Summary
Chemical messengers released into the blood that regulate growth, metabolism and reproduction.
In depth
Classes: peptides (insulin), steroids (cortisol, oestrogen), amines (adrenaline, thyroxine). They act on target cells with specific receptors. Effects can be slow but long-lasting compared with nerve signals.
Hormones are carried in blood and act on cells with receptors. They regulate growth, metabolism, reproduction and mood. Endocrine disorders are treated by replacement or suppression.
Example: thyroid hormone replacement treats hypothyroidism.
Hormones are chemical messengers made by endocrine glands or cells and carried in the blood to target cells, which have specific receptors. They act in tiny concentrations and often over longer periods than nerve impulses, controlling growth, metabolism, reproduction, mood and water balance.
Chemically they are peptides or proteins (insulin), steroids (cortisol, oestrogen), amines (adrenaline, thyroxine) or fatty acid derivatives (prostaglandins). Their levels are controlled mainly by negative feedback. Hormones are broken down by the liver and excreted by the kidneys, so effects last for limited periods.
Example: ADH from the posterior pituitary causes the kidney to retain water.
Key idea: slower than nerves, but widespread and long-lasting.
Frequently asked questions
What is Hormones?
Chemical messengers released into the blood that regulate growth, metabolism and reproduction.
Which area of biology covers Hormones, and how advanced is it?
Hormones is one of the 54 topics in Reproduction & Endocrinology. It is rated Beginner, so it suits learners who are starting out in biology. Related topics in this area include Steroid and Peptide Hormone Mechanisms, Endocrine Glands, Negative Feedback in Endocrine Control.
Can you give an example of Hormones?
Hormone concentrations are measured in blood by immunoassay.
What should I learn before Hormones?
Hormones is a Beginner topic, so no earlier topic is required. Other Beginner topics in Reproduction & Endocrinology that pair well with it include Reproduction, Asexual Reproduction, Sexual Reproduction.
What topics are related to Hormones?
The closest topics to Hormones are Steroid and Peptide Hormone Mechanisms, Endocrine Glands, Negative Feedback in Endocrine Control, Hypothalamic-Pituitary Axis. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Hormones?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Hormones. To practise the whole of Reproduction & Endocrinology, use the Reproduction & Endocrinology quiz.
How is Hormones different from Steroid and Peptide Hormone Mechanisms?
Hormones: Chemical messengers released into the blood that regulate growth, metabolism and reproduction. Steroid and Peptide Hormone Mechanisms: Steroid hormones cross membranes and alter transcription; peptide hormones bind surface receptors and activate second messengers. Read both side by side and note what each one explains.
How should I study Hormones step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Steroid and Peptide Hormone Mechanisms and explain the difference aloud. Finally, take the Reproduction & Endocrinology quiz and come back to this page for any question you miss.