Name the different constituents of blood and write about their functions.

Constituents of Blood and Their Functions

Blood is broadly composed of a liquid matrix called plasma, and several types of formed elements suspended within it. These formed elements include red blood cells, white blood cells, and platelets.

1. Plasma

Plasma is the yellowish, liquid component of blood, making up approximately 55% of the total blood volume. It is primarily composed of water (about 90-92%), with the remaining percentage consisting of dissolved proteins, mineral salts, hormones, nutrients (glucose, amino acids, lipids), waste products, and gases.

Functions of Plasma:

• Transportation: Plasma serves as the medium for transporting blood cells, nutrients (e.g., glucose, amino acids), hormones, enzymes, and metabolic waste products (e.g., urea, carbon dioxide) throughout the body.
• Maintaining Osmotic Balance: Plasma proteins, particularly albumin, are crucial in maintaining the blood's osmotic pressure, which helps regulate fluid balance between the blood and body tissues, preventing fluid leakage.
• Immunity: It contains antibodies (immunoglobulins) and other proteins that play a vital role in the body's defense mechanisms against infections.
• Blood Coagulation: Plasma carries essential clotting factors like fibrinogen, globulins, and prothrombin in an inactive form, which are crucial for hemostasis and preventing excessive blood loss.
• pH and Temperature Regulation: Plasma components act as buffers to maintain the body's pH within a normal range (7.35-7.45) and help regulate body temperature by distributing heat.

2. Red Blood Cells (Erythrocytes)

Red blood cells (RBCs) are the most abundant cells in the blood, accounting for about 40-45% of its volume. They are biconcave, anucleated (lacking a nucleus in mature mammalian cells) disks that are produced in the bone marrow and have an average lifespan of about 120 days. Their characteristic red color comes from the iron-containing protein hemoglobin.

Functions of Red Blood Cells:

• Oxygen Transport: The primary function of RBCs is to transport oxygen from the lungs to various tissues and organs throughout the body. Hemoglobin reversibly binds with oxygen in the lungs to form oxyhemoglobin and releases it in oxygen-deprived tissues.
• Carbon Dioxide Transport: RBCs also play a significant role in transporting carbon dioxide, a waste product, from the tissues back to the lungs for exhalation. Some carbon dioxide binds directly to hemoglobin, while a larger portion is converted into bicarbonate ions within the RBCs and transported in the plasma.
• Maintaining Blood pH: Hemoglobin acts as a buffer, contributing to the regulation of blood pH.

3. White Blood Cells (Leukocytes)

White blood cells (WBCs) are larger than RBCs, nucleated, and significantly fewer in number, making up less than 1% of the blood's volume. They are crucial components of the body's immune system, defending against infections and diseases. WBCs are broadly classified into granulocytes and agranulocytes.

Types and Functions of White Blood Cells:

• Granulocytes: Characterized by granular cytoplasm.
  • Neutrophils: The most abundant WBCs (60-70%), they are phagocytic cells that engulf and destroy bacteria, fungi, and foreign debris, acting as the first line of defense against infection.
  • Eosinophils: (2-4% of WBCs) Involved in allergic reactions, combating parasitic infections, and modulating inflammatory responses.
  • Basophils: (0.5-1% of WBCs) Release histamine and heparin during allergic reactions and inflammation, playing a role in immune responses and preventing blood clots.
• Agranulocytes: Lacking cytoplasmic granules.
  • Lymphocytes: (20-25% of WBCs) Key players in adaptive immunity. B lymphocytes produce antibodies, while T lymphocytes directly attack infected cells and regulate immune responses.
  • Monocytes: (6-8% of WBCs) These are large phagocytic cells that differentiate into macrophages in tissues, engulfing pathogens, cellular debris, and presenting antigens to lymphocytes, initiating further immune responses.

4. Platelets (Thrombocytes)

Platelets are small, irregular, anucleated cell fragments produced from megakaryocytes in the bone marrow. They have a lifespan of about 8-10 days and are critical for hemostasis, the process of stopping bleeding.

Functions of Platelets:

• Blood Clotting (Coagulation): Platelets aggregate at the site of injury to form a temporary plug, sealing the damaged blood vessel. They also release clotting factors that initiate the coagulation cascade, leading to the formation of a stable fibrin clot, which prevents further blood loss.
• Wound Healing: Beyond clotting, platelets also release growth factors that promote tissue repair and regeneration at the site of injury.

Blood Constituent	Approximate Percentage of Blood Volume	Key Functions
Plasma	55%	Transport of nutrients, hormones, waste; osmotic balance; immunity; coagulation; pH and temperature regulation.
Red Blood Cells (RBCs)	40-45%	Oxygen transport (via hemoglobin); carbon dioxide transport; blood pH regulation.
White Blood Cells (WBCs)	<1%	Immune defense against pathogens, allergic reactions, inflammation, specific immunity.
Platelets	<1%	Blood clotting (hemostasis); wound healing.