Example 1
A hormone reaches cells A and B, but only A has its receptor. Which responds directly?
A is the direct target under the stated conditions. Circulation alone does not make B a responsive target.
Year 12 · SACE Stage 2
Endocrine signals and integration
Match glands, hormones, targets and feedback sequences.
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Method and worked examples
Endocrine glands release hormones into the blood. Only cells with suitable receptors respond strongly to a particular hormone, even though the blood carries it widely. Hormones include amino-acid derivatives, peptides, proteins and steroids. Nervous signalling is typically rapid and directed along neurons; hormonal signalling travels through circulation and often produces longer-lasting effects.
The pituitary releases thyroid-stimulating hormone, which stimulates the thyroid to produce thyroxine. Thyroxine influences metabolic activity and feeds back to reduce upstream stimulation when levels are sufficient. Sympathetic nervous signals can stimulate the adrenal medulla to release adrenaline during a rapid stress response. Nervous and endocrine systems can therefore operate together. Distinguish a hormone’s source from its target: the gland releasing a message is not necessarily the tissue where its main effect occurs.
Example 1
Example 2
Order thyroxine, thyroid gland and TSH in the pathway.
Pituitary TSH → thyroid stimulation → thyroxine release. Rising thyroxine feeds back to reduce upstream stimulation.
Watch out: A cell needs the appropriate receptor and response machinery.