Cells, Tissue & Regulation Workshop: Fluid Compartments, Diffusion, Osmosis & Active Transport

Learning Objectives

By the end of this topic, you should be able to:

1. Fluid Compartments: Identify and describe major fluid compartments of the body.

2. Composition Differences: Compare interstitial fluid and intracellular fluid (ICF) compositions.

3. Membrane Function: Explain how plasma membranes separate extracellular fluid (ECF) from ICF.

4. Blood Composition: Identify the basic components of blood.

5. Plasma Influence: Describe the relationship between blood plasma and interstitial fluid, and how they influence ICF.

6. Concept of Osmolarity: Explain osmolarity and how a 1 molar NaCl solution gives approximately a 2 osmolar solution.

7. Laws of Diffusion: Understand diffusion laws and their biological implications for molecular movement in body fluids and gases.

8. Osmosis: Describe osmosis and the concepts of iso-, hypo-, and hypertonicity.

9. Plasma Proteins: Discuss the role of plasma proteins related to capillary permeability and colloid osmotic pressure.

10. Facilitated Diffusion: Explain facilitated diffusion, including carrier saturation and selectivity.

11. Active Transport: Describe the Na⁺-K⁺-ATPase pump and its ubiquity in cell functions.

12. Endocytosis Types: Differentiate between non-specific and receptor-mediated endocytosis, phagocytosis, and pinocytosis.

Major Fluid Compartments

• Interstitial Fluid: Also referred to as tissue fluid or intercellular fluid (distinct from intracellular fluid).

Electrolyte Concentration in Body Fluids

• Sodium (Na⁺): 140-160 mEq/L

• Potassium (K⁺): 120-140 mEq/L

• Calcium (Ca²⁺): Varies

• Chloride (Cl^-): Varies

• Bicarbonate (HCO₃^-): Varies

• Phosphate (HPO₄^2-): Varies

• Magnesium (Mg²⁺): Varies

• Colloid Osmotic Pressure: Influenced by proteins in blood plasma.

Osmosis and Tonicity

• Isotonic Solutions: Cells maintain normal size and shape; water moves freely in and out.

• Hypertonic Solutions: Cells lose water and shrink due to higher external solute concentration.

• Hypotonic Solutions: Cells absorb water, swell, and may burst due to lower external solute concentration.

Active Transport and Membrane Proteins

• Active Transport: Necessary for molecules that are:

  • Too large for channel proteins

  • Not lipid soluble

  • Cannot move down concentration gradients

• Na⁺-K⁺ Pump:

  • Operates using ATP, moves Na⁺ outside and K⁺ inside the cell against their gradients.

Role of Alcohol in Fluid Dynamics

• Diuretic Effect of Alcohol: Increases urine production and can lead to dehydration.

• Symptoms Related to Fluid Loss: Higher concentration of plasma proteins leads to more fluid pulled from ECF, contributing to headaches.

Diffusion Processes

• Diffusion: Movement based on concentration gradients; influenced by kinetic energy and temperature.

• Facilitated Diffusion: Requires membrane proteins for substances to cross the lipid bilayer.

Conclusion

Understanding fluid compartments, diffusion, osmosis, and active transport mechanisms are critical for comprehending bodily functions and responses to environmental changes. Apply this knowledge to clinical scenarios for better patient management.