Hormones act through specific receptors on target cells. Hormone receptors are large proteins that determine the specificity of hormone action. Hormones can act by changing membrane permeability, binding to intracellular receptors to affect gene expression, or activating second messengers through G-protein coupling which then mediate the hormone's physiological response. Hormone action can also occur via tyrosine kinase activation either through receptors with intrinsic tyrosine kinase activity or receptors that activate tyrosine kinases.

1. BY
HORMONE: RECEPTORS AND
MECHANISM OF ACTION

2. MCQ
• Which of the following is not considered a
second messenger?
A. Ca2+
B. Cyclic AMP
C. diacylglycerol (DAG)
D. guanylyl cyclase
E. Inosital triphosphate (IP3

3. • guanylyl cyclase

4. Hormone receptors
All hormones act through
specific receptors. Almost all
hormone receptors are large
proteins present in hormone
sensitive target cells.

5. Specificity of hormone action is
because of specific receptors.

7. Characteristics of hormone receptors

8. Mechanism of action of hormones

9. Action through change in membrane
permeability

10. Action through effect on gene expression by
binding of hormones with intracellular receptors

11. Action of hormones through their effect
of gene expression.

14. Action through second messengers

15. Schematic mechanism of coupling by G-protein
leading to increase in second messenger which
mediates hormone’s physiological response

17. Mechanism of action of hormone via tyrosine
kinase activation

18. Mechanism of action of hormone via tyrosine kinase
activity: A, by receptors that possess intrinsic tyrosine
activity: and B, by receptors that do not possess
intrinsic tyrosine activity

20. Measurement of hormones

22. Enzyme-linked immunosorbent assay method