Cell Membrane: Transport, Osmosis, and Body Fluids Flashcards
Membrane Transport
Cell membranes are selectively permeable
What are the two properties that influence whether they can permeate the cell membrane without assistance?
- Relative solubility of particle in lipid
- Size of the particle
Two forces are involved in accomplishing transport
- Passive forces (no energy required)
- Active forces (energy/ATP required)
Diffusion
Depends on the random movement of molecules.
Establishes equilibrium without energy.
Molecules move from areas of high concentration to low concentration.
Occurs across a permeable membrane.
Is crucial to survival of every cell.
Facilitated Diffusion
Molecule binds and causes conformational change in order to release through membrane
Ex: GLUT 1 (glucose transporter in erythrocytes) is needed for cellular respiration
Non-permeable membrane
When a solute is too large or too hydrophilic to move through membrane
Channel-mediated transport
Gated ion channel that is specific to one type of ion.
Opens in response to stimulus and lets many ions in at once
Primary Active Transport
Ex: The Na+/K+ ATPase
Utilized ATP for a switch of Na and K (3 Na out and 2 K in)
Critical for survival
Secondary Active Transport
ATP is not directly used
Ex: Glucose transport (SGLT1): Na provides energy, glucose is moved against concentration gradient
Osmosis
Net diffusion or movement of water down its concentration gradient
Water moves by osmosis to the area of higher solute concentration
Relationship between solute and water concentration in solution
Higher the solute concentration, the lower the concentration of water
Channels
Water is small enough to permeate the plasma membrane
The driving force for movement is the concentration gradient
Ex: aquaporins
Permeable Membrane
Membrane allows both water and solute to pass
Semi-permeable membrane
Membrane allows water to pass but not solute
Ex: water will move (osmosis) to balance out solute concentration
Hydrostatic Pressure
Solute can’t move across membrane thus water has to move and creates a lower level of fluid where water moves from and higher level where water moved to.
The difference is called hydrostatic pressure difference
Osmolarity (mOsm/L) / Osmolality (mOsm/kg)
Total amount of particles per amount of solution
The intracellular and extracellular fluid is essentially identical (~290 mOsm)
Higher concentration of impermeable substance in a cell:
Water is forced to move and cell volume and shape change
Tonicity
Ultimate effect a solution has on cell volume which determines whether cell size remains the same, swells, or shrinks when a solution surrounds the cell
Effective osmolarity
refers to the osmolarity of non permeable particles in solution
controls the actual movement of water
Isotonic
No net movement of water; no change in cell volume
Intracellular osmolarity = extracellular osmolarity
Hypotonic
Water diffuses into cells; cell swells
Hypertonic
Water diffuses out of cells; cells shrink
Clinical Signs of Hydrations Status
- Skin turgor (elasticity after tenting)
- Mucous membranes (pink and moist)
- Capillary Refill time (should be quick)
- Eyes (normal vs. sunken)
- Hematocrit; more quantifiable, more reliable
Intracellular fluid
Fluid contained within the cells
Extracellular fluids
fluid outside the cells (plasma, interstitial fluid, minor ECF components)
Total Body Water (TBW)
ICF + ECF = ICF + ISF + Plasma
Total plasma protein (g/dL)
Hematocrit
Fraction of plasma occupied by red blood cells (RBC) after centrifugation
Body Water Dynamics: Basic Principles
-Water shifts between compartments to maintain equality
-Electrolytes, such as Na, do not cross cell membranes and are confined to ECF
-Any loss or gain of water and/or electrolytes must initially occur in the ECF
-Changes in TBW, total plasma protein and hematocrit may occur
