LECTURE 7a: Blood Components and RBC Lifecycle.

Plasma: Volume and Layers

• Plasma: watery extracellular matrix; volume about 5{-}6\,\mathrm{L} in adults.

• After centrifugation, blood separates into three layers: top plasma, buffy coat (<1\%) containing WBCs and platelets, bottom RBCs.

• Plasma is crucial for transport of substances in blood.

Plasma Proteins and Functions

• Major plasma protein classes: alpha and beta globulins (transport); gamma globulins (antibodies).

• Liver produces globulins; roles in transport, regulation (pH, temperature, water content, acid-base balance), protection.

• Fibrinogen is converted to fibrin during clot formation.

Formed Elements:

Erythrocytes (RBCs)

• Erythrocytes: most numerous formed element; designed for O2 transport.

• Structure: biconcave disc; lack a nucleus and organelles (no mitochondria); cannot reproduce or perform major metabolic reactions.

• Membrane: strong and flexible to squeeze through capillaries.

• Hb: hemoglobin is the O2 carrying protein; roughly 1 RBC holds about 2.8\times 10^{8} Hb molecules.

RBC Life Cycle

• Life span: ~120\text{ days}.

• Old RBCs broken down; iron salvaged and transported to bone marrow by transferrins for reuse; the remainder forms bilirubin.

• Bilirubin is excreted into bile and gives feces their yellow-brown color.

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• Next: review of white blood cells (WBCs).