Blood and the Cardiovascular System

Overview of the Cardiovascular System

The cardiovascular system is essential for transporting substances throughout the body and maintaining homeostasis. It consists of three main components:

• The heart: A muscular pump that propels blood.

• Blood vessels: A series of conducting hoses that distribute blood.

• Blood: A fluid connective tissue that serves as the transport medium.

Components and Functions of Blood

Definition and General Properties

Blood is a specialized connective tissue composed of cells suspended in a fluid matrix called plasma. It performs several vital functions:

• Transport: Dissolved gases (O2, CO2), nutrients, hormones, and metabolic wastes.

• Regulation: pH and ion composition of interstitial fluids.

• Restriction: Limits fluid loss at injury sites.

• Defense: Protects against toxins and pathogens.

• Stabilization: Maintains body temperature.

Physical Characteristics of Blood

• Temperature: 38°C (100.4°F)

• Viscosity: High, due to cellular and protein content.

• pH: Slightly alkaline, ranging from 7.35 to 7.45.

• Volume: Approximately 7% of body weight in liters. For a 75-kg (165-lb) person, this is about 5.4 liters (5.4 quarts).

Composition of Whole Blood

Whole blood consists of two main components:

• Plasma: The fluid portion.

• Formed elements: Cells and cell fragments.

Fractionation is the process of separating whole blood into plasma and formed elements for analysis or medical use.

Plasma

Plasma makes up about 55% of blood volume and is primarily water (over 90%). It also contains dissolved plasma proteins and other solutes. Plasma is similar in composition to interstitial fluid because water, ions, and small solutes are exchanged across capillary walls.

Table: Composition of Whole Blood

Plasma Proteins

Plasma proteins are crucial for maintaining osmotic pressure, transporting substances, and immune defense. The major types include:

• Albumins (60%): Major contributors to plasma osmolarity; transport fatty acids, thyroid hormones, and some steroid hormones.

• Globulins (35%): Include antibodies (immunoglobulins) for immune defense and transport globulins (hormone-binding proteins, metalloproteins, apolipoproteins, and steroid-binding proteins).

• Fibrinogen (4%): Soluble protein involved in blood clotting; converted to insoluble fibrin during clot formation.

• Other plasma proteins (1%): Enzymes, hormones, and other regulatory proteins.

Origins of Plasma Proteins

• More than 90% are synthesized in the liver (albumins, fibrinogen, most globulins, and proenzymes).

• Antibodies are produced by plasma cells.

• Peptide hormones are made by endocrine organs.

Formed Elements

The formed elements of blood include:

• Red blood cells (erythrocytes): Transport oxygen and carbon dioxide.

• White blood cells (leukocytes): Defend against pathogens.

• Platelets (thrombocytes): Cell fragments involved in clotting.

Hemopoiesis is the process of producing formed elements, primarily occurring in red bone marrow.

Example:

A blood sample from a healthy adult typically separates into plasma (top layer, pale yellow) and formed elements (bottom layer, red), with a thin "buffy coat" of white blood cells and platelets in between.

Additional info: Plasma proteins play a key role in maintaining blood volume and pressure, and their concentrations can change in response to disease or dehydration.