Blood Composition and Characteristics

Blood Composition and Characteristics

• Blood is connective tissue comprised of cellular elements and an extracellular matrix.
• Cellular elements are referred to as formed elements.
• Formed elements include red blood cells (RBCs), white blood cells (WBCs), and platelets.
• Formed elements constitute about 45% of the total blood volume.
• The extracellular matrix, or plasma, is a fluid that suspends the formed elements, enabling circulation.
• Plasma constitutes about 55% of the total blood volume.
• Blood makes up approximately 8% of adult body weight.
• Adult males average about 5 to 6 liters of blood, while adult females average 4–5 liters.
• Arterial blood is bright red due to high oxygen levels, while venous blood is darker due to lower oxygen.
• Hemoglobin is a pigment that changes color based on oxygen saturation.
• The normal blood pH range is 7.35 to 7.45, which is slightly alkaline.
• Venous blood usually has a lower pH than arterial blood due to the presence of carbon dioxide.
• Blood contains buffers that help regulate pH.
• Blood is about three to five times thicker than water due to blood cells and plasma proteins.
• Blood viscosity contributes to normal blood pressure.
• The normal blood temperature is about 38°C, slightly higher than normal body temperature, due to friction and resistance.

Blood Functions

• Blood transports oxygen, carbon dioxide, nutrients, hormones, drugs, and metabolic waste products.
• White blood cells defend the body from external and internal threats, like bacteria, viruses, and mutated cells.
• Blood regulates body temperature through the transport of blood to body periphery.
• Blood helps regulate water and electrolytes.
• Blood helps regulate pH.
• Platelets regulate blood clotting and minimize blood loss (hemostasis).
• Centrifuged blood comprises plasma (55% of whole blood) and formed elements (45% of whole blood).
• The buffy coat consists of WBCs and platelets, making up less than 1% of whole blood.
• Erythrocytes or RBCs make about 45% of whole blood.
• Hematocrit (HCT) is the percentage of formed elements (mainly RBCs) to total blood volume.
• In men, the hematocrit is 45% (± 7%); in women, it is 42% (± 5%).

Plasma Components

• Plasma is about 91% water.
• Plasma transports nutrients, such as glucose, amino acids, and minerals, throughout the body.
• Plasma transports waste products, such as urea and creatinine, to the kidneys for excretion.
• Hormones produced by endocrine glands are carried in the plasma to their target organs.
• Carbon dioxide is carried in the plasma as bicarbonate ions (HCO3-) and is reformed and exhaled in the lungs.

Plasma Proteins

• Proteins make up about 7% of the plasma volume.
• Plasma proteins include unique plasma proteins and regulatory proteins like enzymes and hormones.
• Albumin is the most abundant plasma protein (60% of plasma protein) and is produced by the liver.
• Albumin acts as a transport vehicle for fatty acids and steroid hormones.
• Albumin is a significant contributor to osmotic pressure, holding water inside blood vessels.
• The normal serum level of albumin is 3.5–5 g/dl blood.
• Globulins area the 2nd most common plasma protein (36% of plasma proteins), produced by the liver.
• Alpha, beta globulins transport iron, lipids, and fat-soluble vitamins (A, D, E, and K).
• Gamma globulins are antibodies released by plasma cells during immune response.
• The normal serum level of globulins is 1–1.5 g/dl blood.
• Fibrinogen is the least abundant plasma protein (7% of plasma proteins) and is produced by the liver.
• Fibrinogen is converted into fibrin threats at the end of clotting cascade.
• The normal serum level of fibrinogen is 0.2–0.45 g/dl blood.

Plasma Solutes

• Plasma contains electrolytes like sodium, potassium, and calcium ions.
• Plasma contains dissolved gases, such as oxygen, carbon dioxide, and nitrogen.
• Plasma contains organic nutrients, such as vitamins, lipids, glucose, and amino acids.
• Plasma contains metabolic wastes.
• All non-protein solutes combined contribute about 1% to the total plasma volume.

Erythrocytes (RBCs)

• Erythrocytes are small cells shaped like biconcave discs.
• Mature erythrocytes lack a nucleus and organelles.
• Erythrocytes are filled with hemoglobin (Hb), which functions in gas transport.
• Erythrocytes have stretchable fibers that allow them to change shape.
• Erythrocytes lack mitochondria, so they do not consume the oxygen they transport.
• Erythrocytes are the major factor contributing to blood viscosity.
• Males have about 5.5 million erythrocytes/ml, and females have about 4.8 million erythrocytes/ml.
• The function of erythrocytes is to transport respiratory gases (oxygen and carbon dioxide).
• Erythrocytes catalyze the formation of carbonic acid (H2CO3 ↔ CO2 + H2O) due to carbonic anhydrase.
• Hemoglobin is a protein and iron molecule.
• Hemoglobin binds easily and reversibly with oxygen.
• Most oxygen carried in blood is bound to hemoglobin.
• Male adult normal hemoglobin values are 14 – 16 g /100 ml of blood, female adult values are 12 – 14 g/ (100 ml of blood)
• Hemoglobin is made up of the protein globin and the red heme pigment.
• Globin consists of two alpha and two beta polypeptide chains, each bound to a heme group containing an iron atom.
• Each hemoglobin molecule can transport four molecules of oxygen due to the presence of iron atoms.
• A single red blood cell contains approximately 250 million hemoglobin molecules.
• When oxygen binds to iron, hemoglobin becomes oxyhemoglobin (bright red).
• In the tissues, oxygen detaches from iron, resulting in deoxyhemoglobin (dark red).
• In the capillaries, about 76% of carbon dioxide dissolves, while the rest forms bicarbonate ion or binds to hemoglobin.
• About 23–24% of carbon dioxide binds to amino acids in hemoglobin, forming carbaminohemoglobin or carboxyhemoglobin.

Erythrocyte Production, Regulation, and Destruction

• Blood cell formation is called hematopoiesis or hemopoiesis and occurs in the red bone marrow.
• In adults, red marrow is found in the axial skeleton, girdles, and proximal epiphyses of the humerus and femur.
• Each type of blood cell is produced in different numbers based on changing body needs and regulatory factors.
• The marrow makes approximately 100 billion new cells per day.
• The number of circulating erythrocytes reflects a balance between red blood cell production and destruction.
• Too few erythrocytes (anemia) lead to tissue hypoxia, and too many RBCs (polycythemia) make the blood undesirably viscous.
• Erythropoiesis is controlled hormonally and depends on iron, amino acids, and B vitamins (B6, B12, B9).
• Erythropoietin (EPO) is the direct stimulus for erythrocyte formation.
• The kidneys play a major role in EPO production as they accelerate EPO when kidney cells become hypoxic.
• Reduced numbers of red blood cells, insufficient hemoglobin, or reduced oxygen availability triggers EPO formation.
• Red blood cells have a lifespan of 100 to 120 days and become trapped and fragmented in smaller circulatory channels, especially in the spleen.
• The spleen is called the "red blood cell graveyard."

Leukocytes (WBCs)

• Leukocytes and erythrocytes originate from hematopoietic stem cells but are very different.
• Leukocytes are far less numerous than erythrocytes, with typically 5000 to 10,000/ml.
• WBCs are generally also larger than erythrocytes
• WBCs are complete cells with a nucleus and organelles.
• There are many types of leukocytes, unlike erythrocytes.
• Most leukocytes have a shorter lifespan than erythrocytes.
• Leukocytes routinely leave the bloodstream to perform defensive functions.

Classification and Lifecycle of Leukocytes

• Granulocytes have visible cytoplasmic granules.
• Granulocyte Neutrophils are the most numerous (50–70%) and increase explosively during acute bacterial infections.
• Granulocyte Eosinophils make 2–4% of leukocytes and counterattack parasitic worms while lessening allergies.
• Granulocyte Basophils average 0.5–1% and contain histamine-containing granules, acting as a vasodilator.
• Agranulocytes lack visible cytoplasmic granules.
• Agranulocyte Lymphocytes make up 25% or more of WBCs.
• T lymphocytes (T cells) function in the immune response against virus-infected and tumor cells.
• B lymphocytes (B cells) give rise to plasma cells, which produce antibodies (immunoglobulins).
• Agranulocyte Monocytes(3–8% of WBCs) differentiate into mobile macrophages for defense against viruses and infections.
• Leukocytes have a short lifespan, with production beginning in the bone marrow under the influence of CSFs and interleukins.
• Granulocytes have a short lifespan (0.5 to 9 days), while monocytes may live for several months, and lymphocytes have lifespans of days to decades.

Platelets and Hemostasis

• Thrombopoietin, secreted by the kidneys and liver, helps regulate platelet formation.
• Platelets are fragments of megakaryocyte cytoplasm surrounded by a plasma membrane.
• Platelets are descended from myeloid stem cells and are large (50–100 µm in diameter).
• Each megakaryocyte releases 2000–3000 platelets.
• Platelets are small (2-4 µm in diameter) and are present with 150,000–160,000 per µL of blood.
• Approximately one-third of platelets migrate to the spleen for storage and are released in response to blood vessel rupture.
• Platelets are activated to limit blood loss and remain for about 10 days before being phagocytized by macrophages.
• Platelets are necessary for hemostasis, or the prevention of blood loss.
• Hemostasis involves a series of reactions to stop bleeding.
• The hemostasis response is fast, localized, and controlled by blood coagulation factors (13 factors).
• During hemostasis includes vascular spasms, platelet plug formation, and coagulation.
• Blood loss is permanently prevented when fibrous tissue grows into the clot.
• Coagulation transforms blood from a liquid to a gel involves prothrombin activator that is formed.
• Prothrombin activator converts prothrombin into thrombin.
• Thrombin converts fibrinogen into a fibrin mesh, trapping blood cells.

Human Blood Groups

• RBC plasma membranes have glycoproteins (antigens) that identify each unique individual.
• Transfused RBC proteins may be recognized as foreign, causing agglutination and destruction.
• RBC antigens that promote agglutination are called agglutinogens.
• Over 50 antigens have been identified on erythrocyte membranes and are classified under ABO and Rh blood groups.

ABO Blood Group

• ABO blood groups are based on the presence or absence of type A and type B antigens.
• Individuals can be of type blood group as A, B, AB, or O.
• The O blood group has neither antigens, while AB has both antigens.
• Presence of either A or B antigen results in blood group A or B, respectively.
• Agglutinins are preformed antibodies that act against RBCs carrying ABO antigens absent on individual's own cells.
• Newborns lack these antibodies, but they appear in the plasma within two months and reaching adult levels between 8 and 10 years of age.
• Group O individuals possess both anti-A and anti-B antibodies.
• Group A individuals have anti-B antibodies, while Group B individuals have anti-A antibodies, AB do not produce any antibodies.

Rh Blood Groups

• There are 45 different types of Rh agglutinogens, each an Rh factor.
• Antigen D is the only clinically important Rh antigen.
• Individuals with Rh D antigen are Rh positive (Rh+), and those without it are Rh negative (Rh−).
• The Rh system is named after an antigen (agglutinogen D) found in rhesus monkeys that was later discovered in humans..
• Person’sblood groups reported together (O+, A–).
• Anti-Rh antibodies are not spontaneously formed in (Rh negative).
• Rh- individuals that receive Rh+ blood, the immune system creates and triggers anti-Rh antibodies.
• The second time after the first transfusion that anti Rh is introduced, reactions in the RBCs occur.
• Rh factor problem, includes when Rh– pregnant that carry Rh+ babies .
• The first pregnancy results in in delivery of a healthy baby.
• However, bleeding from uterus detaching of placenta cause sensitization from Rh+ antigens passing bloodstream.
• Anti-Rh antibodies, unless the immune response is controlled forms and prevents sensitization through antiRh antibodies.
• Precautions are applied to women with abortion or miscarriage fetus.