From the Guidelines
Baroreceptors primarily affect vascular resistance to maintain blood pressure within a normal range. Baroreceptors are specialized sensory nerve endings located in the walls of blood vessels, particularly in the carotid sinus and aortic arch, that detect changes in blood pressure 1. When blood pressure increases, baroreceptors are stretched and send signals to the cardiovascular center in the medulla oblongata of the brain. This triggers a reflex that decreases sympathetic nervous system activity and increases parasympathetic activity, resulting in decreased heart rate, decreased cardiac output, and decreased vascular resistance to lower blood pressure back to normal. Conversely, when blood pressure decreases, baroreceptors send fewer signals, leading to increased sympathetic activity that causes vasoconstriction, increased heart rate, and increased cardiac output to raise blood pressure.
The baroreceptor reflex is a crucial homeostatic mechanism that helps maintain blood pressure within a normal range by primarily affecting vascular resistance and cardiac function 1. The most recent and highest quality study, published in 2018, highlights the importance of baroreceptors in regulating vascular resistance and cardiac function to maintain blood pressure homeostasis 1.
Key points to consider:
- Baroreceptors detect changes in blood pressure and send signals to the brain to trigger a reflex response 1.
- The baroreceptor reflex decreases sympathetic nervous system activity and increases parasympathetic activity to lower blood pressure when it increases 1.
- The baroreceptor reflex increases sympathetic activity to raise blood pressure when it decreases 1.
- Vascular resistance is a key factor in maintaining blood pressure, and baroreceptors play a crucial role in regulating it 1.
From the Research
Baroreceptor Effects
- Baroreceptors are mechanosensitive elements that maintain cardiovascular homeostasis by coordinating responses to external and internal environmental stressors 2.
- They modulate sympathetic vasomotor and parasympathetic cardiac neural autonomic drive to avoid excessive fluctuations in vascular tone and maintain intravascular volume 2.
- Baroreceptors also modulate non-cardiovascular physiological responses, including pain perception, sleep, consciousness, and cognition 2.
- The intracranial baroreceptor mechanism contributes to the regulation of systemic arterial blood pressure to maintain cerebral blood flow 3.
- Baroreceptors trigger robust, non-habituating, proportional sympathetic and cardiovascular responses to physiological changes in brain perfusion 3.
Vascular Resistance and Blood Pressure
- Baroreceptor stimulation can modulate both sympathetical and vagal activity, and as a consequence, heart rate, contractility, and vascular resistance 4.
- The intracranial baroreceptor mechanism resets the arterial baroreflex centrally, allowing regulation of systemic blood pressure at a higher level required to counteract reduced brain perfusion 3.
- Arterial baroreceptors play a role in setting the long-term level of mean arterial pressure (MAP), but their ability to buffer imposed increases in MAP is limited by a process termed "resetting" 5.
- Baroreflexes play little role in setting the long-term level of blood pressure, but they act as an effective buffer of short-term blood pressure fluctuations 6.
Answer to the Question
- Baroreceptors affect vascular resistance by modulating sympathetic vasomotor and parasympathetic cardiac neural autonomic drive 2, 4.
- They do not directly affect the central venous pressure (COP), but they contribute to the regulation of systemic arterial blood pressure, which can indirectly affect COP.
- Therefore, the correct answer is B. Increase vascular resistance, as baroreceptors can modulate vascular resistance through their effects on sympathetic and parasympathetic activity 2, 4.