Explain how the endocrine system and the cardiovascular system are integrated to respond to a sudden stressful situation.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
When an organism perceives a threat, a coordinated whole-body response is initiated within seconds, preparing the body for rapid physical action.
Model answer (4 marks)
The adrenal medulla releases adrenaline into the bloodstream when the sympathetic nervous system is activated by a threat. Adrenaline travels through the blood to the heart, where it binds to β1‑adrenergic receptors, raising heart rate and stroke volume, thus increasing cardiac output. It also causes vasodilation of arterioles in skeletal muscle and vasoconstriction of vessels supplying non‑essential organs, redirecting blood flow to the muscles. This coordinated endocrine‑cardiovascular response supplies more oxygen and glucose to active tissues, enabling the fight‑or‑flight reaction.
Examiner tips
- Mention adrenaline release from adrenal medulla
- Show its effect on heart rate and cardiac output
- Explain redistribution of blood flow via vasodilation/vasoconstriction
- Link increased supply to muscles with fight‑or‑flight
Common mistakes
- Confusing adrenal cortex hormones with adrenaline
- Forgetting to state the sympathetic trigger
- Failing to mention redistribution of blood flow
Mark scheme (4 marks)
- The adrenal glands (medulla) secrete adrenaline into the blood in response to stress / sympathetic nervous stimulation.
- Adrenaline travels via the blood to the heart and increases heart rate / cardiac output.
- Adrenaline causes vasodilation of blood vessels supplying skeletal muscle / vasoconstriction of vessels supplying non-essential organs, redistributing blood flow.
- The integrated response ensures more oxygen and glucose are delivered to muscles / tissues, enabling increased metabolic activity for the 'fight or flight' response.
Key terms in this question
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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