Blood Composition and Physiology

Blood Composition

• Blood Composition
  • Blood is a fluid connective tissue comprised of:
  • Plasma: Non-living fluid matrix (55% of blood)
  • Formed elements: Living cells suspended in plasma
    • Erythrocytes: Red blood cells (RBCs)
    • Leukocytes: White blood cells (WBCs)
    • Platelets: Cell fragments involved in clotting

Separation of Blood Components

• When blood is spun in a centrifuge, it separates into three layers:
  • Plasma: Top layer, ~55%
  • Erythrocytes: Bottom layer, ~45% (total volume known as hematocrit)
  • Buffy coat: Middle layer with WBCs and platelets (<1%)
• Hematocrit: Percentage of blood volume that is RBCs
  • Normal values: 47% ± 5% for males; 42% ± 5% for females

Physical Characteristics of Blood

• Physical Characteristics:
  • Sticky, opaque fluid with metallic taste
  • Color:
  • High O2: Scarlet
  • Low O2: Dark red
  • pH: 7.35–7.45
  • Volume:
  • Males: 5-6 L
  • Females: 4-5 L

Functions of Blood

• Distribution Functions:
  • Deliver O2 and nutrients to body cells
  • Transport metabolic wastes to lungs and kidneys for elimination
  • Transport hormones from endocrine organs to target organs
• Regulation Functions:
  • Maintain body temperature
  • Maintain normal pH using buffers (bicarbonate ions)
  • Maintain adequate fluid volume in the circulatory system
• Protective Functions:
  • Prevent blood loss through clot formation
  • Prevent infection via antibodies and WBCs

Blood Plasma

• Composition of Plasma:
  • 90% water
  • Contains over 100 dissolved solutes (nutrients, hormones, waste, proteins)
  • Plasma Proteins: Most abundant solutes in plasma
  • 60% albumin: Substance carrier, blood buffer, osmotic pressure contributor
  • 36% globulins: Antibodies and transport proteins
  • 4% fibrinogen: Essential for blood clotting

Formed Elements of Blood

• Formed Elements:
  • Red Blood Cells (Erythrocytes):
  • Biconcave discs, 7.5 μm diameter, anucleate
  • Contain hemoglobin for gas transport
  • Lack mitochondria, rely on anaerobic respiration
  • White Blood Cells (Leukocytes):
  • Less than 1% of blood volume
  • Defense against disease; diapedesis allows movement through capillaries
  • Two Categories of WBCs:
    • Granulocytes (neutrophils, eosinophils, basophils)
    • Agranulocytes (lymphocytes, monocytes)
  • Platelets:
  • Cytoplasmic fragments involved in clotting
  • Normal range: 150,000 – 400,000 platelets/ml of blood

Vascular System

• Blood Vessels:
  • Arteries: Carry blood away from the heart (usually oxygenated)
  • Capillaries: Microscopic vessels that facilitate gas and nutrient exchange
  • Veins: Return blood to the heart (typically deoxygenated)

Blood Vessel Structure

• Arterial System:
  • Elastic Arteries: Large arteries (e.g., aorta) that act as pressure reservoirs
  • Muscular Arteries: Deliver blood to organs, more smooth muscle
  • Arterioles: Control flow into capillaries via vasodilation/vasoconstriction
• Venous System:
  • Thinner walls than arteries but larger lumens
  • Valves prevent backflow; blood reservoirs (capacitance vessels)
  • Venous return aided by the muscular pump, respiratory pump, and venoconstriction

Circulation Physiology

• Blood Pressure (BP): Force exerted on vessel walls; drives blood movement
• Resistance Factors:
  • Blood viscosity ("stickiness") and blood vessel length

Summary of Blood Vessel Anatomy

• Maintenance of blood pressure and circulation depends on the structure and function of arteries and veins

Major Types of Blood Vessels

• Major Arteries: Head, trunk, arms, and legs
• Major Veins: Return blood from various body regions to the heart

General Observations

• Blood plays a critical role in transport, regulation, and protection in the body
• The vascular system's structure supports its varied functions.