Cardiovascular System: Structure, Function, and Blood Composition

Unit 1: Cardiovascular System

Overview of the Cardiovascular System

The cardiovascular system is a closed circulatory system responsible for transporting blood throughout the body. It consists of the heart, blood vessels (arteries, veins, capillaries), and blood. This system works in direct coordination with all other body systems to maintain homeostasis and support physiological functions.

• Closed Circulatory System: Blood is contained within vessels and circulates unidirectionally from the heart, through the vessels, and back to the heart.

• Main Components: Heart, vessels (arteries, veins, capillaries), and blood.

• Integration: Works directly with respiratory, digestive, endocrine, and other systems.

Functions of the Cardiovascular System

Transport and Homeostasis

The cardiovascular system performs essential functions through the movement of blood:

• Transport:

  • Gases: Oxygen (O2) and carbon dioxide (CO2).

  • Nutrients and Wastes: Delivers nutrients to tissues and removes metabolic wastes.

  • Hormones and Immunity: Distributes hormones and immune cells throughout the body.

• Homeostasis:

  • Regulates body temperature, pH, blood pressure, and tissue fluid composition.

  • Maintains stable internal conditions necessary for cellular function.

The Blood: Composition and Function

Blood as a Connective Tissue

Blood is a specialized connective tissue composed of formed elements (cells and cell fragments) suspended in plasma (liquid matrix). It constitutes approximately 8% of total body weight.

• Whole Blood = Formed Elements + Plasma

• Volume: ~8% of body weight

Blood Composition in Detail

Blood is divided into two main components:

• Formed Elements (45%):

  • Red Blood Cells (Erythrocytes): Transport oxygen and carbon dioxide.

  • White Blood Cells (Leukocytes): Immune defense.

  • Platelets (Thrombocytes): Blood clotting.

• Plasma (55%):

  • Water (92%): Solvent for carrying other substances.

  • Proteins (7%): Albumins, globulins, fibrinogen (for osmotic balance, transport, and clotting).

  • Other Solutes (1%): Electrolytes, nutrients, gases, hormones, wastes.

Hematocrit (PCV) Measurement

Hematocrit (Packed Cell Volume, PCV) is the percentage of red blood cells in whole blood. It is measured by centrifuging blood in a capillary tube:

• Formula: $\text{PCV} = \left(\frac{C}{A}\right) \times 100$

• Typical Values:

  • Plasma: 55%

  • Buffy coat (leukocytes and platelets): <1%

  • Red cells: 45% (hematocrit)

Blood Composition Table

The following table summarizes the main components of blood and their functions:

Component	Percentage	Main Function
Red Blood Cells (Erythrocytes)	~95% of formed elements	Transport O2 and CO2
White Blood Cells (Leukocytes)	<1% of formed elements	Immune defense
Platelets (Thrombocytes)	<1% of formed elements	Blood clotting
Plasma	55% of whole blood	Transport of nutrients, wastes, hormones, and proteins

Plasma Proteins

• Albumins (60%): Maintain osmotic pressure.

• Globulins (36%): Transport lipids, fat-soluble vitamins, and function as antibodies.

• Fibrinogen (4%): Key role in blood coagulation (clotting).

Example: Clinical Application

Measuring hematocrit is important in diagnosing anemia (low RBC count) or polycythemia (high RBC count). Plasma protein levels are assessed in cases of liver disease or malnutrition.

Additional info: The notes reference a blood table assignment, which is a common exercise to reinforce understanding of blood composition and function. Students are encouraged to use multiple resources (lecture notes, textbook, and PowerPoint slides) to complete this assignment.