Which of the following statements is TRUE about the endocrine system?

• A. Endocrine glands secrete hormones into the bloodstream to act on distant target cells.
• B. Endocrine glands primarily communicate using neurotransmitters across synapses.
• C. Endocrine glands release their secretions through ducts directly onto epithelial surfaces.
• D. Endocrine signaling always produces rapid responses measured in milliseconds, similar to nerve impulses.

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the role of the endocrine system. The endocrine system consists of glands that secrete hormones directly into the bloodstream, allowing these chemical messengers to travel to distant target cells throughout the body.
2. Step 2: Differentiate between endocrine and nervous system communication. Endocrine glands use hormones for signaling, which is slower and longer-lasting compared to the nervous system that uses neurotransmitters to communicate rapidly across synapses.
3. Step 3: Recognize the difference between endocrine and exocrine glands. Endocrine glands are ductless and release hormones into the blood, whereas exocrine glands secrete substances through ducts onto epithelial surfaces.
4. Step 4: Consider the timing of responses. Endocrine signaling generally produces slower responses (seconds to minutes or longer), unlike nerve impulses that act within milliseconds.
5. Step 5: Based on these clarifications, identify the true statement: 'Endocrine glands secrete hormones into the bloodstream to act on distant target cells.' This accurately describes the endocrine system's mode of action.