Physiology Chapter 1

Physiology

• Describes the physicochemical mechanisms responsible for the origin, development, and progression of life.
• Divided into various branches: viral, bacterial, cellular, plant, invertebrate, vertebrate, mammalian, and human physiology.
• Human physiology focuses on specific characteristics and mechanisms of the human body, integrating functions of cells, tissues, and organs.

Cells as Living Units

• Cells are the basic living units of the body, specialized to perform various functions; approximately 30-40 trillion human cells exist.
• Microorganisms, known as microbiota, significantly outnumber human cells and inhabit areas like skin, mouth, gut, and nose; they can contribute to disease.

Extracellular Fluid (Internal Environment)

• Comprises 50-70% (about 2/3) of the human body fluids, known as intracellular fluid, while 1/3 is extracellular fluid (ECF).
• Vital for transporting ions and nutrients; ECF maintains the body’s internal environment ("milieu intérieur").
• Necessary concentrations of oxygen, carbohydrates, ions, amino acids, and fatty acids are critical for health.

Differences in Fluid Composition

• Extracellular fluid (ECF) characterized by high sodium and chloride levels.
• Intracellular fluid (ICF) contains large amounts of potassium, magnesium, and phosphate.

Homeostasis

• Coined by Walter Cannon in 1929; refers to maintaining stable internal conditions despite external changes.
• Homeostasis involves maintaining ranges rather than fixed values; involves integrated control systems for physiological functions.
• Disease can disrupt homeostasis and results in compensatory mechanisms that may have trade-offs.

Blood Circulation and Transport

• Blood circulates through the body in blood vessels, with fluids exchanged in capillaries and interstitial spaces.
• Blood travels the entire circuit approximately once per minute at rest, increasing to six times during activity.
• Capillaries facilitate the exchange of extracellular fluid between plasma and interstitial fluid; they are impermeable to large plasma proteins.

Nutrient Origins in Extracellular Fluid

• Respiratory system: Oxygen diffuses from alveoli into capillaries, facilitated by a thin alveolar membrane.
• Gastrointestinal Tract: Proteins, fatty acids, and amino acids are absorbed from digested food into extracellular fluid.
• Liver and other metabolic organs modify and store substances, making them usable; also involved in waste elimination.
• Musculoskeletal system allows for the movement necessary to seek nutrition and provides protection.

Removal of Metabolic End Products

• Carbon dioxide is expelled by the lungs, a primary metabolic waste product.
• Kidneys filter plasma, removing urea, uric acid, excess ions, and water, reabsorbing needed substances.
• The gastrointestinal tract excretes undigested materials as feces, while the liver detoxifies and excretes waste into bile.

Regulation of Body Functions

• The nervous system has three major components: sensory input, central nervous system (CNS) processing, and motor output; autonomic nervous system controls internal organs subconsciously.
• The endocrine system complements nervous function, involving hormonal regulation via endocrine glands sending hormones through extracellular fluid to various body regions.
• Key hormones include thyroid hormones (regulating metabolic reactions), insulin (carbohydrate metabolism), and hormonal influence on sodium/potassium levels and bone mineral balance.

Protection of the Body

• The immune system comprises white blood cells, thymus, lymph nodes, and lymph vessels, distinguishing self from harmful entities.
• The integumentary system (skin and appendages) provides a physical barrier, cushioning, thermoregulation, sensory functions, and excretion.