Study Notes: Blood (Anatomy & Physiology, Chapter 19)

Chapter 19: Blood

Introduction to 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 plasma and formed elements, including erythrocytes, leukocytes, and platelets.

• Blood Volume: Average adult blood volume is about 5 liters.

• Main Functions: Transport of gases, nutrients, hormones, and waste; regulation of pH and temperature; protection against pathogens and blood loss.

The Three Visible Layers of Blood

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

• Plasma: The top, pale yellow layer, making up about 55% of blood volume. It is the liquid component containing water, proteins, and solutes.

• Buffy Coat: The thin, middle layer (about 1%), consisting of leukocytes (white blood cells) and platelets.

• Erythrocytes: The bottom, red layer (about 44%), composed of red blood cells.

Example: In a centrifuged blood sample, plasma is at the top, buffy coat in the middle, and erythrocytes at the bottom.

Plasma Components and Functions

Plasma is the fluid matrix of blood, containing water, proteins, and various solutes. Each component has specific functions essential for homeostasis.

Plasma Component	Function
Water	90% of plasma volume; solvent that dissolves and transports many solutes through the body
Plasma Proteins	9% of plasma volume; multiple functions
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% of plasma volume; multiple functions
Glucose, amino acids	Nutrition; used for protein synthesis
Ions	Electrolyte and acid-base homeostasis
Dissolved gases (small amounts of oxygen and carbon dioxide)	Oxygen delivered to the tissues; carbon dioxide delivered to the lungs to be exhaled
Wastes	Delivered to the appropriate organ for excretion

• Key Term: Osmotic pressure is the force that helps maintain water balance between blood and tissues.

• Key Term: Electrolyte homeostasis is crucial for nerve and muscle function.

Example: Albumin prevents excessive fluid loss from blood vessels into surrounding tissues.

Formed Elements of Blood

The formed elements are the cellular components of blood, each with specialized functions.

• Erythrocytes (Red Blood Cells): Most numerous; transport oxygen and carbon dioxide.

• Leukocytes (White Blood Cells): Defend against pathogens and mediate immune responses.

• Platelets: Cell fragments involved in blood clotting.

Additional info: Erythrocytes contain hemoglobin, a protein that binds oxygen. Leukocytes are classified into granulocytes and agranulocytes based on the presence of granules in their cytoplasm.

Summary

• Blood is composed of plasma and formed elements, each with distinct roles in transport, regulation, and protection.

• Plasma contains water, proteins, and solutes essential for homeostasis.

• Formed elements include erythrocytes, leukocytes, and platelets, each contributing to the overall function of blood.