Human Physiology: Historical Note

In the 8th century AD. a prominent Muslim scientist and physician named Abu Bakar Al Razi first described some key physiological characteristics of human body. Subsequently, it was another Muslim scientist by the name of Al Kindi who wrote a paper on human physiology. Later in the 17th century, the anatomist William Harvey wrote about the human blood circulation, thus starting the field later came to be known as experimental physiology. Another prominent figure in the history of the field of physiology is Herman Boerhaave who is often called the father of physiology. He was not only a prominent teacher of physiology but also authored the textbook named “Institutiones Medicae”

Human Physiology: A Brief Introduction

Human physiology is the scientific study of various functions of the human body in its normal state. These functions could be mechanical or biochemical in nature. The study of animal physiology and related experiments has provided much of the basis for studying human physiology. Along with anatomy, human physiology is one of the basic sciences in the medical field with its application throughout the medical care.

To maintain normal human health, the physiological variables such as blood glucose, body temperature, blood chemistry, etc. must be maintained within a narrow range. One of the principal concepts in human physiology is called homeostasis, which means the maintenance of a stable internal body environment despite changes in the external environment. In fact, the main function of many human organ systems is to maintain this homeostasis. For example, the renal or kidney system works to maintain normal water levels and normal blood chemistry in the body via urination and elimination of various waste products. Similarly, the job of the circulatory system is to maintain a constant and adequate supply of oxygen and nutrients to various organs as well as removal of waste products.

Human Physiology: Major Systems

Human physiology is the most advanced and complex area in physiology and hence it is further sub-divided into several branches. Although various different human organ systems are often studied as separate entities, in reality, however, they all interact with each other and work together to keep the human body functioning in a normal and healthy fashion. Following is a brief description of major components of the human physiological system.

Nervous System: This system is composed of two sub-systems, the central nervous system consisting of the brain and spinal cord, and the peripheral nervous system. It is the human brain that is responsible for the critical functions that separate us from other non-human animal species. This is where thoughts are generated, emotions are felt, and the sensory perceptions are processed. Brain is also responsible for many crucial aspects of communication as well as management of various other systems and functions. Neuroscience is the study of the nervous system itself whereas study of its diseases is called neurology, which is a branch of medicine. The medical field dealing with the study of mental illness and behavioral disorders is called psychiatry. Humans have five special senses namely vision, hearing, taste, touch, and smell.

Musculoskeletal System: This system is comprised of two sub-systems, the skeletal system that consists of bones, ligaments, tendons, and cartilage, and the muscular system that consists of muscles. This system provides basic body structure and affords humans the ability to move about. In addition to providing the body with structural support, the long bones in the body contain bone marrow, which plays a central role in the production of cells. There are two medical branches that primarily deal with the diseases of the bones and joints, orthopedics and rheumatology.

Circulatory System: This is comprised of heart and blood vessels. The blood vessels are of three types, arteries, veins, and capillaries. The heart acts like a mechanical pump as it propels the circulation of the blood to and from various parts of the body. The blood acts as a transportation system as it carries oxygen, nutrients, waste products, immune cells, and hormones from one part of the body to another. The medical branch involved in the study of diseases of the blood is called hematology, whereas the one that deals the diseases of the heart is called cardiology.

Gastrointestinal System: Consists of the digestive tract including mouth, esophagus, stomach, small and large intestines, and rectum, as well as other organs involved in the digestive process such as liver, pancreas, gallbladder, and salivary glands. The primary function of this system is to convert food into small, absorbable molecules that are then distributed by blood to all other body parts, and to rid the body of unused and waste products. The medical specialty involved in the study of diseases of this system is called gastroenterology.

Respiratory System: This consists of the nose, pharynx, trachea, and lungs. It is involved in taking in oxygen from the air and expelling carbon dioxide and water back into the air. The study of this system is called respiratory physiology whereas the medical branch dealing with the diseases of this system is known as pulmonology.

Renal System: This system is made up of kidneys, ureters, bladder, and urethra. It is responsible for removing excess water from the blood and producing urine, which carries with it a number of waste products and excess ions and water out of the body. The study of the function of the urinary system is called renal physiology while the medical specialty dealing with diseases of this system is known as urology.

Immune System: This system protects the body against foreign elements including germs and it consists of the white blood cells, the thymus, lymph nodes and lymph channels. The immune system enables the body to distinguish its own cells and tissues from foreign cells and substances and to neutralize or destroy the latter by using specialized proteins known as antibodies, cytokines, and many others. The medical branch dealing with the study of the immune system is called immunology.

Endocrine System: This is the system of hormones and consists primarily of the major endocrine glands such as the pituitary, thyroid, adrenals, pancreas, parathyroids, and gonads. It should be noted, however, that many other organs and body tissues are also involved in producing hormones. These hormones function as signals from one system of the body to another conveying information about a wide variety of conditions, and triggering different bodily reactions as a result. The medical specialty involved in the study of the endocrine system is called endocrinology.

Reproductive System: The essential function of this system is to facilitate the reproductive activities for the organism. It consists of the gonads and the internal and external sexual organs. This system is first involved in the production of gametes in each sex, then in facilitating a mechanism for combining these gametes from two opposite sexes, and later providing a nurturing environment for the growing fetus inside the mother’s uterus for 9 months. The scientific field involved in the study of this system is known as reproductive physiology, whereas the study of medical disorders of the reproductive system is called reproductive medicine or gynecology (for female reproductive disorders) and andrology (for male reproductive disorders). The study of the developing fetus inside the mother’s womb is called embryology.

Integumentary System: This system consists of the skin and structures it contains such as the hair, nails and important glands including the sweat glands and sebaceous glands. The skin not only acts as a container for other body organs providing them structure and protection, but also it serves as a major sensory connection between the organism and its environment. The medical study of skin disorders is called dermatology.

Adipose Tissue: This consists of different kinds of body fat found not only under the skin but also surrounding the internal organs. It functions as the storage for fuel and as insulation. It is also involved in generating signals to other systems about the body’s nutritional status. The scientific study of the functions of this system is quite new so that as of now there is not a commonly known name for it.

The aforementioned divisions by distinct body system are actually somewhat arbitrary since many body organs interact with more than one system. Then, there are often complex interactions within various systems, for instance, there is a close and important working relationship between the nervous system and the endocrine system; this specialized subsystem is called neuro-endocrine system and its study is known as neuro-endocrinology. In addition, there are several other aspects of physiology that cannot be easily classified under one or the other traditional organ system categories. Examples of some of these highly specialized and fascinating aspects of physiology include:

Exercise Physiology: Focuses on human body’s functioning during physical exercise Myophysiology: Involves the study of the function of muscles
Cell Physiology: Relates to study of individual cell functions
Environmental Physiology: Study of human’s adaptation to their environment
Membrane Physiology: Study of the functioning of cell membranes and movement of molecules across them.