Blood and the Cardiovascular System: Structure, Composition, and Function

Introduction to Blood and the Cardiovascular System

Overview of the Cardiovascular System

The cardiovascular system is essential for transporting substances throughout the body and maintaining homeostasis. It consists of three main components:

• The heart: A muscular pump that propels blood through the vessels.

• Blood vessels: A network of tubes (arteries, veins, capillaries) that conduct blood throughout the body.

• Blood: A specialized fluid of connective tissue containing cells suspended in a fluid matrix.

Functions of Blood

Blood plays a vital role in the body by transporting materials to and from cells. Its main functions include:

• Transporting oxygen and carbon dioxide

• Delivering nutrients

• Carrying hormones

• Distributing immune system components

• Removing waste products

Physical Characteristics of Blood

Important Functions of Blood

• Transportation of dissolved substances (gases, nutrients, hormones, wastes)

• Regulation of pH and ion composition of interstitial fluids

• Restriction of fluid losses at injury sites (clotting)

• Defense against toxins and pathogens (immune response)

• Stabilization of body temperature

Components of Whole Blood

Blood is composed of two main components:

• Plasma: The fluid matrix, consisting of water, dissolved plasma proteins, and other solutes.

• Formed elements: All cells and cell fragments (red blood cells, white blood cells, and platelets).

Composition of Whole Blood

Component	Percentage of Whole Blood	Main Constituents
Plasma	~55% (Range 46-63%)	92% Water, 7% Plasma Proteins, 1% Other Solutes
Formed Elements	~45% (Range 37-54%)	99.9% Red Blood Cells,

Types of Formed Elements

• Red blood cells (RBCs) or erythrocytes: Transport oxygen.

• White blood cells (WBCs) or leukocytes: Part of the immune system.

• Platelets: Cell fragments involved in blood clotting.

Hematopoiesis and Fractionation

• Hematopoiesis: The process of producing formed elements, primarily by myeloid and lymphoid stem cells.

• Fractionation: The process of separating whole blood into plasma and formed elements for clinical analysis.

General Physical Properties of Blood

• Temperature: 38°C (100.4°F) is the normal temperature of blood.

• Viscosity: Blood is highly viscous (thicker than water).

• pH: Blood is slightly alkaline, with a pH range of 7.35–7.45.

Blood Volume

• Blood volume is approximately 7% of body weight (in kilograms).

• Adult male: 5–6 liters

• Adult female: 4–5 liters

Plasma

Composition of Plasma

Plasma makes up 50–60% of blood volume and is more than 90% water. It is part of the body's extracellular fluids, along with interstitial fluid (IF). Materials such as water, ions, and small solutes are exchanged between plasma and IF across capillary walls.

Plasma Proteins

• Albumins (60%): Responsible for osmotic pressure and transport of substances such as fatty acids, thyroid hormones, and steroid hormones.

• Globulins (35%): Include antibodies (immunoglobulins) and transport globulins for small molecules (e.g., hormone-binding proteins, metalloproteins, apolipoproteins, and steroid-binding proteins).

• Fibrinogen (4%): Functions in clotting by forming insoluble fibrin strands.

Plasma Protein	Percentage of Plasma Proteins	Main Function
Albumins	60%	Osmotic pressure, transport of substances
Globulins	35%	Immunity (antibodies), transport of small molecules
Fibrinogen	4%	Clotting (forms fibrin)

Other solutes in plasma include electrolytes, nutrients, and waste products.

Exchange Between Plasma and Interstitial Fluid

• Water, ions, and small solutes are exchanged across capillary walls between plasma and interstitial fluid, maintaining fluid and electrolyte balance.

Summary Table: Major Components of Blood

Component	Percentage of Whole Blood	Key Functions
Plasma	~55%	Transport of nutrients, hormones, proteins, and waste products
Red Blood Cells	~45%	Oxygen and carbon dioxide transport
White Blood Cells	<0.1%	Immune defense
Platelets	<0.1%	Blood clotting

Example: In a clinical setting, blood is often separated (fractionated) into plasma and formed elements to analyze specific components, such as in blood typing or measuring hemoglobin levels.

Additional info: The plasma proteins are primarily synthesized in the liver, except for antibodies (produced by plasma cells) and peptide hormones (produced by endocrine organs).