Overview
This lecture reviews the main processes that move fluids and solutes within the body, including cell membrane transport, diffusion, osmosis, and the roles of hydrostatic and oncotic pressure in fluid balance.
Cell Membrane Structure and Function
- The cell membrane is made up of a phospholipid bilayer with hydrophilic heads and hydrophobic tails.
- The bilayer acts as a barrier, allowing some substances to pass based on size and charge.
- Channel and carrier proteins in the membrane help transport certain molecules.
Types of Diffusion
- Simple Diffusion: Movement of small, non-charged molecules (like Oâ‚‚ and COâ‚‚) from high to low concentration without energy.
- Facilitated Diffusion: Movement of larger or charged molecules (like glucose and ions) from high to low concentration with the help of membrane proteins; also passive and does not require energy.
Active Transport
- Active transport moves molecules from low to high concentration ("against" the gradient) using energy (ATP) and membrane proteins.
- This process is essential for maintaining certain cellular conditions.
Osmosis
- Osmosis is the passive movement of water across a semi-permeable membrane to balance solute concentrations inside and outside the cell.
- Water moves toward areas with higher solute concentration (higher osmolarity).
- Osmosis can cause cells to swell (if water moves in) or shrink (if water moves out), depending on relative osmolarity.
Hydrostatic and Oncotic Pressure
- Oncotic (Colloidal Osmotic) Pressure: Pulls water into capillaries, mainly created by plasma proteins like albumin.
- Low albumin reduces oncotic pressure, causing fluid to leave capillaries and resulting in swelling.
- Hydrostatic Pressure: Pushes water out of capillaries into the interstitial space, highest in arteries and created by heart contractions.
- Hydrostatic pressure enables filtration, moving water and nutrients to tissues.
- These pressures work together to maintain proper fluid distribution between blood vessels and tissue spaces.
Key Terms & Definitions
- Phospholipid bilayer — cell membrane structure with hydrophilic heads and hydrophobic tails.
- Simple diffusion — passive movement of small/non-charged molecules from high to low concentration.
- Facilitated diffusion — passive movement of large/charged molecules via membrane proteins.
- Active transport — movement of molecules from low to high concentration using ATP.
- Osmosis — passive water movement across a semi-permeable membrane toward higher solute concentration.
- Oncotic pressure — pulling force on water by plasma proteins, mainly albumin.
- Hydrostatic pressure — pushing force of fluid inside blood vessels, generated by the heart.
Action Items / Next Steps
- Review additional videos on IV fluids and osmosis as suggested in the lecture.
- Study more on fluid and electrolyte balance in upcoming lectures or readings.