Genetic Disorders. Oxygen Transport. Overview Oxygen is transported within the blood in a simple dissolved form as well as a chemically-bound form associated with hemoglobin See: Gases in Liquids. Oxygen transport in the body occurs in two basic steps involving the reversible loading and unloading of hemoglobin with oxygen.
Hemoglobin is loaded with oxygen as it passes through the pulmonary capillaries and is then transported to the peripheral tissues where the oxygen is unloaded. The primary factor determining whether oxygen is loaded or unloaded onto hemoglobin is the surrounding partial pressure of oxygen. The quantitative relationship between oxygen partial pressure and the percent of hemoglobin molecules bound to oxygen is provided by the "Oxygen-Hemoglobin Dissociation Curve" described below.
Careful analysis of this dissociation curve can provide valuable insights into how oxygen transport is regulated. Oxygen Transport in Outline Oxygen is loaded in blood in the pulmonary capillaries where the oxygen tension is mm Hg as a result of alveolar ventilation.
Oxygen is unloaded from the blood in the peripheral tissues where the oxygen tension is roughly 40 mm Hg as a result of peripheral tissue oxygen consumption. The curve can be generated by placing a sample of human blood in an oxygen-free environment and then slowly increasing the partial pressure of oxygen from 0 mm Hg to roughly mm Hg. The percent of hemoglobin within the sample bound to oxygen can be measured using optical techniques, allowing for an assessment of the hemoglobin oxygen-saturation for every value of oxygen partial pressure.
The Oxygen-Hemoglobin Dissociation Curve is obtained by plotting the hemoglobin saturation against the oxygen partial pressure. Qualitative Features The key feature of the dissociation curve is its non-linear, sigmoid shape.
As observed, the saturation of hemoglobin changes substantially when the partial pressure of oxygen ranges between 20 - 60 mm Hg but tends to plateau at oxygen partial pressures above 80 mm Hg. Consequently, the amount of oxygen released from blood may be very different given the starting and ending partial pressures of oxygen. For example, a drop in oxygen partial pressure from mm Hg to 80 mm Hg will result in little release of hemoglobin-bound oxygen; however, a drop in oxygen partial pressure from 60 mm Hg to 40 mm Hg will result in an enormous release of hemoglobin bound oxygen even though in both cases the oxygen partial pressure was reduced by 40 mm Hg.
The sigmoid shape of the oxygen-hemoglobin dissociation curve is the result of hemoglobin's unique biochemistry which allows for oxygen binding in a cooperative fashion. These biochemical features of hemoglobin will be added to this text later under a Hemoglobin Biochemistry page. Quantitative Features of the Oxygen-Hemoglobin Dissociation Curve The Oxygen-Hemoglobin dissociation curve is derived by quantifying the saturation of hemoglobin in blood as the partial pressure of oxygen in the blood is slowly raised.
Each of those factors generally increase gas exchange as those factors are increased i. Cellular respiration is the metabolic process by which an organism obtains energy through the reaction of oxygen with glucose to produce water, carbon dioxide and ATP, which is the functional source of energy for the cell.
The oxygen supply for cellular respiration comes from the external respiration of the respiratory system. Overview of cellular respiration : A diagram of cellular respiration including glycolysis, the Krebs cycle also called the citric acid cycle , and the electron transport chain.
Cellular respiration includes three major steps, and occurs mainly in the cytoplasm of the cell and within the mitochondria of the cell. The net formula for cellular respiration is:. The carbon dioxide waste is the result of the carbon from glucose C 6 H 12 O 6 being broken down to produce the pyruvate and NADH intermediates needed to produce ATP at the end of respiration.
The energy stored in ATP can then be used to drive processes that require energy, including biosynthesis, locomotion, or transportation of molecules across cell membranes. Cellular respiration can occur anaerobically without oxygen, such as through lactic acid fermentation. This process is very inefficient compared to aerobic respiration, as without oxidative phosphorylation, the cell cannot produce nearly as much ATP 2 ATP compared to 38 during cellular respiration. Hemoglobin is the primary transporter of oxygen with an oxygen binding capacity between 1.
About Hemoglobin is a protein found in red blood cells also called erythrocytes. There are roughly million hemoglobin molecules in a single red blood cell, and each contains 4 heme groups. The function of Hgb is to provide a binding site for oxygen to carry oxygen throughout the bloodstream to the systemic tissues for cellular respiration.
Hemoglobin : Hemoglobin is the iron-containing, oxygen-transport metalloprotein in the red blood cells of all vertebrates.
About 1. It has an oxygen binding capacity between 1. The percentage of oxygen that is saturated in the hemoglobin of blood is generally represented by a curve that shows the relationship between PaO 2 and O 2 saturation. Saturation of O 2 in hemoglobin is an indicator for how much O 2 is able to reach the tissues of the body. Higher PaO 2 means higher saturation of oxygen in blood. The carrying capacity can be increased if more hemoglobin is added to the system, such as through greater red blood cell generation in high altitude, or from blood transfusions.
The lower areas of the curve show saturation when oxygen is unloaded into the tissues. The oxyhaemoglobin dissociation curve : The oxygen—hemoglobin dissociation curve plots the percent hemoglobin saturation y-axis against the partial pressure of oxygen in the blood PO 2. The blue curve is standard curve, while the red and green curves are right and leftward shifts respectively.
The oxyhemoglobin dissociation curve can shift in response to a variety of factors. A change in the P 50 of the curve is a sign that the dissociation curve as a whole has shifted. Rightward shifts indicate a decreased affinity for the binding of hemoglobin, so that less oxygen binds to hemoglobin, and more oxygen is unloaded from it into the tissues. The curve shifts right during decreased blood pH called the Bohr effect , increased temperature, and during exercise among other things.
Anemia a disorder marked by a decreased red blood cell count and less hemoglobin also causes a rightward shift, but also changes the shape of the curve so that it moves downward as well as a result of the reduced levels of hemoglobin. Leftward shifts indicate an increased affinity for the binding of hemoglobin, so that more oxygen binds to hemoglobin, but less oxygen is unloaded from it into the tissues.
Causes of leftward shifts include increased blood pH, decreased temperature, and carbon monoxide exposure. Carbon monoxide binds to hemoglobin in place of oxygen, so that less oxygen reaches the tissues; this can be fatal if severe enough. CO 2 is carried in blood in three different ways: dissolved in plasma, bound to hemoglobin, or as a biocarbonate ion. Carbon dioxide is the product of cellular respiration, and is transported from the cells of tissues in the body to the alveoli of the lungs through the bloodstream.
Carbon dioxide is carried in the blood through three different ways. Carbon dioxide has a much higher solubility than oxygen, which explains why a relatively greater amount of carbon dioxide is dissolved in the plasma compared to oxygen.
Structure of human hemoglobin : Hemoglobin is a tetramer of alpha red and beta blue subunits with iron containing heme groups green. While oxygen binds to the iron content in the heme of hemoglobin, carbon dioxide can bind to the amino acid chains on hemoglobin.
When carbon dioxide clings to hemoglobin it forms carbanimohemoglobin. Carbanimohemoglobin gives red blood cells a bluish color, which is one of the reasons why the veins that carry deoxygenated blood appear to be blue. A property of hemoglobin called the Haldane effect states that deoxygenated blood has an increased capacity to carry carbon dioxide, while oxygenated blood has a decreased capacity to carry carbon dioxide.
This property means that hemoglobin will primarily carry oxygen in systemic circulation until it unloads that oxygen and is able to carry a relatively higher amount of carbon dioxide. The reaction that describes the formation of bicarbonate ions in the blood is:.
Diffusion can be described by either a phenomenological approach using Fick's laws or an atomistic approach applying the principle known as the random walk of the diffusing particles another example of which is Brownian motion. Thus, although the global oxygen delivery oxygen flux may be manipulated through changes in cardiac output and oxygen content, at a tissue level diffusion distance and partial pressure gradients will have the greatest effect in altering the diffusive oxygen flux.
This is shown in Figure 3. A diagram illustrating the importance of diffusion distance from capillary to cell and local oxygen tension in determining diffusive oxygen flow rate.
Whole-body oxygen transport and utilization can be estimated using two principle approaches: It is worth noting that expired gas analysis, although less invasive, is more direct in its measurement of cellular oxygen consumption. Estimation of oxygen mass transport, through separate measurement of cardiac output and the elements of oxygen content. In combination with the latter approach, additional measurement of mixed venous oxygen content allows calculation of oxygen extraction and therefore oxygen consumption.
Evaluation of oxygen consumption through measurement of steady state, or dynamically changing, oxygen uptake using expired gas analysis to measure gas flows and concentrations [cardiopulmonary exercise testing CPET , metabolic cart]. In addition to its use in the physiological assessment of elite athletes, CPET has been developed as a tool to assess a patient's preoperative functional capacity, that is, their ability to do external physical work, before major surgery.
Also determining V O 2peak , a subject's ventilatory anaerobic threshold AT may be calculated. While this is often presented as being evidence of the demand for oxygen outstripping supply, it may in fact be more closely related to the recruitment of muscle fibres with different patterns of metabolism. A high level of functional capacity physical fitness is an index of a substantial physiological reserve over and above resting values.
This in turn is inferred to provide benefit in withstanding the physiological challenge of major surgery. In patients undergoing major surgery, postoperative morbidity and mortality are consistently increased in individuals with lower values of AT and V O 2peak.
An example of a CPET nine-panel plot data from authors' laboratory. Panels 1—3 are in the first row, 4—6 in the second row, and 5—9 in the third row. The AT can also be ascertained by evaluating: the ventilatory equivalents for oxygen and carbon dioxide in panel 4; end-tidal oxygen tension in panel 7; and ventilatory equivalents against workload in panel 9.
The vertical red line denotes the AT. Originally, measurement of these variables required thermodilution techniques and a pulmonary artery right heart catheter; 27 however, this modality has subsequently gone out of favour following concerns about its safety. GDT is used perioperatively in anaesthesia and critical care.
Theoretically, by improving D O 2 convection to the tissues, the oxygen concentration gradient between the microcirculation and the cells increases, causing increased oxygen diffusion or rather increased diffusive flux. However, although GDT may provide more oxygen at tissue level, this will not necessarily affect oxygen utilization in the absence of supply-dependency.
It is also assumed that capillary surface area and diffusion coefficient remain constant, which may not hold if tissue fluid status changes, for example, in the case of the tissue oedema often seen in critically unwell patients. A more in-depth review of GDT is beyond the scope of this article; however, see the clinical reviews by Lobo and de Oliveira, 29 Ramsingh and colleagues, 30 and Lees and colleagues, 31 and also the Cochrane Review by Grocott and colleagues 32 for further information.
The convective and diffusive transport of oxygen from the air into the tissues is clearly complex, with each step in the process affected by multiple factors. However, understanding how our respiratory and cardiovascular systems combine to facilitate the movement of oxygen from where it enters the circulation in the pulmonary capillary to where it is ultimately utilized in mitochondria within cells is fundamental for anaesthetists.
His institution has also received charitable donations and grants from Smiths Medical Endowment, Deltex Medical and Fresenius-kabi. He does a small amount of Private Medical Practice. He also serves no renumeration for any of these roles as a director of Oxygen Contol Systems Ltd, as a director of the Bloomsbury Innovation Group a novel community interest group using an innovative low-cost open source IP model to drive innovation and development in medical devices in the areas of anaesthesia and critical care within the NHS and is chair of the board of the Xtreme-Everest Community Interest Company jointly owned by University of Southampton and UCL; maintenance, development and exploitation of the Xtreme Everest Bioresource.
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