Cardiovascular System: The Blood

Overview of Blood Components

The blood is a vital fluid connective tissue that plays a central role in the cardiovascular system. It consists of several types of cells and cell fragments suspended in plasma, each with specialized functions.

• Erythrocytes (Red Blood Cells): Responsible for oxygen transport.

• Leukocytes (White Blood Cells): Involved in immune defense.

• Platelets (Thrombocytes): Essential for blood clotting.

Example: A micrograph of blood shows erythrocytes as biconcave discs, platelets as small fragments, and leukocytes as larger nucleated cells.

Fluids of the Body

Blood and Interstitial Fluid

All body cells are serviced by two main fluids: blood and interstitial fluid. These fluids are essential for the transport of nutrients, gases, and wastes.

• Blood:

  • Composed of plasma (liquid matrix) and a variety of cells.

  • Transports nutrients, gases, hormones, and metabolic wastes.

• Interstitial Fluid:

  • Bathes and surrounds the body’s cells.

  • Acts as a medium for exchange between blood and cells.

• Nutrients and oxygen diffuse from blood → interstitial fluid → cells.

• Wastes move in the reverse direction.

Definition: Hematology is the study of blood and blood disorders.

Functions of Blood

Major Functions

Blood performs several critical functions necessary for homeostasis and survival.

• Transportation:

  • Transports oxygen (O2), carbon dioxide (CO2), metabolic wastes, nutrients, heat, and hormones throughout the body.

• Regulation:

  • Helps regulate pH through buffers.

  • Regulates body temperature via the coolant properties of water and vasodilation of surface vessels to release heat.

  • Maintains water content of cells by interacting with dissolved ions and proteins.

• Protection:

  • Protects against disease (immune response) and prevents loss of blood through clotting mechanisms.

Physical Characteristics of Blood

Properties and Volume

Blood has unique physical and chemical properties that distinguish it from other body fluids.

• Viscosity: Blood is thicker (more viscous) than water and flows more slowly.

• Temperature: Average temperature is 100.4°F (38°C).

• pH: Slightly alkaline, with a normal range of 7.35–7.45 (average 7.4).

• Body Weight: Blood constitutes about 8% of total body weight.

• Blood Volume:

  • Average male: 5 to 6 liters

  • Average female: 4 to 5 liters

• Homeostasis: Hormonal negative feedback systems maintain constant blood volume and osmotic pressure.

Additional info: The viscosity of blood is primarily due to the presence of formed elements (cells) and plasma proteins, which are much higher in concentration than in water.