Describe the mechanism of steroid and peptide hormone action with a diagram.

(N/A) Hormones produce their effects on target tissues by binding to specific proteins called hormone receptors located in the target tissues only.
Hormone receptors present on the cell membrane of the target cells are called membrane-bound receptors,and the receptors present inside the target cell are called intracellular receptors,mostly nuclear receptors. Binding of a hormone to its receptor leads to the formation of a hormone-receptor complex.
Each receptor is specific to one hormone only and hence receptors are specific.
Hormone-receptor complex formation leads to certain biochemical changes in the target tissue.
$\Rightarrow$ Target tissue metabolism and hence physiological functions are regulated by hormones.
On the basis of their chemical nature,hormones can be divided into:
$(i)$ Peptide,polypeptide,protein hormones (e.g.,insulin,glucagon,pituitary hormones,hypothalamic hormones,etc.)
$(ii)$ Steroids (e.g.,cortisol,testosterone,estradiol,and progesterone)
$(iii)$ Iodothyronines (thyroid hormones)
$(iv)$ Amino-acid derivatives (e.g.,epinephrine).
Hormones which interact with membrane-bound receptors normally do not enter the target cell but generate second messengers (e.g.,cyclic $AMP$,$IP_3$,$Ca^{++}$,etc.) which in turn regulate cellular metabolism.
Hormones which interact with intracellular receptors (steroid,iodothyronines,etc.) mostly regulate gene expression or chromosome function by the interaction of the hormone-receptor complex with the genome.
$\Rightarrow$ Cumulative biochemical actions result in physiological and developmental effects.