An endocrine gland secretes its product directly into the blood and/or lymph. Together, the endocrine glands form the endocrine system.
An exocrine gland has a duct to take the gland's secretion to its site of action, for example salivary glands with ducts to the buccal (mouth) cavity.
The product of an endocrine gland is a hormone.
- A molecule that acts as a chemical messenger.
- Travels in the blood and lymph all over the body.
- Causes a specific response in specific target cells or tissues.
- May be a steroid, such as oestrogen, progesterone or testorene.
- May be a protein, such as insulin or glucagon.
- May be derived from an amino acid, like thyroxine and adrenaline.
Hormones act in two different ways when they reach a target tissue.
- Steroids and thyroxine pass through the plasma membrane and bind with receptors in the nucleus. The hormone-receptor complex binds with DNA and regulates transcription.
- Protein hormones and…