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Vital Functions for Human Life In this section, you will be introduced to the major organ systems of the body. To put these systems in context, we will first discuss vital functions of life. Within any organism, there are a multitude of functions taking place at any given time. Humans, for example, can breathe, talk, digest food, process visual images, and move their bodies all at the same time. While all of these activities are important, some are essential to the survival of the human body itself. They are vital functions - processes or actions of the body on which life is directly dependent. You will examine four main vital functions in this course: exchange with the environment; transport within the body; structure, support, and movement; and control and regulation. For human life, there are several vital functions. So you now know that all multicellular organisms need to do the following in order to survive: • • • • Exchange with the environment Transport fluids and material throughout the body Provide structure, support, protection and movement Regulate and control processes So what does this mean? What does this involve? How does the human body do these things? Try answering the questions below to begin broadly thinking about bodily function within these categories and how they are linked to one or more of the primary organ systems. Exchange with the Environment An organism constantly interacts with its environment. In order to survive, the human body must obtain food, water, and oxygen from the world around it. The human body must also rid itself of wastes before they build up to toxic levels. Two organ systems are primarily responsible for exchange of material with the environment. The digestive system brings food and water into the body and eliminates solid wastes. The respiratory system brings in oxygen and removes carbon dioxide. The urinary system doesn’t take in anything from the environment, but does eliminate waste products of metabolism from the body fluid. However, this is just one of several roles that the urinary system plays in maintaining homeostasis of body fluids, so it will be explored more extensively in the next vital function category involving body fluids. Fluid Transport within the Body Single-celled organisms can absorb nutrients and oxygen directly from the environment into the cells, where they are used to support basic cell functions. Waste products are excreted from these single cells in a similar fashion. In multi-celled organisms like humans, however, most cells are not exposed directly to the outside environment. Instead, body cells rely on organ systems to transport and regulate the composition of internal fluids throughout the body. Three main body systems, the cardiovascular system, the lymphaticsystem, and the urinary system take care of this vital bodily function. The cardiovascular and lymphatic systems also participate in the function of immunity, to help defend the body's cells from foreign organisms that may enter the body tissues or fluids. The lymphatic system returns interstitial fluid to blood and the urinary system filters blood to regulate body fluid homeostasis, including volume, pressure, and chemical composition. Structure, Support, Protection, and Movement For the organs of the human body to function, they must be protected from potentially damaging substances in the environment. One level of defense is provided by the integumentary system, made up of the skin, hair, and nails. This system prevents many potentially harmful irritants from entering the body. Eyelashes, for example, help keep sand or other items out of the eyes, where they could potentially cause serious damage, and the skin prevents most pathogens (disease-causing microorganisms) from entering the body and destroying healthy body cells. Certain parts of the skeletal system, such as the skull and ribcage, also help to protect the internal organs, such as the brain, heart and lungs, from damage. The skeletal system and the muscular system also support the body and allow it to move away from danger, toward food sources, etc. The cardiovascular and lymphatic systems also help defend the body’s cells from foreign organisms that may enter the body tissues or fluids through the process of immunity. Control and Regulation To keep itself in a state of equilibrium, an organism must constantly gather information and react accordingly. In humans, the nervous system, made up of the brain, nerves, spinal cord and sensory organs, reacts to stimuli in the environment and signals other systems when actions are needed to bring the body back into balance. The endocrine system, which produces hormones and other regulatory substances, plays a key role in maintaining balance among chemical messengers within the body. Locally, most body cells can produce chemical messages that influence the metabolism of other cells. And there are some organs in other body systems that produce chemicals that can travel through the body to regulate metabolic processes in other organs. As you can see, several organ systems work together to accomplish these various vital functions throughout the body. Since the organ systems are distributed throughout large regions of the human body, it is necessary to define orientation within the body and communicate the proper terminology as you study these integrated structures and functions.