Physiology

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Physiology

Physiology is the study of how an organism and its body parts work or function normally. It is closely related to anatomy, which studies an organism's structure. There are different types of physiology, such as human physiology, plant physiology, and comparative physiology.

As a branch of biology that studies exactly how the different processes in living things work, physiology seeks to answer a more difficult question than its counterpart anatomy. Where anatomy wants to know how things are built, shaped, and how they fit together, physiology wants to know how something functions. For example, how does human lung tissue work? How can a seal survive underwater for ten minutes without taking a breath? How do camels survive so long without water? These and many other questions have been asked by people ever since they started to wonder about the natural world. In order to answer them, physiology must examine an organism's functions at several different structural levels.

At the simplest or chemical level, physiology studies atoms and molecules. The cellular level is next and focuses on cells, which are the smallest units of a living thing. In complex organisms like humans, groups of similar cells form tissues, resulting in the tissue level. An organ is composed of two or more tissue types that perform a certain function, and it is at the organ level that really complex functions take place. Organs that work together to accomplish a common purpose form an organ system. Together, all the organ systems make up the living body or the complete organism. This is the highest structural level, and each of the levels has its own physiology (functions). It is difficult if not impossible to study the body's functions without some knowledge of how it is built and organized (anatomy). Studying physiology without an understanding of anatomy would be like trying to understand how a car's engine works without having any idea what an engine looks like.

HISTORY OF PHYSIOLOGY

Physiology is thought to have first developed in the Greek Hippocratic school of medicine (before 350 b.c.). Around the same time, the Greek philosopher Aristotle (384–322 b.c.) stated that every part of the body is made for a purpose, and, therefore, that the function (physiology) of something can be figured out by learning its structure (anatomy). The publication that marks the beginning of modern physiology, On the Movement of the Heart and Blood in Animals, was published by the English physician, William Harvey (1578–1657), in 1628.

For nearly the next three centuries, physiology was closely associated with anatomy, and it was not until the nineteenth century that it became recognized as a separate discipline. By the middle of that century, discoveries suggesting the unity of all life (as well as the functions of all living things) led to the development of general physiology. This branch seeks to learn the physiological functions that are common to all living things. Comparative physiology is similar and tries to find the evolutionary connections between living things. One of the fundamental concepts of both is the notion of "homeostasis." This is the ability of an organism to function under very different conditions. Put another way, it is the ability of an organism to maintain an internal environment that compensates or corrects for changes that take place in its external environment. It is important to the survival of any organism that it be able to adapt quickly to its environment while at the same time keeping its internal functions and systems in a steady or balanced state. Control is another concept that is very important to physiologists. It is related to homeostasis and might be described as the way in which an organism's different systems communicate with and influence each other.

ARISTOTLE

Greek philosopher (a person who studies the source and nature of human knowledge) and naturalist Aristotle (384 b.c.–322 b.c.) is considered not only the greatest philosopher who ever lived but also the father of biology. His great interest in the natural world led him to closely observe living things and to classify them according to a system. He taught the world that true knowledge could be obtained by observation and experience.

Aristotle was born in Stagira, Macedonia, then a Greek colony north of Greece. His father was physician to the Macedonian king, Amyntas II. It is said that Aristotle lost both parents at an early age and was brought up by a family friend. At age seventeen, he traveled to Athens and joined Plato's Academy. Plato (c. 427 b.c.–c. 347 b.c.) was one of the greatest philosophers of all time, and Aristotle became his best pupil. When Plato died, Aristotle began a journey to various parts of the Greek world and was able to pursue his long-held interest in the natural world. The study of animals was his first love, and he began to systematically learn as much as could about them. However, in 342 b.c. he was called to Macedon by the new king, Philip II, the son of Amyntas II, to become tutor to his own young son named Alexander II (later called Alexander the Great). Aristotle schooled the young man for about six years until Alexander became king when Philip II was assassinated. When the new king began his own conquering campaigns, he no longer needed a tutor, and Aristotle returned to Athens. There he founded his own school he called the Lyceum, where he would do his research and give lectures. When Alexander II died in 323 b.c., however, Aristotle moved to his mother's hometown called Chalcis, where he died the next year.

Aristotle wrote on many subjects, from logic (the principles of reasoning) and ethics (the general nature of morality), to politics and biology. However, of all of his scientific writings, most consider his work in biology to be the most successful. To begin with, he was one of the first to look at animals in a scientific way. Always a careful observer, he eventually began to place all of the known animals in to some sort of order. This is called classification. After studying, observing, and even dissecting (cutting apart for anatomical study) them, Aristotle arranged more than 500 animals according to their physical similarities and tried to understand the relationships between them. Always an excellent observer, he noticed, for example, that dolphins give birth to live young, so he put them in with all of the land beasts (now known as mammals) despite the fact that they were considered fishes. He also dissected a great many animals and wrote about the complex stomach of cattle. His work on the developing embryo of the chick showed that this early phase of life was equally worthy of study. In his writings on biology, he first taught that the form of natural objects is determined by their purpose. This, he said, leads to the conclusion that the structures of organisms are determined by the functions they are supposed to serve. He also hinted at an idea of evolution (the process by which living things change over generations) because he arranged living things in a lower-to-higher order that suggested a sort of chain of progress.

While known today for his ethical and political writings, it was Aristotle who showed the earliest "natural philosophers," or scientists, that experience, observation, and experiment are necessary when one investigates the natural world. He regularly stressed the importance of theory being based on facts. For this and his regular observations, not to mention his love of the natural world, he is rightly called the father of biology.

HUMAN PHYSIOLOGY

Human physiology is the branch that studies how the human body and its parts work or function. Among the major functional systems studied are the integumentary system (the skin), the skeletal system (the framework), the muscular system (causing movement), the nervous system (control), the endocrine system (glandular control), the circulatory system (transport and delivery), the respiratory system (oxygen supply), the digestive system (breakdown and absorption of food), the urinary system (eliminating waste), and the reproductive system (to produce offspring). These highly organized and complex systems work together and contribute to what are called the necessary life functions. These are: movement (actively getting around), responsiveness (sensing and reacting to stimuli), digestion (breaking down food so it can be absorbed), metabolism (all the chemical reactions in cells), excretion (removing waste), reproduction (producing new life), and growth (increasing in size). Taken together, these are the internal processes and functions that maintain life, the study of which is physiology.

While human physiology is of great value to medicine, plant physiology is most useful to agriculture and forestry. However, whether the type of physiology studied is that of plants or animals, it is important to know how a living organism works normally or is supposed to function, since only then can one determine if something is wrong and what might be done to correct the problem. Without the knowledge of anatomy, physiology would not be as useful as it now.