What is the primary function of blood?

The primary function of blood is to transport substances throughout the body, making it essential for maintaining homeostasis and facilitating various physiological processes. Blood carries oxygen from the lungs to the cells and returns carbon dioxide to be expelled. It also transports nutrients absorbed from the digestive tract to the tissues, hormones that regulate various bodily functions, and waste products to the kidneys for excretion. This comprehensive transportation system supports all organs and tissues, providing them with necessary substances for energy and function, while also removing waste to keep the internal environment stable.

Other functions of blood, such as absorption of nutrients, protection from diseases, and regulation of body temperature, while important, are secondary to its primary role in transportation. For instance, while blood does contribute to protection through immune cells, it is primarily the transport system that underscores its essential function in the body.