Hormones are secreted by endocrine glands directly into the bloodstream. They act on specific target organs through receptor binding.

Peptide hormones: Insulin (pancreas, lowers blood glucose — deficiency causes diabetes mellitus), glucagon (pancreas, raises blood glucose), oxytocin (pituitary, uterine contractions).

Amino acid derivatives: Adrenaline/epinephrine (adrenal medulla, fight-or-flight response — increases heart rate, blood glucose), thyroxine (thyroid, contains 4 iodine atoms, regulates metabolism — deficiency causes hypothyroidism/goiter).

Steroid hormones: Derived from cholesterol. Testosterone (male sex hormone), estrogen/progesterone (female sex hormones), cortisol (adrenal cortex, stress response, anti-inflammatory).

For JEE: Know hormone-gland-function-deficiency disease connections. Insulin-diabetes, thyroxine-goiter, growth hormone-gigantism/dwarfism are most commonly tested.