Cardiovascular System: Blood – Structure, Composition, and Function

Cardiovascular System

Overview

The cardiovascular system is responsible for the transport of substances throughout the body, including nutrients, gases, waste products, and signaling molecules. It consists of three main components: blood, the heart, and blood vessels.

• Blood: Composed of plasma, formed elements, and produced via hematopoiesis.

• Heart: Functions as the pump for blood circulation; includes structures, blood flow pathways, and its own blood supply.

• Blood Vessels: Network for blood transport; includes general characteristics, pulmonary and systemic circulations, and regional blood supply.

Blood

Functions of Blood

Blood serves as the primary transport medium in the body, facilitating the movement of essential substances and maintaining homeostasis.

• Nutrients: Delivers glucose, amino acids, lipids, and other nutrients to tissues.

• Respiratory Gases: Transports oxygen from lungs to tissues and carbon dioxide from tissues to lungs.

• Waste Products: Removes metabolic wastes such as urea and ammonia.

• Signaling Molecules: Circulates hormones and other regulatory molecules.

• Immune Cells: Distributes cells of the immune system for defense against pathogens.

Blood Circulation

Blood circulation is powered by the heart, ensuring the delivery of oxygen and nutrients and the removal of wastes.

• Oxygen and nutrients diffuse across capillary walls to body tissues.

• Helps regulate body temperature by distributing heat.

Blood as a Connective Tissue

Blood is classified as a specialized connective tissue due to its cellular components and extracellular matrix.

• Formed Elements: Blood cells including erythrocytes, leukocytes, and platelets.

• Plasma: The liquid portion of blood, serving as the matrix.

• Origin: Develops from mesenchyme during embryonic development.

• Structure: Consists of cells surrounded by a nonliving matrix (plasma).

Blood Volume

The total volume of blood in the human body varies by sex.

• Males: 5–6 liters

• Females: 4–5 liters

Composition of Blood

Main Components

• Plasma: Straw-colored, sticky fluid making up about 55% of blood volume. Contains water, ions, nutrients, wastes, and proteins.

• Formed Elements: Cellular components including erythrocytes (red blood cells), leukocytes (white blood cells), and platelets.

Plasma

Plasma is the liquid portion of blood and is essential for transport and homeostasis.

• Approximately 90% water

• Contains over 100 types of molecules, including:

  • Ions: Sodium (Na+), Chloride (Cl-)

  • Wastes: Carbon dioxide (CO2), urea, ammonia

  • Nutrients: Glucose, lipids, amino acids

  • Proteins: Albumin, globulins, fibrinogen

Major Plasma Proteins

• Albumin: Maintains osmotic pressure and prevents water loss from blood vessels.

• Globulins: Includes antibodies and transport proteins for lipids, iron, and copper.

• Fibrinogen: Involved in blood clotting processes.

Formed Elements

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

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

• Leukocytes (White Blood Cells): Defend against infection and disease.

• Platelets (Thrombocytes): Involved in blood clotting.

Summary Table: Blood Components

Component	Main Function	Key Features
Plasma	Transport medium	90% water, proteins, nutrients, wastes, ions
Erythrocytes	Oxygen transport	Biconcave, no nucleus, contains hemoglobin
Leukocytes	Immune defense	Several types, nucleated, phagocytic or antibody-producing
Platelets	Clotting	Cell fragments, initiate clot formation

Key Terms and Definitions

• Plasma: The liquid, extracellular matrix of blood.

• Formed Elements: The cellular components of blood (erythrocytes, leukocytes, platelets).

• Hematopoiesis: The process of blood cell formation, primarily occurring in bone marrow.

• Mesenchyme: Embryonic connective tissue from which blood develops.

Relevant Equations

• Hematocrit: Percentage of blood volume occupied by red blood cells. $\text{Hematocrit} = \frac{\text{Volume of RBCs}}{\text{Total Blood Volume}} \times 100\%$

Example Application

When a person donates blood, approximately 0.5 liters are removed, which is about 10% of the total blood volume for an average adult male. The body rapidly replaces the lost plasma and formed elements through hematopoiesis.

Additional info: Expanded definitions and context for plasma proteins, hematopoiesis, and blood volume were added for completeness and clarity.