Chemoreceptors detect chemical changes in the blood, mainly changes in pH caused by carbon dioxide concentration. They are found in the aorta, the carotid arteries and the medulla oblongata.During exercise, muscles respire faster and release more carbon dioxide into the blood. Carbon dioxide reacts with water to form carbonic acid, which dissociates to release hydrogen ions:CO2 + H2O → H2CO3 → H+ + HCO3− So a rise in blood carbon dioxide concentration lowers the pH of the blood.
The chemoreceptors detect this fall in pH and send impulses to the cardiovascular centre. The cardiovascular centre sends more impulses along the accelerator nerve to the SAN, which increases heart rate. Blood flows faster through the lungs, so more carbon dioxide is removed and the pH rises back towards normal.When carbon dioxide concentration falls (for example at rest after exercise), the pH rises. The chemoreceptors reduce their impulses, fewer impulses pass along the accelerator nerve and more pass along the vagus nerve, so heart rate returns to its resting level.Like the baroreceptor response, this is negative feedback controlled by the autonomic nervous system. Chemoreceptors also help to adjust breathing rate, which removes carbon dioxide even more quickly.
The chemoreceptors detect this fall in pH and send impulses to the cardiovascular centre. The cardiovascular centre sends more impulses along the accelerator nerve to the SAN, which increases heart rate. Blood flows faster through the lungs, so more carbon dioxide is removed and the pH rises back towards normal.When carbon dioxide concentration falls (for example at rest after exercise), the pH rises. The chemoreceptors reduce their impulses, fewer impulses pass along the accelerator nerve and more pass along the vagus nerve, so heart rate returns to its resting level.Like the baroreceptor response, this is negative feedback controlled by the autonomic nervous system. Chemoreceptors also help to adjust breathing rate, which removes carbon dioxide even more quickly.