Chemical regulation of respiration is not affected by-
Ans. is 'd' i.e., Mean BP * Central chemoreceptors are located in a chemosensitive area on the ventral surface of the medulla near the exit of the ninth and tenth cranial nerves. The primary stimulus for the central chemoreceptors is an increase in the hydrogen ion concentration. Stimulation of central chemoreceptors by increased hydrogen ion concentration leads to excitation of the respiratory neurons, thereby producing an increase in the rate and depth of respiration.* Although the primary stimulus for central chemoreceptors is an increase in hydrogen ion concentration, in actual practice the physiological stimulus is an increase in PCO2. The reason is that hydrogen ions cannot cross blood - brain barrier. Therefore, a change in the blood hydrogen ion concentration does not change the hydrogen ion concentration in the immediate vicinity of the chemosensitive neurons (i.e., in CSF and brain interstitial fluid). On the other hand, CO2 being lipid soluble can easily cross blood brain barrier. It enters the brain, where it is hydrated to give rise to H+ and HCO2 ions. Now these H+ directly stimulate the central chemoreceptors.* Thus, central chemoreceptors are directly stimulated by an increase in H+ concentration in CSF and brain inerstitial tissue, which is brought about by change in arterial PCO2 (PaCO2).* Change in CSF & Brain interstial tissue - | H+ concentration (Primary direct stimulus).* Change in Blood - | PCO2 (Actual physiological stimulus).* Central chemoreceptors are not stimulated by hypoxia; rather like any other cells, they are depressed by hypoxia.Peripheral chemoreceptors* The peripheral chemoreceptors which regulate respiration are located in the carotid body and aortic bodies. These bodies are located in the connective tissue associated with the vessel wall, at the bifurcation of the common carotid, and on the arch of aorta, respectively. The characteristic cells of both these structures are called glomus cells. Type I glomus cells have a high dopamine content, which they possibly employ as a neurotransmetter. Peripheral chemoreceptors convey information to the DRG of neurons in medulla, for which purpose the afferent neurons from the carotid bodies pass through glossopharyngeal nerve and from the aortic bodies pass through vagus nerve.* The most potent natural stimulus for peripheral chemoreceptors is low arterial PO2 (hypoxic hypoxia). The other stimuli which activate peripheral chemoreceptors are high arterial PCO2, and an increase in arterial hydrogen ion concentration (acidosis or low pH). The response to activation of peripheral chemoreceptors is an increase in pulmonary ventilation through an increase in the rate and depth of breathing.* It is good to keep in mind that stimulation of peripheral chemoreceptors not only stimulates medullary respiratory centers but also medullary vasomotor center. Therefore, the response to their stimulation is tachycardia, vasoconstriction and increase BP, along with hyperventilation.
PO2
PCO2
pH
Mean BP
Respiratory System