Blood: Structure, Function, and Components (Anatomy & Physiology Chapter 16 Study Notes)

Blood: Structure, Function, and Components

Overview of Blood

Blood is a specialized connective tissue essential for the transport of substances, regulation of physiological parameters, and protection against disease. It consists of a fluid matrix called plasma and various formed elements including erythrocytes, leukocytes, and platelets.

• Plasma: The liquid component of blood, making up about 55% of its volume.

• Formed Elements: Cellular components suspended in plasma, including:

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

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

  • Platelets: Cell fragments crucial for blood clotting (hemostasis).

Main Functions of Blood

Blood performs several vital functions in the body, grouped into three main categories: transport, regulation, and protection.

• Transport:

  • Delivers hormones, oxygen (O2), and nutrients to tissues.

  • Removes metabolic wastes (e.g., carbon dioxide, urea) to lungs and kidneys for excretion.

• Regulation:

  • Maintains body temperature by distributing heat.

  • Regulates pH through buffers dissolved in plasma.

  • Controls fluid volume, thus influencing blood pressure.

• Protection:

  • Participates in immune responses via leukocytes.

  • Prevents blood loss through clotting mechanisms (hemostasis).

Blood Structure and Composition

Blood is composed of plasma and formed elements, each with distinct roles and characteristics.

• Plasma: Fluid matrix containing water, proteins (e.g., albumin, globulins, fibrinogen), electrolytes, nutrients, hormones, and waste products.

• Formed Elements:

  • Erythrocytes (RBCs): Biconcave, anucleate cells specialized for gas transport.

  • Leukocytes (WBCs): Nucleated cells involved in defense and immunity.

  • Platelets: Small, anucleate cell fragments derived from megakaryocytes, essential for clot formation.

Key Blood Topics

Understanding blood involves studying its functions, components, and clinical relevance.

• Life Cycle of Erythrocytes: Includes production (erythropoiesis), lifespan, and destruction.

• Leukocyte Types and Life Cycles: Classification and roles in immunity.

• Platelets and Hemostasis: Mechanisms of clot formation and prevention of blood loss.

• Health Applications:

  • Blood typing for transfusions (ABO and Rh systems).

  • Normal values for blood components (e.g., hematocrit, hemoglobin concentration).

Example: Blood Separation by Centrifugation

When blood is centrifuged, it separates into three layers:

• Plasma: Top layer (~55% of blood volume).

• Buffy Coat: Middle thin layer (

  • Erythrocytes: Bottom layer (~45%), most dense component.

Additional info:

• Hematocrit: The percentage of blood volume occupied by erythrocytes. Normal values: males ~47%, females ~42%.

• Hemoglobin: The oxygen-carrying protein in RBCs. Normal concentration: males 13-18 g/100 mL, females 12-16 g/100 mL.

• Blood pH: Maintained between 7.35 and 7.45.