Endocrine system Flashcards
Neuroendocrine system
- general funciton: communication, integration, and control
- secreting cells send hormone molecules by way of the blood to specific target cells
- hormones are carried to almost every point in the body and can regulate most cells
- endocrine glands are “ductless glands” composed of glandular epithelium
Endocrine glands
Responsible for secreting hormones directly into the blood
- ductless glands
- widely scattered throughout the body
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Hormones
Tropic - sex - anabolic - steroid - non steroid
Steroid hormones
- synthesized from cholesterol
- lipid soluble
Nonsteroid hormones
- synthesized primarily from amino acids
- protein hormones
- glycoproteins hormones
- peptide hormones
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General principles of hormone action
- hormones signal a cell by inning to the target cell’s specific receptors in a “lock and key” mechanisms
- different hormone receptor interactions produce different regulatory changes within the target cell through chemical reactions
- combine hormone actions: synergism, permissiveness, antagonism
How hormones work
- diffuse into the blood and are transported to almost every point in the body
- a given hormone affects only specific target cells
- effects work more slowly and last longer than those of neurotransmitters
Primary effect
Directly regulate target cells
Secondary effects
Influence or modulate other regulatory mechanism in target cells
- endocrine glands produce more hormone molecules than are actually needed
- unused hormones are quickly excreted by the kidneys or broken down by metabolic processes
Mechanism of steroid hormone action
- steroid hormones are lipid soluble, and their receptors are normally found in the target cell’s cytosol
- after a steroid hormone molecule has diffused into the target cell, it binds to a receptor molecule to form a hormone receptor complex
- mobile-receptor model: hormone passes into the nucleus, where it binds to a mobile receptor and activates a certain gene sequence to begin the transcription
Mechanisms of nonsteroid action
Most operate using second messenger model
- first messenger: non steroidal hormone delivers chemical message to fixed receptor on target cell’s plasma membrane. Message is then passed into the cell
- second messenger: picks up message passed into cell by first messenger. Triggers appropriate cellular changes
Second messenger mechanism
- amplifies effects of the hormone.
- doesn’t take a lot of nonsteroid hormone to produce a huge effect
- faster than steroid mechanism
- produce effects in seconds to minutes (vs 45 min-days with steroid hormones)
Regulation of hormone secretion
Most hormonal regulatory systems are negative feedback loops. Tend to reverse any deviation of the internal environment away from its stable point
- a few are positive feedback loops
- responses that result from the operation of feedback loop within the endocrine system are called endocrine reflexes
- regulated by:
1. Signals from the nervous system
2. Chemical changes in the blood
3. Other hormones