Blood: Structure, Function, and Disorders – Anatomy & Physiology Study Notes

Blood: Structure, Function, and Disorders

Functions of Blood

Blood is a vital connective tissue that performs several essential functions in the human body. Its roles can be categorized into three main areas:

• Transport: Blood transports oxygen, nutrients, metabolic waste products, and hormones throughout the body.

• Regulation: Blood helps maintain homeostasis by regulating heat, pH, and fluid volume.

• Protection: Blood contributes to hemostasis (prevention of blood loss) and protects against infection through immune responses.

Physical Characteristics of Blood

The physical properties of blood are influenced by its oxygenation level and composition.

• Color: Oxygen-rich blood is scarlet red, while oxygen-poor blood is dark red.

• Volume: Average blood volume is 5-6 liters in males and 4-5 liters in females.

• pH: Blood is slightly alkaline, with a pH range of 7.35 – 7.45.

Composition of Blood

Blood consists of two main components: plasma and formed elements. The formed elements are further divided into erythrocytes, leukocytes, and platelets.

• Plasma: The liquid matrix of blood, making up about 55% of total blood volume.

• Buffy Coat: A thin layer containing leukocytes (white blood cells) and platelets, found between plasma and erythrocytes after centrifugation.

• Erythrocytes: Red blood cells, which make up the majority of the formed elements.

Plasma: Composition and Functions

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

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

• Dissolved Solutes: Includes nutrients, hormones, gases (O2 and CO2), electrolytes, and proteins.

• Proteins: The main plasma protein is albumin, which maintains osmotic balance between blood and interstitial fluid.

Osmotic Pressure: Refers to the "pulling" pressure exerted by plasma proteins (mainly albumin) to draw water into the blood vessels, maintaining fluid balance.

• Osmosis: The movement of water molecules from an area of lower solute concentration to an area of higher solute concentration across a semipermeable membrane.

Example: If blood has more solutes than surrounding tissue, water moves into the blood vessel to achieve balance.

Formed Elements of Blood

The formed elements are cellular components suspended in plasma. They include erythrocytes, leukocytes, and platelets.

• Erythrocytes (Red Blood Cells): Specialized for oxygen and carbon dioxide transport.

• Leukocytes (White Blood Cells): Involved in immune defense and response.

• Platelets: Cell fragments essential for blood clotting.

Key Plasma Components and Their Functions

Component	Main Function
Water	Solvent, temperature regulation
Electrolytes	Osmotic balance, membrane permeability
Gases (O2, CO2)	Respiratory gas transport
Proteins (Albumin)	Osmotic pressure maintenance
Hormones	Regulation of physiological processes

Additional info:

• Blood is classified as a connective tissue due to its origin from mesenchyme and its function in connecting body systems.

• Albumin is the most abundant plasma protein and is crucial for maintaining blood volume and pressure.

• Plasma also contains clotting factors, antibodies, and waste products.