Organ structure refers to the arrangement and organization of tissues within an organ, which is a group of tissues working together to perform specific functions. Each organ is made up of different types of tissues, such as muscle tissue, nervous tissue, epithelial tissue, and connective tissue, which collaborate to carry out the organ's role in the body. For example, the heart is an organ composed of cardiac muscle tissue that pumps blood, surrounded by connective tissue that provides support. The lungs consist of epithelial tissue for gas exchange and connective tissue for structure. Understanding organ structure helps in studying how organs function and interact within the human body.