Blood and the Cardiovascular System

Functions of the Blood

The blood is a vital connective tissue responsible for multiple essential functions in the human body. It serves as the main transport medium and plays a key role in maintaining physiological balance.

• Transport: Blood carries oxygen (O2), carbon dioxide (CO2), nutrients, water, minerals, hormones, antibodies, defense cells, and waste products throughout the body.

• Thermoregulation: Blood helps regulate body temperature by distributing heat.

• Homeostasis: Maintains the stability of the internal environment, including pH and osmotic balance.

• Defense: Blood contains immune cells and antibodies that protect against pathogens.

• Haemostasis: Blood is involved in the prevention of blood loss through clotting mechanisms.

Blood Composition

Physical and Chemical Properties

Blood constitutes approximately 7-8% of total body weight. It can be separated into cellular components and fluid (plasma).

• Cellular Components: Includes red blood cells, white blood cells, and platelets.

• Plasma: The liquid portion of blood, which can be further divided into serum (plasma without fibrinogen) and fibrinogen (a key clotting protein).

• Haematocrit: The percentage of blood volume occupied by cells. Normal values: 39-50% in men, 35-45% in women.

Composition of Blood Plasma

Blood plasma is a complex solution containing electrolytes, proteins, and other solutes. The following table summarizes its main components:

Key Terms: Albumin is the most abundant plasma protein, maintaining osmotic pressure; globulins include antibodies; fibrinogen is essential for blood clotting.

Blood Cells

Classification and Numbers

Blood contains three main types of cells, each with distinct functions and normal concentration ranges:

• Red Blood Cells (Erythrocytes): 4.5 – 5 million/μl. Responsible for oxygen and carbon dioxide transport.

• White Blood Cells (Leucocytes): 4,000 – 11,000/μl. Involved in immune defense. Subdivided into:

  • Granulocytes: 50-75% of WBCs. Includes neutrophils, eosinophils, and basophils.

  • Lymphocytes: 25-35% of WBCs. Includes B cells, T cells, and natural killer cells.

  • Monocytes: 4-10% of WBCs. Precursors to macrophages.

• Thrombocytes (Platelets): 150,000 – 400,000/μl. Essential for blood clotting (haemostasis).

Example: Blood Cell Classification Table

Additional info:

• Haematocrit is calculated as:

• Blood plasma proteins are crucial for maintaining osmotic pressure, immune responses, and coagulation.

• Granulocytes are further classified based on staining properties: neutrophils (neutral), eosinophils (acidic), and basophils (basic).