What is the importance of blood, heart and veins?

Blood is a connective tissue in humans and other animals that functions to transport substances such as nutrients (glucose, amino acids and fatty acids) and oxygen (through haemoglobin) to the cells and transports metabolic waste products such as carbon dioxide, urea and lactic acid away from those cells.

Heart is a muscular pumping organ that pumps blood throughout the body. Blood carries carbon dioxide from cells to the lungs for removal and transports oxygen from the lungs to the heart. The heart pumps blood to all the cells of the body.

The role of veins is to return deoxygenated blood from human organs back to the heart.