Baroreceptors Affect Vascular Resistance, Not Colloid Oncotic Pressure
Baroreceptors primarily affect vascular resistance through sympathetic regulation of blood vessel tone, not colloid oncotic pressure (COP). 1
Baroreceptor Function and Mechanism
Baroreceptors are specialized stretch receptors located in the:
- Carotid sinus
- Aortic arch
- Great thoracic vessels
These receptors play a critical role in maintaining blood pressure homeostasis through a feedback loop that regulates vascular tone and cardiac function 1. When activated by changes in arterial pressure, baroreceptors transmit information via:
- Glossopharyngeal nerves (IX) from the carotid sinus
- Vagus nerves (X) from the aortic arch
- To vasomotor centers in the brainstem 1
Physiological Effects of Baroreceptor Activation
When baroreceptors detect increased blood pressure:
- Parasympathetic output to the heart increases
- Sympathetic output to heart and blood vessels decreases
- This results in:
- Decreased heart rate (bradycardia)
- Decreased cardiac contractility
- Vasodilation of resistance vessels (decreased vascular resistance) 1
Conversely, when baroreceptors detect decreased blood pressure:
- Parasympathetic output decreases
- Sympathetic output increases
- This results in:
- Increased heart rate
- Increased cardiac contractility
- Vasoconstriction of resistance vessels (increased vascular resistance) 1
Long-term Regulation by Baroreceptors
While historically it was thought that baroreceptors only controlled short-term blood pressure changes, recent evidence indicates they also participate in:
- Long-term control of sympathetic output
- Fluid volume regulation by the kidney
- Chronic blood pressure adjustment 2
Clinical Significance
Baroreceptor dysfunction can lead to:
- Orthostatic hypotension due to impaired vasoconstriction upon standing 1
- Increased risk of sudden cardiac death in post-MI patients 1
- Reduced baroreceptor sensitivity is associated with poorer outcomes in cardiovascular disease 1, 3
Recent therapeutic applications include electrical stimulation of the carotid sinus as a potential treatment for systemic hypertension 2.
Baroreceptors as Mechanoreceptors
TRPV1 receptors expressed on baroreceptive nerve endings function as mechanoreceptors to detect increases in blood pressure and maintain homeostasis 4. This provides further evidence that baroreceptors are directly involved in sensing pressure changes and regulating vascular resistance, not colloid oncotic pressure.