Blood: Structure, Composition, and Function (Chapter 19 Study Notes)

Chapter 19: Blood

Introduction to Blood

Blood is a specialized connective tissue that plays a vital role in the transport of substances, regulation of physiological processes, and protection against disease. It consists of cellular elements suspended in a liquid extracellular matrix called plasma.

• Functions of Blood: Transport of gases, nutrients, wastes, hormones; regulation of pH, temperature, and fluid balance; protection via immune responses and clotting.

• Main Components: Plasma (liquid matrix) and formed elements (cells and cell fragments).

The Three Visible Layers of Blood

Blood Composition and Centrifugation

When a blood sample is centrifuged, it separates into three distinct layers based on density:

• Plasma: The top, pale yellow layer; makes up about 55% of blood volume. Contains water, proteins, nutrients, hormones, and waste products.

• Buffy Coat: The thin, middle layer; less than 1% of blood volume. Contains leukocytes (white blood cells) and platelets.

• Erythrocytes: The bottom, red layer; about 44% of blood volume. Composed of red blood cells (RBCs).

Example: In a centrifuged tube, the plasma is on top, the buffy coat is a thin white layer in the middle, and erythrocytes settle at the bottom.

Plasma: Components and Functions

Major Plasma Components

Plasma is the liquid portion of blood, making up about 55% of its total volume. It serves as a transport medium for many substances.

Plasma Component	Function
Water	90% of plasma volume; solvent that dissolves and transports many solutes through the body
Plasma Proteins (9%)	Multiple functions (see below)
Albumin	Maintains osmotic pressure
Immune proteins	Produced by leukocytes; function in immunity
Transport proteins	Bind and transport hydrophobic compounds through the blood
Clotting proteins	Stop blood loss from damaged vessels
Other Solutes (1%)	Multiple functions (see below)
Glucose, amino acids	Nutrition; used for protein synthesis
Ions	Electrolyte and acid-base homeostasis
Dissolved gases (O2, CO2)	Oxygen delivered to tissues; carbon dioxide delivered to lungs for exhalation
Wastes	Delivered to the appropriate organ for excretion

• Albumin: The most abundant plasma protein; helps maintain blood osmotic pressure, which is essential for fluid balance between blood and tissues.

• Immune Proteins (Globulins): Include antibodies that help defend the body against pathogens.

• Transport Proteins: Carry hydrophobic molecules (e.g., hormones, lipids) that cannot dissolve in plasma water.

• Clotting Proteins (e.g., Fibrinogen): Essential for blood coagulation to prevent excessive bleeding.

• Electrolytes: Such as sodium, potassium, and calcium ions, are crucial for nerve and muscle function and maintaining acid-base balance.

Additional info: Plasma also contains hormones, vitamins, and metabolic waste products such as urea and creatinine.