Physiology of red blood cells. Erythron.
Respiratory pigments.
Rheological properties of blood.
The primary function of blood is to supply oxygen and nutrients as well as constitutional elements to tissues and to remove waste products. Blood also enables hormones and other substances to be transported between tissues and organs. Problems with blood composition or circulation can lead to downstream tissue malfunction. Blood is also involved in maintaining homeostasis by acting as a medium for transferring heat to the skin and by acting as a buffer system for bodily pH.
The blood is circulated through the lungs and body by the pumping action of the heart. The right ventricle pressurizes the blood to send it through the capillaries of the lungs, while the left ventricle re-pressurizes the blood to send it throughout the body. Pressure is essentially lost in the capillaries, hence gravity and especially the actions of skeletal muscles are needed to return the blood to the heart.
Blood is a fluid tissue of human body, classified as a tissue of inner environment. However, its intercellular substance is a liquid, and its cells are not in a fixed position as is the case in other tissues. The blood of adult vertebrates is a red liquid, which circulates in a closed system of tubes, the blood vessels. It is pumped from the heart into arteries, from the arteries into capillaries, and from the capillaries it flows into veins for return to the heart.
Each system of the human body plays an important part in maintaining homeostasis in the internal cellular environment, but the movement of the blood through the circulatory system is of fundamental importance.
The chief function of the blood is to maintain normal cell function by the constant exchange of nutrients and wasted with all cells.
The blood must also maintain optimum pH and temperature of the intracellular fluid if the cells’ enzyme systems are to work efficiently.The blood transports oxygen from the lungs to the tissues, and carbon dioxide to the lungs for elimination.
It transport nutrients from the intestine to all parts of the body, and it carries certain waste products to the kidneys for excretion. The blood distributes the heat produced in active muscles and thus aids in the regulation of body temperature.It transports internal secretions from the glands in which they are produced to the tissues on which each exerts its effects.The buffers in the blood help to maintain acid – base balance.The blood also is involved in immunity to disease and in protecting the body against invading bacteria.Blood is divisible into 2 parts, the formed elements and the plasma, in which the formed elements are suspended and in which a variety of important proteins, hormones and other substances are dissolved.
In an average healthy adult, the volume of blood is about one-eleventhof the body weight. Most sources state the volume of blood inan average human adult, who is between 60
Functions of the blood review:
1 Respiratory function (transport of gases: O2 from the lungs to tissues, CO2 from tissues to the lungs).
2 Trophic function (transport of nutrients from gastro-intestinal tract and other organs to all the tissues of the organism).
3 Excretory function (transport of metabolic products to the excretory organs).
4 Regulatory function (transport of hormones and biologically active substances from endocrine glands to aim-organs).
5 Protective function (transport of phagocytes and immunoglobulins).
6 Thermoregulatory function (transport of heat from organs that maintain warmness – liver and other internal organs to the skin).
Besides, pathogenic factors are transported with blood: microorganisms, toxins, tumor cells. Transport of the last one will lead to the development of metastasis of malignant tumor.
Except the transport function, blood plays an important role in maintaining homeostatic features of the organism. That is why the second important function of the blood is homeostatic function. There are several types of it:
1 Maintenance of the constant chemical content and physical properties of the blood (osmotic pressure, pH, temperature, concentration of ions and other).
2 Maintenance of the constant volume of the circulating blood.
3 Maintenance of the antigenic homeostasis.
The third, important function of the blood is creative function. Macromolecules, which are transported with blood, perform intercellular information transferring, which provides regulation of intracellular processes of protein synthesis, keeping the level of cell differentiation, renovation and maintenance of tissue structure.
The cells of blood are of three major functional classes: red blood cells (erythrocytes), white blood cells (leucocytes) and platelets (thrombocytes).
Erythrocytes are primarily involved in oxygen and carbon dioxide transport, the leucocytes constitute an important part of the defense and immune systems of the body, and platelets are a vital component of the blood clotting mechanism. All these cell types are formed in the bone marrow by a process called hemopoiesis. Erythrocytes and platelets function entirely within blood vessels whereas leucocytes act mainly outside blood vessels in the tissues. Thus the leucocytes found in circulating blood are merely in transit between their various sites of activity.
Composition of plasma
Plasma contains 90 % water and 10 % solutes by volume. These solutes include plasma proteins and other organic compounds as well as inorganic salts.
Plasma contains a rich variety of soluble proteins, 7 % by volume. There are three main types: albumins, globulins and fibrinogen. Collectively, the plasma proteins exect a colloidal osmotic pressure within the circulatory system, which helps to regulate the exchange of aqueous solution between plasma and extra cellular fluid.
Albumin – this is the most abundant plasma protein (3,4-5 g/dl of blood) and is mainly responsible for maintaining the osmotic pressure of blood. Substances that are partly or completely water-insoluble (eg, lipids) are transported in the plasma in association with albumin.
The globulins are a diverse group of proteins, which include the antibodies of the immune system, and certain proteins responsible for the transport of lipids and some heavy metal ions.
Alpha, beta, and gamma globulins are globular proteins dissolved in the plasma. The gamma globulins are antibodies and are called immunoglobulins.
Fibrinogen – this protein is converted by blood-borne enzymes into fibrin during clot formation. Fibrinogen is synthesized and secreted by the liver.
Other organic compounds – Other organic molecules in plasma, 2.1 % by volume, include nutrients such as amino acids and glucose, vitamins, and a variety of regulatory peptides, steroid hormones, and lipids.
Inorganic salts in plasma, 0.9 % by volume, include blood electrolytes such as sodium, potassium, and calcium salts.
Blood is studied by spreading a drop on a slide to produce a single layer of cells (blood smear). The cells are stained, differentiated by type, and counted to reveal any disease-related changes in their relative numbers. The smears are usually stained with modifications of dye mixtures containing eosin and methylene blue, ie, Romanovsky-type mixtures.
All of the descriptions of the staining properties of blood cells refer to their appearance after staining with Romanovsky-type mixtures (e.g., Wright’s stain or Giemsa stains). Blood and their components exhibit 4 major staining properties that allow the cell types to be distinguished:
1. Basophilia – is an affinity for methylene blue. Basophilic structures stain purple to black.
2. Azurophilia – is an affinity for the oxidation products of methylene blue called azures. Azurophilic structures stain red-blue.
3. Eosinophilia, or acidophilia, is an affinity for eosin. Eosinophilic structures stain yellow-pink to orange.
4. Neutrophilia is an affinity for a complex of dyes (originally thought to be neutral) in the mixture. Neutrophilic structures stain salmon pink to lilac.
The Formed Elements
Erythrocytes, or red blood cells, are the most prevalent cells in peripheral blood. The peripheral blood of an individual contains 25,000,000,000,000 (twenty-five trillion) erythrocytes, and the spleen and bone marrow contain many more.
Each cubic millimeter of blood contains approximately 5 x 106 red cells. The total peripheral blood volume is approximately
Structure. Most mammalian erythrocytes are biconcave disks without nuclei. When suspended in the isotonic medium, human erythrocytes are 7,5 μm in diameter, 2.6 μm thick at the rim, and 0.8 μm thick in the center. The biconcave shape provides erythrocytes with large surface-to-volume ratio, thus facilitating gas exchange. Erythrocytes with diameters greater than 9 μm are called macrocytes, and those with diameters less than 6 μm are called microcytes. A presence of a high percentage of erythrocytes with great variations in size is called anisocytosis.
Scanning electron microscopy of a normal erythrocyte
Normal blood smear
Anisocytosis.
The erythrocytes are quite flexible, a property that permits it to adapt to the irregular shapes and small diameters og capillaries. Observations in vivo show that when traversing the angels of capillary bifurcations, erythrocytes containing normal adult hemoglobin (Hb A) are easily deformed and frequently assume a cup-like shape.
Erythrocytes are surrounded by plasmalemma; because of its ready availability, this is the best-known membrane of any cell. It consists of about 40% lipid, 50% protein and 10% carbohydrates. About half the proteins span the lipid bilayer and are known as integral membrane proteins. Several peripheral proteins are associated with the inner surface of erythrocyte membrane. The peripheral proteins seem to serve as a membrane skeleton that determines the shape of the erythrocyte. They also permit the flexibility of the membrane necessary for the large changes in shape that occur when the erythrocyte passes through capilaries. Because the erythrocytes are not rigid, the viscosity of blood normally remains low.
Mature RBCs lack nuclei and cytoplasmic organelles, which they lose during differentiation. Because they lack mitochondria, the energy needed to maintain the hemoglobin in a functional state must be derived from anaerobic glycolysis. Because they lack ribosomes, the glycolytic enzymes and other important proteins cannot be renewed.
Red blood cells are structurally and functionally specialized to transport oxygen from the lungs to other tissues. Their cytoplasm contains the 33% solution of oxygen-binding protein hemoglobin – the O2 – carrying protein that account for their acidophilia. About 1/3 of the erythrocyte mass is hemoglobin. Each hemoglobin molecule consists of 4 polypeptide subunits, each of which includes an iron-containing heme group.
Hemoglobin (Hb) – is the main erythrocyte compound. It makes 90% of the total solids of the cell. The fact that hemoglobin is kept inside the cell is very important. If hemoglobin was inside the blood plasma, it could cause a number of disorders.
1 A large amount of free Hb does a toxic influence on different tissues (neurons, kidneys).
2 In bloodstream Hb is turned to methemoglobin, but in the erythrocyte there are fermentative systems, which predict this to happen.
3 The amount of hemoglobin, needed for the transport of the enough amount of oxygen will increase stickiness.
4 Hb will increase an oncotic pressure of plasma that will lead to dehydration of tissues.
5 The part of Hb will be filtrated through the kidneys and it will choke pores of kidney’s filter.
The structure of hemoglobin
Hemoglobin (Hb) – is a red pigment, chromoprotein, which is situated in erythrocytes and transports oxygen.
There is
Hemoglobin has globular molecule, which is formed with 4 subunits. Each subunit contains heme. Heme – is Fe-inclusive substance, the derivative of porphyrin. Heme molecule consists of 4 pyrrol. The ion of Fe2+ is situated in the center.
Deoxygenated hemoglobin Oxygenated hemoglobin
Heme is connected with a polypeptide. The complex of polypeptides is called globin part of hemoglobin molecule (globin). There are two pairs of polypeptide chains. Each chain contains more than 140 amino acids. In dependence of number and order of amino acids there are 4 types of chains: α, β, γ, δ (α – 141, β – 146, γ – 146 amino acids) chains, each connected to heme. Heme is disc shaped .
There are 2α and 2β
The main hemoglobin forms and compositions
Depending of protein chains there are following forms of hemoglobin iormal state.
· Hb P (primitive) in embryo for the first 7-12 weeks
· Hb F (fetal) in fetus. Appears ointh week. Consists of 2α- and 2γ- chains. Hb F can bind and transport oxygen easier (due to lesser similarity HbF to 2,3-BPG). That’s why in the blood of fetus there is enough amount of HbO2 formed, regardless lower tension of O2. Normally after birth fetal hemoglobin is changed to adult hemoglobin.
· HbA1 (adult). It contains 2α- and 2β- chains. HbA1 is 95% of all hemoglobin of adult.
· HbA2 – it contains 2α and 2δ chains. It is 5% of all hemoglobin of adult.
In some inheritable diseases, there are defects of genes, which encode α- or β- chains and the synthesis of Hb is disturbed. These sicknesses are called thalassemias.
In α-thalassemia, the synthesis of α-chains is disturbed. Erythrocytes are target-shaped, that’s why α-thalassemia is also called target-shaped anemia. In β-thalassemias synthesis of β-chains is disturbed (Kulee sickness).
Defects of the primary structure of hemoglobin also belong to the pathological changes of hemoglobin. Mutative genes, which produce abnormal hemoglobins, are widely spread. There are a lot of forms of abnormal hemoglobins. For example, if glutamate is changed to valine in β-chain, pathological HbS is formed. In deoxygenated state its dissolubility decreases 100 times, and it forms sediment. These crystals deform erythrocyte. Erythrocyte gets sickle-shape, hardly passes through small capillaries and phagocyted by macrophages. It is called sickle-cell anemia.
Main physiological compositions of hemoglobin
1) HbO2 (oxygemoglobin) is the composition of Hb with oxygen. It has red color, which define the red color of the arterial blood.
Due to no oxidation occuring during interaction between Hb and O2 and oxidation degree of iron does not change; the reaction is called oxygenation (not oxidation).
Hb (recovered Hb or deoxy Hb) – Hb, that releases O2. It has cherry color, which defines the color of the venous blood. Reaction of releasing the oxygen is called deoxygenation.
2) HbCO2 (carbhemoglobin) – the composition of Hb with CO2.
Pathological composition of Hb:
HbCO (carboxyhemoglobin) – the composition of Hb with CO.
Chemical relativity of Hb to CO is in 300 times higher than O2. That’s why carbon monoxide displaces O2 from hemoglobin, decreasing the ability of the blood to bind oxygen. Even small number of CO leads to the significant increase in formation of HbCO. When concentration of the CO in the air is 0,1% – 80% Hb binds not with O2, but with CO. When concentration of CO in the air is 1%, in few seconds it will cause death.
It is dangerous because HbCO is persistent and Hb cannot transport oxygen anymore.
Low intoxication with CO is a reversible process and after breathing fresh air, CO will gradually detach. Breathing with clean oxygen has positive effect.
Normally HbCO is 1% of all the Hb. In smokers body it is 3%, after heavy pull – 10%.
Met Hb (HbOH – methemoglobin) – hemoglobin, which contains Fe3+ and has brown color. Oxidation of Fe2+ to Fe3+ in hemoglobin occurs when interacting with strong oxidizers (KMnO4, aniline), and also with medicine of oxidative properties. Insignificant oxidation of hemoglobin to methemoglobin also occurs iormal conditions. But with the help of fermenting systems of erythrocyte (NADH-methemoglobinreductase system) methemoglobin turns in to hemoglobin. Inherited absence of this fermentation can cause inherited methemoglobinemia.
In pathological conditions, when methemoglobin is formed, blood with high oxygen content circulates in the organism, but it is not entering tissues.
The amount of hemoglobin in blood of healthy human is 140-160 g/L for men, 120-140 g/L for women, 200 g/L – for newborns.
The definition of hemoglobin content:
Definition of the amount of bonded oxygen (1g of Hb can bind 1,34 ml of O2).
Analysis of iron level in blood (iron content in hemoglobin is 0,34%).
Tintometry (comparison of blood color with color of standard solution) – Sali method.
Spectrophotometry.
Method 1 and 2 require sophisticated apparatus. Third – is inaccurate. Fourth method is very popular nowadays. Blood is mixed with the solution of potassium ferricyanide, potassium cyanide, sodium bicarbonate. These substances will cause destruction of erythrocytes; Hb turns to cyan methemoglobin (HbCN). Unlike Hb, HbCN is stable and it can be stored for few weeks. The solution is rayed with monochromatic light with λ = 546nm, then extinction is defined. The content of Hb is defined by special calibration scale.
The following showings are important in estimation of eryt forms of anemia:
1) Average hemoglobin content in one erythrocyte (AHC) – characterizes the absolute number of Hb in the erythrocyte.
AHC = Hb / E
Normally AHC = 26-36 picogram
When AHC is normal, than erythrocytes, they are called normochromic.
When AHC is less thaormal, erythrocytes are called hypochromic.
When AHC is higher thaormal, erythrocytes are called hyperchromic.
2) Color index (CI) – the index which characterizes the relative content of Hb in 1 erythrocyte.
CI = Hb / first three numbers in the amount of erythrocytes
Normally CI = 0,85 – 1,15
If CI is normal, erythrocytes (and anemia) are normochromic. If CI is lower than normal – hypochromic. If CI is higher thaormal – hyperchromic.
3) Oxygen-carrying capacity of blood (OCC) – the amount of oxygen, which is transported with
OCC = Hufner’s number • Hb (in g/l).
Regulation of erythrocyte content in peripheral blood
The erythrocyte content in peripheral blood of the adult is 3,5 – 5•1012/liter. The changes of this value (decrease or increase) can lead to the dangerous changes in human organism. The decrease in the erythrocyte amount leads to the interruption of the oxygen transport in blood, which cause ischemia of organs and tissues. The increase in the erythrocyte amount is the reason of the increase in blood stickiness and the increase of load on heart. When there is essential increase of blood stickiness, the movement of the blood in vessels is impossible.
Regulation of erythrocyte content is provided by regulation of its formation (erythropoiesis) and destruction (haemolysis).
Variations iumber of red blood cells
Physiological variations
I Increase in the red blood cell count is known as polycythemia. If it occurs in physiological conditions, it is called physiological polycythemia. It occurs in the following conditions:
1) Age
At birth, the red blood cell count is 8 -10 millions/cu mm of blood, The count decreases within 10 days after birth due to destruction of cells causing physiological jaundice in some infant. However, in infants and growing children, the cell count is at a level higher than the value in adults.
2) Sex
Before puberty and after menopause in females the red blood cell count is similar to that in males. During reproductive period of females, the count is less than in males (4.5 millions/cu mm).
3) High Altitude
The inhabitants of mountains (above
4) Muscular Exercise
There is a temporary increase in red blood cell count after exercise. This is because of mild hypoxia and contraction of spleen, which is the reservoir of blood.
5) Emotional Conditions
The red blood cell count is increased during the emotional conditions like anxiety, because of sympathetic stimulation.
6) Increased Environmental Temperature
The increase in the atmospheric temperature increases red blood cell count.
7) After Meals
There is a slight increase in the red blood cell count after taking meals.
II Decrease in red blood cell count occurs in the following physiological conditions:
1) High Barometric Pressures
At high barometric pressures as in deep sea, when the oxygen tension of blood is higher, the red blood cell count decreases.
2) After Sleep
The red blood cell count decreases slightly after sleep.
3) Pregnancy
In pregnancy, the red blood cell count decreases. This is because of increase in extracellular fluid volume. Increase in extracellular fluid volume, increases the plasma volume also resulting in hemodilution. So, there is a relative reduction in the red blood cell count.
Erythrocyte sedimentation rate (ESR)
Erythrocytes caot sedimentate inside blood vessels. Due to:
· constant blood movement;
· the charge of blood vessel wall and the charge of erythrocyte is the same (negative) so cells repel from it.
If we put the blood inside the test-tube and add anticoagulant than in few minutes we can observe the sedimentation of erythrocytes, because the density of erythrocytes (1,090 g/cm3) is higher, than the density of blood plasma (1,025 – 1,034 g/cm3). The mechanism of the process is as follows. At first erythrocytes form complexes with each other (10-12 erythrocytes form “monetary column”). After these complexes interact with plasma proteins, they become heavier and they start to settle faster. Due to this process is not equable in time (slow in the beginning, faster in the end) ESR is determined for the fixed period of time, usually 1 hour.
Iormal state ESR of men is 2-10 mm/hour, of women 2-15 mm/hour.
Factors, which affect ESR
The main mechanism of influence of all factors is the changes in stickiness. There is inversed dependence between stickiness and ESR (the higher stickness – the lower ESR, the lower stickness – the higher ESR). That means that the factors, which increase stickiness – they decrease ESR and otherwise.
The first group of factors – plasma factors:
1 The protein content of blood plasma
The influence of this factor is proved in the following experiment. Erythrocytes of the patient with increased ESR are put in blood plasma of the healthy man with the same blood group. Erythrocytes of the patient sediments with normal speed, otherwise erythrocytes of healthy man sediments in patient’s blood plasma with higher speed.
Different proteins affect ESR in different ways. When albumins concentration is increased, ESR decreases. When concentration of high molecular proteins, globulins or fibrinogen increases – ESR increases. Possibly, high molecular proteins decrease electric charge on the erythrocytes membrane, depress the electric repulsion of blood cells. Due to this the aggregation properties of erythrocytes increase, ESR increase. Globulins concentration increases in case of inflammatory processes, infectious sicknesses and malignant tumors. That is why these patients have increased level of ESR.
The amount of fibrinogen increases in 2 times in the second half of pregnancy, that’s why before the delivery ESR of the pregnant woman can reach 40 – 50 mm/hour.
2 Plasma volume
When increased plasma volume, hematocrit decreases, blood stickiness decreases, and as a consequence ESR increases.
The second group of factors – erythrocyte factors.
1 The amount of erythrocytes in blood volume (hematocrit)
The higher amount of erythrocytes – the higher stickness – the lower ESR.
The lower amount of erythrocytes – the lower stickness – the higher ESR.
This is the reason of increase in ESR in anemic patients.
2 The ability of erythrocytes to aggregate
The increase of erythrocyte ability to aggregate leads to the decrease of stickiness, because the resistance of the aggregates to friction is lower, than the resistance of separate cells because of the decrease of correlation of the surface to the volume. Aggregates sediments faster and ESR increases. The increase of erythrocyte ability to aggregate is observed when inflammatory processes and malignant tumors.
3 Erythrocytes shape
The change of the erythrocytes shape (for example when sickle-cell anemia) or its modification (for example, when pernicious anemia) can cause the oppression of the erythrocytes ability to aggregate. It causes the increase of stickiness and, as a consequence, the decrease of ESR.
Except these factors, there are some other ones, which affect ESR. For example, steroid hormones (estrogen, glucocorticoid hormones) and some medicine (salicylates) increase ESR. Erythrocytes sedimentation rate increases when the content of cholesterol in blood increases, during alkalosis, and it decreases when content of bilious pigments and bilious acids in blood increases and also during acidosis.
LEUCOCYTES
Leukocytes, or white blood cells, are nucleated and are larger and less numerous than erythrocytes. Leukocytes can be divided into 2 main groups, granulocytes and agranulocytes, according to their content of cytoplasmic granules.
Each of these groups can then be further divided on the basis of size, nuclear morphology, ratio of nuclear to cytoplasmic volume, and staining properties. Two classes of cytoplasmic granules occur in leukocytes, specific and azurophilic granules. Specific granules are found only in granulocytes; their staining properties (neutrophilic, eosinophilic, or basophilic) distinguish the 3 granulocytes types.
Azurophilic granules are found in both agranulocytes and granulocytes. Azurophilic granules stain purple and are lysosomes.
Unlike the RBCs, all leukocytes can leave the capillaries by passing between endothelial cells, and penetrating the connective tissue by means of the process called diapedesis. The types and levels of activity expressed by extravascular leukocytes depends upon the specific cell type.
Platelets
Platelets, or thrombocytes, the smallest formed elements in the blood, are dislike cell fragments that vary in diameter from 2 to 5 μm. In humans, they lack nuclei and originate by budding from large cells in the bone marrow called megakaryocytes. They range iumber from 150,000 to 300,000 microliter of blood and have a lifespan of about 10 days. In blood smears they appear in clumps. Each platelet has a peripheral hyalomere region that stains a faint blue and a dense central granulomere that contains a few mitochondria and glycogen granules and a variety of purple granules. Dense bodies, or delta granules, are 250-300 μm in diameter and contain calcium ions, pyrophosphate, ADP, and ATP; they take up and store serotonin. Alpha granules are 300-500 μm in diameter and contain fibrinogen, platelet-derived growth factor, and other platelet-specific proteins. Lambda granules (platelet lysosomes) are 175-200 μm in diameter and contain only lysosomal enzymes. The hyalomere contains a marginal bundle of microtubules that helps to maintain the platelet’s discoid shape. The glycocalyx is unusually rich in glycosaminoglycans and is associated with adhesion, the major functional characteristic of platelets. Platelets have an important physical role in plugging wounds. They promote blood clotting and help repair gaps in the walls of blood vessels, preventing loss of blood.
Electron micrograph of human platelets.
Platelets as they appear in blood smear.
The Role of Platelets is controlling hemorrhage can be summarised as follows.
1. Primary aggregation – Discontinuities in the endothelium, produced by blood vessel lesions, are followed by absorption of plasma proteins on the subjacent collagen. Platelets immediately aggregate on this damaged tissue, forming a platalet plug.
2. Secondary aggregation – Platelets in the plug release the contents of their alpha and delta granules. ADP is a potent inducer of platelet aggregation.
3. Blood coagulation – Platelets release fibrinogen in addition to that normally found in the plasma. The fibrinogen is converted by the clotting factor cascade into fibrin, which forms a dense fibrous mat to which more platelets and other blood cells attach to form blood clot or thrombus.
4. Clot Retraction: The clot (thrombus) that initially bulges into the blood vessel lumen contracts because of the interaction of platelet actin, myosin, and ATP.
5. Clot Removal: Protected by the clot, the vessel wall is restored by new tissue formation. The clot is then removed, mainly by the proteolytic enzyme plasmin, formed, through the activation of the plasma proenzyme plasminogen activators. Enzymes released from platelet lambda granules also contribute to clot removal.
A marked reduction in the number of blood platelets is called thrombocytopenia, and a marked increase in the number of blood platelets is called thrombocytosis.
The following are normal complete blood count results for adults:
|
Red blood cell count |
Male: 4.32-5.72 1012/L |
|
Hemoglobin |
Male: 130-160 grams/L Female: 120-140 grams/L |
|
Hematocrit |
Male: 38.8-50.0 percent Female: 34.9-44.5 percent |
|
White blood cell count |
3.5-10.5 billion cells/L(3,500 to 10,500 cells/mcL) |
|
Platelet count |
150-450 billion/L (150,000 to 450,000/mmol) |
Hematopoiesis
Mature blood cells have a relatively short life span, and consequently the population must be continuously replaced with the progeny of stem cells produced in the hematopoietic organs. In the earliest stages of embryogenesis, blood cells arise from the yolk sac mesoderm. Sometime later, the liver and spleenserve as temporary hematopoietic tissues, but by the second month the clavicle has begun to ossify and begins to develop bone marrowin its core. As the prenatal ossification of the rest of the skeleton accelerates, the bone marrow becomes an increasingly important hematopoietic tissue.
After birth and on into childhood, erythrocytes, granular leukocytes, monocytes, and platelets are derived from stem cells located in bone marrow. The origin and maturation of these cells are termed, respectively, erythropoiesis, granulopoiesis, monocytopoiesis, and megakaryocytopoiesis. The bone marrow also produces cells that migrate to the lymphoid organs, producing the various types of lymphocytes.
Before attaining maturity and being released into the circulation, blood cells go through specific stages of differentiation and maturation. Because these processes are continuous, cells with characteristics that lie between the various stages are frequently encountered in smears of blood or bone marrow.
Stem Cells, Growth Factors, & Differentiation
Stem cells are pluripotential cells capable of self-renewal.
Pluripotential Hematopoietic Stem Cells
It is believed that all blood cells arise from a single type of stem cell in the bone marrow. Because this cell can produce all blood cell types, it is called a pluripotential stem cell. These cells proliferate and form one cell lineage that will become lymphocytes (lymphoid cells) and another lineage that will form the myeloid cells that develop in bone marrow (granulocytes, monocytes, erythrocytes, and megakaryocytes). Early in their development, lymphoid cells migrate from the bone marrow to the thymus, lymph nodes, spleen, and other lymphoid structures, where they proliferate Progenitor & Precursor Cells.
Stem Cells, Growth Factors, & Differentiation
Stem cells are pluripotential cells capable of self-renewal.
Pluripotential Hematopoietic Stem Cells
It is believed that all blood cells arise from a single type of stem cell in the bone marrow. Because this cell can produce all blood cell types, it is called a pluripotential stem cell. These cells proliferate and form one cell lineage that will become lymphocytes (lymphoid cells) and another lineage that will form the myeloid cells that develop in bone marrow (granulocytes, monocytes, erythrocytes, and megakaryocytes). Early in their development, lymphoid cells migrate from the bone marrow to the thymus, lymph nodes, spleen, and other lymphoid structures, where they proliferate Progenitor & Precursor Cells.
Hematopoiesis is therefore the result of simultaneous, continuous proliferation and differentiation of cells derived from stem cells whose potentiality is reduced as differentiation progresses. This process can be observed in both in vivo and in vitro studies, in which colonies of cells derived from stem cells with various potentialities appear. Colonies derived from a myeloid stem cell can produce erythrocytes, granulocytes, monocytes, and megakaryocytes, all in the same colony.
In these experiments, however, some colonies produce only red blood cells (erythrocytes). Other colonies produce granulocytes and monocytes. Cells forming colonies are called colony-forming cells (CFC) or colony-forming units (CFU). The convention iaming these various cell colonies is to use the initial letter of the cell each colony produces. Thus, MCFC denotes a monocyte-forming colony, ECFC forms erythrocytes, MGCFC forms monocytes and granulocytes, and so on.
Hematopoiesis depends on:
1-Favorable micro-environmental conditions and
2-The presence of growth factors.
Once the necessary environmental conditions are present, the development of blood cells depends on factors that affect cell proliferation and differentiation. These substances are called growth factors, colony-stimulating factors (CSF), or hematopoietins (poietins).
Bone Marrow
Under normal conditions, the production of blood cells by the bone marrow is adjusted to the body’s needs, increasing its activity several-fold in a very short time. Bone marrow is found in the medullary canals of long bones and in the cavities of cancellous bones.Two types of bone marrow have been described based on their appearance on gross examination:
1-red, or hematogenous, bone marrow, whose color is produced by the presence of blood and blood-forming cells; and
2-yellow bone marrow, whose color is produced by the presence of a great number of adipose cells.
Iewborns, all bone marrow is red and is therefore active in the production of blood cells. As the child grows, most of the bone marrow changes gradually into the yellow variety. Under certain conditions, such as severe bleeding or hypoxia, yellow bone marrow is replaced by red bone marrow.
Red Bone Marrow
Red bone marrow (Figure 1) is composed of a stroma (from Greek, meaning bed), hematopoietic cords, and sinusoidal capillaries.
The stroma is a three-dimensional meshwork of reticular cells and a delicate web of reticular fibers containing hematopoietic cells and macrophages. The stroma of bone marrow contains collagen types I and III, fibronectin, laminin, and proteoglycans. Laminin, fibronectin, and another cell-binding substance, hemonectin, interact with cell receptors to bind cells to the stroma.
The sinusoids are formed by a discontinuous layer of endothelial cells.
Section of active bone marrow (red bone marrow) showing some of its components. Five blood sinusoid capillaries containing many erythrocytes are indicated by arrowheads. Note the thinness of the blood capillary wall. Giemsa stain. Medium magnification.
Maturation of Erythrocytes
A mature cell is one that has differentiated to the stage at which it has the capability of carrying out all its specific functions. The basic process in maturation is the synthesis of hemoglobin and the formation of an enucleated, biconcave, small corpuscle, the erythrocyte. During maturation of the erythrocyte, several major changes take place.
These Changes are :
1- Cell volume decreases, and
2- The nucleoli diminish in size until they become invisible in the light microscope.
3- The nuclear diameter decreases, and
4- The chromatin becomes increasingly more dense until the nucleus presents a pyknotic appearance and is finally extruded from the cell.
5- There is a gradual decrease in the number of polyribosomes (basophilia decreases),
6- A simultaneous increase in the amount of hemoglobin (an acidophilic protein) within the cytoplasm.
7- Mitochondria and other organelles gradually disappear .
There are three to five intervening cell divisions between the proerythroblast and the mature erythrocyte. The development of an erythrocyte from the first recognizable cell of the series to the release of reticulocytes into the blood takes approximately 7 days.
The hormone erythropoietin and substances such as iron, folic acid, and cyanocobalamin (vitamin B12) are essential for the production of erythrocytes. Erythropoietin is a glycoprotein produced mainly in the kidneys that stimulates the production of mRNA for globin, the protein component of the hemoglobin molecule.
Differentiation of erythrocytes
The differentiation and maturation of erythrocytes involve the formation (in order) of proerythroblasts, basophilic erythroblasts, polychromatophilic erythroblasts, orthochromatophilic erythroblasts (normoblasts), reticulocytes, and erythrocytes .
1- Proerythroblastis the first recognizable cell in the erythroid series. It is a large cell with loose, lacy chromatin and clearly visible nucleoli; its cytoplasm is basophilic.
2- The next stage is represented by the basophilic erythroblast, with a strongly basophilic cytoplasm and a condensed nucleus that has no visible nucleolus. The basophilia of these two cell types is caused by the large number of polyribosomes involved in the synthesis of hemoglobin.
3- During the next stage, polyribosomes decrease, and areas of the cytoplasm begin to be filled with hemoglobin. At this stage, staining causes several colors to appear in the cell—the polychromatophilicerythroblast.
4- In the next stage, the nucleus continues to condense and no cytoplasmic basophilia is evident, resulting in a uniformly acidophilic cytoplasm—the orthochromatophilicerythroblast.
5- At a given moment, this cell puts forth a series of cytoplasmic protrusions and expels its nucleus, encased in a thin layer of cytoplasm. The expelled nucleus is engulfed by macrophages. The remaining cell still has a small number of polyribosomes that, when treated with the dye brilliant cresyl blue, aggregate to form a stained network. This cell is the reticulocyte,
6- Reticulocyte which soon loses its polyribosomes and becomes a mature erythrocyte.
Buffer systems and how they work
Enzyme Carbonic anhydrase (CA) made acid/base equilibrium H2O/CA/CO2/NaHCO3
There are several important buffer systems, that act in the human organism and allow pH of the organism to be constant iarrow interval allowed changes (pH = 7.36) despite the fact, that organism produces great amount of acidic products – the amount of acidic products is equivalent to
HHb H+ + Hb
and salt form
NaHb Na+ + Hb–
and remember, that the salt is a strong electrolyte and the presence of Hb ions due to salt shifts the dissociation equilibrium of the acid to the left, we can explain, why pH is not changed, when strong acid or base is added to buffer system. If acid is added, the H3O+ ions of the strong acid react with the basic component of the buffer – Hb– ion:
H3O++ Hb– HHb + H2O
Thus, the strong acid (H3O+) is transformed into a weak one (HHb) and, as the dissociation degree of the weak acid decreases with the growth of concentration, H+ concentration and, hence, pH will remain constant. When a base is added to buffer system, it will react with the buffer acid – HHb:
In such a way, the strongest possible base in water solution – the OH– – ion is transformed into a buffer Brønsted base – salt Hb– ion. HHb is used for this, but, as grows the HHb concentration, with the decrease H+ concentration pH will remain the same. (This “chemical” mechanism of buffer action is absolutely similar to the mechanism of any other buffer system that is composed from a weak acid and its salt, therefore it will not be repeated for all the following biological buffer systems.) Second buffer system of the human blood is oxyhemoglobin buffer system HHbO2/NaHbO2. Oxyhemoglobin is a product of hemoglobin reaction with oxygen, or, in other words, it is a molecule of hemoglobin, that has bound a molecule of oxygen.
3) a very important buffer system of the human organism is the hydro carbonate buffer system, where carbonic
anhydrase(CA) keeps CO2 as acid and base salt is the bicarbonate ion HCO3– respectively H2O/CA/CO2/NaHCO3 which equilibrium constant pK=7.0512 value very close to blood buffer systems made pH=7.36.
4) Next buffer system, that is present in blood, is the protein buffer system. This one has to be explained a little more, as it differs from the usual buffer systems that are composed from an acid and a salt. A protein is a long chain of amino acid remainders, but this long chain still has free carboxylic groups and free amino groups. For this reason here and further for general explanations about proteins we will use for it a following notation:
showing both free functional groups of protein molecule in such a way.
As the carboxylic group has acidic properties and the amino group – basic properties, no other component of buffer system is required – a protein molecule itself can stand both addition of an acid or a base. If an acid is added to solution, containing protein, the H3O+ ions will react with the amino group:
and the strong acid will be transformed into a weak one.
If a strong base is added to protein-containing solution, OH– ions react with the carboxylic groups of protein:
5) The next important biological buffer system is the phosphate buffer system
NaH2PO4 / Na2HPO4.
6) Besides the inorganic phosphate buffer system, a buffer system of the organic esters of phosphoric acid also exists:
(If there are any difficulties to understand the structure of last two compounds, remember, that phosphoric acid can be shown in structure as
In the ester of phosphoric acid one of the hydrogen atoms is replaced by an organic radical. Practically the buffer system consists of a mono substituted and bi substituted salts of the ester). Not all of these 6 buffer systems act in the same place.
In erythrocytes the main buffer systems are both hemoglobin-based buffer systems and hydrogen carbonate buffer system.
In blood plasma – hydrogen carbonate, protein and phosphate buffer systems.
In sweat, urine and digestive apparatus, the phosphate system is the main one.
Besides the normal “chemical” mechanisms of buffer action in maintaining constant pH=7.36, hemoglobin, oxyhemoglobin and by carbonic anhydrase CA driven hydrogen carbonate buffer systems have a joint physiological mechanism of action, which carries out the exchange of breathed in O2 and breathed out CO2 between air in lungs and tissues and environment of human body.
PHYSIOLOGICAL MECHANISM breathed in O2 and breathed out CO2 ACTION OF HEMOGLOBIN, OXYHEMOGLOBIN AND HYDROCARBONATE BUFFER SYSTEMS
Before any discussion of the mechanism, we have to know the sequence of strengths of the three acids, involved in the three buffer systems. The strongest one of these three acids is oxyhemoglobin, next one is carbonic anhydrase CA made acid with value pK=7.0512 and the weakest one is hemoglobin: KHHBO2>KH2O/CA/CO2>KHHb
(The sequence of acid strength will be necessary for further explanation).
Venous blood, which flows to lungs, contains two components of these buffer systems –
NaHCO3 and HHb (NaHCO3 is a transport form of CO2).
As soon as a portion of venous blood reaches lungs, the following processes occur:
Processes in lungs on cell wall membrane aquaporins penetrating water and oxygen
1) HHb + O2 HHbO2
2) As the oxyhemoglobin acid, which is formed in this process, is stronger than H2O/CA/CO2,
it starts to react with NaHCO3:HHbO2 + NaHCO3 Na++HbO2– + H+ + HCO3–
Carbonic anhydrase turn back carbonic dioxide to bicarbonate anion H++HCO3–/CA/H2O+CO2:
Carbonic acid H++HCO3–H2CO3on lung epithelial cell surface with absence carbonic anhydrase made equilibrium is unstable and decomposes outside cell: membraneH+ + HCO3– H2CO3 H2O + CO2
This transport H+ HCO3– is catalyzed by a special enzymes bicarbonate HCO3– and proton H+ channels (pumps), which are a transport enzymes. The epithelial cell surface of lungs has the specific building: super thin 0.6 nm water layer on surface 9·105 nm2 S=950 nm x 950 nm within small volume 0.5·106 nm3 creates acidity increase up to pH=5.5 if one proton crosses the membrane channel reaching the surface and that cause fast evolving CO2 gas breathed out, because otherwise blood flows away from lungs, while carbonic acid is not completed and decomposed outside cell. CO2, liberated on last step reaction on epithelial cell surface breathed out, but oxygen O2, which adsorbed on hemoglobin transport form NaHbO2 transported to tissues in human body. It is necessary to increase the removing rate of bicarbonate and hydrogen ions out of cells.
For the reasons, discussed above, arterial blood contains NaHbO2, [CO2]=0.0076M and [HCO–3]=0.0154 M total sum which releases 56.23 mL of gaseous CO2 on 100 mL of blood sample.
As soon as the arterial blood reaches tissues, the following reactions occur. Processes in tissues
1) NaHbO2 loses oxygen if blood oxygen concentration [O2] =6·10–
2) CO2, which is a product of metabolism comes from tissues and is dissolved in blood. In blood it reacts with water, forming carbonic anhydrase made equilibrium: CO2 + 2H2O CA H3O++HCO3–
Carbonic anhydrase equilibrium constant pK=7.0512 shifts reaction towards bicarbonate anion to prevent of carbonic dioxide accumulation, according Le Chatelier’s due to high water H2O concentration
3) As carbonic anhydrase made equilibrium acid is a stronger acid, than HHb, bicarbonate and hydrogen ion reacts with NaHb:
H++HCO3– + NaHb NaHCO3 + HHb
In this way, we have got back the content of venous blood – we have followed one full cycle of the process.
Let us consider now, why this sequence of acid strengths (given in the beginning) is necessary.
First, if it happened, that H2O/CA/CO2, was a stronger acid, than HHb, gas CO2 would stay in its water soluble transport form NaHCO3– and could not be liberated up to in lungs via bicarbonate HCO3– and proton H+ channels out of cells to epithelial lung cell surface having absent carbonic anhydrase.
Second, if HHb was a weaker acid than H2O/CA/CO2, HHb not react with NaHCO3 and is transported to lungs in the form of bicarbonate. Opposite is dangerous, because accumulation and formation of CO2 bubbles could occur in blood vessels, thus interfering the blood circulation.
VIII. pH OF BLOOD
As it was mentioned before, three main buffer systems act in blood: HHb/NaHb HHbO2/NaHbO2 H2O/CA/CO2/NaHCO3
When these buffer systems struggle with acidic products of metabolism, more and more of the acid forms of the buffer systems are produced. For this reason, the acid forms have to be transported out of organism.
It is easy to imagine, that hemoglobin cannot be evolved out of organism, therefore there is only one buffer system, suitable for regulation of acid form’s presence by breathing out CO2, that decrease metabolic acid production caused problems for organism.
Carbonic anhydrase equilibrium constant pK=7.0512 decreases concentration acid form CO2 into water H2O (avoid carbonic acid H2CO3 formation) and hydrogen carbonate HCO–3 + hydrogen ion H+ are included into equation for blood pH:
pH = 7.0512 +log = 7.36; =
the ratio [NaHCO3]/[CO2] being approximately 2/1. (usually in medical literature CO2 concentration is given, but as 1 mole CO2 creates 1 mole H2O/CA/CO2, it is the same).
There is a chain of equilibria, which have to be shifted from carbonic anhydrase made equilibrium to transport CO2 out as gas: CO2(gas) CO2(dissolved) CO2 + 2H2O CA H3O++HCO3–
The gaseous CO2, which is contained in the alveolar air, is in equilibrium with CO2, dissolved in blood. The dissolved into water H2O carbonic dioxide CO2 occurring in cell converted with carbonic anhydrase CA to
H+ + HCO3–, that H2O carbonic dioxide CO2, finally, is in direct equilibrium with its ions H+and HCO–3.
A– 0% 50% 100% salt – buffer system base
HA 100%50% 0% weak acid buffer component
As soon as H+ concentration grows for some reason, all the chain of equilibriums is shifted to left and CO2 transported out by breathing. If H+ concentration decreases, all the equilibriums are shifted to the right and the extra amount of HCO–3 through kidneys passes into urine and is transported out.
The numerical value
The alkaline reserve 2.036/1=[HCO–3]/[CO2] of the organism can be controlled by adding H2SO4 to a sample of blood (H2SO4 reacts with NaHCO–3 and the CO2, included in salt, is liberated). If 56.23 mL of gaseous CO2 are liberated from 100 mL of blood, the alkaline reserve is normal and total alkaline reserve amount concentration 0.023M = [HCO–3]+[CO2] is normal as [HCO–3] =
Controlled instructions the alkaline reserve of the organism by adding H2SO4 to a sample of blood
(H2SO4 reacts with NaHCO–3 and the CO2, included in salt, is liberated).
If 50–60 mL of gaseous CO2 is liberated from 100 mL of blood, the alkaline reserve is normal.
Two types of diseases occur, if the acid-base balance is distorted in the organism alkalosis and acidosis.
1) Respiratory alkalosis occurs, if lungs are hyperventilated, for example, during anesthesia. If CO2 concentration decreases due to hyperventilation, the blood vessels are broadened and their tonus is lowered as a result of it, therefore O2 supply to brain is shortened.
For this reason it is necessary to use mixtures of O2 and CO2 during anesthesia instead of pure oxygen. If respiratory alkalosis occurs for other reasons than hyperventilation of lungs, the ratio 2/1 of the buffer components can be re-established in a longer period of breathing normal, CO2-containing air 350 ppm.
2) Respiratory acidosis occurs in the cases, when the concentration of CO2 in the air is increased. The result of this is that the action of breathing muscles becomes more difficult. Again, this can be canceled, if the patient starts breathing normal air. Hoverer, if increased CO2 content in the air lasts long, a metabolic acidosis can occur. In the case of metabolic acidosis the ability of hemoglobin to bound oxygen is lowered.
For this reason only the concentrations of carbonic dioxide CO2 into water H2O (avoid carbonic acid H2CO3 formation) and hydrogen carbonate HCO–3 + hydrogen ion H+ are included into equation for blood pH:
pH = 7.0512 +log = 7.36 ; =
the ratio [NaHCO3]/[CO2] being approximately 2/1. (usually in medical literature CO2 concentration is given instead of H2O/CA/CO2, but as 1 mole CO2 creates 1 mole H2O/CA/CO2, it is the same).
There is a chain of equilibria, which have to be shifted for transporting CO2 out:
CO2(gas) CO2(dissolved) CO2 + H2O CA H+ + HCO3–
The gaseous CO2, which is contained in the alveolar air, is in equilibrium with CO2, dissolved in blood. The dissolved into water H2O carbonic dioxide CO2 occurring in cell converted with carbonic anhydrase CA to
H+ + HCO3–, that H2O carbonic dioxide CO2, finally, is in direct equilibrium with its ions H+and HCO3–.
Age features of physical and
chemical properties of the blood
Newborns and babies of the first year have different features of the blood than adults. So, newborns have higher density and stickiness of the blood, which is determined by higher erythrocytes concentration. Till the end of the first month of life, these features decrease and approach to the one, adults have, or they become lower.
Placental blood circulation and labor complicate interchange of gases. That is why children have acidosis before birth (pH = 7,13 – 7,23). During the first hours (or days) after birth, acidosis gradually disappears.
The concentration of plasma proteins in newborn organism is lower (50 – 56 g/l). It will reach the level of adult in age of 3 – 4 years. The high concentration of γ-globulins is specific for the newborn, which the newborn gets from the mother. Till the end of third month its content decreases, but in future, with the help of its own antibodies formation, it will gradually increase. The concentration of α and γ-globulins reaches the adult level till the end of the first year of life.
With age, most of the physical and chemical properties of the blood (pH, osmotic pressure, sodium and potassium concentration, viscosity), stay on the same level. Other features can change. So, ECR increases, osmotic resistance of erythrocytes, hematocrit, ablolute and relative albumins concentration decrease.
APPENDIX
I. Blood plasma content values
Inorganic part:
Fe (iron) 8,53 – 28,06 mkmol/l
K (potassium) 3,8 – 5,2 mmol/l
Na (sodium) 138-217 mkmol/l
Ca (calcium) 0,75 – 2,5 mkmol/l
Mg (magnesium) 0,78 – 0,91 mkmol/l
P (phosphorus) 0,646 – 1,292 mkmol/l
Chlorides of blood 97 – 108 mkmol/l
Filtrate nitrogen (not-protein) 14,28 – 25 mkmol/l
Urea 3,33 – 8,32 mmol/l
Creatinine 53 – 106,1 mkmol/l
Creatine Men 15,25 – 45,75 mkmol/l
Women 45,75 – 76,25 mkmol/l
Uric acid Men 0,12 – 0,38 mkmol/l
Women 0,12 – 0,46 mkmol/l
Organic part:
Total protein 65 – 85 g/l
Albumins 35 – 50 g/l
(52 – 65%)
Lactatedehydrogenase (LDH) < 7 mmol (hour/l)
Aldolase 0,2 – 1,2 mmol (hour/l)
α-amilase (diastase of blood) 12 – 32 g/l (hour/l)
Aspartateaminotransferase (AST) 0,1 – 0,45 mmol (hour/l)
Alaninaminotransferase (ALT) 0,1 – 0,68 mmol (hour/l)
Cholinesterase 160 – 340 mol (hour/l)
Basic phosphatase 0,5 – 1,3 mmol (hour/l)
Creatinkinase 0,152–0,305mmol (hour/l)
Creatinphosphokinase (KPK) to 1,2 mmol
Lipase 0,4 – 30 mmol (hour/l)
Globulins 3 – 35 g/l (35 – 48%)
Total bilirubin 8,5 – 20,5 mkmol/l
free bilirubin
(indirect, not conjugated) 1,7 – 17,11 mkmol/l
conjugated bilirubin (direct) 0,86 – 5,1 mkmol/l
Lipids (total amount) 5 – 7 g/l
Triglicerids 0,59 – 1,77 mmol/l
Total cholesterol 2,97 – 8,79 mmol/l
Lipoproteins of very low density 1,5 – 2,0 g/l
(0,63 -0,69 mmol/l)
low density 4,5 g/l
(3,06 – 3,14 mmol/l)
high density 1,25 – 6,5 g/l
(1,13 – 1,15 mmol/l)
Chylomicrons 0 – 0,5 g/l
(0 – 0,1 mmol/l)
Glucose of the blood 3,3 – 5,5 mmol/l
Glycolized hemoglobin 4 – 7%
II. Normal Values for Erythrocyte and Leukocyte
Measurements
Hemoglobin 13–18 g/dL (males);
12–16 g/dL (females)
Hematocrit 42–52% (males);
37–48% (females)
Erythrocyte count (male) 4.5–6.0 × 106/mm3
(females) 4.0–5.5 ×106/mm3
Leukocyte count 5 × 103–10 × 103/mm3
Differential Leukocyte Count
Neutrophils 55–75%
Eosinophils 2–4%
Basophils 0.5–1%
Lymphocytes 20–40%
Monocytes 3–8%
Short review:
The Blood
Fluids of the Body
Cells of the body utilize 2 fluids:
Blood
Composed of plasma and a variety of cells
Transports nutrients and wastes
Interstitial fluid
Bathes the cells of the body
Nutrients and oxygen diffuse from the blood into the interstitial fluid & then into the cells
Wastes move in the reverse direction
Functions of Blood
Transportation
O2, CO2, metabolic wastes, nutrients, heat & hormones
Regulation
helps regulate pH through buffers systems (discussed in later chapters)
Carbonic-Acid-Bicarbonate Buffer System
Phosphate buffer system
Protein buffer system
helps regulate body temperature
H2O in plasma has high specific heat capacity, buffering large fluctuations in temp
Vessels direct warm blood to where it’s needed, or to the skin for heat dissipation
Protection from disease & loss of blood
Physical Characteristics of Blood
Thicker (more viscous) than water, and flows more slowly than water
Temperature of
pH 7.4 (7.35 – 7.45)
If pH 7 is neutral, blood at 7.4 is slightly alkaline
Average Blood volume:
Females: 4 –
Males: 5 –
Hormonal negative feedback systems maintain constant blood volume and pressure
Components of Blood
55% plasma
45% cells
99% RBCs
< 1% WBCs and platelets
Hematocrit (Hct) & Hemoglobin (Hb)
Hematocrit (Hct) – percentage of blood volume occupied by RBCs
volume of red blood cells ÷ total blood volume
Normal Hematocrit range:
adult female: 38 – 46% (average of 42%)
adult male: 40 – 50% (average of 45%)
Hemoglobin (Hb) – the protein responsible for transporting oxygen in the blood
Normal Hemoglobin range:
adult females: 12 – 16 g/100mL of blood
adult males: 13.5 – 18 g/100mL of blood
Anemia – not enough RBCs, hemoglobin
Polycythemia – too many RBCs (over 50%)
Blood Plasma
Over 90% water
7% plasma proteins
created in liver
confined to bloodstream
albumin
Blood osmotic pressureTransporter substances
globulins
Immunoglobulins (antibodies)
Defense against foreign proteins
fibrinogen
Clotting protein precursor
2% other substances
electrolytes, nutrients, hormones, gases, waste products
Formed Elements of Blood
Red blood cells (erythrocytes)
Platelets (thrombocytes)
White blood cells (leukocytes)
granular leukocytes
Neutrophils
Eosinophils
Basophils
agranular leukocytes
lymphocytes (T cells, B cells, and natural killer cells)
monocytes
Formed Elements of Blood
Normal RBC count: ~ 5 million/drop
Males: 5.4 million/drop
Female: 4.8 million/drop
Platelet count: 150,000-400,000/drop
WBC count: 5,000 – 10,000/drop
Ratio:
RBC : Platelet : WBC
700 : 40 : 1
Hematopoiesis: Formation of Blood Cells
Most blood cell types need to be continually replaced
Blood cells die within hours, days, or weeks
Hematopoiesis (or hemopoiesis) – the process of blood cell formation
In adults
Occurs only in red marrow of flat bones (pelvis, sternum, ribs, vertebrae, & skull, and in ends of long bones)
Hematopoiesis of All Blood Cells
All blood cells develop from the same uncommitted stem cells in bone marrow
Red Blood Cells or Erythrocytes
Contain oxygen-carrying protein hemoglobin that gives blood its red color
1/3 of cell’s weight is hemoglobin
Biconcave disk
Increased surface area:volume ratio
Flexiblity for narrow passages
No nucleus or other organelles
No mitochondrial ATP formation
New RBCs enter circulation at 2-3 million/second
Hemoglobin
Hemoglobin Molecule:
>> 4 globular protein subunits
>> each containing 1 heme group (red pigment)
>> each containing 1 iron ion (Fe+2)
>> each capable of binding (reversibly) to 1 oxygen (O2) molecule
1 RBC = ~ 280 million Hemoglobins
1 Hemoglobin = 4 Heme Groups
1 Heme Group = 1 Iron atom = 1 O2 molecule
Therefore, 1 RBC contains ≈ 1.12 x 109 O2 molecules
Function of Hemoglobin
Each hemoglobin molecule can carry 4 O2 or CO2 molecules
Hemoglobin also acts as a buffer and balances pH of blood
Hemoglobin transports 23% of total CO2 waste from tissue cells to lungs for release
combines with amino acids in globin portion of Hb
Forms of Hb:
Oxyhemoglobin: hemoglobin + O2
Deoxyhemoglobin: hemoglobin – O2
Carbaminohemoglobin: hemoglobin + CO2
Hemoglobin Affinity
CO2 vs O2
Deoxyhemoglobin’s affinity for carbon dioxide (CO2) is greater than its affinity for oxygen (O2)
Carbon dioxide (CO2) can lower O2-Hb affinity through changes in its partial pressure (pCO2) or pH (carbonic acid reaction)
CO vs O2 (Carbon Monoxide Poisoning):
Hemoglobin’s affinity for carbon monoxide (CO) is 250 times greater than its affinity for oxygen (O2)
CO is colorless, odorless, flammable, and highly toxic
CO binds irreversibly to the Fe2+ in hemoglobin. Treatment requires oxygen therapy, or hyperbaric oxygen therapy, depending on severity of poisoning
The drop in Hb O2 saturation goes unnoticed for a while because chemoreceptors rely primarily on [CO2] for the “urge to breathe”
Erythropoiesis: Production of RBCs
Multipotent stem cell differentiates into Proerythroblast
Proerythroblast begins producing hemoglobin, becoming erythroblast
Erythroblast ejects nucleus, becoming a reticulocyte
Reticulocyte escapes from bone marrow into the blood.
In 1-2 days, reticulocyte ejects remaining organelles, becoming Erythrocyte
Factors required for Erythropoiesis:
Erythropoietin (EPO) from kidneys
Vitamin B12 (cobalamin)
Iron (Fe)
Negative Feedback Control of Erythropoiesis
Hypoxia – inadequate oxygen supply to tissues
generalized hypoxia – systemic oxygen deprivation
tissue hypoxia – local oxygen deprivation
Common Causes:
High altitudes
decreased atmospheric pressure
Anemia
RBC or hemoglobin production < RBC destruction
Kidney response to hypoxia:
Release Erythropoietin (EPO)
Speeds up cell division of erythroblasts, and maturation and release of erythrocytes
Negative Feedback Control of Erythropoiesis
Negative Feedback Control of Erythropoiesis
RBC Life Cycle
