesterol and often lipid solubleo Downregulation  Decreasing receptor levels on target cellso Upregulation  Increasing receptor levels on target cellso Permissiveness  Process of hormones regulating the receptor levels of other hormones Consequence  presence of one hormone is required for another hormone- Hormone Synthesiso Hormone levels don’t approach zero, they fluctuate between high and lowo Neurotransmitter release is an all-or-none process that varies in its frequencyo Peptide and protein hormones are encoded by geneso Amino acid derivatives are synthesized from amino acids within vesicleso Multiple peptide hormones can be encoded by one geneo Signal peptide  directs hormones to correct intracellular organelle for processing- Hormone Secretiono Regulated in response to Changes in a critical physiological factor like ions Direct input from the CNS through neurohormone release Actions of other hormones Mechanical stresses or cellular metabolism- Hormone Transporto Water-soluble are usually transported directly in the plasmao Lipid-soluble are transported through blood complexed to transport proteins Can exist in free (1%) or bound (99%) form Only free form can interact with target cells- Hormone Excretiono Water-soluble, free hormones Can be excreted through urine since smaller than kidney filtration barriero Lipid-soluble hormones Can be excreted through urine if chemically modified Otherwise excreted through GI tracto Half-life  time required to reduce blood concentration of a hormone by 50% Can be altered by rate of synthesis, secretion, metabolism, and excretion- Hormone Metabolismo Metabolism can change hormone levels or activity Peptide and protein hormones can be degraded by proteases Steroids can be rendered inactive by addition/removal of chemical groups- Hormone Receptorso Agonist  compound that can bind to hormone receptor and produce same effectso Antagonist  compound that binds the receptor and blocks signal transductiono Three main types of hormone receptors GPCRs- Integral membrane protein- Extracellular region of receptor binds the hormone- Intracellular regions signal the cell interior via G-protein- When activated, GTP binds and alpha subunit dissociates from trimeric complex and interacts with other proteins- Major target of cAMP is PKA, an enzyme that phosphorylates many proteins within a cell- cAMP is degraded by PDE 1-TMS- Integral membrane proteins- Extracellular region binds hormone- Intracellular region contains kinase domain  directly actives enzymes without G-proteins Nuclear Receptors- Receptors found inside cell that act as transcription factors- Generally cytoplasmic proteins complexed with heat shock proteins- Hormone binding leads to dissociation of HSPs, dimerization to a secondbound receptor, and translocation to the nucleus- Diseases caused by Mutations in Hormone Receptors16.5: Endocrine Tissues: Hypothalamus and


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