المحاضرة الأولى فسيو (قبل التعديل)

Body Water

• Water: Accounts for 65% of body weight
• Body fluid compartments:
  • Intracellular fluid (ICF): Inside cells, 2/3 of total body fluids, ~25-28 liters
  • Extracellular fluid (ECF): Outside cells, 1/3 of total body fluids, ~14-15 liters
  • ECF Breakdown
    • Plasma: Inside blood vessels, ~3-3.5 liters
    • Interstitial fluid: In spaces between cells, ~10-12 liters
    • Trans-cellular Fluid: In body cavities like GIT, eyes, joints, and cerebrospinal fluid (CSF), ~1 liter
• Body fluid composition:
  • ECF: High in Sodium, Chloride, and Bicarbonate ions
  • ICF: High in Potassium, Protein, Phosphate, and Magnesium

Measuring body fluid compartments

• Indicator/dye dilution technique: Useful for measuring fluid compartments
  • Inject: Known amount of dye into body
  • Distribution: Allow dye to distribute within the compartment
  • Measure: Dye concentration in the target compartment
  • Calculate: Compartment volume using the formula: Volume of fluid = Amount of dye injected / Concentration of dye
• Key indicator characteristics:
  • Non-toxic
  • Not metabolized
  • Not rapidly excreted
  • Rapid and even distribution throughout the compartment
  • Easily measurable
• Measuring total body water (TBW):
  • Indicators: Deuterium oxide (D2O), Aminopyrine, Tritium oxide
  • Distribution: Evenly in ICF and ECF
• Measuring ECF volume:
  • Indicators: Mannitol, Inulin, Sucrose
  • Distribution: ECF only, does not enter ICF
• Measuring ICF volume:
  • Formula: ICF volume = TBW - ECF volume
• Measuring plasma volume:
  • Indicators: Evans blue dye (binds to plasma protein), Serum albumin labeled with radioactive iodine
• Percentage of TBW:
  • Female: 50%
  • Male: 60%
  • Children: 70%
  • Old age: Decreased

Function of body water

• Regulation of chemical reactions: Crucial for all biochemical processes
• Thermoregulation: Evaporating 1 gram of water requires 0.58 calories (latent heat of evaporation)
• Solvent: Allows many substances to dissolve
• Digestive function: Involved in digestive secretions and enzyme activity
• Filtration: In kidneys
• Osmotic function: Maintaining osmotic balance
• Moistening and lubrication: Keeps tissues like mouth, eyes, and nose moist and lubricates joints
• Absorption: In the gastrointestinal tract and kidneys.
• Excretion: Through the gastrointestinal tract, kidneys, and skin

Homeostasis

• Homeostasis: The state of maintaining a stable internal environment crucial for body function. Controlled through systems.
• Body systems:
  • Nervous system: Provides rapid control
  • Endocrine system: Provides slow control
• Feedback mechanisms: Mechanisms that help maintain homeostasis:
  • Negative feedback: The response counters the original stimulus
  • Examples:
    • Increase in CO2 leads to hyperventilation, reducing CO2 levels
    • Increase in blood glucose triggers insulin secretion, lowering glucose levels
    • Increase in arterial blood pressure triggers vasodilation and decreased heart rate, reducing blood pressure
  • Positive feedback: The response enhances the original stimulus. Often disruptive but can be useful.
  • Examples:
    • Heart failure leads to decreased cardiac output, reducing arterial blood pressure, further compromising blood flow and exacerbating heart failure.
    • Heat stroke leads to increased metabolic rate, producing more heat.
    • Cervical dilation during labor triggers uterine contractions, pushing the baby further down, leading to more dilation and contractions until delivery.

Body Water

• Body water is maintained by balancing water input and output.
• Water intake is approximately 2400 ml per day.
• Sources of water intake include exogenous water (ingested water and liquids) and endogenous water (synthesized through metabolism).
• Water output is also approximately 2400 ml per day.
• Water output includes urine, insensible loss (water vapor from lungs and skin), sweating, and feces.
• Control of water input is primarily regulated by thirst sensation.
• Thirst sensation is triggered by increased plasma osmolarity (hypertonicity), decreased blood volume (hypovolemia), and Angiotensin II.
• Control of water loss is mainly controlled by adjusting urine volume via antidiuretic hormone (ADH).
• ADH is secreted from the posterior pituitary gland and its secretion is stimulated by hypertonicity and hypovolemia.

Homeostasis

• Homeostasis refers to the maintenance of a stable internal environment.
• Key aspects of homeostasis include regulating body water, ions, body temperature, blood glucose, pH, and physiological processes.
• Mechanisms of homeostasis include negative and positive feedback systems.
• In negative feedback systems, the response inhibits the stimulus, ultimately restoring balance.
• In positive feedback systems, the response amplifies the stimulus, potentially causing harm.
• Some positive feedback systems can be beneficial, such as during labor.

Human Body Organization

• The human body is structured hierarchically: Cells, tissues, organs, systems, and the whole body.
• Cells are the basic units of structure and function, containing a nucleus and cell organelles.
• Cells are surrounded by a plasma membrane, which allows selective communication between the intracellular and extracellular compartments.
• Body fluid is composed of water and dissolved substances, including organic molecules (carbohydrates, proteins, lipids, nucleic acids) and inorganic molecules (ions).
• Body fluids represent approximately 65% of body weight, with ICF (intracellular fluid) constituting 2/3 and ECF (extracellular fluid) constituting 1/3 of total bodily fluids.

Body Fluid Compartments

• The ECF comprises plasma, interstitial fluid, and trans-cellular fluid.
• The ECF is separated from the ICF by the capillary wall.
• The composition of body fluids differs between ECF and ICF.
• The ECF primarily contains sodium, chloride, and bicarbonate ions.
• The ICF primarily contains potassium, protein, phosphate, and magnesium.

Measurement of Body Fluid Volumes

• The volume of body fluid compartments can be measured using the indicator or dye dilution technique.
• The volume of a compartment is calculated by dividing the amount of dye injected by the concentration of dye in the compartment.
• The indicator or dye must be non-toxic, non-metabolized, not rapidly excreted, rapidly and evenly distributed, and easily measurable.
• Total body water (TBW) can be measured using indicators like deuterium oxide, aminopyrine, and tritium oxide.
• ECF volume can be measured using indicators like mannitol, inulin, and sucrose.
• ICF volume can be calculated by subtracting ECF volume from TBW.
• Plasma volume can be measured using indicators like Evans blue dye and radioactive iodine labeled serum albumin.
• The percentage of TBW varies by age, sex, and fat content.
• Higher fat percentage and increased age lead to lower percentages of body water.

Functions of Body Water

• Body water is crucial for regulating chemical reactions, transporting substances, maintaining arterial blood pressure, dissolving substances, digestive function (digestive secretions and enzyme activity), filtration (kidney), osmotic function, moistening tissues (mouth, eyes, nose), lubricating joints, absorption (GIT and kidney), and excretion (GIT, kidney, and skin).
• The latent heat of evaporation of water (0.58 cal/g) is important for regulating body temperature.