Biomedical Engineering Reference
In-Depth Information
3.5.5
Oxygen Sensor
The cardiovascular system responds to imbalances between oxygen supply and
demand and adapts the blood flow. When oxygen demand changes, oxygen supply
and/or extraction from circulating RBCs are adjusted to match the demand. Oxygen
delivery is determined mostly by the vascular resitances of the arteriolar bed that
irrigates the tissue of interest. Oxygen extraction occurs mainly in small arterioles
and capillaries.
Erythrocytes have a dominant role in the supply of oxygen to tissues. Erythro-
cytic hemoglobin carries about 98% of blood oxygen. It releases oxygen to tissues
owing to temperature, pH, and P
CO
2
(that shift the oxygen dissociation curve).
According to the concept of metabolic control of the local blood flow, the
concentration of vasodilators released from cells into the interstitial fluid that bathes
resistance vessels results from the level of cell metabolism. Vasodilators, such as
adenosine, nitrosothiols (e.g.,
S
nitrosohemoglobin [Hb
SNO
]) and nitrite, do not fill
all criteria of a specific oxygen sensor [
129
]. Nitric oxide can modulate both the
supply of oxygen via its vasodilatory action on resistance vessels as well as the
demand for oxygen via its inhibitory effect on oxygen consumption via cytochrome-
C oxidase in mitochondria [
129
].
Erythrocytes can operate as mobile sensors for local oxygenation by the oxygen-
dependent release of ATP vasodilator [
130
]. Insulin at normal concentrations
inhibits the O
2
-dependent release of ATP from red blood cells, thereby impairing
O
2
delivery to fit the metabolic demand.
3.5.6
Blood Groups of the RBC Plasma Membrane
Erythrocyte surface contains proteins, glycoproteins, and glycolipids. Some define
blood types. K. Landsteiner (1868-1943) described ABO blood types in 1900
from identification of blood agglutinins. Later (1937-1940), with A. Wiener, he
worked on Rhesus blood group. The ABO and Rhesus blood groups are the main
blood groups considered in transfusion. Many of the blood type antigens and
corresponding antibodies have been discovered from transfusion incompatibilities.
There are 30 identified blood groups with multiple distinct types. Some blood group
molecules contribute to substance binding at the cell surface as well as chemical
import or export.
31
31
Duffy glycosylated membrane protein (Duffy blood group) acts as a non-specific receptor for
several chemokines. In addition, Duffy binding-like receptors are used by some plasmodium
parasites, such as Plasmodium vivax and falciparum.
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