Body Fluids and Their Distribution

Body Fluids

• Extracellular Fluid (ECF): The fluid environment where cells live (fluid outside the cells)

  • Contains: ions, oxygen, nutrients, and waste products
  • Two components:
    • Plasma: Inside the blood cells
    • Interstitial Fluid: Around the cells

• Intracellular Fluid (ICF): Fluid contained within all body cells

  • Higher level of K+ and less Na+
  • Contains protein with a negative charge

• ICF accounts for 2/3 of total body water, ECF accounts for 1/3.

  • Total Body Water = 42L (in a 70kg male)
  • ICF = 28L
  • ECF = 14L
    • Plasma: 3.5L
    • Interstitial Fluid: 10.5L

• Why is there more water in ICF? (Not elaborated in the text)

• Why is there more water in the interstitial space? (Not elaborated in the text)

Balancing the Internal and External Environment

• Cells exchange nutrients and waste with their surroundings.

• The intracellular fluid is influenced by the interstitial fluid, which is influenced by the plasma. The plasma, in turn, is influenced by the organ systems it passes through.

• Internal environment = fluid surrounding the cells (extracellular fluids)

Homeostasis

• Definition: The maintenance of relatively stable internal environments (extracellular fluids).
• Structural design enables physiological mechanisms to operate effectively, each organ's structure supports its function.
• Example: Rib cage protects the heart and lungs while also contributing to breathing.

Levels of Organization

• 1. Chemical: Atoms (smallest part of the body) and molecules (un-living things made up of atoms)
  • Examples of atoms: Oxygen, Nitrogen, Carbon, Hydrogen
  • Examples of molecules: Water, CO2, CHO, Proteins
• 2. Cellular: The basic live organizational unit of the human body. The smallest unit that can perform life's processes.
  • Examples: Muscle cells, nerve cells
• 3. Tissue: A group of similar cells (structure and specialized functions) that work together on a task.
  • Examples: Epithelia, connective, muscle, and nerve tissue
• 4. Organs: Made up of different tissues that work together for a common function.
• 5. System Level: Made up of multiple organs that work together.
• 6. Organism Level: Includes all the systems working together.
• The whole body (organism) is made up of 12 systems.

Tissue (Further Explanation)

• Few cells surrounded by a lot of extracellular material: This material supports and secures different body parts and allows for material exchange between the cell and its environment.

Organism and Homeostasis

• Homeostasis: Maintaining a dynamic state of internal consistency.
  • The internal environment remains relatively stable despite changes in the external environment.
  • Stable does not mean rigid; values can vary within a narrow range (normal physiological range).
• Golden goal of every organ: To maintain homeostasis.
• Homeostasis is essential for survival and function of all cells.

Factors Homeostatically Regulated

• Concentration of nutrients (glucose, oxygen, carbon dioxide, and waste products)
• Concentration of water, salt, and other electrolytes
• pH
• Blood volume and pressure
• Body temperature

Homeostasis & Controls

• Successful compensation: Homeostasis established
• Failure to compensate: Pathophysiology, Illness, Death

Homeostatic Control Mechanisms

• Three (3) parts:
  • Receptor: Detects changes in the internal environment (stimuli)
  • Control Center: Determines the "set-point" (the desired value for the regulated factor)
  • Effector: Initiates a response to change the regulated factor back to the set-point.

Regulation of Internal Constancy = Homeostasis

• Homeostasis is NOT a static state: It's dynamic - values fluctuate around a set-point.
• Relies on negative feedback loops:
  • Sensor: Monitors internal conditions and detects changes.
  • Integrating center (controller): Receives and integrates information.
  • Effector: Responds to changes by altering its activity to return the condition to normal levels.

Homeostatic Control Mechanisms

• Feedback Control:
  • Positive (Amplifies the initial stimulus, usually not homeostatic)
  • Negative (Reduces the initial stimulus, usually homeostatic)

Basic Cell Functions

• Obtaining nutrients and oxygen from the environment.
• Performing chemical reactions to provide energy (metabolism).
• Eliminating waste products (CO2).
• Synthesizing cellular components (e.g., protein).
• Controlling the movement of substances in and out of the cell.
• Sensing and responding to changes in the environment.
• Reproduction (except for nerve and muscle cells).

Specialized Cell Functions

• Each cell has a specific function.
• Example: White blood cells phagocytize foreign materials, while red blood cells carry oxygen.

Cell Membrane

• Thin and mechanically weak membrane surrounding each cell (also called the plasma membrane).
• Functions:
  • Maintaining cell structure.
  • Controlling the movement of substances in and out (selective permeability).
  • Regulating cell-cell interactions.
  • Acting as an interface between the cytoplasm and the external environment.

Cell Membrane Importance

• Creates a barrier between the ICF and ECF.
• If the cell membrane breaks, the cell dies.
• Creates concentration differences between the intracellular and extracellular solutions.
  • For example, there is a higher K+ concentration inside the cell than outside, and a higher Na+ concentration outside the cell than inside.

Cell Membrane Composition

• Protein (55%)
• Phospholipids (25%)
• Cholesterol (13%)

Simple Diffusion

• Permeable to:

  • Non-polar molecules (O2)
  • Lipid-soluble molecules (steroids)
  • Small polar covalent bonds (CO2)
  • Water (small size, lack of strong charge)

• The degree of diffusion is determined mostly by lipid solubility.

• Impermeable to:

  • Large polar molecules (glucose)
  • Charged inorganic ions (Na+)

• Process: Substances move directly through the intermolecular spaces of the membrane (simple diffusion).

• Energy-independent: Does not require cellular energy.

Facilitated diffusion

• Process: The diffusion of lipid-insoluble or water-soluble substances across the membrane down their concentration gradients, aided by membrane proteins.
• Substances: K+, Na+, Ca2+, glucose, amino acids, urea, etc.