Blood Composition and Plasma Quiz

Blood Composition

• Blood is a complex fluid containing plasma (extracellular fluid rich in proteins) and formed elements (red blood cells, white blood cells, and platelets).
• Total blood volume is approximately 70 mL/kg in women and 80 mL/kg in men.

Whole Blood

• Spinning down a blood sample with an anticoagulant separates formed elements (RBCs, WBCs, and platelets) at the bottom (buffy coat) and plasma at the top.
• Red blood cells have the highest density, forming the bottom layer.
• Hematocrit measures the fraction of the total blood column occupied by red blood cells. Normal hematocrit is about 40% in women and 45% in men. It is 55% in newborns and goes down to 35% by 2 months.

Plasma

• Plasma is a liquid, pale-white solution containing electrolytes, proteins, carbohydrates, and lipids.
• A pink color in plasma indicates hemolysis (red blood cell breakdown).
• A brown-green color suggests elevated bilirubin.
• Plasma protein concentration is typically ~7.0 g/dL, contributing to colloid osmotic pressure (oncotic pressure) ~25 mm Hg.
• Major plasma proteins include albumin, fibrinogen, globulins, and coagulation factors. Molecular weights of plasma proteins range up to 970 kDa.
• Albumin (3.5-5.5 g/dL) is produced by the liver, with a 20-day half-life and crucial for colloidal osmotic pressure.
• Hepatic cirrhosis often leads to a lower plasma albumin concentration.

Coagulation

• Coagulation involves a complex cascade resulting in the cleavage of fibrinogen into fibrin monomers.
• Fibrin polymers trap blood cells, forming a clot. Fibrinogen is a liver-produced dimer that circulates at 150-300 mg/dL
• Acute-phase response significantly enhances fibrinogen synthesis.
• Serum is plasma with fibrinogen removed, containing albumin, antibodies, and other proteins. Plasma clots don't retract as they lack platelets.

Erythrocytes (Red Blood Cells)

• Erythrocytes are the most abundant blood cells, responsible for oxygen transport and carbon dioxide removal.
• They are nonnucleated, biconcave cells, ~7.5 μm in diameter and with a ~90 fL volume.
• Hemoglobin is the main component of red blood cells (high concentration).
• Structure is crucial for efficient gas exchange.

Hematopoiesis

• Hematopoiesis is the formation of blood cells.
• It begins with pluripotent hematopoietic stem cells in bone marrow, which differentiate into various cell lineages (erythrocytes, leukocytes, platelets).
• Cytokines like GM-CSF, G-CSF, M-CSF, IL-3, IL-5, TPO, and EPO regulate hematopoiesis.

Bone Marrow

• Bone marrow is the primary site for hematopoiesis.
• It contains stem cells that differentiate into all types of blood cells.
• Cytokines like EPO and TPO stimulate the production of specific blood cells.

Erythropoietin

• Erythropoietin (EPO) is a glycoprotein produced mainly in the kidney.
• It stimulates erythropoiesis (red blood cell production).

Blood Viscosity

• Blood viscosity is non-Newtonian, meaning its relationship between shear stress and shear rate is not linear.
• Factors such as hematocrit and fibrinogen concentration affect blood viscosity, especially at low shear rates.
• Higher hematocrit generally leads to increased viscosity, particularly at high concentrations.
• Radius of blood vessels influences viscosity at low shear rates (especially in capillaries). Cells tend to move to the center of smaller vessels for less resistance.

Leukocytes (White Blood Cells)

• Leukocytes are crucial for immune responses and combat infections.
• Granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes) are two main groups.
• Neutrophils are most abundant. Lymphocytes (T and B cells) are involved in cell-mediated and humoral immunity respectively.
• Monocytes differentiate into macrophages, which play roles in immune responses.

Platelets

• Platelets are cell fragments (not full cells) necessary for hemostasis and blood clotting.
• Their lifespan is about 10 days.
• Megakaryocytes produce platelets in bone marrow. Factors like TPO and IL-3 are important.