Many physiologic variables (such as Blood Glucose (sugar) level, Body Temperature , blood PH , and so on) must be maintained within narrow limits for proper health. An overriding theme in physiology is that of '' Homeostasis '', maintaining a stable internal environment despite external fluctuations. Indeed, the primary functions of many organ systems are to maintain homeostasis. For instance, the Urinary System helps to control water levels as well as that of blood pH and various waste products, and the Circulatory System ensures a constant supply of oxygen and nutrients to tissues and the removal of waste products.
Traditionally, the academic discipline of physiology views the body as a collection of interacting systems, each with its own combination of functions and purposes.
- The consists of the Human Skeleton (which includes Bone s, Ligament s, Tendon s, and Cartilage ) and attached Muscle s. It gives the body basic structure and the ability for movement. In addition to their structural role, the larger bones in the body contain Bone Marrow , the site of production of blood cells. Also, all bones are major storage sites for Calcium and Phosphate . The study of the skeleton is termed Osteology ; with a focus on bone disorders it is termed Orthopedics .
- The consists of the Heart and blood vessels ( Arteries , Vein s, Capillaries ). The heart propels the circulation of the Blood , which serves as a "transportation system" to transfer Oxygen , fuel, nutrients, waste products, immune cells, and signalling molecules (i.e., Hormones ) from one part of the body to another. The study of the circulatory system is termed Cardiovascular physiology; with a focus on disease it is Cardiology .
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- The consists of the Mouth , Esophagus , Stomach , Gut ( Small and Large Intestine s), and Rectum , as well as the Liver , Pancreas , Gallbladder , and Salivary Gland s. It converts food into small, nutritional, non-toxic Molecule s for distribution by the circulation to all tissues of the body, and excretes the unused residue. The study of this system is termed Gastroenterology .
with relation to the lungs (from an older edition of '' Gray's Anatomy '')]]
- The consists of the Kidney s, Ureter s, Bladder , and Urethra . It removes water from the blood to produce urine, which carries a variety of waste molecules and excess Ion s and water out of the body. The study of the function of the urinary system is termed Nephrology or Renal Physiology ; with a focus on structural disease it is Urology .
- The ''', Thyroid , Adrenal s, Pancreas , Parathyroid s, and Gonad s, but nearly all organs and tissues produce specific endocrine Hormone s as well. The endocrine hormones serve as signals from one body system to another regarding an enormous array of conditions, and resulting in variety of changes of function. The study of this system is termed Endocrinology .
- The consists of the Gonad s and the internal and external Sex Organ s. The reproductive system produces Gamete s in each Sex , a mechanism for their combination, and a nurturing environment for the first 9 months of development of the offspring. The study of the physical function of this system is termed reproductive physiology; when applied to the disorders of reproduction it is termed Gynecology or Andrology . The study of the behavioral aspects is Sexology and when applied to the developmental aspects is termed Embryology .
- The consists of the covering of the body (the Skin ), including Hair and Nails as well as other functionally important structures such as the Sweat Gland s and Sebaceous Gland s. The skin provides containment, structure, and protection for other organs, but it also serves as a major sensory interface with the outside world. The study of skin is Dermatology .
- The tissue consists of several types of body fat, below the skin and surrounding the internal organs. It serves principally as storage for fuel, as Insulation , and provides signals about nutritional status to other systems. The study of the functions of this system is new enough that there is not a widely used name for the discipline.
The traditional divisions by system are somewhat arbitrary. Many body parts participate in more than one system, and systems might be organized by function, by embryological origin, or other categorizations. In particular, is the "", the complex interactions of the neurological and endocrinological systems which together regulate physiology. Furthermore, many aspects of physiology are not as easily included in the traditional organ system categories.
The study of how physiology is altered in disease is Pathophysiology .
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