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Carotid Body

 
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The carotid body (carotid glomus or glomus caroticum) is a small cluster of chemoreceptors and supporting cells located near the fork (bifurcation
Bifurcation

Bifurcation means the splitting of a main body into two parts.Bifurcation or Bifurcated may refer to:*Bifurcation , the division of issues in a trial for example the division of a page into two parts....
) of the carotid artery (which runs along both sides of the throat).

The carotid body detects changes in the composition of arterial blood flowing through it, mainly the partial pressure of oxygen
Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
, but also of carbon dioxide
Carbon dioxide

Carbon dioxide is a chemical compound composed of two oxygen atoms covalent bond to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state....
. Furthermore, it is also sensitive to changes in pH
PH

pH is a measure of the Acid or Base of a solution. It is defined as the cologarithm of the Activity of dissolved hydrogen ions . Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations....
 and temperature
Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature....
.

carotid body is made up of two types of cell: type I (glomus) cells, and type II (sustentacular) cells.






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The carotid body (carotid glomus or glomus caroticum) is a small cluster of chemoreceptors and supporting cells located near the fork (bifurcation
Bifurcation

Bifurcation means the splitting of a main body into two parts.Bifurcation or Bifurcated may refer to:*Bifurcation , the division of issues in a trial for example the division of a page into two parts....
) of the carotid artery (which runs along both sides of the throat).

The carotid body detects changes in the composition of arterial blood flowing through it, mainly the partial pressure of oxygen
Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
, but also of carbon dioxide
Carbon dioxide

Carbon dioxide is a chemical compound composed of two oxygen atoms covalent bond to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state....
. Furthermore, it is also sensitive to changes in pH
PH

pH is a measure of the Acid or Base of a solution. It is defined as the cologarithm of the Activity of dissolved hydrogen ions . Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations....
 and temperature
Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature....
.

Composition

The carotid body is made up of two types of cell: type I (glomus) cells, and type II (sustentacular) cells. Glomus cells are derived from neural crest
Neural crest

The neural crest, a transient component of the ectoderm, is located in between the neural tube and the epidermis of an embryo during neural tube formation....
, which, in turn are derived from neuroectoderm
Neuroectoderm

Neuroectoderm is the term for ectoderm which receives inhibitory signals from proteins such as Noggin , which leads to the development of the nervous system from this tissue....
. They release a variety of neurotransmitter
Neurotransmitter

Neurotransmitters are chemistry which relay, amplify and modulate signals between a neuron and another cell . Neurotransmitters are packaged into vesicles that cluster beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to receptors in the membrane on the postsynaptic side of...
s, including acetylcholine
Acetylcholine

The chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including homo sapiens....
, ATP
Adenosine triphosphate

This article is about the chemical used by cells as an energy carrier. For other uses, see ATP .Adenosine-5'-triphosphate is a multifunctional nucleotide, and plays an important role in cell biology as a coenzyme that is the "molecule unit of currency" of intracellular energy transfer....
, and dopamine
Dopamine

Dopamine is a neurotransmitter occurring in a wide variety of animals, including both vertebrates and invertebrates. In the human brain, this phenethylamine functions as a neurotransmitter, activating the five types of dopamine receptors ? D1, D2, D3, D4 and D5, and their variants....
 that trigger EPSPs in synapsed neurons leading to the respiratory center.

Type II cells resemble glia
Glial cell

Glial cells, commonly called neuroglia or simply glia , are non-neuronal cell that provide support and nutrition, maintain homeostasis, form myelin, and participate in signal transmission in the nervous system....
, express the glial marker S100 and act as supporting cells.

Function

The carotid body functions as a sensor, it responds to a stimulus, primarily O2 partial pressure, which is detected by the type I (glomus) cells, and triggers an action potential
Action potential

An action potential is a self-regenerating wave of electrochemical activity that allows nerve cells to carry a signal over a distance. It is the primary electrical signal generated by nerve cells, and arises from changes in the permeability of the nerve cell's axonal Cell membranes to specific ions....
 in an afferent nerve fiber, the carotid sinus nerve, which relays the information to the central nervous system.

Stimulus

While the central chemoreceptors in the brainstem are highly sensitive to CO2 the carotid body is a peripheral chemoreceptor that mainly provides afferent input to the respiratory center that is highly O2 dependent. However, the carotid body also senses increases in CO2 partial pressure and decreases in arterial pH, but to a lesser degree than for O2

The output of the carotid bodies is low at an oxygen partial pressure
Partial pressure

In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....
 above about 100 mmHg (torr
Torr

The torr is a non-International System of Units unit of pressure defined as 1/760 of an Atmosphere . It was named after Evangelista Torricelli, an Italian physicist and mathematician who discovered the principle of the barometer in 1644....
) (at normal physiological pH), but below this the activity of the type I (glomus) cells increases rapidly.

Detection

The mechanism for detecting reductions in PO2 is not well understood. There may be a heme
Heme

A heme or haem is a prosthetic group that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin....
-containing protein in the glomus cell which responds to the loss of complexed
Complex (chemistry)

In chemistry, a complex, also called a "coordination compound" or "metal complex", is a structure consisting of a central atom or molecule connected to surrounding atoms or molecules....
 oxygen by reducing the probability of potassium channels being open. Another possibility is that low PO2 inhibits NADPH oxidase
NADPH oxidase

The NADPH oxidase is a membrane-bound enzyme complex. It can be found in the plasma membrane as well as in the membrane of phagosome....
 in mitochondria. This would increase the ratio of reduced glutathione to oxidised glutathione, which blocks potassium channels.

An increased PCO2 is detected because the CO2 diffuses
Diffusion

Molecular diffusion, often called simply diffusion, is a net transport of molecules from a region of higher concentration to one of lower concentration by random molecular motion....
 into the cell, where it increase the concentration of carbonic acid
Carbonic acid

Carbonic acid has the Molecular formula H2CO3. It is also a name sometimes given to solutions of carbon dioxide in water , which contain small amounts of H2CO3....
 and thus protons. These protons displace calcium from high-conductance calcium channels
BK channel

In the field of molecular biology, BK channels, also called Maxi-K or slo1, are ion channels which conduct potassium ions through cell membranes....
, reducing potassium current.

Arterial acidosis
Acidosis

Acidosis is an increased acidity . If not further qualified, it usually refers to acidity of the blood plasma.Acidosis is said to occur when arterial pH falls below 7.35, while its counterpart occurs at a pH over 7.45....
 (either metabolic
Metabolic acidosis

In medicine, metabolic acidosis is a process which if unchecked leads to acidemia, i.e. blood pH is low due to increased production of hydrogen by the body or the inability of the body to form bicarbonate in the kidney....
 or from altered PCO2
Respiratory acidosis

Respiratory acidosis is acidosis due to decreased Ventilation of the lung alveoli, leading to elevated artery carbon dioxide concentration ....
) inhibits acid-base transporters (e.g. Na+-H+) which raise intracellular pH, and activates transporters (e.g. Cl--HCO3-) which decrease it. Changes in proton concentration caused by acidosis (or the opposite from alkalosis
Alkalosis

Alkalosis refers to a condition reducing hydrogen ion concentration of artery blood plasma . Generally alkalosis is said to occur when pH of the blood exceeds 7.45....
) inside the cell stimulates the same pathways involved in PCO2 sensing.

Action potential

The type I (glomus) cells in the carotid (and aortic bodies) are derived from neuroectoderm and are thus electrically excitable. A decrease in oxygen partial pressure, an increase in carbon dioxide partial pressure, and a decrease in arterial pH can all cause depolarization
Depolarization

In biology, depolarization is a decrease in the absolute value of a cell's membrane potential. Thus, changes in membrane voltage in which the membrane potential becomes less positive or less negative are both depolarizations....
 of the cell membrane
Cell membrane

The cell membrane is the interface between the cellular machinery inside the cell and the fluid outside.It is a semipermeable lipid bilayer found in all cell ....
, and they effect this by blocking potassium
Potassium

Potassium is a chemical element. It has the symbol K , atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash, hence the name....
 currents. This reduction in the membrane potential
Membrane potential

Membrane potential , is the voltage difference between the interior and exterior of a cell. Because the fluid inside and outside a cell is highly conductive, whereas a cell's plasma membrane is highly resistive, the voltage change in moving from a point outside to a point inside occurs largely within the narrow width of the membrane itself...
 opens voltage-gated calcium
Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft grey alkaline earth metal, and is the fifth most abundant element by mass in the earth's Crust ....
 channels, which causes a rise in intracellular calcium concentration. This causes exocytosis
Exocytosis

Exocytosis is the durable process by which a cell directs the contents of secretory Vesicle_ out of the cell membrane. These membrane-bound vesicles contain soluble proteins to be secreted to the extracellular environment, as well as membrane proteins and lipids that are sent to become components of the cell membrane....
 of vesicles containing a variety of neurotransmitters, including acetylcholine
Acetylcholine

The chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including homo sapiens....
, noradrenaline, dopamine
Dopamine

Dopamine is a neurotransmitter occurring in a wide variety of animals, including both vertebrates and invertebrates. In the human brain, this phenethylamine functions as a neurotransmitter, activating the five types of dopamine receptors ? D1, D2, D3, D4 and D5, and their variants....
, adenosine
Adenosine

Adenosine is a nucleoside composed of a molecule of adenine attached to a ribose sugar molecule moiety via a ?-N9-glycosidic bond....
, ATP
ATP

ATP may refer to:...
, substance P
Substance P

In the field of neuroscience, substance P is a neuropeptide: an undecapeptide that functions as a neurotransmitter and as a neuromodulator which alters the excitability of the dorsal horn ganglion ....
, and met-enkephalin
Met-enkephalin

Met-enkephalin is an endogenous opioid peptide neurotransmitter found naturally in the brains of many animals, including humans. It is one of the two forms of enkephalin; the other is leu-enkephalin....
. These act on receptors
Receptor (biochemistry)

In biochemistry, a receptor is a protein molecule, embedded in either the plasma membrane or cytoplasm of a cell, to which a mobile signaling molecule may attach....
 on the afferent nerve fibres which lie in apposition to the glomus cell to cause an action potential.

Relay

The feedback from the carotid body is sent to the cardiorespiratory centers in the medulla oblongata
Medulla oblongata

The medulla oblongata is the lower portion of the brainstem. It deals with Autonomic nervous system functions, such as breathing and blood pressure....
 via the afferent branches of the glossopharyngeal nerve
Glossopharyngeal nerve

The glossopharyngeal nerve is the ninth of twelve pairs of cranial nerves . It exits the brainstem out from the sides of the upper Medulla oblongata, just rostral to the vagus nerve....
 . The cell bodies of this nerve are located in the petrosal ganglion. The afferent fibres of the aortic body chemoreceptors are relayed by the vagus nerve
Vagus nerve

The vagus nerve is the tenth of twelve paired cranial nerves, and is the only nerve that starts in the brainstem and extends, through the jugular foramen, down below the head , to the neck, chest and abdomen, where it contributes to the innervation of the viscera....
. These centers, in turn, regulate breathing and blood pressure.

Disorders

A paraganglioma
Paraganglioma

A paraganglioma is a rare neoplasm that can be found in the abdomen, thorax, and in the head and neck region. They are usually considered benign and complete surgical removal results in cure....
 is a tumor that may involve the carotid body and is usual benign
Benign

A benign tumor is a tumor that lacks all three of the malignant properties of a cancer. Thus, by definition, a benign tumor does not grow in an unlimited, aggressive manner, does not invade surrounding tissue , and does not metastasize....
.

See also

  • Aortic body
    Aortic body

    In the human heart, the aortic body is one of several small clusters of chemoreceptors, baroreceptors, and supporting cells located along the aorta....
  • Peripheral chemoreceptors
    Peripheral chemoreceptors

    Peripheral chemoreceptors act most importantly to detect variation of the oxygen in the arterial blood, in addition to detecting arterial carbon dioxide and pH....


External links

  • at Kirksville College of Osteopathic Medicine