Chapter 50, Problem 1TY

Which is the defining feature of hormones?

1. a. They are only produced in endocrine glands.
2. b. They are secreted into the blood, where they may reach one or more types of distant target cells, thereby altering cell function throughout the body.
3. c. They are released only by neurons.
4. d. They are never released by neurons.
5. e. They are secreted into ducts, where they diffuse to another nearby gland or other structure.

Summary Introduction

Introduction: The chemical messengers that are produced in the body are called hormones. Hormones act on target tissues as their secretions are directly poured in the bloodstream. Usually, endocrine glands constitute the hormone-producing cells. These hormone-producing cells make up the endocrine system.

Answer to Problem 1TY

Correct answer: Hormones are chemical messengers that are directly secreted into the bloodstream. In the bloodstream, they reach the target cells, thereby alter the functioning of the cells throughout the body of an individual. Hence, the correct answer is option b.

Explanation of Solution

Reason for correct answer:

Hormones are chemical messengers that may be produced by endocrine and exocrine glands. Endocrine glands in the body produce hormones which control functions of various parts and organs present in the body of an individual. These endocrine glands are ductless glands due to which they pour their secretions directly in the bloodstream. Hormones released by the ductless glands reach the target cell or tissue, and alter their function throughout the body of an individual.

Option b. is given as “They are secreted into the blood where they may reach one or more types of distant target cells, thereby altering cell function throughout the body”.

Hormones are chemical secretions released by endocrine glands directly in the bloodstream and alter the function of the target tissue or cell. Hence, the correct answer is option b.

Reasons for the incorrect answer:

Option a. is given as, “They are only produced in endocrine glands”.

Hormones are chemical messengers which are produced usually in endocrine glands. However, secretions of the pancreas are produced in endocrine as well as exocrine glands. Thus, hormones are not exclusively produced in endocrine glands. Hence option a. is incorrect.

Option c. is given as, “They are released only by neurons”.

The secretions of the neurons are called neurotransmitters. These neurotransmitters are not hormones but constitute sensory stimulus which in turn activates the endocrine system to produce hormones. Thus, hormones are the secretions of exocrine and endocrine glands. Hence, option c. is incorrect.

Option d. is given as, “They are never released by neurons”.

Neurons released neurotransmitters stimulate the endocrine glands to secrete hormones. Hormones are poured directly into the bloodstream to act on the target tissue by the ductless endocrine glands. Hence, option d. is incorrect.

Option e. is given as; “They are secreted into ducts where they diffuse another nearby gland or structure”.

Ductless endocrine glands put their secretions known as hormones directly into the bloodstream. These hormones are transported to a distant site where they act on the target tissue to produce their action. However, exocrine glands have ducts which produce the hormone in the local environment. Hence, option e. is incorrect.

Hence, the options a., c., d., and e. are incorrect.

Conclusion

Hormones are chemical messengers secreted by endocrine glands. The endocrine glands pour these hormones directly in the bloodstream where they act on the target tissue to produce an action.