Types of chemical messengers

There are two types of chemical messengers :

  1. Hormones
  2. Neurotransmitters.

(i) Hormones :

Classification of hormones : Based on their chemical structure ; hormones fall into three classes.

Steroid hormones :

Peptide hormones :

Amine hormones :

Those which are neither steroids nor peptides. These are water soluble amine compounds.

(ii) Neurotransmitters :

*Nerves transfer message through neurotransmitters.

*There are small molecules such as acetyl choline, dopamine and  serotonin.