Central chemoreceptors
Encyclopedia
Central chemoreceptors of the central nervous system, located on the ventrolateral medullary
surface, are sensitive to the pH
of their environment.
These act to detect the changes in pH of nearby cerebral spinal fluid (CSF) that are indicative of altered oxygen or carbon dioxide concentrations available to brain tissues. An increase in carbon dioxide tension of the arteries, often resulting from increased CO2 intake (hypercapnea), indirectly causes the blood to become more acidic; the cerebral spinal fluid pH is closely comparable to the plasma
s, as carbon dioxide
easily diffuses across the blood/brain barrier.
However, a change in plasma pH alone will not stimulate central chemoreceptors as H+ are not be able to diffuse across the blood-brain barrier
into the CSF. Only CO2 levels affect this as it can diffuse across, reacting with H2O to form carbonic acid
and thus decrease pH. Central chemoreception remains, in this way, distinct from peripheral chemoreceptors
.
The central chemoreception system has also been shown experimentally to respond to hypercapnic hypoxia (elevated CO2, decreased O2) and aqueous sodium cyanide injection into the whole animal and in vitro slice preparation. These methods can be used to mimic some forms of hypoxic hypoxia and they are currently being studied including the detection of variation in arterial CO2 tension acting as a quick-response-system for short term (or emergency) regulation.
This system utilizes a negative feedback system, therefore if the pH of the cerebral spinal fluid does not compare to an ideal “set” level, then the receptor will send an error signal to the effectors and appropriate action may be executed.
Medulla oblongata
The medulla oblongata is the lower half of the brainstem. In discussions of neurology and similar contexts where no ambiguity will result, it is often referred to as simply the medulla...
surface, are sensitive to the pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
of their environment.
These act to detect the changes in pH of nearby cerebral spinal fluid (CSF) that are indicative of altered oxygen or carbon dioxide concentrations available to brain tissues. An increase in carbon dioxide tension of the arteries, often resulting from increased CO2 intake (hypercapnea), indirectly causes the blood to become more acidic; the cerebral spinal fluid pH is closely comparable to the plasma
Blood plasma
Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...
s, as carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
easily diffuses across the blood/brain barrier.
However, a change in plasma pH alone will not stimulate central chemoreceptors as H+ are not be able to diffuse across the blood-brain barrier
Blood-brain barrier
The blood–brain barrier is a separation of circulating blood and the brain extracellular fluid in the central nervous system . It occurs along all capillaries and consists of tight junctions around the capillaries that do not exist in normal circulation. Endothelial cells restrict the diffusion...
into the CSF. Only CO2 levels affect this as it can diffuse across, reacting with H2O to form carbonic acid
Carbonic acid
Carbonic acid is the inorganic compound with the formula H2CO3 . It is also a name sometimes given to solutions of carbon dioxide in water, because such solutions contain small amounts of H2CO3. Carbonic acid forms two kinds of salts, the carbonates and the bicarbonates...
and thus decrease pH. Central chemoreception remains, in this way, distinct from peripheral chemoreceptors
Peripheral chemoreceptors
Peripheral chemoreceptors act principally to detect variation of the oxygen concentration in the arterial blood, whilst also monitoring arterial carbon dioxide and pH. They are located in the aortic body and carotid body, on the arch of the aorta and on the common carotid artery, respectively. The...
.
The central chemoreception system has also been shown experimentally to respond to hypercapnic hypoxia (elevated CO2, decreased O2) and aqueous sodium cyanide injection into the whole animal and in vitro slice preparation. These methods can be used to mimic some forms of hypoxic hypoxia and they are currently being studied including the detection of variation in arterial CO2 tension acting as a quick-response-system for short term (or emergency) regulation.
This system utilizes a negative feedback system, therefore if the pH of the cerebral spinal fluid does not compare to an ideal “set” level, then the receptor will send an error signal to the effectors and appropriate action may be executed.