What is human physiology?
Human physiology is a branch of medicine that is concerned with studying functions of the human body. The term physiology was derived from two Greek words: “physics” which means “origin” or “nature” and “-logia” which means “study of.”
Human physiology uses two different approaches when studying mechanisms of cause-and-effect. One approach focuses on explaining the purpose of physiological processes (why?). The other approach focuses on explaining the underlying mechanisms of physiological processes (how?). For example, the question: “Why do people sweat when they feel hot?” could be answered in two ways. Firstly, researchers could explain the phenomenon of sweating in the context of meeting a bodily need and say that it's to help cool down, because sweating releases heat. Secondly, researchers could put the answer in the context of the cause-and-effect sequence and say that the temperature-sensitive receptors in the body detect a rise in temperature and send a signal to the thermoregulatory centers in the brain. In response, the brain sends signals down the sympatric nervous system pathways which activate sweat glands which release water.
Is there a difference between structure and function?
Even though physiology primarily studies function, it is also closely related to anatomy which studies structure. Mechanisms that underlie physiological processes in the body largely depend on the shape of different tissues, structures, and organs and their mutual relationship. It is, therefore, impossible to make a clear distinction between structure and function.
Some relations between structure and function are obvious - the heart is perfect for pumping blood through the body because it is a hollow organ. The difference in the shape and size of teeth determines their role in eating (incisors cut while molars grind food). The knee is perfectly designed to allow the bending movement of the lower leg. There are also, however, examples of when the interdependent relationship between structure and function is more sophisticated. It may not be obvious that the air has to travel from the mouth and nose all the way to the smallest air sacs called alveoli. Alveoli contain a well-developed capillary network and allow the exchange of oxygen and carbon-dioxide between the red blood cells and the lungs.
How is our body organized?
The most basic level of organization is called the chemical level. This level considers the mutual interaction between different atoms and molecules which are the basic building blocks of any matter. The human body is mostly made of oxygen, carbon, hydrogen, and nitrogen. These chemical elements interact with each other and form organic and inorganic molecules such as proteins, fats, sugars, and nucleic acids.
The second level of organization is called the cellular level. Cells are unique because they can carry out processes which are associated with life. The interior of cells contains atoms and molecules which are organized in a specific way and protected from the surrounding environment by the semipermeable plasma membrane.
The most complex level of organization is an organism. Organisms are independent living entities which are capable of sustaining life. The simplest organisms such as bacteria, paramecium, or green euglena are called single-celled organisms because they only have one cell. On the other hand, multicellular organisms have many different functional entities made of many millions of independent cells. In the simplest multicellular organisms such as the sponge, all cells are quite similar. But more complex organisms like plants, animals, and humans have many different types of cells such as muscle, neural, reproductive and other cells which are very distinct and responsible for different functions. A human body has around 200 different types of cells.
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