Human Physiology Introduction by Talib F. Abbas

Introduction and overview Physiology, study of the functioning of living organisms, animal or plant, and of the functioning of their constituent tissues or cells. Discoveries of unity of structure and functions common to all living things resulted in the development of the concept of general physiology, in which general principles and concepts applicable to all living things are sought.

History The publication in 1628 of Harvey’s Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus (An Anatomical Dissertation Upon the Movement of the Heart and Blood in Animals) usually is identified as the beginning of modern experimental physiology. Elementa Physiologiae Corporis Humani (Elements of Human Physiology) by Albercht Von Haller. Claude Bernard in France; Johannes Müller, Justus von Liebig, and Carl Ludwig in Germany; and Sir Michael Foster in England may be numbered among the founders of physiology.

milieu intérieur Many important ideas in physiology were investigated experimentally by Bernard, who also wrote books on the subject. He recognized cells as functional units of life and developed the concept of blood and body fluids as the internal environment (milieu intérieur) in which cells carry out their activities. The very fact that we remain alive is almost beyond our control, for hunger makes us seek food and fear makes us seek refuge.

Homeostasis and Body fluids Homeostasis in a general sense refers to stability, balance or equilibrium. It is the body's attempt to maintain a constant internal environment. Maintaining a stable internal environment requires constant monitoring and adjustments as conditions change. For example, in regulating body temperature there are temperature receptors in the skin, which communicate information to the brain, which is the control center, and the effector is our blood vessels and sweat glands in our brain.

Homeostasis

“internal sea” of extracellular fluid (ECF) The ECF is more dilute than present-day seawater, but its composition closely resembles that of the primordial oceans in which, presumably, all life originated. the ECF is divided into two components: the interstitial fluid and the circulating blood plasma. The plasma and the cellular elements of the blood, principally red blood cells, fill the vascular system, and together they constitute the total blood volume.

Intracellular fluid In the average young adult male, 18% of the body weight is protein and related substances, 7% is mineral, and 15% is fat. The remaining 60% is water. The intracellular component of the body water accounts for about 40% of body weight and the extracellular component for about 20%. Approximately 25% of the extracellular component is in the vascular system (plasma = 5% of body weight) and 75% outside the blood vessels (interstitial fluid = 15% of body weight). The total blood volume is about 8% of body weight.

Total Body Volume

Differences between Extracellular and Intracellular Fluids 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. The intracellular fluid differs significantly from the extracellular fluid; specifically, it contains large amounts of potassium, magnesium, and phosphate ions instead of the sodium and chloride ions found in the extracellular fluid.

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