mbbs ims msu

Diffusion SummaryDiffusion Summary

• Diffusion is the movement of Diffusion is the movement of molecule from one location to molecule from one location to another by random thermal motionanother by random thermal motion

The net flux between the two The net flux between the two compartments always proceed from compartments always proceed from higher to lower concentrationhigher to lower concentration

Diffusion equilibirum is reached when Diffusion equilibirum is reached when the two concentration become equalthe two concentration become equal

Osmosis SummaryOsmosis Summary

• Water crosses membranes by diffusing Water crosses membranes by diffusing through protein channels in the through protein channels in the membranemembrane

• Osmosis is the diffusion of water from Osmosis is the diffusion of water from higher water concentration to lower water higher water concentration to lower water concentration. Osmolarity total solute concentration. Osmolarity total solute concentration in the solution. The higher concentration in the solution. The higher osmolarity of a solution the lower the osmolarity of a solution the lower the water concentration.water concentration.

• Osmosis across membrane permeable to water Osmosis across membrane permeable to water but impermeable to solute leads to increase but impermeable to solute leads to increase volume in the compartment that initially had volume in the compartment that initially had higher osmolarity.higher osmolarity.

• Application to a solution of sufficient pressure Application to a solution of sufficient pressure will prevent the osmotic flow of water into the will prevent the osmotic flow of water into the solution from the compartment of pure water. solution from the compartment of pure water. This pressure is osmotic pressure.This pressure is osmotic pressure.

• The greater the osmolarity of a solution the The greater the osmolarity of a solution the greater the osmotic pressuregreater the osmotic pressure


• The osmolarity of the extracellular fluid is The osmolarity of the extracellular fluid is about 300 mOsm. Intracellular fluid has about 300 mOsm. Intracellular fluid has osmolarity equal to that of extracellular osmolarity equal to that of extracellular fluidfluid

• Na and Cl ions are major effectively Na and Cl ions are major effectively nonpenetrating solutes in the nonpenetrating solutes in the extracellular fluids. K ions and various extracellular fluids. K ions and various organic solute are nonpenetrating solute organic solute are nonpenetrating solute in the intracellular fluid in the intracellular fluid


Endocytosis and ExocytosisEndocytosis and Exocytosis

• During endocytosis vesicles will be formed During endocytosis vesicles will be formed that enclose a small volume of extracellular that enclose a small volume of extracellular materialmaterial

• Three classes of endocytosis (1) fluid Three classes of endocytosis (1) fluid endocytosis (2) adsorptive endocytosis and endocytosis (2) adsorptive endocytosis and (3) phagocytosis(3) phagocytosis

• Vesicles content digested by lysosome Vesicles content digested by lysosome enzymeenzyme

• Exocytosis provide a means of adding Exocytosis provide a means of adding components to the plasma membrane and a components to the plasma membrane and a route to release impermeable molecules into route to release impermeable molecules into extracellular fluid extracellular fluid

Mediated Transport SystemMediated Transport System

• Involve binding of the transported Involve binding of the transported solute to transporter protein in the solute to transporter protein in the membrane. Changes in the membrane. Changes in the conformation of the transporter conformation of the transporter move the binding site to the opposite move the binding site to the opposite side of the membraneside of the membrane

• The binding sites exhibit chemical The binding sites exhibit chemical specificity and saturationspecificity and saturation

• Facilitated diffusion move molecule Facilitated diffusion move molecule from higher to lower concentration from higher to lower concentration across the membrane by means of across the membrane by means of transporter. Metabolic energy is not transporter. Metabolic energy is not required.required.

• Active transport moves molecules Active transport moves molecules against an electrochemical gradient against an electrochemical gradient across a membrane by means of across a membrane by means of transporter and require energytransporter and require energy


• Primary active transport uses the Primary active transport uses the phosphorylation of the transporter by ATP to phosphorylation of the transporter by ATP to drive the transport processdrive the transport process

• Secondary active transport uses the binding Secondary active transport uses the binding of ions (often Na) to the transporter to drive of ions (often Na) to the transporter to drive the transport processthe transport process

• In secondary active transport the downhill In secondary active transport the downhill flow of an ion is linked to the uphill flow of an ion is linked to the uphill movement of a second solute either in the movement of a second solute either in the same direction as the ion (cotransport) or same direction as the ion (cotransport) or opposite direction of the ion opposite direction of the ion (countertransport) (countertransport)


Epithelial TransportEpithelial Transport

• Molecules can cross epithelial layer by (1) Molecules can cross epithelial layer by (1) through the extracellular spaces between through the extracellular spaces between the cells (paracellular pathway) and (2) the cells (paracellular pathway) and (2) through the cell across both luminal and through the cell across both luminal and basolateral membranebasolateral membrane

• The permeability and transport The permeability and transport characteristics of the luminal and characteristics of the luminal and basolateral plasma membrane differ, basolateral plasma membrane differ, resulting in the ability of the cells to resulting in the ability of the cells to actively transport a substance between actively transport a substance between the fluid on one side of the cell and the the fluid on one side of the cell and the fluid on the opposite side of the cell fluid on the opposite side of the cell

• Major chemical substance in Major chemical substance in extracellular fluid are Na and Cl. extracellular fluid are Na and Cl. Intracellular contain high K and Intracellular contain high K and negatively charged proteins and negatively charged proteins and phosphate compoundphosphate compound

• Electrical resulting from this Electrical resulting from this distribution have a significant role in distribution have a significant role in cell integration and communicationcell integration and communication

Membrane PotentialsMembrane Potentials

• Potential difference determine the Potential difference determine the difference in the amount of charge difference in the amount of charge between two points.between two points.

• The movement of electric charge is The movement of electric charge is called currentcalled current

• The current depends on the potential The current depends on the potential difference between the chargesdifference between the charges

Membrane PotentialsMembrane Potentials

Terms describing the Terms describing the membrane potentialmembrane potential

• Potential – Potential difference: The Potential – Potential difference: The difference between two pointsdifference between two points

• Membrane potential: The voltage Membrane potential: The voltage between inside and outside the cell between inside and outside the cell

• Resting potential: The steady Resting potential: The steady membrane potential of a cell that is membrane potential of a cell that is not producing an electric signal not producing an electric signal

Ion DistributionIon Distribution

• Particles / moleculesParticles / molecules– electrically chargedelectrically charged

• AnionsAnions– negatively chargednegatively charged

• CationsCations– positively charged positively charged

• Anions (-)Anions (-)– Large intracellular proteinsLarge intracellular proteins– Chloride ions Cl-Chloride ions Cl-

• Cations (+)Cations (+)– SodiumSodium Na+Na+– Potassium Potassium K+ K+

Ion DistributionIon Distribution

The resting Membrane The resting Membrane PotentialPotential

• All cells have potential difference, All cells have potential difference, inside negatively charged with inside negatively charged with respect to the outside. This potential respect to the outside. This potential is the resting membrane potential is the resting membrane potential

• Separation of electric Separation of electric charge across charge across plasma membranes plasma membranes known as Membrane known as Membrane PotentialPotential

• Membrane Potential Membrane Potential provides an electric provides an electric force that influences force that influences the movement of the movement of ions across the ions across the membrane. membrane.

Role of Electric Forces on Role of Electric Forces on Ion MovementIon Movement

Resting Membrane PotentialResting Membrane Potential

• The magnitude of the resting The magnitude of the resting membrane potential determined by membrane potential determined by two factors:two factors:

1.1. Differences in specific ion Differences in specific ion concentration in the intracellular concentration in the intracellular and extracellular fluidsand extracellular fluids

2.2. Differences in the membrane Differences in the membrane permeabilities to the different ionspermeabilities to the different ions

• Plasma membrane Na, K- ATPase Plasma membrane Na, K- ATPase pumps maintain intracellular Na pumps maintain intracellular Na concentration low and K highconcentration low and K high

• In almost all resting cells, the plasma In almost all resting cells, the plasma membrane is much more permeable membrane is much more permeable to K than to Na to K than to Na

Resting Membrane PotentialResting Membrane Potential

Electrochemical GradientElectrochemical Gradient

• The Direction and Magnitude of ion fluxes across The Direction and Magnitude of ion fluxes across membranes depend on both the concentration membranes depend on both the concentration difference and the electrical difference.difference and the electrical difference.

• These two forces are collectively known as the These two forces are collectively known as the electrochemical gradientelectrochemical gradient..

Graded Potentials and Action Graded Potentials and Action PotentialsPotentials

• Changes in the membrane potential from Changes in the membrane potential from its resting level produce electric signalsits resting level produce electric signals

• These signals occur in two forms: graded These signals occur in two forms: graded potentials and action potentialspotentials and action potentials

• Graded signaling over short distance while Graded signaling over short distance while action potentials are long distance signals action potentials are long distance signals of nerve and muscle membrane of nerve and muscle membrane

Health & Medicine

mbbs ims msu