The body is a complex network of cells that group together into distinct structures that allows for the body to function. In order to begin to understand this we must first look at how the body is built from the various building blocks, figure 6, which leads to the body. In this, we must think of the body as being built in layers of ascending complexity beginning with the atom and ending with the entire organism. Each level of complexity is developed through an increase in the various components that are interacting within that level. Which begins with the atom and the subatomic components (electrons, neutrons, protons) followed by the interaction of atoms with other atoms (or molecules) and then single molecules with other molecules forming the macromolecules that we tend to think about in biology (e.g., carbohydrates, lipids, proteins). From these macromolecules we have interactions that eventually from the organelles and cells that will interact with each other leading to the formation of the tissues. Tissues are conglomerations of cells that share a similar function for the body that will work and interact with each other. Developing into regulated (or control) organs, a conglomeration of tissues with a shared function within the homeostasis of the body. These organs eventually coordinate their independent functions into the systems that comprise the body that we typically think about when discussing human anatomy and physiology.
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The tissues and organs made of the various types of cells that conglomerate during fetal development based on the dermal layer they arise from, table 8. From this conglomeration we stipulate that the endoderm will give rise to the gastrointestinal organs, endocrine glands, and lungs. The mesoderm will give rise to the musculoskeletal tissues, cardiovascular organs, connective tissues, and the dermis of the integument. The ectoderm leads to the development of the epidermis & accessory organs of integument, the nervous tissues and enamel of teeth. From these developmental origins, and the development and integration of organs there will be 10 basic organ systems that we will discuss through the remainder of this text, figure 17. These systems include the musculoskeletal (skeletal muscle and skeletal) systems, the nervous system, the cardiorespiratory (cardiovascular and respiratory) systems, the immune system, the excretory system, the digestive system, the neuroendocrine system, the reproductive system and the integumentary system, table 9. While each system will have an independent function, they function in a coordinate manner so as to ensure that the body is able to remain in a stable state and respond effectively to any stimulus that might disrupt this stability
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