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how do hormones travel through the body
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.
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.
Water-soluble hormones like glucagon cannot cross a cell's fatty membrane. They bind a receptor on the outside surface and stay out.
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.
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.
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.
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.
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.
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.
Hormones are broadcast, not delivered: the blood reaches everyone, and only the cells with the right receptor listen.