Quotes from John E. Hall

The nervous system is composed of three major parts: the sensory input portion, the central nervous system (or integrative portion), and the motor output portion.

thyroid hormone increases the rates of most chemical reactions in all cells, thus helping to set the tempo of bodily activity.

Insulin controls glucose metabolism;

adrenocortical hormones control sodium and potassium ions and protein metabolism;

The nervous system regulates many muscular and secretory activities of the body, whereas the hormonal system regulates many metabolic functions. The nervous and hormonal systems normally work together in a coordinated manner to control essentially all of the organ systems of the body.

Located in the body are eight major endocrine glands and several organs and tissues that secrete chemical substances called hormones.

The science of human physiology attempts to explain the specific characteristics and mechanisms of the human body that make it a living being.

About 60 percent of the adult human body is fluid, mainly a water solution of ions and other substances. Although most of this fluid is inside the cells and is called intracellular fluid, about one third is in the spaces outside the cells and is called extracellular fluid.

The extracellular fluid contains large amounts of sodium, chloride, and bicarbonate ions plus nutrients for the cells, such as oxygen, glucose, fatty acids, and amino acids. It also contains carbon dioxide that is being transported from the cells to the lungs to be excreted, plus other cellular waste products that are being transported to the kidneys for excretion.

The intracellular fluid differs significantly from the extracellular fluid; for example, it contains large amounts of potassium, magnesium, and phosphate ions instead of the sodium and chloride ions found in the extracellular fluid.

Thus, homeostatic compensations that ensue after injury, disease, or major environmental challenges to the body may represent a "trade-off" that is necessary to maintain vital body functions but may, in the long term, contribute to additional abnormalities of body function. The discipline of pathophysiology seeks to explain how the various physiological processes are altered in diseases or injury.

The cell contains highly organized physical structures, called intracellular organelles.

To summarize, the body is actually a social order of about 100 trillion cells organized into different functional structures, some of which are called organs.