Blood: Anatomy and Physiology Study Notes

Blood – Internal Transport System

Overview of Blood Functions

Blood is a vital connective tissue that serves as the transport medium of the cardiovascular system. Understanding its anatomy and physiology is essential for clinical practice and patient care.

• Transport: Blood delivers oxygen (O2) and nutrients to body cells, removes metabolic wastes, and transports hormones.

• Regulation: Blood maintains body temperature, pH balance, and fluid volume.

• Protection: Blood prevents blood loss through clotting and protects against infection via immune agents.

Functions of Blood

Transport

Blood is responsible for the movement of essential substances throughout the body.

• Delivering O2 and nutrients: Supplies tissues with oxygen and nutrients required for metabolism.

• Removing metabolic wastes: Transports waste products to the lungs (for CO2 removal) and kidneys (for excretion).

• Hormone transport: Carries hormones from endocrine glands to target organs.

Regulation

Blood helps maintain homeostasis in the body.

• Body temperature: Absorbs and distributes heat throughout the body.

• pH balance: Uses buffers, such as the alkaline reserve of bicarbonate ions, to maintain normal pH (7.35–7.45).

• Fluid volume: Maintains adequate fluid volume in the circulatory system.

Protection

Blood provides defense mechanisms against blood loss and infection.

• Prevention of blood loss:

  • Plasma proteins and platelets initiate clot formation.

• Prevention of infection:

  • Blood carries agents of immunity, including antibodies, complement proteins, and white blood cells.

Composition of Blood

Blood as a Connective Tissue

Blood is the only fluid tissue in the body and is classified as a connective tissue. It consists of a nonliving fluid matrix called plasma and living blood cells known as formed elements.

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

• Formed elements:

  • Erythrocytes (red blood cells, RBCs)

  • Leukocytes (white blood cells, WBCs)

  • Platelets

Blood Separation and Hematocrit

When blood is centrifuged, it separates into three layers:

• Erythrocytes: Settle at the bottom (~45% of whole blood). The percentage of blood volume occupied by RBCs is called the hematocrit.

  • Normal hematocrit values: Males: 47% ± 5% Females: 42% ± 5%

• Buffy coat: Thin, whitish layer (

  • Plasma: Rises to the top (~55% of whole blood).

Major Components of Whole Blood

The following table summarizes the main components of whole blood after centrifugation:

Component	Percentage of Whole Blood	Description
Plasma	~55%	Least dense; contains water, proteins, nutrients, hormones, wastes
Buffy coat	<1%	Leukocytes and platelets; thin layer
Erythrocytes	~45%	Most dense; red blood cells (hematocrit)

Physical Characteristics and Volume of Blood

Physical Properties

Blood is a sticky, opaque fluid with a metallic taste. Its color varies depending on oxygen content:

• High O2 levels: Scarlet red color

• Low O2 levels: Dark red color

The pH of blood is tightly regulated between 7.35 and 7.45.

Blood Volume

Blood accounts for approximately 8% of total body weight.

• Average volume:

  • Males: 5–6 liters

  • Females: 4–5 liters

Key Terms and Concepts

• Plasma: The liquid matrix of blood, primarily water with dissolved solutes.

• Formed elements: The cellular components of blood (RBCs, WBCs, platelets).

• Hematocrit: The percentage of blood volume occupied by erythrocytes.

• Buffy coat: The layer containing leukocytes and platelets after centrifugation.

Example: Blood Centrifugation

When a blood sample is centrifuged, the components separate by density: erythrocytes settle at the bottom, the buffy coat forms a thin middle layer, and plasma remains at the top. This separation is used clinically to assess hematocrit and diagnose various blood disorders.

Additional info: Plasma proteins such as albumin, globulins, and fibrinogen play crucial roles in maintaining osmotic pressure, immune function, and clotting, respectively.