physio

Definition and Scope of Human Physiology

  • Etymological Origin: The term physiology is derived from the Greek words physis, meaning nature, and logia, meaning the study of. It literally translates to the study or knowledge of nature.

  • Modern Definition: The study of the normal functions of the human body and its component parts, including cells, tissues, organs, and organ systems. It encompasses all chemical and physical processes within living organisms and the various mechanisms that allow them to function.

  • Integrated Activities: Physiology deals with the integrated activities of different organs and organ systems and the conditions that determine the normal functioning of body parts.

  • Regulatory Focus: It is sometimes referred to as the science of regulation of physiologic parameters. It is concerned with the specific characteristics and mechanisms of the human body that make it a living being, specifically those that facilitate adaptation and homeostasis.

  • Goal of Physiology: To explain the physical and chemical factors responsible for the origin, development, and progression of life.

  • Clinical Relevance: Learning the normal physiologic phenomena is essential for identifying, diagnosing, and treating abnormalities or pathologies.

Historical Foundations of Physiology

  • William Harvey (1628): Known as the father of physiology. He laid the discipline's foundation by correctly describing the circulation of blood. He established that the heart acts as a pump, arteries transport oxygenated blood, substance exchange occurs at systemic capillaries, and veins return deoxygenated blood.

  • Claude Bernard (19th Century): The French physiologist who introduced the concept of the extracellular fluid (ECF) that bathes every cell. He described this fluid environment as the "internal environment of the body" or Milieu intérieur. He posited that this fluid contains optimal amounts of nutrients, gases, hormones, enzymes, water, and electrolytes.

  • Walter Cannon (1929): A prominent physiologist from the first half of the 20th century who coined the term homeostasis to describe the maintenance of constant conditions within the internal environment (ECF).

Branches and Quantitative Nature of Physiology

  • Fields of Physiology: The discipline ranges from simple to complex life forms:

    • Viral physiology

    • Bacterial physiology

    • Cellular physiology

    • Plant physiology

    • Human physiology (subdivided into systems like Cardiovascular (CV), Renal, Respiratory (RS), and Central Nervous System (CNS)).

  • Quantitative Expression: Physiology is a quantitative science. All physiological parameters are expressed in numbers and units. Examples include Blood Pressure (BP), Blood Glucose Level (BGL), Body Temperature (BT), and Heart Rate (HR).

  • Related Sciences: Physiology is highly integrated with Anatomy, Biochemistry, Pathology, Pharmacology, and Physics.

Units of Measurement in Physiology

  • Length Conversion:

    • 1 cm=10 mm=0.3937 inches1\text{ cm} = 10\text{ mm} = 0.3937\text{ inches}

    • 1 inch=2.54 cm1\text{ inch} = 2.54\text{ cm}

    • 1 mm=1000 μm1\text{ mm} = 1000\, \mu\text{m}

    • 1 μm=1 nm=10 A˚1\, \mu\text{m} = 1\text{ nm} = 10\, \text{\AA}

    • 1 A˚=0.1 nm1\, \text{\AA} = 0.1\text{ nm}

  • Volume Conversion:

    • 1 L=1000 ml=1000 cc1\text{ L} = 1000\text{ ml} = 1000\text{ cc}

    • 1 dl=100 ml=0.1 L1\text{ dl} = 100\text{ ml} = 0.1\text{ L}

    • 1 ml=1000 μL1\text{ ml} = 1000\, \mu\text{L}

  • Weight Conversion:

    • 1 mg=1000 μg1\text{ mg} = 1000\, \mu\text{g}

    • 1 μg=1000 ng1\, \mu\text{g} = 1000\text{ ng}

    • 1 ng=1000 pg1\text{ ng} = 1000\text{ pg}

  • Temperature Conversion:

    • 0 ∘C=32 ∘F=273 ∘K0\, ^\circ\text{C} = 32\, ^\circ\text{F} = 273\, ^\circ\text{K}

    • ∘C=59×(∘F−32)^\circ\text{C} = \frac{5}{9} \times (^\circ\text{F} - 32)

    • ∘F=95×(∘C)+32^\circ\text{F} = \frac{9}{5} \times (^\circ\text{C}) + 32

Composition and Fluid Compartments of the Human Body

  • Average Adult Body Composition (by weight):

    • Water: 60%60\%

    • Proteins: 18%18\%

    • Fats: 15%15\%

    • Minerals: 7%7\%

  • Total Body Water (TBW): Approximately 60%60\% of human body weight, totaling roughly 42 L42\text{ L} in a 70 kg70\text{ kg} individual.

    • Intracellular Fluid (ICF): Constitutes about two-thirds of the total volume (28 L28\text{ L}).

    • Extracellular Fluid (ECF): Constitutes about one-third (14 L14\text{ L}). It comprises the Blood Plasma ($$2\text{ L