Physiology of oxygen transport | BJA Education | Oxford Academic
Blood haemoglobin: the relationship between oxygen capacity and iron content of blood in men An artificial standard for use in the estimation of haemoglobin. Haemoglobin. By Jennifer McDowall. Link to the structural features of haemoglobin. When we breathe in oxygen, the red blood cells transport it around to every. Haemoglobin and the oxygen dissociation curve1,5–7 This relationship between haemoglobin, oxygen binding, carbon dioxide tension, and pH The associated MCQs (to support CME/CPD activity) can be accessed at.
The use of pulse oximetry reduces the need for arterial blood gas analysis SaO2 as many patients who are not at risk of hypercapnic respiratory failure or metabolic acidosis and have acceptable SpO2 do not necessarily require blood gas analysis. While arterial sampling remains the gold-standard method of assessing ventilation and oxygenation, in those patients in whom blood gas analysis is indicated, arterialised capillary samples also have a valuable role in patient care.
The clinical role of venous blood gases however remains less well defined. Short abstract Understand the role of oximetry in clinical practice and how oxygen delivery, saturation and partial pressure relate http: Oxygen delivery is dependent on oxygen availability, the ability of arterial blood to transport oxygen and tissue perfusion [ 1 ].
Of the oxygen transported by the blood, a very small proportion is dissolved in simple solution, with the great majority chemically bound to the haemoglobin molecule in red blood cells, a process which is reversible.
The content or concentration of oxygen in arterial blood CaO2 is expressed in mL of oxygen per mL or per L of blood, while the arterial oxygen saturation SaO2 is expressed as a percentage which represents the overall percentage of binding sites on haemoglobin which are occupied by oxygen.
The maximum volume of oxygen which the blood can carry when fully saturated is termed the oxygen carrying capacity, which, with a normal haemoglobin concentration, is approximately 20 mL oxygen per mL blood. Oxygen delivery to the tissues Oxygen delivery to the tissues each minute is the product of arterial oxygen content and cardiac output.
Hence oxygen delivery can be compromised as much by a low haemoglobin concentration or low cardiac output as by a fall in the SaO2. The level of oxygenation of peripheral venous blood, however, will vary depending on local metabolism and oxygen consumption.
Global oxygen delivery, or oxygen dispatch, describes the total amount of oxygen delivered to the tissues each minute, and is a product of the cardiac output and arterial oxygen content.
Oxygen diffuses from both the alveoli into the pulmonary capillaries and the systemic capillaries into the tissues, according to Fick's laws of diffusion and the random walk of the diffusing particles.
Bohr effect - Wikipedia
Oxygen is vital for life-sustaining aerobic respiration in humans and is arguably the most commonly administered drug in anaesthesia and critical care medicine. Within the mitochondrial inner membrane, oxygen acts as the terminal electron acceptor at the end of the electron transport chain whereby oxidative phosphorylation results in the synthesis of adenosine triphosphate ATPthe coenzyme that supplies energy to all active metabolic processes.
This article will discuss the key physiological concepts underpinning the movement of oxygen within the human body and also highlight some clinical applications that serve as examples of these concepts. Convective vs diffusive oxygen transport 1—4 With respect to human physiology, oxygen transport can be divided into that occurring through convection and that occurring by diffusion. In this context, convection describes the movement of oxygen within the circulation, occurring through bulk transport.
This is an active process requiring energy, in this case derived from the pumping of the heart. On the other hand, diffusion describes the passive movement of oxygen down a concentration gradient, for example, from the microcirculation into the tissues and ultimately the mitochondria. The physiology of control of ventilation and the determinants of alveolar oxygen partial pressure, ventilation—perfusion matching, and diffusion within the alveolar—capillary unit are dealt with elsewhere. What is the coordination number of Fe in the oxygenated heme group?
Briefly, justify your answer by describing the ligands to which Fe is coordinated. Conformational Changes Upon Binding of Oxygen Careful examination of Figure 4 shows that the heme group is nonplanar when it is not bound to oxygen; the iron atom is pulled out of the plane of the porphyrin, toward the histidine residue to which it is attached. This nonplanar configuration is characteristic of the deoxygenated heme group, and is commonly referred to as a "domed" shape.
The valence electrons in the atoms surrounding iron in the heme group and the valence electrons in the histidine residue form "clouds" of electron density.
Electron density refers to the probability of finding an electron in a region of space. Because electrons repel one another, the regions occupied by the valence electrons in the heme group and the histidine residue are pushed apart.
- Relating oxygen partial pressure, saturation and content: the haemoglobin–oxygen dissociation curve
Hence, the porphyrin adopts the domed nonplanar configuration and the Fe is out of the plane of the porphyrin ring Figure 5, left. However, when the Fe in the heme group binds to an oxygen molecule, the porphyrin ring adopts a planar configuration and hence the Fe lies in the plane of the porphyrin ring Figure 5, right.
Figure 5 On the left is a schematic diagram showing representations of electron-density clouds of the deoxygenated heme group pink and the attached histidine residue light blue.
These regions of electron density push one another apart, and the iron atom in the center is drawn out of the plane. The nonplanar shape of the heme group is represented by the bent line.
On the right is a schematic diagram showing representations of electron-density clouds of the oxygenated heme group pinkthe attached histidine residue light blueand the attached oxygen molecule gray. The oxygenated heme assumes a planar configuration, and the central iron atom occupies a space in the plane of the heme group depicted by a straight red line.
The shape change in the heme group has important implications for the rest of the hemoglobin protein, as well. When the iron atom moves into the porphyrin plane upon oxygenation, the histidine residue to which the iron atom is attached is drawn closer to the heme group.
This movement of the histidine residue then shifts the position of other amino acids that are near the histidine Figure 6. When the amino acids in a protein are shifted in this manner by the oxygenation of one of the heme groups in the proteinthe structure of the interfaces between the four subunits is altered. Hence, when a single heme group in the hemoglobin protein becomes oxygenated, the whole protein changes its shape. In the new shape, it is easier for the other three heme groups to become oxygenated.
Thus, the binding of one molecule of O2 to hemoglobin enhances the ability of hemoglobin to bind more O2 molecules. This property of hemoglobin is known as "cooperative binding. When hemoglobin is deoxygenated leftthe heme group adopts a domed configuration.
When hemoglobin is oxygenated rightthe heme group adopts a planar configuration. As shown in the figure, the conformational change in the heme group causes the protein to change its conformation, as well.
Please click on the pink button below to view a QuickTime movie showing how the amino acid residues near the heme group in hemoglobin shift as the heme group converts between the nonplanar domed and the planar conformation by binding and releasing a molecule of O2. Explain, in terms of electron repulsion, why the heme group adopts a nonplanar domed configuration upon deoxygenation. Explain how a change in the heme group configuration causes the entire hemoglobin subunit to change shape.
Spectroscopy and the Color of Blood The changes that occur in blood upon oxygenation and deoxygenation are visible not only at the microscopic level, as detailed above, but also at the macroscopic level. Clinicians have long noted that blood in the systemic arteries traveling from the heart to the oxygen-using cells of the body is red-colored, while blood in the systemic veins traveling from the oxygen-using cells back to the heart is blue-colored see Figure 7.
The blood in the systemic arteries is oxygen-rich; this blood has just traveled from the lungs where it picked up oxygen inhaled from the air to the heart, and then is pumped throughout the body to deliver its oxygen to the body's cells. The blood in the systemic veins, on the other hand, is oxygen-poor; it has unloaded its oxygen to the body's cells exchanging the O2 for CO2, as described belowand must now return to the lungs to replenish the supply of oxygen.
Hence, a simple macroscopic observation, i. What causes this color change in the blood? We know that the shape of the heme group and the hemoglobin protein change, depending on whether hemoglobin is oxygenated or deoxygenated. The two conformations must have different light-absorbing properties. The oxygenated conformation of hemoglobin must absorb light in the blue-green range, and reflect red light, to account for the red appearance of oxygenated blood. The deoxygenated conformation of hemoglobin must absorb light in the orange range, and reflect blue light, to account for the bluish appearance of deoxygenated blood.
We could use a spectrophotometer to examine a dilute solution of blood and determine the wavelength of light absorbed by each conformation.
By Jennifer McDowall
For an approximate prediction of the wavelength of light absorbed and for the colors of light absorbed for a given complementary color, a table such as Table 1 in the introduction to the Experiment "Relations Between Electronic Transition Energy and Color" could be used. Questions on Spectroscopy and the Color of Blood Propose an explanation for why the change in heme group conformation results in a color change.
A researcher prepares two solutions of deoxygenated hemoglobin. One solution is ten times as concentrated as the other solution. The researcher then obtains absorption spectra for the two solutions. Do you expect the wavelength of maximum absorption lmax to be the same or different for the two solutions?
If lmax is different for the two solutions, indicate which solution will have a higher lmax. Briefly, explain your reasoning.
Metal Complex in the Blood
Do you expect the absorbance A at lmax to be the same or different for the two solutions? If the absorbance is different for the two solutions, indicate which solution will have a higher absorbance.
This phenomenon, known as the Bohr effect, is a highly adaptive feature of the body's blood-gas exchange mechanism. The blood that is pumped from the heart to the body tissues and organs other than the lungs is rich in oxygen Figure 7.
These tissues require oxygen for their metabolic activities e. Hence, it is necessary for oxygen to remain bound to hemoglobin as the blood travels through the arteries so that it can be carried to the tissuesbut be easily removable when the blood passes through the capillaries feeding the body tissues.Oxygen Hemoglobin Dissociation Curve Explained Clearly (Oxyhemoglobin Curve)
In the lungs, the reverse effect occurs: Blood rich in carbon dioxide is pumped from the heart into the lungs through the pulmonary arteries. Arteries are blood vessels carrying blood away from the heart; veins are blood vessels carrying blood to the heart.
In the lungs, CO2 in the blood is exchanged for O2. The oxygen-rich blood is carried back to the heart through the pulmonary veins.