Regulation of Breathing (Chemoreceptors) - Anatomy and Physiology
- Which chemoreceptors mainly detect a fall in arterial pH caused by metabolic acid, such as ketoacids?
- The peripheral chemoreceptors (mainly the carotid bodies), because H+ in the blood does not readily cross the blood-brain barrier.
- Where are the central chemoreceptors located?
- Near the ventral surface of the medulla oblongata, bathed by cerebrospinal fluid.
- What is the direct stimulus detected by central chemoreceptors?
- H+ concentration in the cerebrospinal fluid, which rises when arterial CO2 diffuses into the CSF and forms carbonic acid.
- A person hyperventilates for one minute. How does this change the chemical drive to breathe, and why?
- It decreases. Arterial PCO2 falls, CSF H+ falls, and central chemoreceptor stimulation drops.
- What does the Hering-Breuer inflation reflex do?
- Pulmonary stretch receptors signal via the vagus nerve to inhibit inspiration, preventing overinflation of the lungs.
- Which cranial nerves carry signals from the carotid bodies and the aortic bodies?
- Carotid bodies: glossopharyngeal nerve (CN IX). Aortic bodies: vagus nerve (CN X).
- Where are the peripheral chemoreceptors located?
- In the carotid bodies (at the common carotid bifurcation) and the aortic bodies (on the aortic arch).
- Which blood variable is the main minute-to-minute regulator of ventilation in a healthy person?
- Arterial PCO2, acting mainly through central chemoreceptors. Small rises in PCO2 strongly increase ventilation.
- Below about what arterial PO2 do peripheral chemoreceptors strongly increase ventilation?
- About 60 mmHg. Above that level, falls in PO2 have little effect on ventilation.
- Why do changes in arterial CO2 affect central chemoreceptors faster than changes in blood H+?
- CO2 crosses the blood-brain barrier easily, while H+ crosses poorly; CO2 then forms H+ in the CSF.
- Which part of the brainstem contains the basic respiratory rhythm generator?
- The medulla oblongata (including the pre-Botzinger complex and dorsal and ventral respiratory groups).