Steroids: sculpted from cholesterol, never stored
Every steroid hormone begins as cholesterol. A chain of enzymes — the pathway called steroidogenesis — converts cholesterol into cortisol, aldosterone, testosterone, estradiol, and the rest. Each step is one small chemical edit. The four-ring skeleton stays the same; only the trimmings change, and those trimmings are the whole identity of the hormone.
Here is the consequence that matters: steroids are fat-loving, so they slip straight through cell membranes. That means a cell cannot trap them in granules — they would just leak back out. So steroid-making glands store the raw material (cholesterol) instead, and synthesize the hormone fresh whenever they are told to. Steroid output is therefore slower to switch on than a peptide burst, but it is governed by how fast the cell can run steroidogenesis.
Amines: two molecules, two destinies
Amine hormones start from a single amino acid, usually tyrosine — yet tyrosine leads to two very different products. The catecholamines, like epinephrine from the adrenal medulla, are made by a few quick edits. They stay water-loving, so (like peptides) they are stored in secretory granules and released in a rush during a fight-or-flight moment.
Thyroid hormones also start from tyrosine, but take a long, unusual road — and end up fat-loving. That single difference is why we keep thyroid hormones in their own box: chemically they are amines, but in behavior they march with the steroids.
Thyroid hormones: built on a giant scaffold
Thyroid hormone synthesis is the quirkiest in the body. The gland makes a huge protein, thyroglobulin, and pumps in iodine through iodide trapping. An enzyme, thyroid peroxidase, then attaches iodine to tyrosines on that scaffold and welds pairs of them together to form T4 and T3 — while they are still part of the big protein.
STEROID: cholesterol --(many enzymes: steroidogenesis)--> hormone, made FRESH (no granules)
CATECHOLAMINE: tyrosine --(few quick edits)--> epinephrine, STORED in granules
THYROID: thyroglobulin scaffold + trapped iodine --(thyroid peroxidase)--> T4 & T3
stored INSIDE the scaffold as colloid -> months of reserve, freed when neededThe finished hormones stay locked inside thyroglobulin in the gland's storage colloid until the body needs them — enough reserve to last months. So among the lipophilic hormones, thyroid is the exception that does keep a stockpile, just by a clever trick: it stores them attached to a giant protein, not free.