Physiology (in Greek physis = nature and logos = word) is the study of the mechanical, physical, and biochemical functions of living organisms.

Physiology has traditionally been divided into plant physiology and animal physiology but the principles of physiology are universal, no matter what particular organism is being studied. For example, what is learned about the physiology of yeast cells can also apply to human cells.

The field of animal physiology extends the tools and methods of human physiology to non-human animal species. Plant physiology also borrows techniques from both fields. Its scope of subjects is at least as diverse as the tree of life itself. Due to this diversity of subjects, research in animal physiology tends to concentrate on understanding how physiological traits changed throughout the evolutionary history of animals.

Other major branches of scientific study that have grown out of physiology research include biochemistry, biophysics, biomechanics, and pharmacology.

History

It was Abu Bakr Al Razi (popularly known as Rhazes) who described certain physiological parameters when he went to establish a hospital at Baghdad in the eighth century AD. Razi was followed by Al Kindi, who wrote a treatise on human physiology. Anatomist William Harvey described blood circulation in the 17th century, providing the beginning of experimental physiology. Herman Boerhaave is sometimes referred to as the father of physiology due to his exemplary teaching in Leiden and textbook 'Institutiones medicae'(1708).

Areas of physiology

Human and animal

Human physiology (main article) is the most complex area in physiology. This area has several subdivisions which overlap with each other. Many animals have similar anatomy to humans and so share many of these areas.

• myophysiology deals with the operation of muscles
• neurophysiology concerns the physiology of brains and nerves
• cell physiology addresses the functioning of individual cells
• membrane physiology focuses on the exchange of molecules across the cell membrane
• respiratory physiology goes into the mechanics of gaseous exchange at the lung
• circulation also known as cardiovascular physiology, deals with the heart, blood and blood vessels and issues arising
• renal physiology focuses on the excretion of ions and other metabolites at the kidney
• endocrinology covers endocrine hormones which affect every cell in the body
• neuroendocrinology concerns the complex interactions of the neurological and endocrinological systems which together regulate physiology
• reproductive physiology concerns the reproductive cycle

Plant

Plant physiology has differing subdivisions. For example, since plants do not have muscles and nerves, neither myophysiology nor neurophysiology applies.

• Transpiration is the study of water loss from the plant leaves
• Photosynthesis is the conversion of sunlight energy, water and CO₂ to form sugars (glucose).bg:Физиология