Organ and organ system
- The basic tissues organize to form organs, which in turn associate to form organ systems in the multicellular organisms.
- Each organ in our body is made of one or more type of tissues.
For example, our heart consists of all the four types of tissues- epithelial, connective, muscular and neural.
- The complexity in organ and organ systems displays certain discernable trend. This discernable trend is called evolutionary trend.
- Morphology is the study of form or externally visible features.
- Anatomy is the study of morphology of internal organs.

Fig. Heart, an organ