Cardiovascular System: Blood

Introduction to Blood

Blood is a specialized fluid connective tissue essential for the maintenance of homeostasis and the transport of substances throughout the body. It consists of a liquid matrix called plasma and various formed elements, including cells and cell fragments.

• Definition: Blood is a fluid connective tissue composed of plasma (liquid matrix) and formed elements (cells and cell fragments).

• Main Components: Plasma (~55% of blood volume) and formed elements (~45% of blood volume).

• Average Blood Volume: Females: 4–5 L; Males: 5–6 L.

Functions of Blood

Blood performs several vital functions necessary for survival and health.

• Transport: Carries gases (O2, CO2), nutrients, waste products, processed molecules (e.g., vitamin D), and regulatory molecules (e.g., hormones).

• Regulation: Maintains pH (7.35–7.45) and osmosis via buffers; regulates body temperature by distributing heat.

• Protection: Defends against foreign substances (antibodies, immune cells) and initiates clot formation to prevent blood loss.

Composition of Blood

Blood is made up of plasma and formed elements, each with distinct roles and characteristics.

• Plasma: The liquid matrix of blood, a colloid containing water, proteins, ions, nutrients, waste products, gases, and regulatory substances.

• Formed Elements: Includes red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes).

Plasma

• Water Content: ~91% of plasma is water.

• Proteins: Albumins (58%), globulins (38%), and fibrinogen (4%).

• Other Components: Ions (Na+, K+, Ca2+), nutrients (glucose, amino acids), waste products (urea, uric acid), gases (O2, CO2), and regulatory substances (hormones, enzymes).

Formed Elements

• Red Blood Cells (Erythrocytes): Transport oxygen and carbon dioxide; biconcave disc shape increases surface area for gas exchange.

• White Blood Cells (Leukocytes): Defend against pathogens; include granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes).

• Platelets (Thrombocytes): Cell fragments involved in blood clotting.

Key Terms

• Plasma: The liquid, non-cellular part of blood.

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

• Hemoglobin: Oxygen-carrying protein in red blood cells.

• Antibody: Protein produced by B cells that binds to specific antigens.

• Antigen: Substance recognized as foreign by the immune system.

Example

When a person inhales, oxygen enters the lungs and diffuses into the blood, where it binds to hemoglobin in red blood cells. The blood then transports this oxygen to tissues throughout the body, supporting cellular respiration and energy production.