Blood Composition and Plasma Proteins

Blood Composition

• Blood is 8% of body weight, approximately 5.6 liters in adult males
• Blood circulates throughout the cardiovascular system via heart pumping action
• Plasma (55%) is a clear yellow fluid, 3.5 liters, 5% of body weight
• Serum is the fluid remaining after blood clots
• Plasma composition consists of water (90%), organic substances (9.1%; proteins, lipids, glucose, wastes, vitamins), inorganic substances (.9%; Na+, Cl-, HCO3-, etc.), and blood gases (O2, CO2, N2)
• Blood cells constitute 45% of volume: red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes).

Plasma Proteins

• Plasma proteins (7.2-7.4 g/dl) are essential for various functions
• Albumin is the most abundant plasma protein, with a molecular weight of 69,000, playing a crucial role in osmotic pressure
• Globulins (α, β, γ), fibrinogen, and prothrombin are also important components, with varying molecular weights and functions.
• Albumin, fibrinogen, and prothrombin are primarily produced in the liver
• 50% of globulins are generated in the liver; the remaining 50% are produced by plasma cells of the reticuloendothelial system (γ globulins).
• The albumin-to-globulin ratio (A/G) is typically 1.2-1.6 and can be altered by diseases (liver or kidney).

Functions of Plasma Proteins

• Plasma proteins maintain osmotic pressure, regulating fluid balance between blood and tissues
• They transport hormones, vitamins, lipids, and minerals
• They defend the body against microorganisms and toxins.
• They are involved in blood clotting, with prothrombin and fibrinogen playing key roles.
• The viscosity of blood also is regulated by plasma proteins
• Various plasma proteins maintain the pH (7.4) of the blood within the normal range.

Erythrocytes (RBCs)

• Biconcave discs, lack nuclei, and rely on anaerobic glycolysis for energy production.
• Critical role in gas transport.
• Contain hemoglobin, K+ (intracellular cation), and carbonic anhydrase enzyme for CO2 transport.
• Advantages of biconcave shape include a higher surface area to volume ratio and greater flexibility to squeeze through capillaries without rupture.
• Hemoglobin is the red oxygen-carrying pigment found in RBCs. The content is measured in grams per 100ml of blood.
• Normal adult male hemoglobin count: 15-16 g/dl
• Normal adult female hemoglobin count: 13-14 g/dl
• Newborn hemoglobin count: 19 g/dl
• Different hemoglobin types (HbA, HbF) exist with varying oxygen affinities.
• The average lifespan of an RBC is 120 days.

Erythropoiesis (RBC Formation)

• Erythropoiesis occurs in the red bone marrow throughout life
• The red bone marrow located in certain flat bones (skull, sternum, ribs, vertebra, pelvis) plays a crucial role in RBC production
• Erythropoietin (EPO) stimulates RBC production in response to low oxygen levels.
• Hypoxia (low oxygen) stimulates EPO release, primarily from kidney-derived endothelial cells

Anemia

• Anemia is characterized by reduced oxygen-carrying capacity of the blood—a consequence of decreased RBC or hemoglobin levels within the blood
• Types of anemia include normochromic normocytic, microcytic hypochromic (iron deficiency), and macrocytic (vitamin B12 or folic acid deficiency)
• Causes of anemia include hemolytic anemia, hemorrhagic anemia, and aplastic anemia

Hemostasis (Blood Clotting)

• Hemostasis is the process that prevents blood loss.
• It involves local vasoconstriction, platelet plug formation, and blood clot formation
• 3 main stages including:
  • Local vasoconstriction
  • Formation of platelet plug
  • Formation of blood clot

Blood Coagulation (Clotting)

• Blood coagulation is a complex cascade of reactions involving various clotting factors.
• Intrinsic and extrinsic pathways play vital roles, ultimately leading to the formation of a fibrin mesh that traps blood cells and platelets.
• Limiting reactions exist to prevent unwanted blood clotting, such as the fibrinolytic system, anticoagulant proteins, and specific reactions that limit the blood clotting cascade.

Anticoagulants

• Substances that prevent or inhibit blood clotting in vitro (test tubes or outside the body) or in vivo (within the body).
• In vitro anticoagulants include removal of calcium ions (oxalates, citrates), silicon-coated tubes, or heparin.
• In vivo anticoagulants include heparin, thromboxane A2 and prostacyclin, thrombin, antithrombin , Protein C, and Protein S.

Platelets

• Small, oval-shaped, non-nucleated cell fragments.
• Their number in normal blood: 300,000/mm³
• Key role in blood clotting.
• Platelets have various structures (e.g., membrane, cytoplasm) and granular components
• Platelets are significant in initiating the coagulation process by adhering to exposed surfaces and activating clotting factors.

Iron Metabolism

• Iron has a crucial role in oxygen transport. It is a part of hemoglobin and oxidative enzymes.
• Iron is absorbed in the small intestine (duodenum) and is transported in the blood via transferrin
• Iron is stored in the liver and spleen as ferritin.
• Iron deficiency is a frequent cause of microcytic hypochromic anemia.