Blood Composition and Function

• Blood is a fluid connective tissue, crucial for transport and homeostasis in the body
• Blood consists of plasma and formed elements (cells and cell fragments)

Blood Composition

• Plasma is the liquid component; it constitutes about 55% of blood volume
• Formed elements include erythrocytes (red blood cells), leukocytes (white blood cells), and thrombocytes (platelets); they make up about 45% of blood volume

Plasma Components

• Water: 90% of plasma volume; acts as a solvent and suspending medium for blood components
• Proteins: 7-8% of plasma volume; include albumins, globulins, and fibrinogen
  • Albumins maintain osmotic pressure and transport lipids and steroid hormones
  • Globulins include antibodies (immunoglobulins) for defense and transport globulins binding ions, hormones, and lipids
  • Fibrinogen is essential for blood clotting
• Electrolytes: Ions such as sodium, potassium, calcium, chloride, and bicarbonate; maintain osmotic pressure and pH buffering, and regulate membrane permeability
• Nutrients: Glucose, amino acids, lipids, and vitamins; provide nourishment to cells
• Wastes: Urea, creatinine, bilirubin, and lactic acid; products of metabolism transported to excretory organs
• Gases: Oxygen, carbon dioxide, and nitrogen; involved in respiration and cellular function

Erythrocytes (Red Blood Cells)

• Structure: Biconcave discs, anucleate (without a nucleus) in mammals, and contain hemoglobin
• Function: Transport oxygen from the lungs to tissues and carbon dioxide from tissues to the lungs
• Hemoglobin is a protein containing iron that binds to oxygen
• Production: Erythropoiesis occurs in the bone marrow, stimulated by erythropoietin hormone from the kidneys
• Lifespan: About 120 days; aged or damaged RBCs are removed by macrophages in the spleen and liver

Leukocytes (White Blood Cells)

• Function: Immune defense and inflammatory response
• Types: Granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes)
• Neutrophils: Phagocytic; ingest bacteria and cellular debris
• Eosinophils: Combat parasitic infections and are involved in allergic reactions
• Basophils: Release histamine and heparin; mediate inflammation
• Lymphocytes: Include T cells (cellular immunity), B cells (humoral immunity producing antibodies), and NK cells (natural killer cells, involved in cell-mediated cytotoxicity)
• Monocytes: Differentiate into macrophages; phagocytic cells that ingest pathogens, dead cells, and debris

Thrombocytes (Platelets)

• Structure: Cell fragments derived from megakaryocytes in the bone marrow
• Function: Blood clotting (hemostasis)
• Mechanism: Form a platelet plug at the site of injury and release factors that initiate the coagulation cascade

Blood Functions

• Transport:
  • Oxygen: From lungs to tissues
  • Carbon Dioxide: From tissues to lungs
  • Nutrients: From digestive system to cells
  • Hormones: From endocrine glands to target tissues
  • Waste Products: From cells to excretory organs
• Regulation:
  • Body Temperature: Distributes heat throughout the body
  • pH: Buffers acids and bases to maintain stable pH
  • Fluid Balance: Regulates water content of cells via osmotic pressure
• Protection:
  • Immune Response: White blood cells defend against pathogens
  • Blood Clotting: Platelets and clotting factors prevent blood loss

Blood Characteristics

• Volume: Approximately 5-6 liters in males and 4-5 liters in females
• Color: Varies from bright red (oxygen-rich) to dark red (oxygen-poor)
• Viscosity: Thicker than water because of formed elements and plasma proteins
• pH: Slightly alkaline, with a normal range of 7.35-7.45
• Temperature: Slightly higher than body temperature (about 38°C or 100.4°F)

Overview of blood as a fluid connective tissue. Includes plasma, erythrocytes, leukocytes, and thrombocytes. Covers the role of water, proteins, and electrolytes.