The steroid hormones bring changes in their target cells in the following manner :
1. Steroid hormones are lipid soluble hormones and can readily pass through the plasma membrane of a target cell.
2. After reaching the cytoplasm they bind to specific intracellular receptor proteins. They form a complex that enters the nucleus and binds to specific regulatory sites on chromosomes.
3. The binding alters the pattern of gene expression, initiating the tanscription of some genes (DNA), while repressing the transcription of others.
4. This results in the production of specific mRNA translation products such as proteins and usually enzymes, thus causing the required effects.
Explain the following :
(1) Insulin lowers the blood sugar level.
(2) Adrenal medulla and the sympathetic nervous system function as a closely integrated system.
(3) Pituitary gland regulates the reproductive system.
(4) Feed back system controls the blood level of many hormones.
