Oxygen capacity of blood. The mechanism of oxygen transport by blood. Oxyhemoglobin dissociation curve analysis. Transport proteins Oxygen is transported in the blood in two forms

Only a small part of O 2 (about 2%) carried by the blood is dissolved in the plasma. The main part of it is transported in the form of a fragile connection with hemoglobin, which in vertebrates is contained in red blood cells. The molecules of this respiratory pigment include a species-specific protein - globin and the prosthetic group, equally constructed in all animals, is heme, containing ferrous iron (Fig. 10.27).

Addition of oxygen to hemoglobin (oxygenation of hemoglobin) occurs without a change in the valence of iron, i.e. without electron transfer, which characterizes true oxidation. Nevertheless, hemoglobin bound with oxygen is usually called oxidized (more correctly - oxyhemoglobin), and the one who gave up oxygen is restored (more correctly - deoxyhemoglobin).

1 g of hemoglobin can bind 1.36 ml of O 2 gas (at normal atmospheric pressure). Considering, for example, that human blood contains approximately 150 g/l of hemoglobin, 100 ml of blood can carry about 21 ml of O 2. This is the so-called oxygen capacity of the blood. Hemoglobin oxygenation (in other words, the percentage by which the oxygen capacity of the blood is used) depends on the partial pressure of 0 2 in the environment with which the blood comes into contact. This dependence is described oxyhemoglobin dissociation curve(Fig. 10.28). Complex S The -shaped shape of this curve is explained by the cooperative effect of the four polypeptide chains of hemoglobin, the oxygen-binding properties (affinity for O2) of which are different.

Thanks to this feature, venous blood, passing the pulmonary capillaries (alveolar P O2 falls on the upper part of the curve), is oxygenated almost completely, and arterial blood in the tissue capillaries (where Po 2 corresponds to the steep part of the curve) effectively releases O 2. Promotes oxygen release

The oxyhemoglobin dissociation curve shifts to the right with increasing temperature and with increasing concentration of hydrogen ions in the medium, which, in turn, depends on Pco 2 (Verigo-Bohr effect). Therefore, conditions are created for a more complete release of oxygen by oxyhemoglobin in tissues, especially where the metabolic rate is higher, for example in working muscles. However, in venous blood, a larger or smaller part (from 40 to 70%) of hemoglobin remains in oxygenated form. So, in humans, every 100 ml of blood gives 5-6 ml of O2 to tissues (the so-called arteriovenous oxygen difference) and, naturally, are enriched with oxygen in the lungs by the same amount.

The affinity of hemoglobin for oxygen is measured by the partial pressure of oxygen at which hemoglobin is 50% saturated (P 50) in humans it is normally 26.5 mmHg. Art. for arterial blood. Parameter R 50 reflects the ability of the respiratory pigment to bind oxygen. This parameter is higher for the hemoglobin of animals living in an oxygen-poor environment, as well as for the so-called fetal hemoglobin, which is contained in the blood of the fetus, which receives oxygen from the mother’s blood through the placental barrier.

Oxygen in the blood is dissolved and combined with hemoglobin. A very small amount of oxygen is dissolved in plasma; every 100 ml of blood plasma at an oxygen tension (100 mm Hg) can carry only 0.3 ml of oxygen in a dissolved state. This is clearly not enough for the life of the body. With such an oxygen content in the blood and the condition of its complete consumption by the tissues, the minute volume of blood at rest would have to be more than 150 l/min. Another mechanism of oxygen transfer is important by combining it with hemoglobin.

Each gram of hemoglobin is capable of binding 1.34 ml of oxygen. The maximum amount of oxygen that can be bound by 100 ml of blood is the oxygen capacity of the blood (18.76 ml or 19 vol%). The oxygen capacity of hemoglobin is a value that reflects the amount of oxygen that can contact hemoglobin when it is completely saturated. Another indicator of the respiratory function of the blood is the oxygen content in the blood, which reflects the true amount of oxygen, both bound to hemoglobin and physically dissolved in the plasma.

100 ml of arterial blood normally contains 19-20 ml of oxygen, the same volume of venous blood contains 13-15 ml of oxygen, while the arteriovenous difference is 5-6 ml.

An indicator of the degree of oxygen saturation of hemoglobin is the ratio of the amount of oxygen associated with hemoglobin to the oxygen capacity of the latter. The oxygen saturation of hemoglobin in arterial blood in healthy individuals is 96%.

The formation of oxyhemoglobin in the lungs and its restoration in tissues depends on the partial oxygen tension of the blood: when it increases, the saturation of hemoglobin with oxygen increases, and when it decreases, it decreases. This relationship is nonlinear and is expressed by an S-shaped oxyhemoglobin dissociation curve.

Oxygenated arterial blood corresponds to a plateau of the dissociation curve, and desaturated blood in tissues corresponds to a steeply decreasing part of it. The gentle rise of the curve in its upper section (zone of high O2 voltage) indicates that a sufficiently complete saturation of arterial blood hemoglobin with oxygen is ensured even when the O2 voltage decreases to 70 mmHg.

Decrease in O2 voltage from 100 to 15-20 mm Hg. Art. has virtually no effect on hemoglobin oxygen saturation (HbO; it decreases by 2-3%). At lower O2 voltage values, oxyhemoglobin dissociates much more easily (the zone of steep decline in the curve). So, when the voltage 0 2 decreases from 60 to 40 mm Hg. Art. hemoglobin oxygen saturation decreases by approximately 15%.

The position of the oxyhemoglobin dissociation curve is usually expressed quantitatively by the partial oxygen tension at which hemoglobin saturation is 50%. The normal P50 value at a temperature of 37°C and pH 7.40 is about 26.5 mm Hg. Art..

Under certain conditions, the oxyhemoglobin dissociation curve can shift in one direction or another, maintaining an S-shape, under the influence of changes:

3. body temperature,

In working muscles, as a result of intense metabolism, the formation of CO 2 and lactic acid increases, and heat production also increases. All these factors reduce the affinity of hemoglobin for oxygen. In this case, the dissociation curve shifts to the right, which leads to easier release of oxygen from oxyhemoglobin, and the ability of tissues to consume oxygen increases.

With a decrease in temperature, 2,3-DPG, a decrease in CO 2 tension and an increase in pH, the dissociation curve shifts to the left, the affinity of hemoglobin for oxygen increases, as a result of which the delivery of oxygen to tissues decreases.

6. Transport of carbon dioxide in the blood. Carbon dioxide is transported to the lungs in the form of bicarbonates and in a state of chemical bonding with hemoglobin (carbohemoglobin).

Carbon dioxide is a metabolic product of tissue cells and is therefore transported by the blood from the tissues to the lungs. Carbon dioxide plays a vital role in maintaining the pH level in the internal environments of the body by mechanisms of acid-base balance. Therefore, the transport of carbon dioxide in the blood is closely related to these mechanisms.

In blood plasma, a small amount of carbon dioxide is dissolved; at PC0 2 = 40 mm Hg. Art. 2.5 ml/100 ml of blood carbon dioxide is tolerated, or 5%. The amount of carbon dioxide dissolved in plasma increases linearly with the PC0 2 level. In blood plasma, carbon dioxide reacts with water to form H + and HCO 3 . An increase in carbon dioxide tension in the blood plasma causes a decrease in its pH value. The carbon dioxide tension in the blood plasma can be changed by the function of external respiration, and the amount of hydrogen ions or pH can be changed by the buffer systems of the blood and HCO 3, for example, by their excretion through the kidneys in the urine. The pH value of blood plasma depends on the ratio of the concentration of carbon dioxide dissolved in it and bicarbonate ions. In the form of bicarbonate, the blood plasma, i.e. in a chemically bound state, transports the main amount of carbon dioxide - about 45 ml/100 ml of blood, or up to 90%. Erythrocytes transport approximately 2.5 ml/100 ml of carbon dioxide, or 5%, in the form of a carbamine compound with hemoglobin proteins. The transport of carbon dioxide in the blood from tissues to the lungs in the indicated forms is not associated with the phenomenon of saturation, as with the transport of oxygen, i.e., the more carbon dioxide is formed, the greater its amount is transported from the tissues to the lungs. However, there is a curvilinear relationship between the partial pressure of carbon dioxide in the blood and the amount of carbon dioxide carried by the blood: the carbon dioxide dissociation curve.

The role of red blood cells in the transport of carbon dioxide. Holden effect.

In the blood of the capillaries of the body's tissues, the carbon dioxide tension is 5.3 kPa (40 mm Hg), and in the tissues themselves - 8.0-10.7 kPa (60-80 mm Hg). As a result, CO 2 diffuses from tissues into the blood plasma, and from it into erythrocytes along the partial pressure gradient of CO 2. In erythrocytes, CO2 forms carbonic acid with water, which dissociates into H+ and HCO3. (C0 2 + H 2 0 = H 2 CO 3 = H + + HCO 3). This reaction proceeds quickly, since C0 2 + H 2 0 = H 2 CO 3 is catalyzed by the enzyme carbonic anhydrase of the erythrocyte membrane, which is contained in them in high concentration.

In red blood cells, the dissociation of carbon dioxide continues continuously as the products of this reaction are formed, since hemoglobin molecules act as a buffer compound, binding positively charged hydrogen ions. In red blood cells, as oxygen is released from hemoglobin, its molecules will bind with hydrogen ions (C0 2 + H 2 0 = H 2 C0 3 = H + + HCO 3), forming a compound (Hb-H +). In general, this is called the Holden effect, which leads to a shift of the oxyhemoglobin dissociation curve to the right along the x-axis, which reduces the affinity of hemoglobin for oxygen and promotes more intense release of it from red blood cells into tissues. In this case, as part of the Hb-H + compound, approximately 200 ml of CO 2 is transported in one liter of blood from the tissues to the lungs. The dissociation of carbon dioxide in erythrocytes can be limited only by the buffer capacity of hemoglobin molecules. HCO3 ions formed inside erythrocytes as a result of the dissociation of CO2 are removed from the erythrocytes into the plasma with the help of a special carrier protein of the erythrocyte membrane, and in their place Cl - ions are pumped from the blood plasma (the “chlorine” shift phenomenon). The main role of the CO 2 reaction inside erythrocytes is the exchange of Cl - and HCO3 ions between the plasma and the internal environment of erythrocytes. As a result of this exchange, the dissociation products of carbon dioxide H + and HCO3 will be transported inside erythrocytes in the form of a compound (Hb-H +), and in the blood plasma - in the form of bicarbonates.

Red blood cells are involved in the transport of carbon dioxide from tissues to the lungs, since C0 2 forms a direct combination with - NH 2 - groups of hemoglobin protein subunits: C0 2 + Hb -> HbC0 2 or carbamine compound. Transport of CO2 in the blood in the form of a carbamine compound and hydrogen ions by hemoglobin depends on the properties of the molecules of the latter; both reactions are determined by the magnitude of the partial pressure of oxygen in the blood plasma based on the Holden effect.

Quantitatively, the transport of carbon dioxide in dissolved form and in the form of a carbamine compound is insignificant compared to its transport of CO 2 in the blood in the form of bicarbonates. However, during the gas exchange of CO 2 in the lungs between the blood and alveolar air, these two forms become of primary importance.

When venous blood returns from the tissues to the lungs, CO 2 diffuses from the blood into the alveoli and PC0 2 in the blood decreases from 46 mm Hg. Art. (venous blood) up to 40 mm Hg. (arterial blood). At the same time, in the total amount of CO 2 (6 ml/100 ml of blood) diffusing from the blood into the alveoli, the proportion of the dissolved form of CO 2 and carbamic compounds becomes more significant relative to bicarbonate. Thus, the proportion of the dissolved form is 0.6 ml/100 ml of blood, or 10%, carbamic compounds - 1.8 ml/100 ml of blood, or 30%, and bicarbonates - 3.6 ml/100 ml of blood, or 60% .

In the red blood cells of the capillaries of the lungs, as the hemoglobin molecules become saturated with oxygen, hydrogen ions begin to be released, carbamine compounds dissociate and HCO3 is again converted into CO 2 (H+ + HCO3 = = H 2 CO 3 = CO 2 + H 2 0), which is excreted through diffusion through lungs along the gradient of its partial pressures between venous blood and alveolar space. Thus, hemoglobin in erythrocytes plays a major role in the transport of oxygen from the lungs to the tissues, and carbon dioxide in the opposite direction, since it is able to bind with 0 2 and H +.

At rest, approximately 300 ml of CO2 is removed from the human body through the lungs per minute: 6 ml/100 ml of blood x 5000 ml/min minute volume of blood circulation.

7. Regulation of breathing. Respiratory center and its divisions. Automation of the respiratory center.

It is well known that external respiration constantly changes under various conditions of the body’s vital activity.

Respiratory need. The activity of the functional respiratory system is always subordinated to satisfying the respiratory need of the body, which is largely determined by tissue metabolism.

Thus, during muscular work, compared to rest, the need for oxygen and the removal of carbon dioxide increases. To compensate for the increased respiratory demand, the intensity of pulmonary ventilation increases, which is expressed in an increase in the frequency and depth of breathing. The role of carbon dioxide. Animal experiments have shown that excess carbon dioxide in the air and blood (hypercapnia) stimulates pulmonary ventilation by increasing and deepening breathing, creating conditions for the removal of excess carbon dioxide from the body. On the contrary, a decrease in the partial pressure of carbon dioxide in the blood (hypocapnia) causes a decrease in pulmonary ventilation up to a complete stop of breathing (apnea). This phenomenon is observed after voluntary or artificial hyperventilation, during which carbon dioxide is removed from the body in excess. As a result, immediately after intense hyperventilation, breathing stops - posthyperventilation apnea.

The role of oxygen. A lack of oxygen in the atmosphere and a decrease in its partial pressure when breathing at high altitudes in a rarefied atmosphere (hypoxia) also stimulate breathing, causing an increase in the depth and especially frequency of breathing. As a result of hyperventilation, the lack of oxygen is partially compensated.

Excess oxygen in the atmosphere (hyperoxia), on the contrary, reduces the volume of pulmonary ventilation.

In all cases, ventilation changes in a direction that helps restore the altered gas state of the body. A process called respiratory regulation is the stabilization of a person's respiratory parameters.

Under the main respiratory center understand the set of neurons of the specific respiratory nuclei of the medulla oblongata.

The respiratory center controls two main functions; motor, which manifests itself in the form of contraction of the respiratory muscles, and homeostatic, associated with maintaining the constancy of the internal environment of the body during shifts in the content of 0 2 and CO 2. The motor, or motor, function of the respiratory center is to generate the respiratory rhythm and its pattern. Thanks to this function, breathing is integrated with other functions. By breathing pattern one should mean the duration of inhalation and exhalation, the tidal volume, and the minute volume of breathing. The homeostatic function of the respiratory center maintains stable values of respiratory gases in the blood and extracellular fluid of the brain, adapts the respiratory function to the conditions of a changed gas environment and other environmental factors.

Transport proteins- a collective name for a large group of proteins that perform the function of transporting various ligands both across the cell membrane or inside the cell (in unicellular organisms), and between different cells of a multicellular organism. Transport proteins can be either integrated into the membrane or water-soluble proteins secreted from the cell, located in the peri- or cytoplasmic space, in the nucleus or organelles of eukaryotes.

The main groups of transport proteins:

chelating proteins;
transport proteins.

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✪ Cell Membranes and Cell Transport

Subtitles

Have you ever imagined what it would be like to be inside a cage? Imagine the genetic material, cytoplasm, ribosomes - you will find them in almost EVERY cell - both prokaryotes and eukaryotes. In addition, eukaryotic cells also have membrane-bound organelles. All these organelles perform different functions. But cells are not isolated little worlds. They have a lot of stuff inside, but they also interact with the outside environment. It makes sense that in order to maintain a stable internal environment - otherwise known as homeostasis - they must control what is happening inside and outside them. A very important structure responsible for all cellular contents is the cell membrane. By controlling what happens inside and outside, the membrane helps maintain homeostasis. Let's take a look at the cell membrane. You can study the cell membrane in detail - it has amazing structure and signaling abilities. But basically it consists of a phospholipid bilayer. Bilayer means 2 layers, i.e. we have 2 layers of lipids. These lipids, called phospholipids, consist of polar heads and non-polar tails. Some molecules have no problem permeating the membrane directly through the phospholipid bilayer. Very small, non-polar molecules fit perfectly into this category. So do some gases. Oxygen and carbon dioxide are good examples. This phenomenon is known as simple diffusion. No energy is expended in moving molecules in and out in this way, so the process falls under the category of passive transport. Simple diffusion follows a concentration gradient. Molecules move from an area of high concentration to an area of low concentration. So when you hear someone say something happens along a gradient, that's what they mean. They involve the movement of molecules from an area of higher concentration to an area of lower concentration. Remember how we said that the cell membrane is actually quite a complex structure? Well, one thing we haven't mentioned yet is membrane proteins, and some of them are transport proteins. Some transport proteins form channels. Some of them change their shape to allow substances to enter. Some of them open and close under the influence of some stimuli. And these proteins are cool things because they help molecules that are either too big to get through on their own or too polar. And then they need the help of transport proteins. This is known as facilitated diffusion. It's still diffusion, and the molecules are still moving along a concentration gradient from high to low. It requires no energy, so it is a type of passive transport. Protein is simply a facilitator, or assistant, in this matter. Charged ions often use protein channels to move. Glucose needs the help of a transport protein. In the process of osmosis, water passes through membrane channels called aquaporins to allow water to pass quickly through a membrane. These are all examples of facilitated diffusion, which is a type of passive transport where movement follows a concentration gradient from high to low. Everything that we have already mentioned concerned only passive transport, i.e. movement from greater concentration to lesser. But what if we need to go in the opposite direction? For example, intestinal cells must absorb glucose. But what if the concentration of glucose inside the cell is higher than outside? We need to absorb glucose inside, and for this it must be dragged against the concentration gradient. The movement of molecules from an area of low concentration to an area of high concentration requires energy because it goes against the flow. Typically, this is ATP energy. Let me remind you that ATP - adenosine triphosphate - includes 3 phosphogroups. When the last phosphate bond is broken, a huge amount of energy is released. It's just an awesome little molecule. ATP can activate active transport, causing molecules to move against a concentration gradient. And one way is to use transport proteins. One of our favorite examples of active transport is the sodium-potassium pump, so it's definitely worth a look! Once again, when a cell needs to expend energy for transport, then we are talking about active transport. But let's assume that the cell needs a very large molecule - a large polysaccharide (if you forgot, take a look at our video about biomolecules). You may need a cell membrane to bind the molecule and thus pull it in. This is called endocytosis - from "endo" - inward. Often this fusion of substances with the cell membrane forms vesicles that can be released inside the cell. Endocytosis is the basic term, but there are several different types of endocytosis, depending on how the cell pulls the substance in. Amoebas, for example, use endocytosis. The pseudopods extend and surround what the amoeba wants to eat, and the substance is pulled into the vacuole. There are other forms, such as bizarre receptor-mediated endocytosis - where cells can be very very very picky about what they take in because the substance they take in has to bind to receptors in order to get in. Or pinocytosis, which allows the cell to absorb liquids. So google it to find out more details about the different types of endocytosis. Exocytosis is the opposite of endocytosis because it takes molecules out ("exo" means out). Exocytosis can be used to rid cells of waste, but it is also very important for moving important materials produced by the cell out. Want a cool example? Back to polysaccharides - did you know that giant hydrocarbons are very important for the formation of a plant cell wall? A cell wall is different from a cell membrane - all cells have membranes, but not all cells have a wall. But if you suddenly need a cell wall, you will need somewhere to - then within the cell hydrocarbons were produced for this wall. This is a great example of the need for exocytosis. That's all! And we remind you - stay curious!

Transport function of proteins

The transport function of proteins is the participation of proteins in the transfer of substances into and out of cells, in their movements within cells, as well as in their transport by blood and other fluids throughout the body.

There are different types of transport that are carried out using proteins.

Transport of substances across the cell membrane

Passive transport is also provided by channel proteins. Channel-forming proteins form aqueous pores in the membrane through which (when open) substances can pass. special families of channel-forming proteins (connexins and pannexins) form gap junctions through which low-molecular-weight substances can be transported from one cell to another (through pannexins and into cells from the external environment).

Microtubules - structures consisting of tubulin proteins - are also used to transport substances inside cells. Mitochondria and membrane vesicles with cargo (vesicles) can move along their surface. This transport is carried out by motor proteins. They are divided into two types: cytoplasmic dyneins and kinesins. These two groups of proteins differ in which end of the microtubule they move cargo from: dyneins from the + end to the - end, and kinesins in the opposite direction.

Transport of substances across the cell membrane

Passive transport is also provided by channel proteins. Channel-forming proteins form aqueous pores in the membrane through which (when open) substances can pass. special families of channel-forming proteins (connexins and pannexins) form gap junctions through which low-molecular-weight substances can be transported from one cell to another (via pannexins and into cells from the external environment).

Transport of substances throughout the body

Transport of substances throughout the body is mainly carried out by blood. Blood carries hormones, peptides, ions from endocrine glands to other organs, carries metabolic end products to excretory organs, transports nutrients and enzymes, oxygen and carbon dioxide.

The most well-known transport protein that transports substances throughout the body is hemoglobin. It transports oxygen and carbon dioxide through the circulatory system from the lungs to organs and tissues. In humans, about 15% of carbon dioxide is transported to the lungs by hemoglobin. In skeletal and cardiac muscles, oxygen transport is carried out by a protein called myoglobin.

Blood plasma always contains transport proteins - serum albumin. Fatty acids, for example, are transported by serum albumin. In addition, proteins of the albumin group, such as transthyretin, transport thyroid hormones. Also, the most important transport function of albumins is the transfer of bilirubin, bile acids, steroid hormones, drugs (aspirin, penicillins) and inorganic ions.

Other blood proteins - globulins - transport various hormones, lipids and vitamins. Transport of copper ions in the body is carried out by globulin - ceruloplasmin, transport of iron ions - transferrin protein, transport of vitamin B12 - transcobalamin.

2.4.1. Transport of oxygen by blood

Functional oxygen transport system- a set of structures of the cardiovascular apparatus, blood and their regulatory mechanisms, forming a dynamic self-regulating organization, the activity of all its constituent elements creates diffusion zeros and gradients of pO2 between the blood and tissue cells and ensures an adequate supply of oxygen to the body.

The purpose of its operation is to minimize the difference between oxygen demand and consumption. Oxidase pathway for oxygen utilization, associated with oxidation and phosphorylation in the mitochondria of the tissue respiration chain, is the most capacious in a healthy body (about 96-98% of consumed oxygen is used). The processes of oxygen transport in the body also provide it antioxidant protection.

Hyperoxia- increased oxygen content in the body.
Hypoxia - reduced oxygen content in the body.
Hypercapnia- increased carbon dioxide content in the body.
Hypercapnemia- increased levels of carbon dioxide in the blood.
Hypocapnia- reduced carbon dioxide content in the body.
Hypocappemia - low carbon dioxide levels in the blood.

Rice. 1. Scheme of breathing processes

Oxygen consumption- the amount of oxygen absorbed by the body per unit of time (at rest 200-400 ml/min).

Degree of blood oxygen saturation- the ratio of the oxygen content in the blood to its oxygen capacity.

The volume of gases in the blood is usually expressed as a volume percentage (vol%). This indicator reflects the amount of gas in milliliters found in 100 ml of blood.

Oxygen is transported by blood in two forms:

physical dissolution (0.3 vol%);
due to hemoglobin (15-21 vol%).

A hemoglobin molecule that is not associated with oxygen is designated by the symbol Hb, and one that has attached oxygen (oxyhemoglobin) is designated by HbO 2. The addition of oxygen to hemoglobin is called oxygenation (saturation), and the release of oxygen is called deoxygenation or reduction (desaturation). Hemoglobin plays a major role in the binding and transport of oxygen. One hemoglobin molecule, when fully oxygenated, binds four oxygen molecules. One gram of hemoglobin binds and transports 1.34 ml of oxygen. Knowing the hemoglobin content in the blood, it is easy to calculate the oxygen capacity of the blood.

Blood oxygen capacity- this is the amount of oxygen associated with hemoglobin found in 100 ml of blood when it is completely saturated with oxygen. If the blood contains 15 g% hemoglobin, then the oxygen capacity of the blood will be 15. 1.34 = 20.1 ml oxygen.

Under normal conditions, hemoglobin binds oxygen in the pulmonary capillaries and releases it into the tissues due to special properties that depend on a number of factors. The main factor influencing the binding and release of oxygen by hemoglobin is the amount of oxygen tension in the blood, which depends on the amount of oxygen dissolved in it. The dependence of oxygen binding by hemoglobin on its voltage is described by a curve called the oxyhemoglobin dissociation curve (Fig. 2.7). On the graph, the vertical line shows the percentage of hemoglobin molecules associated with oxygen (%HbO 2), and the horizontal line shows the oxygen tension (pO 2). The curve reflects the change in %HbO 2 depending on the oxygen tension in the blood plasma. It has an S-shape with kinks in the voltage range of 10 and 60 mm Hg. Art. If pO 2 in the plasma becomes greater, then the oxygenation of hemoglobin begins to increase almost linearly with the increase in oxygen tension.

Rice. 2. Dissociation curves: a - at the same temperature (T = 37 ° C) and different pCO 2: I-oxymyoglobin under normal conditions (pCO 2 = 40 mm Hg); 2 - okenhemoglobin under normal conditions (pCO 2 = 40 mm Hg); 3 - okenhemoglobin (pCO 2 = 60 mm Hg); b - at the same рС0 2 (40 mm Hg) and different temperatures

The binding reaction of hemoglobin with oxygen is reversible and depends on the affinity of hemoglobin for oxygen, which, in turn, depends on the oxygen tension in the blood:

At the usual partial pressure of oxygen in the alveolar air, which is about 100 mm Hg. Art., this gas diffuses into the blood of the capillaries of the alveoli, creating a voltage close to the partial pressure of oxygen in the alveoli. The affinity of hemoglobin for oxygen increases under these conditions. From the above equation it is clear that the reaction shifts towards the formation of okenhemoglobin. Oxygenation of hemoglobin in arterial blood flowing from the alveoli reaches 96-98%. Due to blood shunting between the small and large circles, hemoglobin oxygenation in the arteries of the systemic circulation is slightly reduced, amounting to 94-98%.

The affinity of hemoglobin for oxygen is characterized by the oxygen tension at which 50% of hemoglobin molecules are oxygenated. He is called half-saturation voltage and are designated by the symbol P50. An increase in P50 indicates a decrease in the affinity of hemoglobin for oxygen, and its decrease indicates an increase. The P50 level is influenced by many factors: temperature, acidity of the environment, CO 2 tension, and the content of 2,3-diphosphoglycerate in the erythrocyte. For venous blood, P50 is close to 27 mmHg. Art., and for arterial - to 26 mm Hg. Art.

From the blood of the microcirculatory blood vessels, oxygen constantly diffuses into the tissue through its voltage gradient and its tension in the blood decreases. At the same time, carbon dioxide tension, acidity, and blood temperature of tissue capillaries increase. This is accompanied by a decrease in the affinity of hemoglobin for oxygen and accelerated dissociation of oxyhemoglobin with the release of free oxygen, which dissolves and diffuses into the tissue. The rate of oxygen release from connection with hemoglobin and its diffusion satisfies the needs of tissues (including those highly sensitive to oxygen deficiency), with the HbO 2 content in arterial blood above 94%. When the HbO 2 content decreases to less than 94%, it is recommended to take measures to improve hemoglobin saturation, and when the content is 90%, the tissues experience oxygen starvation and it is necessary to take urgent measures to improve the delivery of oxygen to them.

A condition in which hemoglobin oxygenation decreases to less than 90% and blood pO 2 becomes below 60 mmHg. Art., called hypoxemia.

Shown in Fig. 2.7 indicators of the affinity of Hb for O 2 occur at normal, normal body temperature and a carbon dioxide tension in arterial blood of 40 mm Hg. Art. As the carbon dioxide tension in the blood or the concentration of H+ protons increases, the affinity of hemoglobin for oxygen decreases, and the HbO 2 dissociation curve shifts to the right. This phenomenon is called the Bohr effect. In the body, an increase in pCO 2 occurs in tissue capillaries, which increases the deoxygenation of hemoglobin and the delivery of oxygen to tissues. A decrease in the affinity of hemoglobin for oxygen also occurs with the accumulation of 2,3-diphosphoglycerate in erythrocytes. Through the synthesis of 2,3-diphosphoglycerate, the body can influence the rate of HbO 2 dissociation. In older people, the content of this substance in red blood cells is increased, which prevents the development of tissue hypoxia.

An increase in body temperature reduces the affinity of hemoglobin for oxygen. If body temperature decreases, then the HbO 2 dissociation curve shifts to the left. Hemoglobin more actively captures oxygen, but releases it to tissues to a lesser extent. This is one of the reasons why, when entering cold (4-12 °C) water, even good swimmers quickly experience incomprehensible muscle weakness. Hypothermia and hypoxia of the muscles of the extremities develop due to both a decrease in blood flow in them and a reduced dissociation of HbO 2.

From the analysis of the course of the HbO 2 dissociation curve, it is clear that pO 2 in the alveolar air can be reduced from the usual 100 mm Hg. Art. up to 90 mm Hg Art., and hemoglobin oxygenation will remain at a level compatible with life activity (it will decrease by only 1-2%). This feature of hemoglobin’s affinity for oxygen allows the body to adapt to decreased ventilation and decreased atmospheric pressure (for example, living in the mountains). But in the region of low oxygen tension in the blood of tissue capillaries (10-50 mm Hg), the course of the curve changes sharply. For every unit decrease in oxygen tension, a large number of oxyhemoglobin molecules are deoxygenated, the diffusion of oxygen from red blood cells into the blood plasma increases, and by increasing its tension in the blood, conditions are created for a reliable supply of oxygen to tissues.

Other factors also influence the relationship between hemoglobin and oxygen. In practice, it is important to take into account that hemoglobin has a very high (240-300 times greater than oxygen) affinity for carbon monoxide (CO). The combination of hemoglobin with CO is called carboxyheluglobin. In case of CO poisoning, the victim’s skin in areas of hyperemia may acquire a cherry-red color. The CO molecule attaches to the heme iron atom and thereby blocks the possibility of hemoglobin connecting with oxygen. In addition, in the presence of CO, even those hemoglobin molecules that are associated with oxygen release it to tissues to a lesser extent. The HbO 2 dissociation curve shifts to the left. When there is 0.1% CO in the air, more than 50% of hemoglobin molecules are converted into carboxyhemoglobin, and even when the blood contains 20-25% HbCO, a person requires medical attention. In case of carbon monoxide poisoning, it is important to ensure that the victim inhales pure oxygen. This increases the rate of HbCO dissociation by 20 times. Under normal life conditions, the HbCO content in the blood is 0-2%; after smoking a cigarette, it can increase to 5% or more.

Under the influence of strong oxidizing agents, oxygen is able to form a strong chemical bond with heme iron, in which the iron atom becomes trivalent. This combination of hemoglobin with oxygen is called methemoglobin. It cannot give oxygen to tissues. Methemoglobin shifts the oxyhemoglobin dissociation curve to the left, thus worsening the conditions for the release of oxygen in tissue capillaries. In healthy people under normal conditions, due to the constant intake of oxidizing agents (peroxides, nitrocontaining organic substances, etc.) into the blood, up to 3% of blood hemoglobin can be in the form of methemoglobin.

The low level of this compound is maintained due to the functioning of antioxidant enzyme systems. The formation of methemoglobin is limited by antioxidants (glutathione and ascorbic acid) present in erythrocytes, and its restoration to hemoglobin occurs through enzymatic reactions involving erythrocyte dehydrogenase enzymes. If these systems are insufficient or if substances (for example, phenacetin, antimalarial drugs, etc.) with high oxidative properties enter the bloodstream excessively, msgmoglobinsmia develops.

Hemoglobin easily interacts with many other substances dissolved in the blood. In particular, when interacting with drugs containing sulfur, sulfhemoglobin can be formed, shifting the oxyhemoglobin dissociation curve to the right.

Fetal hemoglobin (HbF) predominates in the blood of the fetus, which has a greater affinity for oxygen than adult hemoglobin. In a newborn, red blood cells contain up to 70% of hemoglobin. Hemoglobin F is replaced by HbA during the first six months of life.

In the first hours after birth, arterial blood pO2 is about 50 mm Hg. Art., and НbО 2 - 75-90%.

In older people, oxygen tension in arterial blood and hemoglobin oxygen saturation gradually decrease. The value of this indicator is calculated using the formula

pO 2 = 103.5-0.42. age in years.

Due to the existence of a close connection between the oxygen saturation of hemoglobin in the blood and the oxygen tension in it, a method was developed pulse oximetry, which is widely used in the clinic. This method determines the saturation of hemoglobin in arterial blood with oxygen and its critical levels at which the oxygen tension in the blood becomes insufficient for its effective diffusion into the tissues and they begin to experience oxygen starvation (Fig. 3).

A modern pulse oximeter consists of a sensor including an LED light source, a photodetector, a microprocessor and a display. Light from the LED is directed through the tissue of the finger (toe), earlobe, and is absorbed by oxyhemoglobin. The unabsorbed part of the light flux is assessed by a photodetector. The photodetector signal is processed by a microprocessor and sent to the display screen. The screen displays the percentage oxygen saturation of hemoglobin, heart rate and pulse curve.

The curve of the dependence of hemoglobin oxygen saturation shows that the hemoglobin of arterial blood, which flows from the alveolar capillaries (Fig. 3), is completely saturated with oxygen (SaO2 = 100%), the oxygen tension in it is 100 mm Hg. Art. (pO2 = 100 mm Hg). After the dissociation of oxymoglobin in the tissues, the blood becomes deoxygenated and in the mixed venous blood returning to the right atrium, under resting conditions, hemoglobin remains saturated with oxygen by 75% (Sv0 2 = 75%), and the oxygen tension is 40 mm Hg. Art. (pvO2 = 40 mmHg). Thus, under resting conditions, tissues absorbed about 25% (≈250 ml) of the oxygen released from oxymoglobin after its dissociation.

Rice. 3. Dependence of oxygen saturation of hemoglobin in arterial blood on oxygen tension in it

With a decrease of only 10% in the saturation of hemoglobin in arterial blood with oxygen (SaO 2,<90%), диссоциирующий в тканях оксигемоглобин не обеспечивает достаточного напряжения кислорода в артериальной крови для его эффективной диффузии в ткани и они начинают испытывать кислородное голодание.

One of the important tasks that is solved by constantly measuring oxygen saturation of hemoglobin in arterial blood with a pulse oximeter is to detect the moment when saturation decreases to a critical level (90%) and the patient needs emergency care aimed at improving the delivery of oxygen to the tissues.

Transport of carbon dioxide in the blood and its relationship with the acid-base state of the blood

Carbon dioxide is transported by blood in the forms:

physical dissolution - 2.5-3 vol%;
carboxyhemoglobin (HbCO 2) - 5 vol%;
bicarbonates (NaHCO 3 and KHCO 3) - about 50 vol%.

The blood flowing from the tissues contains 56-58 vol% CO 2, and the arterial blood contains 50-52 vol%. When flowing through tissue capillaries, blood captures about 6 vol% CO 2, and in the pulmonary capillaries this gas diffuses into the alveolar air and is removed from the body. The exchange of CO 2 associated with hemoglobin occurs especially quickly. Carbon dioxide attaches to the amino groups in the hemoglobin molecule, which is why carboxyhemoglobin is also called carbaminohemoglobin. Most of the carbon dioxide is transported in the form of sodium and potassium salts of carbonic acid. The accelerated breakdown of carbonic acid in erythrocytes as they pass through the pulmonary capillaries is facilitated by the enzyme carbonic anhydrase. When pCO2 is below 40 mm Hg. Art. this enzyme catalyzes the breakdown of H 2 CO 3 into H 2 0 and C0 2, helping to remove carbon dioxide from the blood into the alveolar air.

The accumulation of carbon dioxide in the blood above normal is called hypercapnia, and the decrease hypocapnia. Hypercappia is accompanied by a shift in blood pH to the acidic side. This is due to the fact that carbon dioxide combines with water to form carbonic acid:

CO 2 + H 2 O = H 2 CO 3

Carbonic acid dissociates according to the law of mass action:

H 2 CO 3<->H + + HCO 3 - .

Thus, external respiration, through its influence on the carbon dioxide content in the blood, is directly involved in maintaining the acid-base state in the body. During the day, about 15,000 mmol of carbonic acid is removed from the human body through exhaled air. The kidneys remove approximately 100 times less acid.

where pH is the negative logarithm of the proton concentration; pK 1 is the negative logarithm of the dissociation constant (K 1) of carbonic acid. For the ionic medium present in the plasma, pK 1 = 6.1.

Concentration [СО2] can be replaced by voltage [рС0 2 ]:

[С0 2 ] = 0.03 рС0 2 .

Then pH = 6.1 + log / 0.03 pCO 2.

Substituting these values, we get:

pH = 6.1 + log24 / (0.03.40) = 6.1 + log20 = 6.1 + 1.3 = 7.4.

Thus, as long as the ratio / 0.03 pCO 2 is 20, the blood pH will be 7.4. A change in this ratio occurs with acidosis or alkalosis, the causes of which may be disturbances in the respiratory system.

There are changes in the acid-base state caused by respiratory and metabolic disorders.

Respiratory alkalosis develops with hyperventilation of the lungs, for example, when staying at altitude in the mountains. A lack of oxygen in the inhaled air leads to an increase in ventilation of the lungs, and hyperventilation leads to excessive leaching of carbon dioxide from the blood. The ratio / рС0 2 shifts towards the predominance of anions and the blood pH increases. An increase in pH is accompanied by increased excretion of bicarbonates in the urine by the kidneys. In this case, a lower than normal content of HCO 3 anions will be detected in the blood - or the so-called “base deficiency”.

Respiratory acidosis develops due to the accumulation of carbon dioxide in the blood and tissues due to insufficient external respiration or blood circulation. With hypercapnia, the ratio / pCO 2 decreases. Consequently, the pH also decreases (see the above equations). This acidification can be quickly corrected by increasing ventilation.

With respiratory acidosis, the kidneys increase the excretion of hydrogen protons in the urine in the composition of acid salts of phosphoric acid and ammonium (H 2 PO 4 - and NH 4 +). Along with the increased secretion of hydrogen protons into the urine, the formation of carbonic acid anions increases and their reabsorption into the blood increases. The content of HCO 3 - in the blood increases and the pH returns to normal. This condition is called compensated respiratory acidosis. Its presence can be judged by the pH value and the increase in base excess (the difference between the content in the test blood and in blood with a normal acid-base state.

Metabolic acidosis caused by the intake of excess acids into the body from food, metabolic disorders or the administration of medications. An increase in the concentration of hydrogen ions in the blood leads to an increase in the activity of central and peripheral receptors that control the pH of the blood and cerebrospinal fluid. Increased impulses from them enter the respiratory center and stimulate ventilation of the lungs. Hypocapia develops. which somewhat compensates for metabolic acidosis. The blood level decreases and this is called lack of grounds.

Metabolic alkalosis develops when there is excessive ingestion of alkaline products, solutions, medicinal substances, when the body loses acidic metabolic products or excessive retention of anions by the kidneys. The respiratory system responds to an increase in the /pCO 2 ratio by hypoventilation of the lungs and an increase in carbon dioxide tension in the blood. Developing hypercapnia can to some extent compensate for alkalosis. However, the volume of such compensation is limited by the fact that the accumulation of carbon dioxide in the blood occurs no more than up to a voltage of 55 mm Hg. Art. A sign of compensated metabolic alkalosis is the presence excess bases.

The relationship between the transport of oxygen and carbon dioxide in the blood

There are three important ways of interconnecting the transport of oxygen and carbon dioxide in the blood.

Relationship by type Bohr effect(increased pCO-, reduces the affinity of hemoglobin for oxygen).

Relationship by type Holden effect. It manifests itself in the fact that when hemoglobin is deoxygenated, its affinity for carbon dioxide increases. An additional number of hemoglobin amino groups are released, capable of binding carbon dioxide. This occurs in the tissue capillaries and the reduced hemoglobin can capture large quantities of carbon dioxide released into the blood from the tissues. In combination with hemoglobin, up to 10% of all carbon dioxide carried in the blood is transported. In the blood of the pulmonary capillaries, hemoglobin is oxygenated, its affinity for carbon dioxide decreases, and about half of this easily exchangeable fraction of carbon dioxide is released into the alveolar air.

Another way of the relationship is due to a change in the acidic properties of hemoglobin depending on its connection with oxygen. The dissociation constants of these compounds compared to carbonic acid have the following ratio: Hb0 2 > H 2 CO 3 > Hb. Consequently, HbO2 has stronger acidic properties. Therefore, after formation in the pulmonary capillaries, it takes cations (K +) from bicarbonates (KHCO3) in exchange for H + ions. As a result, H 2 CO 3 is formed. When the concentration of carbonic acid in the erythrocyte increases, the enzyme carbonic anhydrase begins to destroy it with the formation of CO 2 and H 2 0. Carbon dioxide diffuses into the alveolar air. Thus, oxygenation of hemoglobin in the lungs promotes the destruction of bicarbonates and the removal of carbon dioxide accumulated in them from the blood.

The transformations described above and occurring in the blood of the pulmonary capillaries can be written in the form of successive symbolic reactions:

Deoxygenation of Hb0 2 in tissue capillaries turns it into a compound with less acidic properties than H 2 C0 3. Then the above reactions in the erythrocyte flow in the opposite direction. Hemoglobin acts as a supplier of K ions for the formation of bicarbonates and the binding of carbon dioxide.

Transport of gases by blood

Blood is the carrier of oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs. Only a small amount of these gases is transported in a free (dissolved) state. The main amount of oxygen and carbon dioxide is transported in a bound state.

Oxygen transport

Oxygen, dissolving in the blood plasma of the capillaries of the pulmonary circulation, diffuses into red blood cells and immediately binds to hemoglobin, forming oxyhemoglobin. The rate of oxygen binding is high: the half-saturation time of hemoglobin with oxygen is about 3 ms. One gram of hemoglobin binds 1.34 ml of oxygen; in 100 ml of blood there are 16 g of hemoglobin and, therefore, 19.0 ml of oxygen. This quantity is called blood oxygen capacity(KEK).

The conversion of hemoglobin to oxyhemoglobin is determined by the dissolved oxygen tension. Graphically, this dependence is expressed by the oxyhemoglobin dissociation curve (Fig. 6.3).

The figure shows that even at a low partial pressure of oxygen (40 mm Hg), 75-80% of hemoglobin is bound to it.

At a pressure of 80-90 mm Hg. Art. hemoglobin is almost completely saturated with oxygen.

Rice. 4. Oxyhemoglobin dissociation curve

The dissociation curve is S-shaped and consists of two parts - steep and sloping. The sloping part of the curve, corresponding to high (more than 60 mm Hg) oxygen tensions, indicates that under these conditions the content of oxyhemoglobin only weakly depends on the oxygen tension and its partial pressure in the inhaled and alveolar air. The upper sloping part of the dissociation curve reflects the ability of hemoglobin to bind large amounts of oxygen, despite a moderate decrease in its partial pressure in the inspired air. Under these conditions, the tissues are sufficiently supplied with oxygen (saturation point).

The steep part of the dissociation curve corresponds to the oxygen tension normal for body tissues (35 mmHg and below). In tissues that absorb a lot of oxygen (working muscles, liver, kidneys), oxygen and hemoglobin dissociate to a greater extent, sometimes almost completely. In tissues in which the intensity of oxidative processes is low, most of the oxyhemoglobin does not dissociate.

The property of hemoglobin - it is easily saturated with oxygen even at low pressures and easily releases it - is very important. Due to the easy release of oxygen by hemoglobin with a decrease in its partial pressure, an uninterrupted supply of oxygen is ensured to tissues in which, due to the constant consumption of oxygen, its partial pressure is zero.

The breakdown of oxyhemoglobin into hemoglobin and oxygen increases with increasing body temperature (Fig. 5).

Rice. 5. Hemoglobin oxygen saturation curves under different conditions:

A - depending on the reaction of the environment (pH); B - temperature; B - on salt content; G - on the carbon dioxide content. The abscissa is the partial pressure of oxygen (in mmHg). along the ordinate - degree of saturation (in%)

The dissociation of oxyhemoglobin depends on the reaction of the blood plasma environment. With an increase in blood acidity, the dissociation of oxyhemoglobin increases (Fig. 5, A).

The binding of hemoglobin with oxygen in water occurs quickly, but its complete saturation is not achieved, just as the complete release of oxygen does not occur when its partial concentration decreases.
pressure. More complete saturation of hemoglobin with oxygen and its complete release with a decrease in oxygen tension occur in salt solutions and in blood plasma (see Fig. 5, B).

The carbon dioxide content in the blood is of particular importance in the binding of hemoglobin to oxygen: the higher its content in the blood, the less hemoglobin binds to oxygen and the faster the dissociation of oxyhemoglobin occurs. In Fig. Figure 5, D shows the dissociation curves of oxyhemoglobin at different levels of carbon dioxide in the blood. The ability of hemoglobin to combine with oxygen decreases especially sharply at a carbon dioxide pressure of 46 mm Hg. Art., i.e. at a value corresponding to the carbon dioxide tension in the venous blood. The effect of carbon dioxide on the dissociation of oxyhemoglobin is very important for the transport of gases in the lungs and tissues.

The tissues contain large amounts of carbon dioxide and other acidic breakdown products formed as a result of metabolism. Passing into the arterial blood of tissue capillaries, they contribute to a more rapid breakdown of oxyhemoglobin and the release of oxygen to tissues.

In the lungs, as carbon dioxide is released from the venous blood into the alveolar air and the carbon dioxide content in the blood decreases, the ability of hemoglobin to combine with oxygen increases. This ensures the conversion of venous blood into arterial blood.

Carbon dioxide transport

Three forms of carbon dioxide transport are known:

physically dissolved gas - 5-10%, or 2.5 ml/100 ml of blood;
chemically bound in bicarbonates: in plasma NaHC0 3, in erythrocytes KHCO - 80-90%, i.e. 51 ml/100 ml blood;
chemically bound in carbamine compounds of hemoglobin - 5-15%, or 4.5 ml/100 ml of blood.

Carbon dioxide is continuously produced in cells and diffuses into the blood of tissue capillaries. In red blood cells it combines with water to form carbonic acid. This process is catalyzed (accelerated 20,000 times) by the enzyme carbonic anhydrase. Carbonic anhydrase is found in erythrocytes; it is not found in blood plasma. Therefore, carbon dioxide hydration occurs almost exclusively in red blood cells. Depending on the tension of carbon dioxide, carbonic anhydrase is catalyzed with the formation of carbonic acid and its splitting into carbon dioxide and water (in the capillaries of the lungs).

Some carbon dioxide molecules combine with hemoglobin in red blood cells, forming carbohemoglobin.

Thanks to these binding processes, the carbon dioxide tension in erythrocytes is low. Therefore, more and more new amounts of carbon dioxide diffuse into the red blood cells. The concentration of HC0 3 - ions formed during the dissociation of carbonic acid salts in erythrocytes increases. The erythrocyte membrane is highly permeable to anions. Therefore, some of the HCO 3 - ions pass into the blood plasma. Instead of HCO 3 - ions, CI - ions enter the red blood cells from the plasma, the negative charges of which are balanced by K + ions. The amount of sodium bicarbonate (NaHCO 3 -) increases in the blood plasma.

The accumulation of ions inside erythrocytes is accompanied by an increase in osmotic pressure in them. Therefore, the volume of red blood cells in the capillaries of the systemic circulation increases slightly.

To bind most of the carbon dioxide, the properties of hemoglobin as an acid are extremely important. Oxyhemoglobin has a dissociation constant 70 times greater than deoxyhemoglobin. Oxyhemoglobin is a stronger acid than carbonic acid, while deoxyhemoglobin is a weaker acid. Therefore, in arterial blood, oxyhemoglobin, which has displaced K + ions from bicarbonates, is transported in the form of the KHbO 2 salt. In tissue capillaries, KHbO 2 gives up oxygen and turns into KHb. From it, carbonic acid, being stronger, displaces K + ions:

KHb0 2 + H 2 CO 3 = KHb + 0 2 + KNSO 3

Thus, the conversion of oxyhemoglobin to hemoglobin is accompanied by an increase in the blood's ability to bind carbon dioxide. This phenomenon is called Haldane effect. Hemoglobin serves as a source of cations (K+), necessary for the binding of carbonic acid in the form of bicarbonates.

So, in the red blood cells of tissue capillaries an additional amount of potassium bicarbonate is formed, as well as carbohemoglobin, and the amount of sodium bicarbonate increases in the blood plasma. In this form, carbon dioxide is transferred to the lungs.

In the capillaries of the pulmonary circulation, the carbon dioxide tension decreases. CO2 is split off from carbohemoglobin. At the same time, oxyhemoglobin is formed and its dissociation increases. Oxyhemoglobin displaces potassium from bicarbonates. Carbonic acid in red blood cells (in the presence of carbonic anhydrase) quickly decomposes into water and carbon dioxide. HCOX ions enter erythrocytes, and CI ions enter the blood plasma, where the amount of sodium bicarbonate decreases. Carbon dioxide diffuses into the alveolar air. All these processes are shown schematically in Fig. 6.

Rice. 6. Processes occurring in the red blood cell when oxygen and carbon dioxide are absorbed or released into the blood

Oxygen capacity of blood. The mechanism of oxygen transport by blood. Oxyhemoglobin dissociation curve analysis. Transport proteins Oxygen is transported in the blood in two forms

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Subtitles

Transport function of proteins

Transport of substances across the cell membrane

Transport of substances across the cell membrane

Transport of substances throughout the body

see also

See what “Protein transport function” is in other dictionaries:

2.4.1. Transport of oxygen by blood

Transport of carbon dioxide in the blood and its relationship with the acid-base state of the blood

The relationship between the transport of oxygen and carbon dioxide in the blood

Transport of gases by blood

Oxygen transport

Carbon dioxide transport