Chapter 4 Flashcards
Define diffusion
Movement of particles from one location to another
Define flux
Amount of material crossing a surface in a unit of time
Net flux is greater on the side of the membrane
with higher concentration of solute
4 factors that influence net flux magnitude
Temperature, surface area, mass of molecule, medium
Define simple diffusion
Movement of solutes from one location to another due to their random thermal motion
Simple diffusion occurs through a medium such as
Air, water
Diffusion equilibrium means
Over time, solute will become evenly distributed
At diffusion equilibrium, net flux equals
Zero
For diffusion through the lipid bilayer, the hydrophobic interior
Limits diffusion rate
Diffusion through the lipid bilayer means
Passing through the membrane without any channels
Lipid soluble molecules diffuse through lipid bilayer
Rapidly and readily
Examples of molecules that diffuse readily
O2, CO2, N2, urea, fatty acids, steroids, alcohol
Polar and large molecules diffuse
Slowly and can be retained within the cell
Rate of movement depends upon
Permeability coefficients
Membranes effect on the rate of diffusion
1K to 1 M times slower than through the same layer of water
Ions that diffuse through channels
Na+, K+, Cl-, Ca2+
Exocrine glands release secretions into
Ducts
endocrine glands release secretions into
Blood capillaries into ISF
Merocrine, apocrine, and holocrine secretions are types of
Exocytosis via exocrine glands
Glands are
Groups of secretion-forming cells actively engaged in trans cellular movement of materials
Holocrine secretion
Entire cell becomes secretion (sebaceous glands) ex egg release
Merocrine secretion
Secretion released from vesicles (salivary glands)
Apocrine Secretion
Tip of cell becomes secretion
In groin/inguinal regions, not active until puberty
Apical
Luminal
Basolateral
Serosal
Basolateral membrane is near ____ and rests upon ____
Blood vessel network, basement membrane
Epithelial paracellular transport is limited by
Tight junctions, narrow passageway, and permeability varies
In Athsma and allergies
Damage to junctions and epithelial barrier allows pathogens access to restricted areas, sets off toxic cascade
Epithelial paracellular transport
Diffusion of substances between adjacent epithelial cells
Epithelial trans cellular transport
Substances move through apical or basal surface of cell, through cytosol, and exit on opposite surface
Opposite surfaces of epithelial cells have
Different concentration gradients
Na+ transport
Epithelial transcellular: active transport via Na+/K- ATPase pump on basal surface
Passive diffusion into cell on apical surface
Transepithelial osmosis
Movement of water can occur via osmosis as a result of solute concentration changes
When possible, water follows ___ which can cause _________________
Na+, large shifts of water in fluid compartments
Transcellular pathway of water diffusion
Aquaporins in the membrane
Paracellular pathway of water diffusion
Tight junctions between epithelial cells
Ion channels are
Integral membrane proteins (span membrane, simple donut ring or more complex structure)
Specificity is determined by
Pore size of the channel (small diameter blocks large molecules), charge (charged and polar surfaces of channel walls), and binding sites (# H2O molecules associated with diffusing ion)
Diffusion time increases in proportion to
Distance squared (D^2) that molecules diffuse
Diffusion is limited by
Distance
If a substance has to diffuse a long distance
It is very slow. Ineffective way to move solutes
Pneumonia
Lung inflammation/swelling means takes longer for gas to diffuse between alveolus and capillary
All cells have
Membrane potential/polarity difference
Membrane potential is
Separation of electrical charges across membrane of all cells
+ external
- internal
Tends to drive + in cell and - out of cell
Ionic movement (influx/efflux) is influenced by
Membrane potential and total concentration of charges (electrochemical gradient)
Diffusion or movement of charges is a voltage (or EMF) measure in mV using
The Nernst Equation
How is movement of ions across the PM regulated
Channel gating
Conformational change via
Ligand voltage or mechanically regulated ion gates
Permeability of the membrane directly related to
channels available per unit area membrane
Temperature
Permeability of the membrane inversely related to
resistance of each channel
Mass of diffusing substance
Increase in surface area means
Increase in diffusional rate and flux
Passive transport
Particles diffuse from high to low concentration
Net rate of diffusion proportional to
ECF concentration (Co) +/- ICF (Ci)
Fick’s diffusion equation
F(J) = PA (Co +/- Ci)
F(J) = net flux
P = diffusion coefficient of substance moving through membrane
A = area
Co= ECF concentration
Ci = ICF
Electrical potential difference
Electrical charge difference between ECF and ICF
Mediated-transporter systems are mechanisms for
Solutes that are too large, too charged, or both (glucose)
Protein transporters/carriers may be
Passive or active
Tmax
Maximum flux, transporters saturated
Transporters participate in
Facilitated diffusion, primary and secondary active
Magnitude of flux determined by
Solute concentration
Affinity of transporter for solute
#transporters available
Rate of conformational change
Affinity increased by
Increased specificity and increased electrical attraction
Describe carrier mediated / facilitated diffusion
Ligand specific protein escorts substance through membrane
Substance binds to channel protein, conformation change
Sweet smelling urine in diabetes because
Glucose exceeds Tmax, no more transport proteins available, excess glucose in blood stream and not enough in cells
Simple diffusion flux determined by
Concentration gradient
Facilitated diffusion maximal flux determined by
available transporters
GLUTs (glucose transporter proteins) function
Uptake of insulin into insulin dependent tissues such as skeletal and cardiac muscle and adipose tissue
GLUT1
Insulin independent
GLUT4
Insulin dependent
Secondary active transport indirectly uses ATP by
Using the energy created from an ion (electrochemical) gradient established by pumps
Transporters are ATPases that
Break down ATP, self-phosphorylate, enable binding of solute
Sodium pump is catalyzed by
Na+/K-ATPase
Na/K pump moves
3 Na out
2 K in
Movement of ions through pump fueled by
Hydrolysis of ATP
Ca2+ ATPase function
Removes cytosolic calcium to maintain low intracellular Ca vs high Ca in ECF
Ca homeostasis important to
Neurotransmitter release, skeletal muscle
Secondary transporters have
Two or more binding sites
Na concentrations extra and intra cellular
145 mM extra, 15 mM intra
K concentrations
5 mM extra, 150 mM intra
Osmosis driven by
Change in solute concentration on one side of membrane
Where solute concentration is greatest, water concentration is
Less
Addition of solute molecules to pure water
Lowers water concentration in solution
Osmolarity
Total concentration of a solution
Higher osmolarity
Lower water concentration
Water moves into area with
Highest osmolarity / least number of water molecules
Serum osmolarity
300 +/- 10 mOsm/L
Osmolarity directly related to
Osmotic pressure
^ osmolarity ^ osmotic pressure ^ rate of osmosis
Volume at equilibrium
Veq = Vor (Osm or / Osm eq)
Tonicity refers to
Concentration of non penetrating solutes that must be assisted across the PM (trapped in ECF) such as Na and Cl
Ionic composition of ICF and ECF
Na ECF 134-136 mmol/L
ICF 20 mmol/L
+53 mV
K ECF 3.8-5.4 mmol/L
ICF 150 mmol/L
-97 mV
What determines movement of water across a cell membrane
Tonicity
Isotonic
nonpen solutes in ECF = ICF
300 mOsm/L nonpen
Hypotonic
Water influx into cell (cell expands)
Less nonpen solutes in ECF than ICF
<300 mOsm/L nonpen
Hypertonic
water efflux out of cell (cell shrinks)
More nonpen solutes in ECF than ICF
>300 mOsm/L nonpen
Osmolarity measures
Total solutes present (both pen and nonpen)
Isosmotic
300 mOsm/L solute
Hyperosmotic
> 300 mOsm/L
Hypoosmostic
<300 mOsm/L
Blood volume restored by
Infusing isotonic NaCl
More effective than isosmotic soln of pen solute bc would only partially restore blood volume as some solute enters cells so would water, increasing ICF of TBW
Endocytosis ____ PM
Exocytosis ____ PM
Endocytosis removes PM
Exocytosis replenishes PM
Endocytosis
Mvmt of molecules into cell via vesicles
Pinocytosis
Fluid Endocytosis
PM invaginates and captures water + nonspecific dissolved substances into a vesicle
Phagocytosis
Immune cell mediated specific Endocytosis where particles are engulfed by pseudopodia (cytoplasmic projections) with formation of phagosomes that fuse with lysosomes for enzymatic destruction
Receptor mediated Endocytosis
Most specific mechanism
Ligands bind to membrane receptors at clathrin coated pits
Invaginates forming clathrin coated vesicles that move intracellularly
Ex. Cholesterol is removed from blood stream
Potocytosis
Less specific than receptor-mediated
Modified Endocytosis
No fusing with lysosomes
No clathrin
Form caveolus
Exocytosis
Replenishes membrane
Mechanism to secrete large substances from cell
Usually triggered due to calcium influx