In the endocrine system, the specificity of hormone action primarily derives from which factor?

• A. The fact that hormones travel only through lymphatic vessels rather than the bloodstream
• B. The presence of specific receptors on or within target cells that can bind the hormone
• C. The production of hormones exclusively by exocrine glands with ducts
• D. The ability of all hormones to diffuse equally into every cell type in the body

Answer: (B)

Verified step by step guidance

1. Understand that hormones are chemical messengers secreted by endocrine glands into the bloodstream, allowing them to travel throughout the body.
2. Recognize that despite hormones circulating widely, they only affect specific target cells, which is a key concept in hormone specificity.
3. Identify that the specificity of hormone action depends on the presence of specific receptors on or within target cells that can bind to the hormone, enabling a cellular response.
4. Note that the other options are incorrect because hormones do not travel exclusively through lymphatic vessels, are not produced by exocrine glands, and do not diffuse equally into every cell type.
5. Conclude that the defining factor for hormone specificity is the presence of these specific receptors, which ensures that only target cells respond to a given hormone.