22. CHEMICAL CO-ORDINATION AND INTEGRATION
Hormones produce their effects by binding to the specific proteins (hormone receptors) located in target tissues.
A hormone binds to its specific receptor to form hormone-receptor complex. It leads to biochemical changes in target tissue and thereby regulates metabolism and physiological functions.
Hormone receptors are 2 types:
1. Membrane-bound receptors:
- Some hormones (e.g. protein hormone, FSH) interact with membrane-bound receptors (do not enter the target cell).
- It generates second messengers (e.g. cyclic AMP, IP3, Ca2+). It in turn regulates cellular metabolism and causes physiological effects.
2. Intracellular receptors (mostly nuclear receptors):
- Some hormones (e.g. steroid hormones, iodothyronines) interact with intracellular receptors.
- They mostly regulate gene expression or chromosome function by the interaction of hormone-receptor complex with the genome.
- Cumulative biochemical actions result in physiological and developmental effects.
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