Introduction

Pulmonary J-receptors, also known as juxtacapillary receptors, are specialized sensory nerve endings located in the alveolar walls near pulmonary capillaries. They play an important role in detecting changes in pulmonary interstitial volume and pressure, such as during pulmonary congestion or hyperventilation. Their stimulation creates reflexes influencing respiration, heart rate, and blood pressure. This article analyzes the physiological responses elicited by J-receptor activation, focusing on which response is not true during lung hyperventilation.

Location and Function of Pulmonary J-Receptors

• Located in the alveolar walls juxtaposed to pulmonary capillaries, J-receptors detect increases in pulmonary interstitial fluid or capillary pressure.

• They are innervated by vagal C fibers and send afferent signals to the brainstem.

• J-receptor stimulation occurs in conditions like pulmonary edema, embolism, pneumonia, or congestive heart failure and also in hyperventilation of lungs.

Typical Responses to Pulmonary J-Receptor Stimulation

1. Apnea Followed by Rapid, Shallow Breathing

   • Initial brief cessation of breathing (apnea) is typically followed by rapid, shallow breaths. This modulates ventilation during pulmonary distress.

2. Bradycardia (Decreased Heart Rate)

   • J-receptor activation often causes reflex bradycardia mediated via parasympathetic influence.

3. Hypotension (Low Blood Pressure)

   • Reflex responses frequently include vasodilation leading to a drop in systemic blood pressure.

4. Bronchoconstriction (Not Bronchodilation)

   • Unlike irritant receptor activation, J-receptors cause constriction of bronchial smooth muscles, not bronchodilation.

Evaluating the Given Options

Why Bronchodilation is NOT a True Response?

• Bronchodilation typically occurs via sympathetic activation or irritant receptor stimulation.

• J-receptors, on the other hand, when activated, generally induce bronchoconstriction, contributing to a protective reflex limiting airflow in conditions like pulmonary edema.

Clinical and Physiological Significance

• J-receptor reflexes help protect the lungs by adjusting ventilation and circulation during pulmonary congestion and other pathologies.

• Reflex bradycardia and hypotension help reduce pulmonary capillary pressures, preventing damage to delicate pulmonary vessels.

• Understanding these reflexes assists in managing respiratory and cardiovascular complications in diseases causing lung congestion.

Summary Table of Pulmonary J-Receptor Responses

Conclusion

The response which is NOT true for pulmonary J-receptor stimulation by hyperventilation of the lung is:

(1) Bronchodilation