Hormones exert their effects by altering metabolic processes: Synthesize proteins, alter enzyme activity , alter the rate of transport through the cell membranes. etc
Steroid and thyroid hormones
- The more receptors the hormone binds on its target cells, the greater the response.
- A. Steroid hormones and thyroid hormones
→ enter the target cell → Bind with receptors to form hormone-receptor complexes. → activate specific genes →synthesize specific proteins.
The degree of cellular response is proportional to the number of hormone -receptorcomplexes formed.
B. Nonsteroid Hormones
bind with cell surface receptors →stimulate membrane proteins to induce the formation of secondary messenger molecules→ Activate protein kinases →Activate other protein substrates → change cellular processes.
A small number of hormone- receptor complexes can catalyze formation of a large number of secondary messenger ,molecules: thus , cellular response is amplified.
- C. PROSTAGLANDINS (Paracrine substance)
- Prostaglandins are paracrine substances that have powerful hormone- like effects , even in small amounts.
Prostaglandin modulate hormones that regulate formation of cyclic AMP.