Blood: Structure, Function, and Composition

Blood: Overview and Functions

Role in the Cardiovascular System

Blood is a vital fluid connective tissue that serves as the primary transport medium within the cardiovascular system. It is essential for maintaining homeostasis and supporting cellular activities throughout the body.

• Transport of Gases: Blood carries oxygen (O2) from the lungs to tissues and removes carbon dioxide (CO2) from tissues to the lungs.

• Transport of Nutrients and Waste: Delivers nutrients and other substances to cells, and removes metabolic waste products.

• Hormone Distribution: Transports hormones from endocrine glands to target organs.

Regulatory Functions

Blood plays a crucial role in regulating several physiological parameters to maintain internal stability.

• pH Regulation: Blood buffers maintain the pH of body fluids between 7.35–7.45.

• Osmotic Pressure: Plasma proteins and other solutes help regulate osmotic pressure, ensuring adequate fluid volume in tissues.

• Temperature Regulation: Blood transports heat generated in muscles, aiding in the regulation of body temperature.

Protective Functions

Blood contains components that protect the body from blood loss and infection.

• Immune Defense: White blood cells (leukocytes) and antibodies defend against pathogens.

• Hemostasis: Platelets and clotting factors prevent excessive blood loss following injury.

Physical Characteristics of Blood

General Properties

Blood is a unique tissue with distinct physical and chemical properties.

• Appearance: Sticky, opaque fluid with a metallic taste.

• Color: Varies with oxygen content—scarlet red when oxygen-rich, dark red when oxygen-poor.

• pH: Maintained between 7.35–7.45.

• Volume: Accounts for approximately 8% of body weight. Average volume is 5–6 L in males and 4–5 L in females.

Blood Composition

Components of Blood

Blood is classified as a fluid connective tissue, consisting of a non-living matrix (plasma) and living cells (formed elements).

• Plasma: The liquid, non-cellular portion, making up about 55% of blood volume.

• Formed Elements: The cellular components, comprising about 45% of blood volume.

Serum is plasma minus the clotting proteins.

Detailed Blood Composition

Component	Percentage	Main Constituents
Plasma	55%	Water (91%), Proteins (8%), Other solutes (1%)
Formed Elements	45%	Erythrocytes (99.1%), Leukocytes & Platelets (0.9%)

Plasma

Properties and Composition

Plasma is a straw-colored, sticky fluid that serves as the medium for transporting dissolved substances.

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

• Dissolved Solutes: Includes nutrients, gases, hormones, metabolic wastes, proteins, and inorganic ions.

• Plasma Proteins: Most abundant solutes; albumin makes up 60% of plasma proteins and functions as a carrier, blood buffer, and contributor to osmotic pressure.

Formed Elements

Types of Formed Elements

The formed elements are the living cells and cell fragments suspended in plasma, each with specialized functions.

• Erythrocytes (RBC): Red blood cells responsible for oxygen and carbon dioxide transport.

• Leukocytes (WBC): White blood cells involved in immune defense.

• Platelets: Cell fragments essential for blood clotting.

Example: Centrifugation of a blood sample separates plasma, the buffy coat (leukocytes and platelets), and erythrocytes, illustrating the relative proportions of each component.

Additional info: The notes above provide foundational knowledge for understanding blood's role in anatomy and physiology, including its transport, regulatory, and protective functions, as well as its physical and chemical composition. These concepts are essential for further study of hematology, cardiovascular physiology, and clinical applications such as transfusion medicine.