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endocrine system
- releases hormones (chemical messengers) that trigger cells to perform certain functions
- works together with nervous system to control function of all body systems
- hormones effect activity of cells somewhere else in the body
- responses are slower than nervous system responses
- effects are broader than nervous system effects
- nervous system starts/stops release of hormones
- hormones start/stop AP conduction
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target cell
any cell affected by a hormone
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exocrine gland
- produces a product (no hormones) and releases into duct
- into body cavities, organs, surfaces
- ex: sweat glands, oil glands, mucus glands
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endocrine gland
produces hormone and secretes into blood or interstitial fluid
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hormone receptors
- proteins on the surface of target cells that physically bind to hormones
- only target cells for a given hormone have the appropriate receptors
- most target cells have 2,000 - 100,000 receptors for a particular hormone
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down regulation
- number of receptors for a specific hormone decreases when excess hormone is present in the blood
- target cell is less responsive to the hormone
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up regulation
- number of receptors for a specific hormone increases when not enough hormone is present in the blood
- target cell is more responsive to the hormone
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circulating hormones
enter blood, move through body, and act on a target cell far away
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local hormones
act on neighboring cell - do not enter blood
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autocrine hormone
acts on cell that produced hormone
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paracrine hormone
acts on neighboring cell
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water soluble hormones
- biogenic amines
- proteins and peptides
- eicosanoids
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lipid soluble hormones
- steroids
- thyroids
- nitrous oxide
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hormone action
- hormones bind to protein receptors at target cell
- if water soluble - receptor is on surface of target cell - need second messenger
- if lipid soluble - receptor is on inner surface of cell membrane - diffuse easily
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second messenger
- water soluble protein (1st messenger) absorbed by G-protein on the surface of target cell
- G-protein activates Adenylate Cyclase enzyme -> activates ATP -> activates cAMP (2nd messengers) -> activates Protein Kinases -> determines how cell responds to hormone
- Phosphodiesterase deactivates protein K and cAMP to stop the process
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hormone secretion
- most are secreted in short bursts
- when stimulated, secretion is more frequent
- controlled by nervous system, chemical levels, and other hormones
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