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An increase in carbon dioxide causes tension of the arteries, often resulting from increased CO 2 output (hypercapnia), indirectly causes the blood to become more acidic; the cerebrospinal fluid pH is closely comparable to plasma, as carbon dioxide easily diffuses across the blood–brain barrier.
The blood–brain barrier is formed by special tight junctions between endothelial cells lining brain blood vessels. Blood vessels of all tissues contain this monolayer of endothelial cells, however only brain endothelial cells have tight junctions preventing passive diffusion of most substances into the brain tissue. [1]
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 of the cell membrane, and they affect this by blocking potassium currents.
Glomus type I cells are peripheral chemoreceptors which sense the oxygen, carbon dioxide and pH levels of the blood. When there is a decrease in the blood's pH, a decrease in oxygen (pO 2), or an increase in carbon dioxide (pCO 2), the carotid bodies and the aortic bodies signal the dorsal respiratory group in the medulla oblongata to increase ...
These polymodal sensors respond to variations in a number of blood properties, including low oxygen , high carbon dioxide (hypercapnia), and low glucose (hypoglycemia). [4] Hypoxia and hypercapnia are the most heavily studied and understood conditions detected by the peripheral chemoreceptors. Glucose is discussed in a later section.
One of the main roles of extracellular fluid is to facilitate the exchange of molecular oxygen from blood to tissue cells and for carbon dioxide, CO 2, produced in cell mitochondria, back to the blood. Since carbon dioxide is about 20 times more soluble in water than oxygen, it can relatively easily diffuse in the aqueous fluid between cells ...
One of the most important examples of this is drug diffusion across the blood brain barrier. The blood brain barrier consists of a bed of continuous capillaries. Typically only small hydrophobic molecules are able to diffuse across the blood brain barrier. [4] This makes it very difficult to get drugs into the brain without invasively ...
Contrarily, carbon dioxide (CO 2) and other wastes leave tissues and enter capillaries by the same process but in reverse. [5] Diffusion through the capillary walls depends on the permeability of the endothelial cells forming the capillary walls, which may be continuous, discontinuous, and fenestrated. [ 4 ]