Classification of hormone B.Pharmacy 2nd Semester 2025 (2024-2025) Previous Year's Question Papers/Notes Download - HK Technical PGIMS

Hormones can be classified in several ways, most commonly by their chemical nature and
their mechanism of action. These classifications are important because a hormone's
chemical structure directly influences how it interacts with and affects a cell.
Classification by Chemical Nature
This is the most fundamental way to classify hormones, and it's based on the molecules from
which they are derived. There are three main chemical classes:
● Amino Acid-Derived Hormones: These are small, water-soluble molecules derived from
a single amino acid, usually tyrosine or tryptophan. They can't pass through the cell
membrane, so they bind to receptors on the cell's surface. Examples include
epinephrine (adrenaline), norepinephrine, and melatonin.
● Peptide and Protein Hormones: These hormones are made of chains of amino acids.
They range in size from small peptides (like oxytocin and vasopressin) to large proteins
(like insulin and growth hormone). Like amino acid-derived hormones, they are
water-soluble and must bind to cell-surface receptors.
● Lipid-Derived Hormones: These hormones are fat-soluble, which means they can easily
diffuse through the cell membrane. They are primarily derived from cholesterol and are
known as steroid hormones. Examples include testosterone, estrogen, and cortisol.
Another group of lipid-derived hormones, called eicosanoids (like prostaglandins), are
derived from fatty acids.
Classification by Mechanism of Action
This classification divides hormones into two groups based on how they interact with their
target cells.
● Group I (Lipid-Soluble Hormones): These are the steroid and thyroid hormones.
Since they are lipid-soluble, they can pass directly through the cell membrane to bind
with receptors inside the cytoplasm or nucleus. The hormone-receptor complex then
binds to specific DNA sequences, acting as a transcription factor to regulate gene
expression and protein synthesis. This process is slower but has a longer-lasting effect.
● Group II (Water-Soluble Hormones): This group includes peptide/protein and amino
acid-derived hormones. Since they can't cross the cell membrane, they bind to
receptors on the cell's surface. This binding event triggers a cascade of intracellular
signaling molecules, often called second messengers (like cAMP), to carry out the
hormone's message inside the cell. This mechanism is much faster than Group Ihormones but typically has a shorter duration.