Sensory receptors that detect changes in chemical concentrations
Peripheral chemoreceptors (of the
As for their particular function, peripheral chemoreceptors help maintain
Structure
Both
arteries of the
neck, monitor
partial pressure within arterial vessels while aortic body, located on the
aortic arch, monitors oxygen concentration closer to the
heart.
[3] Each of these bodies is composed of a similar collection of cells, and it is the post-transduction
signal processing that differentiates their responses. However, little is known about the specifics of either of these signaling mechanisms.
[6]Microanatomy
Carotid and aortic bodies are clusters of cells located on the
They also receive input from
gap junctions, which might allow for quick communication between cells when transducing signals.
[6]Type II cells occur in a ratio of about 1 to 4 with type I cells. Their long bodies usually occur in close association with type I cells, though they do not entirely encase type I cells.neurotransmitters in chemoreceptive signaling, ATP.
[6]
Development
Sensitivity and physiology of the peripheral chemoreceptors changes throughout the lifespan.[8]
Infancy
Respiration in
premature, care might be improved. For example,
oxygen therapy may be an example of a technique that exposes premature infants to such high oxygen levels that it prevents them from acquiring appropriate sensitivity to normal oxygen levels.
[9]Pregnancy
Increased base rate of
neuroendocrine processes.
[5] However, findings tying peripheral chemoreceptors to pregnancy-induced variations in breathing could just be correlational, so further studies are needed to identify the cause behind this relation.
Physiology
Signal transduction
Peripheral chemoreceptors were identified as necessary to
mitochondrial consumption of oxygen affecting the
AMPK enzyme.
[4]Transferring the signal to the medulla requires that
chromaffin cells. AMPK is an
enzyme activated by an increase in the
AMP:
ATP ratio resulting from increasing
cellular respiration. Once activated, the
enzyme promotes production of ATP and suppresses reactions that consume it. AMPK activation is also a more appealing candidate because it can activate both of the two most common types of potassium channels. Another study identified that AMPK opens and closes potassium channels via
phosphorylation, further underlining the link between the two. The role of AMPK in oxygen sensing in type-1 cells has however also recently been called into question.
[11]This enzyme's function positions type I cells to uniquely take advantage of their mitochondria. However, AMPK is an enzyme found in many more types of cells than chemoreceptors because it helps regulate
calcium channels and neurotransmitters common to many types of nerve cells, and a well-endowed version of the vasculature supporting all aerobic cells.
[4] Further research should identify why type I cells exhibit such a high metabolic rate compared to other cell types, as this may be the truly unique feature of the receptor. And thus, a receptor for an
aerobic organism's most basic energy source is composed of collection of cell structures common throughout the body.
Response to hypoxia
Peripheral chemoreceptors are put under stress in a number of situations involving low access to oxygen, including exercise and exposure to high altitude.
Several studies suggest peripheral chemoreceptors play a role in
inhibitory role. Several studies point to increased circulation of
catecholamine or potassium during exercise as a potential effector on peripheral chemoreceptors; however, the specifics of this effect are not yet understood. All suggestions of peripheral chemoreceptor involvement conclude that they are not solely accountable for this response, emphasizing that these receptors are only one in a suite of oxygen-sensing cells that can respond in times of stress. Collecting information on carotid and aortic body activity in live, exercising humans is fraught with difficulty and often only indicates indirect evidence, so it is hard to draw expansive conclusions until more evidence has been amassed, and hopefully with more advanced techniques.
[5]In addition to ventilatory effects, peripheral chemoreceptors may influence
neuroendocrine responses to exercise that can influence activities other than ventilation.
[5] Circulation of the
glucose-promoting
hormone,
glucagon and a neurotransmitter,
norepinephrine, is increased in carotid- and aortic-body-enervated dogs, suggesting that peripheral chemoreceptors respond to low glucose levels in and may respond to other neuroendocrine signals in addition to what is traditionally considered to be their sole role of ventilatory regulation.
[5]Role of central chemoreceptors
Peripheral chemoreceptors work in concert with
ventral
medulla, the
brainstem area that receives input from peripheral chemoreceptors.
[12] Taken together, these blood oxygen monitors contribute nerve signals to the
vasomotor center of the medulla which can modulate several processes, including breathing,
airway resistance,
blood pressure, and
arousal.
[3] At an evolutionary level, this stabilization of oxygen levels, which also results in a more constant
carbon dioxide concentration and
pH, was important to manage oxygen flow in air-vs.-water breathing,
sleep, and to maintain an ideal
pH for
protein structure, since fluctuations in pH can
denature a cell's enzymes.
[3][13]See also
References
External links
