How do hormones travel through the body?

1into the blood

A hormone has no wire to follow. A gland releases it into the blood, and the circulation carries it around the whole body, one lap in roughly a minute.

2receptors decide

The blood passes every tissue, so every cell is exposed. But only cells carrying the matching receptor protein respond. The receptor, not the route, picks the target.

3surface receptor

Water-soluble hormones like glucagon cannot cross a cell's fatty membrane. They bind a receptor on the outside surface and stay out.

4second messenger

The binding triggers a chain reaction inside: second messengers like cyclic A M P spread through the cell and switch enzymes on. Seconds to minutes, mostly by changing existing proteins.

5inside receptor

Fat-soluble hormones like cortisol and estrogen slip straight through the membrane. They travel in blood on carrier proteins, then meet a receptor inside the cell.

6switching genes

The hormone and receptor together act on D N A, switching genes on or off. New proteins take minutes to hours to appear, but the effect lasts longer.

7feedback loop

What turns the message off? Feedback. After a meal, blood sugar rises, the pancreas releases insulin, cells take up glucose, sugar falls, and insulin release eases.

8opposing pair

A second hormone covers the other direction. When sugar runs low, glucagon tells the liver to release glucose. Two opposing hormones hold blood sugar steady.

9the whole idea

So, the whole idea: a gland pours hormone into the blood, every tissue is bathed in it, and only cells with the right receptor respond, until feedback shuts it off.