Blood is a specialized connective tissue that plays a fundamental role in maintaining the normal functioning of the human body. It is responsible for the transportation of respiratory gases such as oxygen and carbon dioxide, nutrients, hormones, enzymes, and metabolic waste products between different organs and tissues. Blood consists of two main components: plasma and formed elements. Plasma serves as a liquid medium that carries proteins, electrolytes, nutrients, and other dissolved substances, while the formed elements include red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes). Erythrocytes are primarily responsible for oxygen transport due to the presence of hemoglobin, which binds oxygen and delivers it to body tissues. Leukocytes play a crucial role in protecting the body against infections and participate actively in immune responses. Platelets are essential for blood clotting and help prevent excessive bleeding by forming clots at the site of injury. Together, these formed elements make up approximately 45% of the total blood volume and contribute significantly to maintaining homeostasis, immune defense, regulation of body temperature, and tissue repair processes. A comprehensive understanding of the structure, composition, and physiological functions of blood components is essential for explaining many biological processes and diagnosing various pathological conditions related to blood disorders and systemic diseases.