Cell-Extracellular Interactions & Membrane Transport in Physiology

Extracellular Environment

All components of body located outside of cells, critical medium for cellular function and communication.

Intracellular Fluid

67% of total body water.

Extracellular Fluid

33% of remaining water, broken down into 20% blood plasma and 80% interstitial fluid.

Plasma Membrane

Selectively regulates passage of substances, impermeable to large molecules, permeable to small ions, nutrients, and waste products.

Non Carrier-Mediated Transport

Doesn't require specific protein, includes simple diffusion of lipid soluble molecules, ions through channels, and diffusion of water (osmosis).

Carrier Mediated Transport

Requires specific protein to transport molecules across membrane, includes facilitated diffusion and active transport.

Passive Transport

Movement from high to low concentration (gradient) without ATP.

Active Transport

Movement from low to high concentration (against gradient) requiring ATP and specific carrier pumps.

Diffusion

Efficient only over very short distances, driven by random motion until equilibrium.

Osmosis

Water moves from low solute concentration to high solute concentration, requires impermeable membrane to solute.

Osmotic Pressure

Force required to prevent osmosis, describes the tendency to draw water.

Mole

Molecular weight of a compound in grams; one mole contains 6.02 x 10 particles.

Molarity

Moles of solute per liter.

Osmolarity

Total molarity of a solution, accounting for all solute particles.

Tonicity

Effect on volume of a cell by solute concentration impact on osmosis of water.

Isotonic Solution

Solution has the same concentration of solutes as the cell, no net movement.

Hypotonic Solution

Solution has lower solute concentration than the cell, water moves into the cell.

Hypertonic Solution

Solution has higher concentration of solutes than inside the cell, water leaves the cell.

Regulation of Blood Osmolarity

Crucial for cellular function, regulated by a negative feedback system.

Facilitated Diffusion

Form of carrier mediated transport powered by random movement of molecules, no ATP needed.

Primary Active Transport

Energy derived directly from hydrolysis of ATP.

Ca Pump

Pumps calcium out of cytoplasm into extracellular fluid or into cisternae of the ER.

Na/K Pump

Pumps 3 Na ions out of the cell and 2 K ions into the cell for each ATP hydrolyzed.

Secondary Active Transport

Energy to move molecule against gradient is derived from coupling the movement of another molecule down the gradient.

Symport

Other molecule is moved in the same direction as Na (into cell).

Antiport

Other molecule is moved in the opposite direction of Na (out of cell).

Bulk Transport

Includes exocytosis and endocytosis for large molecules.

Exocytosis

Large molecules are secreted from the cell by fusion of a transport vesicle with the plasma membrane.

Endocytosis

Transport of large molecules into the cell by membrane invagination.

Cell Signaling

How adjacent or distant cells communicate with each other, essential for coordinating activities.

Gap Junctions

Channels between adjacent cells that allow direct passage of ions and small regulatory molecules.

Paracrine Signaling

Local signaling where cells secrete molecules that diffuse to nearby target cells.

Synaptic Signaling

Specialized form of paracrine signaling where neurons secrete neurotransmitters across a synapse.

Endocrine Signaling

Long distance signaling where glands secrete hormones into the bloodstream.

Receptor Proteins

Target cell can respond to a chemical signal only if it has specific receptor proteins.

Second Messengers

Intermediaries produced inside the cell after a polar signal molecule binds to a surface receptor.

G-Proteins

Molecular switches that link surface receptor to enzyme that produces second messenger.