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Hormones

Mammalian hormones are substances that stimulate target cells via the blood.

Hormones are part of the endocrine system, which produces slow, long-lasting and widespread responses.

Hormones are released directly into the blood plasma from endocrine glands. Each hormone has specific target cells on which it acts.

Once the hormone reaches a target organ, it affects the target cells by attaching onto specific receptors either on the surface of, or within, the cells.

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The endocrine system

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Glands and hormones

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Exocrine glands

Exocrine glands are also present throughout the body. These contain ducts that carry products straight to target cells on the epithelial layers of internal or external body surfaces.

Exocrine glands do not produce hormones, but secrete other products, for example:

gastric glands – secrete gastric juice onto the stomach lining

mammary glands – secrete milk directly onto the surface of the breast

sebaceous gland – secretes oily lipid-containing sebum onto the surface of the skin.

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Structures in the pancreas

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Which glands?