WHY trace amounts? Because hormones act catalytically on signalling pathways — one hormone molecule triggers an amplified cascade (especially peptides), so you never need much.
Imagine your body is a big city and your blood is the river running through it. Hormones are tiny letters dropped into the river by certain offices (glands). Some letters are written on paper that dissolves in water — these float easily but can't get inside a house (a cell), so they knock on the door and someone inside passes the message along. Other letters are written on oily paper — they need a little boat (carrier protein) to float, but when they reach a house they walk right through the wall and go straight to the house's instruction book (DNA) to change the rules. Door-knockers are quick but their message fades fast; wall-walkers are slow but change things for a long time.
Dekho yaar, hormones basically body ke chemical messages hain — gland se nikalte hain, blood ke through travel karke door kisi target organ pe pahunchte hain, aur waha activity change kar dete hain. Sabse important baat sirf ek hai: hormone paani me ghulta hai ya tel (lipid) me? Bas yahi ek property poori kahani decide kar deti hai, isliye table ratne ki zaroorat nahi.
Peptide hormones (jaise insulin, glucagon, adrenaline) amino acids se bante hain, ye water-soluble hote hain. Water-soluble matlab blood me aaram se ghul jaate hain, koi carrier nahi chahiye. Par cell ki membrane to oily hoti hai — to ye andar nahi ja sakte. Isliye ye membrane ke surface receptor pe baith jaate hain aur andar message bhejne ke liye second messenger (cAMP) use karte hain. Result: effect bahut fast (seconds) lekin short-lived.
Steroid hormones (testosterone, estrogen, cortisol) cholesterol se bante hain, ye lipid-soluble hote hain. Oily hone ki wajah se blood (jo paani jaisa hai) me theek se nahi ghulte — isliye inhe carrier protein ka "boat" chahiye (yaad rakho: oil needs a boat). Par cell ki oily membrane ko ye seedha cross kar jaate hain, andar jaake DNA se bind karke gene transcription on/off karte hain. Naye proteins banane padte hain, isliye effect slow (ghanton me) par long-lasting.
Ek common galti: "adrenaline steroid hai kyunki adrenal gland se aata hai" — galat! Class chemistry se decide hoti hai, gland se nahi. Adrenaline amino-acid derivative hai, peptide-type. Mantra yaad rakho: PEP-SURF-FAST, STER-IN-SLOW.
