Human Blood and Blood Circulation

Blood Characteristics

• Oxygen-rich blood is brightly red, while oxygen-poor blood is darkly red.
• pH of blood must remain between 7.35-7.45 (slightly alkaline).
• Temperature of blood is slightly higher than body temperature.
• Average adult has about 5 liters of blood (~7-8% of body weight).
• There are approximately 1 billion red blood cells in two to three drops of blood.

Functions of Blood

• Transports gases (O₂, CO₂), nutrients, waste products, processed molecules (e.g., proteins), and regulatory molecules (hormones).
• Regulates pH and osmosis.
• Maintains body temperature.
• Protects against foreign substances.
• Forms clots.

Blood Components

• Hematocrit measures the volume of packed erythrocytes per unit of blood (40-50% for men, 35-45% for women).
• Composition of blood: plasma (55%), cells (45%).
• Erythrocytes (RBCs), leukocytes (WBCs), and platelets make up the formed elements of blood.

Plasma

• Composed of water (90%), proteins (8%), albumins (58%), globulins (38%), clotting proteins (4%), and inorganic salts (0.9%).
• Types of plasma proteins include albumins (osmotic pressure maintenance), globulins (lipid transport, immunity), and fibrinogen (clotting).

Erythrocytes (RBCs)

• Specializations: biconcave shape, no nucleus, contain hemoglobin.
• Lifespan: approximately 120 days.
• Functions: transports oxygen from lungs to tissues and carbon dioxide from tissues to lungs.
• Surface antigens: blood groups A, B, AB, O.
• Hemoglobin structure: 4 polypeptide molecules (CO₂ transport), 4 heme molecules (O₂ transport).
• Types of hemoglobin: oxyhemoglobin (Hb carrying O₂), carbaminohemoglobin (Hb carrying CO₂).

Leukocytes (WBCs)

• Much fewer in number compared to RBCs.
• Defense against disease.
• Types: granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes).
• Neutrophils: most numerous, multilobed nucleus, active phagocytes.
• Eosinophils: migrate to sites of allergic reactions, inflammation, and parasitic infection.
• Basophils: initiators of the inflammatory process.
• Lymphocytes: types include B cells (humoral immunity), T cells (cellular immunity), and natural killer cells (attack cancerous and virally infected cells).
• Monocytes: become macrophages in connective tissue, phagocytosis, produce cytokines, and present antigens.

Platelets (Thrombocytes)

• Origin: fragmentation of megakaryocytes.
• Function: promotes clotting and prevents blood loss.
• Structure: hyalomere (transparent, peripheral zone), granulomere (central zone with granules).
• Granule types: α-granules (contains fibrinogen, PDGF), δ-granules (contains calcium, ADP, ATP), λ-granules (contains hydrolytic enzymes).

Bone Marrow

• Types: red bone marrow (hematogenous) and yellow bone marrow (rich in adipose cells).
• Structure: composed of stroma, hematopoietic cords, and sinusoidal capillaries.
• Function: source of stem cells for other tissues.
• Megakaryocytes: precursors for platelets, exhibit polyploid nuclei with azurophilic granules.