Cardiovascular System: Blood – Structure, Function, and Composition

Cardiovascular System: Blood

Overview

The blood is a vital component of the cardiovascular system, serving as a fluid connective tissue that performs essential functions in the human body. It is responsible for the transport of gases, nutrients, wastes, and hormones, as well as for regulation and protection mechanisms.

Blood Characteristics and Volume

Physical Properties

• Color: Blood color varies from bright red (high oxygen content) to dark red (low oxygen content).

• pH: Blood pH is tightly regulated between 7.35 and 7.45.

• Volume: Average blood volume is 5–6 liters in males and 4–5 liters in females, comprising about 8% of total body weight.

Functions of Blood

Distribution Functions

• Oxygen and Nutrient Delivery: Transports O2 and nutrients to body cells.

• Waste Removal: Transports CO2 to the lungs and metabolic wastes to the kidneys for elimination.

• Hormone Transport: Carries hormones from endocrine organs to target tissues.

Regulatory Functions

• Body Temperature: Maintains temperature by absorbing, distributing, and radiating heat.

• pH Balance: Maintains normal pH (~7.4) using buffers, including an alkaline reserve of bicarbonate ions.

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

Protective Functions

• Prevention of Blood Loss: Plasma proteins and platelets initiate clot formation.

• Immunity: Contains antibodies, complement proteins, and white blood cells (WBCs) to fight infection.

Blood Composition

Main Components

Blood is composed of two primary components:

• Plasma: The non-living, fluid matrix of blood.

• Formed Elements: The cellular components suspended in plasma, including:

  • Erythrocytes (Red Blood Cells, RBCs): Responsible for oxygen transport.

  • Leukocytes (White Blood Cells, WBCs): Involved in immune defense.

  • Platelets: Cell fragments essential for blood clotting.

Summary Table: Blood Components

Component	Description	Main Function
Plasma	Non-living fluid matrix (about 55% of blood volume)	Transports nutrients, hormones, and waste; maintains osmotic balance
Erythrocytes (RBCs)	Biconcave, anucleate cells	Transport oxygen and some carbon dioxide
Leukocytes (WBCs)	Nucleated cells	Defend against pathogens and foreign substances
Platelets	Cell fragments	Initiate blood clotting (hemostasis)

Key Terms

• Plasma: The liquid component of blood, containing water, proteins, electrolytes, and other solutes.

• Formed Elements: The cellular portion of blood, including erythrocytes, leukocytes, and platelets.

• Hemostasis: The process of stopping bleeding, involving vascular spasm, platelet plug formation, and coagulation.

Example

When a blood vessel is injured, platelets rapidly adhere to the site, forming a temporary plug. Plasma proteins then initiate a cascade of reactions that result in the formation of a stable blood clot, preventing further blood loss and allowing tissue repair to begin.

Additional info: These notes provide a foundational overview of blood's structure and function, suitable for college-level Anatomy & Physiology students. Further details on each component (e.g., plasma composition, erythrocyte structure, leukocyte types, and hemostasis mechanisms) would be covered in subsequent sections or lectures.