Mechanism of Hormone action
When hormone arrives at it's target cell, it binds to a specific receptors, where it act as influencing chemical or metabolic reactions inside cell
Hormones activate target cells, depending upon chemical nature of hormone.
1. Lipid soluble hormones
2. Water soluble hormones
1. Lipid soluble hormones
Steroid hormones of thyroid gland, diffuse through cell membrane of target cell. Lipid soluble hormone the bind to receptor protein and regulate specific physiological cell activity.
2. Water soluble hormones
Polypeptide, protein, most amino acid hormones bind to receptor protein on plasma membrane of cell. (Insulin, glucagon, adrenaline).
Control of Hormone Release
1. Negative feedback mechanism
2. Positive feedback mechanism
Synthesis and release of most hormone are regulated by negative feed back mechanism.
Hormone secretion is triggered by some internal or external stimulus.
As result, hormone level rise, they cause target organ effect and inhibit further hormone release.
For example;
Beta cells secretes insulin.
Alpha cells secrete Glucagon.
Positive feedback mechanism
Production of some hormones is controlled by positive feedback.
In such system, rising level of hormone is responsible for increasing to other hormone.
For example; positive feedback system is child birth.
During labor, a hormone called oxytocin is release that intensifies and speed up contraction, stimulates contraction of uterus. Oxytocin leads in lactation, hormone level increase and cause increase in milk production.
The hormone produced by hypothalamus causing milk production and uterine contraction is oxytocin.
Endocrine gland release hormone in response following stimuli;
Hormonal stimuli; secrete hormone direct response to changing blood level.
Neural stimuli; nerve fibers stimulate hormone release.
Hormonal stimuli; release hormone in response to hormone produced by other endocrine organ.
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