BackCell Membrane Transport and Body Fluid Compartments: Study Notes
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Cell Membrane Transport
Introduction
Cell membrane transport refers to the mechanisms by which substances move across the plasma membrane of cells. This process is essential for maintaining cellular homeostasis, nutrient uptake, waste removal, and communication between cells.
Cell Membrane: A selectively permeable barrier composed mainly of a phospholipid bilayer and proteins.
Transport Mechanisms: Include passive and active processes that regulate the movement of ions, molecules, and water.
Body Fluid Compartments
Overview of Body Fluid Compartments
The human body contains fluids distributed in distinct compartments, each with unique chemical compositions and physiological roles.
Intracellular Fluid (ICF): Fluid within cells; accounts for approximately two-thirds of total body water.
Extracellular Fluid (ECF): Fluid outside cells; includes plasma (in blood) and interstitial fluid (between cells).
Plasma: The liquid component of blood, making up about 25% of ECF.
Interstitial Fluid: Surrounds tissue cells, comprising about 75% of ECF.
Example: In a 70-kg adult, total body water is about 42 liters, with 28 liters as ICF and 14 liters as ECF.
Fluid Distribution and Chemical Composition
Body fluid compartments differ in their ionic composition, which is crucial for physiological functions such as nerve impulse transmission and muscle contraction.
Intracellular Fluid: High in potassium (K+) and low in sodium (Na+).
Extracellular Fluid: High in sodium (Na+) and low in potassium (K+).
Plasma vs. Interstitial Fluid: Plasma contains proteins (e.g., albumin) not found in interstitial fluid.
Example: The selective permeability of cell membranes maintains these differences, which are essential for cell function.
Table: Major Body Fluid Compartments and Their Properties
Compartment | Volume (L) | Main Ions | Key Features |
|---|---|---|---|
Intracellular Fluid (ICF) | ~28 | K+, Mg2+, PO43- | High potassium, low sodium |
Extracellular Fluid (ECF) | ~14 | Na+, Cl-, HCO3- | High sodium, low potassium |
Plasma | ~3.5 | Na+, Cl-, proteins | Contains plasma proteins |
Interstitial Fluid | ~10.5 | Na+, Cl- | Similar to plasma, but lacks proteins |
Importance of Compartmentalization
Compartmentalization allows for specialized environments necessary for cellular processes. The movement of substances between compartments is tightly regulated by the cell membrane and associated transport proteins.
Homeostasis: Maintains stable internal conditions.
Selective Permeability: Ensures proper distribution of ions and molecules.
Additional info: The differences in ion concentrations across compartments are maintained by active transport mechanisms such as the sodium-potassium pump.
