Skip to main content
Back

Blood: Components, Formed Elements, and Functions

NotesPracticeVideo lessons

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Blood: Components and Functions

Overview of Blood

Blood is a specialized connective tissue that plays a vital role in transporting substances, regulating physiological processes, and protecting the body. It consists of cellular elements suspended in a liquid matrix called plasma.

  • Cellular components: Erythrocytes (red blood cells), leukocytes (white blood cells), and thrombocytes (platelets).

  • Plasma: The fluid portion of blood, making up about 55% of total blood volume.

Composition of Blood

Formed Elements

The formed elements of blood are the cellular components responsible for various functions such as oxygen transport, immune defense, and clotting.

  • Erythrocytes (RBCs): Transport oxygen and carbon dioxide.

  • Leukocytes (WBCs): Defend against pathogens and foreign substances.

  • Thrombocytes (Platelets): Play a key role in blood clotting.

Plasma

Plasma is a pale yellow, sticky fluid that serves as the medium for transporting nutrients, hormones, and waste products.

  • Water: Comprises about 90% of plasma, serving as a solvent and temperature buffer.

  • Electrolytes: Includes Na+, K+, Ca2+, Mg2+, Cl-, HCO3-.

  • Proteins:

    • Albumin: Most abundant plasma protein; maintains osmotic pressure and prevents water loss from blood vessels.

    • Globulins: Includes antibodies and transport proteins for lipids, iron, and copper.

    • Fibrinogen: Essential for blood clotting; involved in chemical reactions forming fibrin threads.

  • Other solutes: Nutrients (glucose, amino acids, lipids), gases (O2, CO2), metabolic wastes (urea, ammonia).

Hematocrit and Blood Separation

Hematocrit

Hematocrit is the percentage of blood volume occupied by red blood cells. It is a key indicator of oxygen-carrying capacity.

  • Normal values: Males: 47% ± 5%; Females: 42% ± 5%

  • Buffy coat: Thin white layer between plasma and RBCs after centrifugation, containing WBCs and platelets.

Blood Separation Process

  1. Blood is withdrawn and placed in a tube.

  2. Tube is centrifuged to separate components by density.

  3. Layers form: plasma (top), buffy coat (middle), erythrocytes (bottom).

Layer

Composition

Relative Density

Plasma

Water, proteins, solutes

Least dense

Buffy coat

Leukocytes, platelets

Intermediate

Erythrocytes

Red blood cells

Most dense

Red Blood Cells (Erythrocytes)

Structure and Function

Red blood cells are biconcave, anucleate cells specialized for oxygen transport.

  • Abundance: 4.8–5.2 million cells per cubic millimeter of blood.

  • No organelles or nuclei: Maximizes space for hemoglobin.

  • Hemoglobin: Oxygen-carrying protein; each molecule has four subunits, each with a heme group containing iron.

  • Oxygen binding: Iron in heme serves as the binding site for O2.

Equation for oxygen transport:

White Blood Cells (Leukocytes)

Types and Functions

White blood cells are crucial for immune defense and are classified into two main groups: granulocytes and agranulocytes.

  • Normal count: 4,800–10,800 cells per microliter.

  • Function: Protect the body from infectious agents and foreign substances.

  • Migration: Can leave the bloodstream to enter tissues.

Classification of Leukocytes

Group

Type

Features

Function

Granulocytes

Neutrophils

Multilobed nucleus, pale granules

Phagocytosis of bacteria

Granulocytes

Eosinophils

Bilobed nucleus, red granules

Combat parasitic infections, modulate allergic responses

Granulocytes

Basophils

Bilobed nucleus, purplish-black granules

Release histamine, mediate inflammation

Agranulocytes

Lymphocytes

Large spherical nucleus

Adaptive immunity, antibody production

Agranulocytes

Monocytes

Kidney-shaped nucleus

Differentiate into macrophages, phagocytosis

Mnemonic for abundance: "Never Let Monkeys Eat Bananas" (Neutrophils > Lymphocytes > Monocytes > Eosinophils > Basophils)

Platelets (Thrombocytes)

Structure and Function

Platelets are small, anucleate cell fragments derived from megakaryocytes. They are essential for blood clotting and wound repair.

  • Function: Form temporary plugs in damaged vessels and release factors for clot formation.

Formation of Blood Cells (Hematopoiesis)

Process and Sites

Hematopoiesis is the process by which blood cells are formed from stem cells in red bone marrow.

  • Stem cell: Hemopoietic blood stem cell.

  • Progenitor lines:

    • Lymphoid stem cells: Give rise to lymphocytes.

    • Myeloid stem cells: Give rise to all other blood cells (RBCs, platelets, granulocytes, monocytes).

Clinical Considerations

Blood Disorders

  • Polycythemia: Excess erythrocytes; increases blood viscosity.

  • Anemia: Low RBC count or hemoglobin; reduces oxygen delivery.

  • Sickle cell anemia: Genetic disorder causing abnormal hemoglobin and RBC shape.

  • Leukemia: Cancer of WBCs; abnormal proliferation of leukocytes.

  • Thrombocytopenia: Low platelet count; increases risk of bleeding.

Example: In anemia, the hematocrit is below normal, leading to fatigue and weakness due to reduced oxygen transport.

Additional info: The notes infer standard values and functions for blood components based on typical Anatomy & Physiology curriculum.

Pearson Logo

Study Prep