Lecture Notes: Osmosis and Osmolarity
Introduction
- Review of basic cell and physiological concepts.
- Previous discussion: Diffusion and facilitated transport.
- Current focus: Movement of solutions and driving factors, especially osmosis.
Understanding Osmosis
- Osmosis: Movement of water (net diffusion) across a membrane due to solute concentrations.
- Water moves to areas of higher solute concentration (e.g., sodium chloride).
- Important for cell membrane dynamics where water causes the cell to swell.
Phospholipid Bilayer and Movement
- Phospholipid bilayer has cracks allowing water movement.
- Water crosses bilayers, despite not being afforded by the phospholipid bilayer's structure.
- Solutes (e.g., NaCl) typically do not cross without assistance (channels or carriers).
Osmosis Demonstration
- Using Chamber: Classic demonstration of osmosis using a glass tube and a semipermeable membrane.
- Water moves across the membrane to balance solute concentrations.
- Addition of solutes on one side causes water to rise on that side due to osmosis.
- Osmotic Pressure: Pressure required to stop water movement across a membrane.
Calculating Osmotic Pressure
- Not required to calculate, but understand the concept.
- 1 Osmole = 19,300 mmHg pressure.
- Normal cells work with milli-osmoles (mOsm/L), less intense pressure.
Cell Osmolarity
- Osmolarity: Concentration of solute particles, which can or cannot move across a membrane.
- Normal cell osmolarity: ~300 mOsm/L.
- Isotonic Solution: Equal solute concentration inside and outside (e.g., in the body).
Effects of Osmolarity on Cells
- Hypotonic Solution: Fewer solutes outside than inside. Water moves into the cell (cell swells).
- Hypertonic Solution: More solutes outside than inside. Water leaves the cell (cell shrinks).
Practical Applications
- Normal Saline: 0.9% saline solution, isotonic with cells (300 mOsm/L).
- Adding dextrose increases osmolarity, making it hyperosmotic, pulling water out of cells.
- Distilled water with dextrose creates a hypoosmotic solution, causing water to enter cells.
Key Takeaways
- Osmolarity is crucial for understanding cell-environment interactions.
- Water movement driven by solute concentration differences (osmosis).
- Understanding osmolarity helps in medical applications like IV fluids.
Ensure to review the concept of osmolarity and the effects of different solutions on cell volume and pressure. The understanding of osmotic pressure and its physiological implications is essential for further exploration in physiology.