Chapter 17: Blood – Structure, Function, and Components

Chapter 17: Blood

Introduction

Blood is a vital fluid connective tissue that plays a central role in the cardiovascular system. It is responsible for the transport of substances, regulation of physiological parameters, and protection against disease. Understanding the composition and function of blood is essential for the study of anatomy and physiology.

Components of the Cardiovascular System

Main Structures

• Heart: Muscular organ that pumps blood and maintains blood pressure throughout the body.

• Blood Vessels: Network of tubes that transport blood. Includes:

  • Arteries: Carry blood away from the heart.

  • Capillaries: Permit exchange of substances between blood and interstitial fluids.

  • Veins: Return blood to the heart.

• Blood: The fluid medium that circulates through the cardiovascular system.

Functions of Blood

Key Roles

• Transport: Carries dissolved gases (oxygen, carbon dioxide), nutrients, hormones, and metabolic wastes.

• Regulation: Maintains pH and ion composition of interstitial fluids.

• Restriction: Limits fluid losses at injury sites through clotting mechanisms.

• Defense: Protects against toxins and pathogens via immune cells and antibodies.

• Stabilization: Helps regulate and stabilize body temperature.

Composition of Blood

Overview

• Blood as Connective Tissue: Composed of plasma (liquid matrix) and formed elements (cells and cell fragments).

• Whole Blood: Blood with all components present.

• Plasma: Makes up about 55% of blood volume; primarily water, with dissolved proteins, nutrients, electrolytes, and wastes.

• Formed Elements: Make up about 45% of blood volume; include red blood cells (RBCs), white blood cells (WBCs), and platelets.

• Blood Volume: 5–6 liters (5.3–6.4 quarts) in males; 4–5 liters (4.2–5.3 quarts) in females.

Plasma Composition

• Water: ~92% of plasma; solvent for carrying other substances.

• Plasma Proteins: ~7% of plasma; include:

  • Albumins: ~60% of plasma proteins; maintain osmotic pressure.

  • Globulins: ~35%; include antibodies (immunoglobulins) and transport globulins.

  • Fibrinogen: ~4%; essential for blood clotting.

• Other Solutes: Electrolytes (Na+, K+, Ca2+, Mg2+, Cl-, HCO3-, HPO42-, SO42-), organic nutrients (lipids, carbohydrates, amino acids), and organic wastes (urea, uric acid, creatinine, bilirubin).

Formed Elements

• Red Blood Cells (Erythrocytes): ~99.9% of formed elements; responsible for oxygen transport.

• White Blood Cells (Leukocytes):

  • Platelets:

Summary Table: Composition of Whole Blood

Component	Percentage of Whole Blood	Main Function
Plasma	~55%	Transport of nutrients, wastes, proteins, hormones
Formed Elements	~45%	Oxygen transport, defense, clotting
Red Blood Cells	~99.9% of formed elements	Oxygen and carbon dioxide transport
White Blood Cells	Immune defense
Platelets	Blood clotting

Key Definitions

• Plasma: The liquid, cell-free part of blood that contains dissolved proteins, nutrients, and wastes.

• Formed Elements: The cellular components of blood, including erythrocytes, leukocytes, and platelets.

• Hematocrit: The percentage of whole blood volume contributed by formed elements (mainly RBCs); average is 45%.

Additional info:

• Plasma proteins are primarily synthesized in the liver.

• Blood volume and composition can vary with age, sex, and health status.