Systems and organs
Structure and Functions (Magill’s Medical Guide, Sixth Edition)
There are essentially nine systems in the human body: the nervous, cardiovascular, respiratory, gastrointestinal, renal, endocrine, reproductive, thermoregulatory, and skeletomuscular systems. All these systems are essential to sustain life, and many work together to perform their functions efficiently. All the other systems need the nervous system to operate or to coordinate their functions. The first six of these systems will be discussed in this article.
The nervous system is composed of the central nervous system (the brain) and the peripheral nervous system (the spinal cord and nerves extending to every part of the body). The brain receives information from the body by way of the sensory nerves. It then evaluates all the information and sends out the appropriate signals to respond. For example, the ears send information to the brain that there are noises coming from behind; the brain tells the head to turn in the direction of the sounds. The eyes send the signals that the noises are coming from, for example, a gorilla. The brain must decide to run, fight, or stand and try to reason with the gorilla. Meanwhile, the brain tells the heart to beat faster and harder. It also tells the stomach and intestines to stop digestion and reduce its blood flow because blood may be needed by the muscles for running. This is called the “fight or flight” response to stress, which the nervous system controls.
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Disorders and Diseases (Magill’s Medical Guide, Sixth Edition)
The body has control mechanisms to ensure that its systems function properly. Many systems use what is called negative feedback to fine-tune their functioning. An example of negative feedback is the control of blood pressure. Sensors in the arteries allow the brain to monitor the body’s blood pressure level. When pressure is too high, the brain tells the cardiovascular system to decrease pressure by slowing the heart and opening the blood vessels and tells the kidneys to excrete fluid. Thus, when blood pressure is high, the feedback that the brain provides is negative, because it causes a response that is opposite to the unwanted change from the normal state.
The endocrine system uses negative feedback to regulate many hormones. The simplest endocrine feedback system involves insulin and glucose. When blood glucose increases, insulin secretion increases, which in turn decreases blood glucose. A decrease in blood glucose tells the pancreas to slow down the secretion of insulin. The failure of this system results in diabetes mellitus, a disease in which the ability to regulate blood sugar is lost. When this control is lost, other systems are damaged as a result, such as the renal and cardiovascular systems.
There are also much more complex feedback control systems. The regulation of the adrenal hormone cortisol serves as an example of such a system. Cortisol secretion is controlled by secretion of the pituitary...
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Perspective and Prospects (Magill’s Medical Guide, Sixth Edition)
In the Middle Ages, it was believed that “spirits” were the essence of life or “vitality”; thus, the treatment for many ailments was bloodletting, the application of leeches to remove the “evil spirit” causing the sickness. It was not until the seventeenth century that William Harvey discovered that blood circulated from arteries to veins in both the lungs and the rest of the body. Oxygen was discovered at the end of the eighteenth century by Joseph Priestley. Knowledge of chemistry, biochemistry, and physiology grew in the nineteenth century, but most of the information about systems and organs contained in this article was revealed in the twentieth century.
Many discoveries have been in the area of how the body’s systems and organs interact with and influence one another. New anatomical techniques of investigation have revealed the minute structures of many organs and tissues. As a result, the presence of previously unknown nervous and other tissue parts has been recognized; their functions are under investigation. Chemical techniques have revealed many new hormone and hormonelike substances through which one tissue or organ can influence another. Research into the molecular structure of some of these biochemical signals is helping to explain how they work.
In addition, the events that occur inside a cell or group of cells have been described in greater detail. How a group of cells produces...
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For Further Information: (Magill’s Medical Guide, Sixth Edition)
Asimov, Isaac. The Human Body: Its Structure and Operation. Rev. ed. New York: Penguin Books, 1992. Asimov offers an easy-to-understand overview of all the body’s organ functions.
Guyton, Arthur C., and John E. Hall. Human Physiology and Mechanisms of Disease. 6th ed. Philadelphia: W. B. Saunders, 1997. This physiology text deals with the function of the body in considerable detail. Excellent advanced reading for the physiology student.
Kittredge, Mary. The Human Body: An Overview. Reprint. Philadelphia: Chelsea House, 2003. This text explains the general workings of the human body. Provides background to the historical development of medical knowledge and addresses many of the pathologies that can arise in the body.
Page, Martyn, ed. Human Body: An Illustrated Guide to Every Part of the Human Body and How It Works. New York: DK, 2009. The first part of the book covers basic human anatomy with full color illustrations, explaining how each individual body system functions. The second part covers diseases and disorders.
Parsons, Jayne, ed. Encyclopedia of the Human Body. New York: DK, 2004. A beautifully illustrated and accessible guide to the human body designed for children and teens, covering anatomical concepts, disease mechanisms, and the history of medicine and its pioneers.
Thibodeau, Gary A., and Kevin T. Patton. The Human Body in...
(The entire section is 231 words.)