A hormone is present at high concentration in the bloodstream passing through a tissue, yet that tissue shows no response. What is the most likely explanation?
AThe tissue is too far from the secreting gland for the hormone to reach it
BThe tissue cells lack the specific receptor for that hormone
CThe hormone has been degraded before reaching the tissue
DThe tissue is responding, but the effect takes too long to measure
Hormones travel through the bloodstream and reach essentially all tissues, so distance is not the barrier. Receptor presence is the gate: a cell responds to a hormone only if it expresses the specific receptor for that hormone. This principle explains tissue specificity — insulin acts on liver, muscle, and fat because those cells express insulin receptors, while neurons in the visual cortex do not respond because they lack them. High circulating hormone concentration is irrelevant without a receptor to bind.
Question 2 True / False
The pancreas is exclusively an endocrine gland because it secretes the hormones insulin and glucagon.
TTrue
FFalse
Answer: False
The pancreas is both endocrine and exocrine. Its endocrine function (islets of Langerhans) secretes insulin and glucagon directly into the bloodstream. Its exocrine function (acinar cells) secretes digestive enzymes (amylase, lipase, proteases) through the pancreatic duct into the small intestine. The distinction is the delivery route: endocrine = ductless secretion into blood; exocrine = secretion through a duct to a body surface or lumen.
Question 3 Short Answer
In what two key ways does endocrine signaling differ from neural signaling in terms of speed and targeting?
Think about your answer, then reveal below.
Model answer: Endocrine signals travel via the bloodstream to distant tissues and act slowly (seconds to days) with long-lasting effects; neural signals travel along specific axons to local synaptic targets and act rapidly (milliseconds) with brief effects.
The difference in mechanisms accounts for the difference in properties: neural signaling uses electrochemical impulses along dedicated wires (axons) to a specific synapse, enabling millisecond-speed, point-to-point communication. Endocrine signaling uses the circulatory system as a broadcast medium — hormones reach all tissues, but only those with the right receptor respond. This broadcast nature makes endocrine signaling ideal for coordinating slow, sustained, system-wide processes like growth, metabolism, and reproduction.