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Transport Processes
Anatomy and Physiology Text and LaboratoryWorkbook, Stephen G. Davenport, Copyright 2006, All
Rights Reserved, no part of this publication can beused for any commercial purpose. Permission requests
should be addressed to Stephen G. Davenport, LinkPublishing, P.O. Box 15562, San Antonio, TX, 78212
Body Fluid
All the cells of the body are linked togetherby body fluid. This fluid serves as the transportmedium for oxygen, carbon dioxide, nutrients,wastes, hormones, electrolytes, antibodies, etc.
Cells organize the body into two anatomic fluidcompartments, the (1) intracellular and the (2) extracellular
compartments.
In order for fluids to enter the body and to movefrom compartment to compartment, they mustpass through the plasma membranes of cells.
Anatomical Fluid
Compartments
The two anatomical fluid compartments
of the body are the intracellular and
extracellular compartments.
Intracellular Fluid Compartment The intracellular fluid compartment is the
compartment formed by all of the spaces withinthe cells of the body, and it containsintracellular fluid (ICF).
Intracellular fluid accounts for about 63% of thebodys total fluid.
Fig. 5.1
Extracellular Fluid Compartment
The extracellular fluid compartment is thecompartment consisting of the spacessurrounding the cells of the body, and it containsextracellular fluid (ECF).
The two major divisions of the extracellular
compartment are the (1) interstitial compartment and the (2) intravascular
compartments.
These extracellular fluid compartments function tomaintain the normal fluid volume and chemicalconcentration of the intracellular compartment.
Interstitial Compartment The Interstitial Compartment consists of the
microscopic spaces, the interstices, amongadjacent cells. The interstitial compartmentcontains interstitial fluid. Interstitial fluid accountsfor about 30% of the bodys total fluid volume.
Fig. 5.2
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Intravascular Compartment The Intravascular Compartment consists of the spaces
within the bodys blood and lymphatic vessels. Its fluidaccounts for about 7% of the bodys total fluid volume.
Plasma is the fluid component of blood, and lymph is thefluid component of the lymphatics.
Fig. 5.3
Photograph of developing adipose tissue with blood vessels
showing extracellular and intracellular compartments (430x).
Fig. 5.4
Transport Processes
Transport across the plasma membrane is by passiveand active processes. Passive movement processes do not directly require the
expenditure of energy (ATP) by the cell, whereas activeprocesses do.
Passive processes include simple diffusion, facilitateddiffusion, osmosis, and dialysis and filtration.
Active processes include transport processes across theplasma membrane. Two active transport processes areATP driven membrane proteins that include carrierproteins and solute pumps and ATP driven vesicular(bulk) transport processes such as endocytosis andexocytosis.
MIXTURES
A mixture is produced when two or morecomponents are physically combined andwhich retain their own properties. Three
common mixtures include solutions,colloids, and suspensions.
Solution A solution is a
homogeneous mixture
(has uniform composition
throughout) formed by
dissolving a solute (solid,
liquid, or gas) in a solvent
(liquid, usually water). Asolution is described as a
single-phase system.
A solute is the substance
that is dissolved by the
solvent.
A solvent is the substance
that dissolves the solute
and is usually present in
the greater amount.Fig. 5.5
Colloid A colloid mixture contains
solutes or larger particles(macromolecules tomicroscopic in size) thanthose of a solution but notso large as to settle out(as in a fine suspension).Usually, the particles
interfere with thetransmission of light andcause light to scatter.
Typically, when a colloidconsists of a substancesuch as starch or gelatin,and the solvent is water,the resulting colloidalmixtures are of agelatinous or gelconsistency
Fig. 5.6
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Suspension A suspension is a mixture
that contains particles
larger than those of a
colloid.
A suspension isconsidered to be a two-
phase system where a
solid phase (fine
particles) is intermixed
with a liquid phase
(water). Typically, over
time the phases separate
and the solids (particles)
settle out.
Fig. 5.7
Lab Activity 1
Molecular and Particle Movement
This lab activity is
designed to visuallydemonstrate
molecular and particle
movement resulting
from kinetic energy.
Fig. 5.9
Milks Brownian Motion Movie
India Ink Movie
PASSIVE MOVEMENT
ACROSS THE PLASMA
MEMBRANE
Passive Movements
The plasma membrane is a selectivelypermeable membrane that surrounds the cell.The passive movement of water and dissolvedsubstances across the membrane requirespermeability through the membrane.
Passive processes that allow permeability arediffusion and filtration. Processes of diffusion are simple diffusion, facilitated
diffusion, osmosis, and dialysis.
Osmosis, the diffusion of water across a selectivelypermeable membrane, and dialysis, the separation ofsolutes by a selectively permeable membrane, areprocesses that utilize simple diffusion.
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Diffusion
Diffusion is a process of equalization which involvesmovement from an area of high concentration to an
area of low concentration (along a concentrationgradient).
Net diffusion is a measurement of how muchequalization occurs. The greater the difference inconcentrations (concentration gradient), the greater theequalization (net diffusion).
The driving force for equalization is molecularmotion. Molecular motion is described as disorderedand is associated with molecular internal energy, themicroscopic energy on the atomic and molecular scale.
Diffusion
The rate of diffusion is how fast the molecules
move through their environment.
The movement of molecules (and particles)through their environment is influenced by
(1) kinetic energy (temperature),
(2) the nature of the environment (gas, liquid, or solid)
and
(3) the size of the molecules (and particles), and
(4) electrical charge.
Temperature
Temperature is a measure of the
kinetic energy associated with the random
microscopic motion of atoms and
molecules. Increasing the temperature
results in an increase of molecular motion
and the rate of diffusion. Decreasing the
temperature decreases the rate of
molecular motion and the rate of diffusion.
Environment
The nature of the environment relates to
the permeability of the molecules for the
environment. Molecules move faster
through environments of increasing
permeability and slower through
environments of decreasing permeability.
Size
The size of the molecules infers that larger
molecules have more mass, offer more
resistance, and move slower than smaller
molecules (when in the same system ofinternal energy). Thus, in the same
environment larger molecules diffuse at a
slower rate than smaller molecules.
Charge
Molecules with electrical charges interactwith other charged molecules in theenvironment. Molecules and atoms having
opposite charges are attracted one toanother, and molecules and atoms havingthe same charge are repelled. Thus, apositively charged substance would diffusefaster into a negatively chargedenvironment than into a positively chargedenvironment.
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Fig. 5.10 Fig. 5.11
Consider the influence of temperature, size, environment, and charge.
Lab Activity 2
Molecular Movement and Weight
In a mixture (of equal temperature), all themolecules or particles are subjected to the sameamount of internal energy. Since influenced bythe same amount of energy, the smaller particles(less mass) move faster than the larger particles(more mass).
This activity studies the influence of size (weight)on the rate of diffusion. The diffusion ofmethylene blue (molecular weight of 320) iscompared to the diffusion of potassiumpermanganate (molecular weight of 158).
Fig. 5.12
Fig. 5.14
Fig. 5.13Fig. 5.15
Simple Diffusion Across the
Plasma MembraneDiffusion is a process of equalization which
involves movement from an area of highconcentration to an area of low concentration
(along a concentration gradient).
Simple Diffusion
Permeability of the substance may be due to
solubility in the membranes phospholipid bilayer,
the presence of membrane channels, or
The presence of carrier proteins. Generally, substances are soluble in the
phospholipid bilayer of the plasma membrane if
they are small, nonpolar, and lipid soluble.
Substances such as oxygen and carbon dioxide
easily diffuse through the phospholipid bilayer
the plasma membrane.
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Lipid solubility allows small nonpolar molecules such as oxygen
and carbon dioxide to diffuse through the plasma membrane.
Diffusion follows a concentration gradient, from high to low.
Fig. 5.17
Lipid Solubility
Membrane channels allow the diffusion of specific substances across
the plasma membrane. Diffusion always follows a concentration
gradient, from high to low.
Fig. 5.18
Membrane Channels
Facilitated Diffusion Facilitated diffusion
utilizes carrier proteinsthat participate in themovement of thesubstance across themembrane. Aninteraction of themembrane proteins withthe diffusing substancecauses the membraneproteins to transport thesubstance across themembrane.
Facilitated diffusiontypically involves thediffusion of largemolecules, such as the
facilitated diffusion ofglucose into the cell.
Fig. 5.19
MOVEMENT OF WATER BY
HYDROSTATIC PRESSURE
Hydrostatic pressure is the
pressure of water against a wall or
membrane.
Sources of Hydrostatic Pressure
Three of the sources of hydrostatic
pressure in our body are the
contraction of the heart (blood pressure),
osmotic movement of water (water volume
changes), and
gravity (such as venous blood pooling in the
legs of a standing individual).
Blood (hydrostatic) pressure
Blood (hydrostatic)
pressure is the driving
force for the
movement of water
and various solutes
from blood vessels
called capillaries into
the interstitial spaces.Fig. 5.3
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Osmosis
The osmotic movement of water facilitates water
flow from one area to another. Osmosis is
essential in interstitial water reabsorption at thecapillaries and water reabsorption by the
kidneys.
Net water movements cause changes in the
shape of cells, in pressure, and the location of
water (interstitial vs intracellular environments).
Filtration
Filtration is the forced movement of asubstance through a filter.
A filter is a porous substance or structureused to separate suspended material inliquids or gases.
Filtration requires a driving pressure to forcethe liquid or gas through the filter.
The pore size of the filter determines whichmaterials will pass through.
The product of fluid filtration is called a filtrate.
Lab Activity 3 Filtration
A setup for a filtration apparatus and expected results due to pore size offilter paper.
Fig. 5.20
Lab Activity 3 FiltrationWhat are the test results for
filtration of solution ofcopper sulfate andstarch? What determinedpassage through themembrane?
Fig. 5.21
Filtration at the Plasma Membrane
The plasma membrane contains protein
channels that function as pores and is
selectively permeable.
Selective permeability means that the plasma
membrane selects what substances can
pass through because the size of its pores or
other physical characteristics of the
membrane.
Filtration at the Plasma Membrane
Blood pressure provides the driving force for filtration at the capillary.
Filtration is one way fluid and solutes are delivered into the interstitial
spaces (forming interstitial fluid) to support cellular metabolism.
Fig. 5.23
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Fenestrated glomerular capillaries in the kidney produce plasma filtrate.
The filtrate passes through a series of tubes where it is modified by
reabsorption (and secretion) into urine.
Fig. 5.24
Filtration at the Plasma Membrane
MOVEMENT OF WATER BYOSMOSIS
Osmosis is the diffusion of waterthrough a selectively permeablemembrane such as the plasma
membrane.
OSMOSIS
Osmosis is the diffusion of water through a
selectively permeable membrane such as the
plasma membrane.
Water diffuses through the lipid bilayer of the
plasma membrane and through plasma
membrane water channels called aquaporins.
Net water movement occurs when the
concentration of a solute that is impermeable to
the plasma membrane differs between the
intracellular and the extracellular fluid.
OSMOSIS
A difference in impermeable solute concentrationsmeans that there is a difference in waterconcentration, and net water movement is from theregion of higher water concentration to the region oflower water concentration.
Water osmotically moves out of a cell when theextracellular fluid has less water (because it has moreimpermeable solutes) than the cell. In this case, themovement of water out of the cell causes the cell toshrink because the cells water (hydrostatic) pressuredecreases.
OSMOSIS
In this illustration, the
extracellular fluid contains
a higher concentration of
impermeable solutes than
the intracellular fluid.Thus, the extracellular
fluid has a lower
concentration of water,
and there is net water
diffusion out of the cell.
Fig. 5.25
Effects of Osmotic Solutions-
Osmolality and Tonicity
Osmolality
The osmolality of a solution is a measure of
the number of particles present in the
solution, regardless of the size or weight ofthe particles.
To be osmotically effective, the particles must
be impermeable to the membrane and at
different concentrations on each side of the
membrane.
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Osmolality and Permeability The osmolality of a
solution is a measure of
the number of particles
present in the solution
If, as shown in thisillustration, both the
solute (Na+ and Cl-) and
the solvent (water) is
permeable to the
membrane, there is no
osmotic effect. Both the
solute and the solvent
(water) reach equilibrium. Fig. 5.26
Tonicity
Tonicity
Tonicity is the effective
osmolality, and is the sum
of the solutes that have theability to affect the
movement of water across
a selectively permeable
membrane. In the
consideration of osmolality
of a solution, both particles
that are permeable and
impermeable to the cell
membrane are considered. Fig. 5.27
Tonicity only considers
the particles that are
osmotically effective,
the particles that are
impermeable, and
have the ability to affect
water movement across
the membrane.
Tonicity
Fig. 5.28
Osmotic pressure
Osmotic pressure is the pressure exerted
by the movement of waterthrough a
selectively permeable membrane that
separates two solutions with different
concentrations of solute.
A solutions osmotic pressure is proportional
to the solutions concentration of membrane
impermeable solutes.
Osmotic pressure
results because of the
osmotic movement of
water and ismeasured
(expressed) as the
pressure required to
oppose the waters
movement.
Osmotic pressure
Fig. 5.29
Tonicities of Solutions
There are three possible tonicities of
solutions:
isotonic,
hypotonic, and
hypertonic.
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An isotonic solution is a solution that
has the same concentration ofimpermeable solutes as within the cell.
Equal concentrations of impermeable solutes
means that there are equal concentrations of
water.
There is no net diffusion of water and no
change in hydrostatic pressure.
There is no net
diffusion of water andno change in
hydrostatic pressure.
Animal cells maintain
a normal shape.
Plant cells maintain
normal turgor, the
normal state of
distension of the cell
and wall.
Fig. 5.30
Isotonic Solution
Hypotonic Solution
A hypotonic solution is a solution that
has a lower concentration of impermeable
solutes than within the cell.
Since the solution has a lower concentration
of solutes, it has a higher concentration of
water, and net water diffusion is into the cell.
Water movement into the cell increases its
hydrostatic pressure.
Cells bounded by onlytheir plasma membranes,such as animal cells,increase in size (swell)and may rupture (lysis).
Plant cells, bounded bycell walls, have anincrease of turgor, thenormal state of distensionof the cell and wall. Theplant tissue becomes firmand rigid.
Hypotonic Solution
Fig. 5.31
Hypertonic Solution
A hypertonic solution is a solution that
has a higher concentration of solutes than
within the cell. Since the solution has a
higher concentration of solutes, it has a
lower concentration of water, and net
water diffusion is out of the cell.
Hypertonic Solution
Cells bounded by onlytheir plasma membranes,such as animal cells,decrease in size (shrink).
Plant cells, bounded by
cell walls, have adecrease of turgor, thenormal state of distensionof the cell and wall, andthe plasma membranespull away from their walls.The cells shrink, and theplant tissue becomes softand pliable.
Fig. 5.32
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Lab Activity 4 Osmometer
An osmometer is a device used to
measure osmotic force
Osmometer Thistle Tube A typical laboratory
osmometer and setup
for laboratorydemonstration isshown in thisillustration.
In this illustration thesolution surroundingthe membrane is
________ and watermoves (into / out of)the thistle tube.
Fig. 5.33
Semi-permeable Membrane
Fig. 5.34
Lab Activity 5
Osmosis and Red Blood Cells
Isotonic Solution - Red Blood Cells
A normal (isotonic)
saline solution is 0.9%
NaCl.
Red blood cells in aisotonic solution have
normal shape and size.
Each red blood cell is a
biconcave disc with a
thin central regionFig. 5.37
Hypertonic Solution - Red Blood Cells
A hypertonic solution hasa higher concentration ofsolutes than within thecell.
Since the solution has ahigher concentration of
solutes, it has a lowerconcentration of water,and net water diffusion isout of the cell.
Water movement out ofthe cell decreases itshydrostatic pressure, andthe cell shrinks. Redblood cells in a hypertonicsolution are crenated.
Fig. 5.39
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Hypotonic Solution - Red Blood Cells
A hypotonic solution hasa lower concentration of
solutes than within thecell.
Since the solution has alower concentration ofsolutes, it has a higherconcentration of water,and net water diffusion isinto the cell.
Water movement into thecell increases itshydrostatic pressure, andthe cell swells.
Fig. 5.41
Lab Activity 6 Osmosis and Potato Cells
Isotonic Solution - Potato Cells
Potato cells have aslightly flexible wallbounded internally by theplasma membrane.Turgor pressure (waterpressure) of thecytoplasm maintains thenormal state of distensionof the cell wall. Osmoticchanges that result in anincrease or a decrease ofwater volume change thecells turgor.
Fig. 5.42
Hypotonic Solution - Potato Cells
Distilled water is
hypotonic to the potato. In
a hypotonic solution,
water diffuses into the
cells of the potato and
their turgor pressure
increases. Increased
turgor pressure results in
increased rigidity of the
potato slice.
Fig. 5.43
Hypotonic Solution - Potato Cells
Fig. 5.43Fig. 5.46
Hypertonic Solution - Potato Cells
Fig. 5.44
The 10%NaCl solution is
hypertonic to the potato.
In a hypotonic solution,
water diffuses out of the
potato cells and theirturgor pressure
decreases. Decreased
turgor pressure results in
decreased rigidity of the
potato slice.
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Hypertonic Solution - Potato Cells
Fig. 5.44
Fig. 5.46
Hypotonic & Hypertonic Solutions
Reversing the
solutions reverses
the osmotic effect.Plasmolyzed cells
become rigid, and
rigid cells become
plasmolyzed.
Fig. 5.45
Lab Activity 7
Osmosis and Elodea
Normal Turgor
Elodea cells with normal turgidity. The plasma
membranes are not seen because they are inintimate contact with the cell walls.
Fig. 5.50
Fig. 5.49
Hypertonic Solution - Elodea
Plasmolysis occurswhen plant cells areplaced in an osmoticsolution that promotesthe outwardmovement of water.
As cytoplasmic waterloss occurs, spacesform between theplasma membranesand the cell walls.
Fig. 5.53
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Hypotonic Solution - Elodea
A hypotonic or an isotonic solution will produce
normal turgor pressure in a plant cell. Turgorpressure is limited by the non-flexible cell wall.
A plasmolyzed cell subjected to a hypotonic
solution will show an increase of turgor
pressure
Lab Activity 8 -
Osmosis and Paramecium
Hypotonic Environment The unicellular Protozoa that live in fresh water, such as
Paramecia and Amoebas, live in a hypotonicenvironment.
The hypotonic environment results in continuedMOVEMENT of fluid into the organism.
Organelles called contractile vacuoles eject excess fluid
from the organism maintaining cytoplasmic osmolarity(solute concentration).
Fig. 5.57
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DIALYSISDialysis is the separation of solutes
according to their size by diffusion through aselectively permeable membrane. Dependingupon the size of the pores of the membrane,
solutes will either diffuse across the membrane orbe restricted by their size.
Dialysis Membrane
Dialysis is theseparation of solutesaccording to their sizeby the utilization of aselective permeablemembrane. Solutesthat are small enoughto diffuse through themembranes poresare separated fromthe larger solutes.
Fig. 5.58
Lab Activity 9 -
Osmosis and Dialysis using
Dialysis Tubing (membrane)
Fig. 5.60
Fig. 5.62
Which line (in any) most correctly
matches the change in weight of the
bag?
OSMOSIS USING
DIALYSIS MEMBRANE
DIALYSIS USING
DIALYSIS MEMBRANE
Fig. 5.64 Fig. 5.66
Which solute/s passed through the
dialysis membrane?
If a solute passed through the
membrane, it would seem that the
dialysis bag would lose weight.However, the dialysis bag gained
weight explain this event.
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Lab Activity 10 -
Osmosis and Dialysis usingMembranous
(Unshelled) Egg
Osmosis
(using membranous egg)
This activitydemonstrates
osmosis by the
change in weight of
the egg. The egg
contains a high
concentration of
natural protein
(albumins).
Fig. 5.70
Membranous Egg - Osmosis
Fig. 5.69
Fig. A
Fig. B
Which Figure shows
effects of hypertonicand which shows
hypotonic solutions?
Which line represents the change in
weight of the membranous egg?
FLUID MOVEMENT ACROSS
THE CAPILLARY
Capillaries are the sites of vascular
and interstitial fluid exchange
Forces of Fluid Movement
Two driving forces for movement of
water between the blood plasma and
interstitial fluid are:
hydrostatic pressure (blood pressure) and
osmosis.
Forces of Fluid Movement
Hydrostatic Pressure Hydrostatic pressure influences fluid
movement from the capillary into the
interstices and fluid movement from theinterstices into the capillary.
Osmotic pressure Osmotic pressure influences fluid movement
from the capillary into the interstices and fluidmovement from the interstices into thecapillary.
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Fluid Movement at the Arterial End
of Capillary
Fluid movement across a capillary is due to
filtration pressure. Net filtration pressure is determined by subtracting
the net osmotic pressure from the net hydrostatic
pressure.
Net filtration pressures differ between the arterial and
venous ends of a capillary. The difference results in
fluid movement from the arterial end (due to
hydrostatic pressure) and into the venous end (due to
osmotic gradients).
Hydrostatic Pressure atArterial End of Capillary
There are two sources of hydrostatic pressures thatinfluencing water MOVEMENT at the arterial end of the
capillary:capillary hydrostatic pressure (or capillary blood
pressure) and
interstitial fluid hydrostatic pressure.
Hydrostatic Pressure at
Arterial End of Capillary There are two sources of
hydrostatic pressures that
influencing water
MOVEMENT at the
arterial end of the
capillary:
capillary hydrostatic
pressure (or capillary blood
pressure) and
interstitial fluid hydrostatic
pressure.Fig. 5.88
Osmotic Pressure at
Arterial End of Capillary There are two sources of
osmotic pressures that
influencing water
MOVEMENT at the
arterial end of the
capillary:
capillary osmotic
pressure (blood colloidal
pressure) and
interstitial fluid osmotic
pressure. Fig. 5.89
Net Driving Pressure
Arterial End of Capillary Thus, to determine the
net driving force (filtrationpressure) at the arterial end ofthe capillary both the nethydrostatic pressure and the
net osmotic pressure must beconsidered. The net filtrationpressure (NFP) of the capillaryis determined by subtractingthe net osmotic pressure(NOP) from the net hydrostaticpressure (NHP). NFP = NHP(35 mm Hg. minus NOP (25mm Hg.) = 10 mm Hg.
Fig. 5.90
Fluid Movement at the Venous
End of Capillary
There are two sources of hydrostatic pressures thatinfluencing water MOVEMENT at the venous end of
the capillary: capillary hydrostatic pressure (or capillaryblood pressure) and interstitial fluid hydrostatic
pressure.
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Hydrostatic Pressure at
Venous End of Capillary There are two sources of
hydrostatic pressures that
influencing water
MOVEMENT at the
venous end of the
capillary:
capillary hydrostatic
pressure (or capillary blood
pressure) and
interstitial fluid hydrostatic
pressure.Fig. 5.91
Osmotic Pressure at
Venous End of Capillary
There are two sources of
osmotic pressures that
influencing water
movement at the venous
end of the capillary:
capillary osmotic
pressure (blood colloidal
pressure) and interstitial
fluid osmotic pressure.
Fig. 5.93
Net Driving Pressure at
Venous End of Capillary Thus, to determine the net
driving force (filtrationpressure) at the venous end ofthe capillary both the nethydrostatic pressure and thenet osmotic pressure must beconsidered. The net filtrationpressure (NFP) of the capillaryis determined by subtractingthe net osmotic pressure(NOP) from the net hydrostaticpressure (NHP). NFP = NHP(17 mm Hg. minus NOP (25mm Hg.) = -8 mm Hg.
Net Fluid Movement at Capillary
Fluid movements between the capillary and the
interstices are driven by the differences in the net
filtration pressures at the arterial and venousends of the capillary.
Fig. 5.94
Summary of Driving Forces
Summary of the driving
forces for fluid movement
between the capillary and
the interstices. Most of
the fluid is osmotically
returned into the venous
end of the capillary. Fluid
that does not return into
the capillary is returned to
venous circulation by way
of the lymphatic system.
Fig. 5.95
ACTIVE PROCESSES
ACROSS THE PLASMA
MEMBRANE
Active transport moves solutes across
the plasma membrane with the
utilization of cellular energy (ATP).
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Active Transport
Two active processes for transport across the cellmembrane are active transport and vesicular transport.
Active transport requires carrier proteins to provide themechanism of solute movement across the plasmamembrane.
Vesicular transport requires that the substances bemoved across the plasma membrane in membranouspouches (sacs) called vesicles. Two types of vesiculartransport are endocytosis and exocytosis. Endocytosis is the movement of substances into the cell, and
Exocytosis is the movement of substances out of the cell.
Active Transport
Active transport moves solutes across the
plasma membrane with the utilization of cellularenergy (ATP).
Active transport requires plasma membrane carrier
proteins that function as solute pumps. Solute
pumps are commonly used for the movement of
solutes such as ionic sodium, potassium, and
calcium. Solute pumps typically transport their
specific solutes from an area of low concentration
to an area of high concentration, thus, against a
diffusion gradient.
Membrane PotentialsPassive processes suchas diffusion, osmosis, anddialysis are processes ofequalization and do notrequire the utilization ofcellular energy (ATP).Processes of equalizationeliminate concentrationgradients. For example, the electrical
potential of excitabletissues would be eliminatedby the diffusion andequalization of electrolytessuch as Na+ and K+
resulting in the inability ofcells to generate andconduct electrical signals
Fig. 5.96
Membrane Potentials
Excitable cells such as
neurons and muscles,
utilize energy (ATP) to
actively maintain
electrical potentials by
membrane solute pumps.
To maintain electrical
potentials, solute pumps
actively transport and
maintain unequal
electrolyte
concentrations.Fig. 5.97
Membrane Potentials An action potential of a
neuron is produced bythe movement of Na+and K+ ions along theportion of the neuroncalled the axon. The
resting membranepotential is reestablishedfor the potential energyneeded for a sequentialaction potential. Sodium-potassium pumps activelymaintain the membranepotential; Na+ in a highconcentration outside ofthe cell and K+ in highconcentration inside thecell. Fig. 5.98
Membrane Potentials
An electrocardiogram
shows the electrical
activity of the heart.
Active transportpumps maintain the
electrolyte gradients
needed to produce
the electrical
potentials.
Fig. 5.99
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Lab Activity 11-
Active Transport in Yeast Dead (boiled) yeast are
stained red because they
do not have the active
transport mechanisms
that prevent the entrance
of the dye, Congo Red,
into the cell. Living yeast
cells have active
transport mechanisms;
thus, are not stained red.
Fig. 5.100
VESICULAR TRANSPORT
Vesicular transportrequires thatsubstances be movedeither into or out ofthe cell inmembranouspouches (sacs) calledvesicles. Two types ofvesicular transportare exocytosis andendocytosis.
Fig. 5.101
Fig. 5.102
Secretion
Secretion is the release
of substances from a cell
(or may be defined as a
glands product).
Secretion of a substance
may occur by exocytosis
or by movement through
plasma membrane
proteins that function as
channels or pumps.
Secretory products
released by exocytosis
include hormones, mucus,milk, enzymes, etc.
Fig. 5.102
Excretion
Excretion is not a type of
vesicular transport.
Excretion is mentioned
here to avoid confusion
with secretion. Excretion
is the release of
modified and isolated
waste matter (such as
urine and sweat) from
the body.
Excretory products such as
urine contain some
secretory products that are
considered as not useful tothe body.
Fig. 5.103
ENDOCYTOSIS
Endocytosis is a process where
substances are incorporation into the cell
by of the substances being entrapped in
membranous vesicles formed from theplasma membrane.
Endocytosis includes phagocytosis,
pinocytosis and receptor mediated
endocytosis.
Phagocytosis Phagocytosis is the
process of engulfingsolid materials such asbacteria or foreign bodiesby a phagocytic cell.
Phagocytosis involves theformation of plasma
membrane extensionscalled pseudopods thatsurround and engulf thesolid material into amembranous vesiclecalled a phagosome. Thephagosome fuses withorganelles calledlysosomes, whichcontribute digestiveenzymes for digestion ofthe material.
Fig. 5.104
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Phagocytes
Phagocytes in the bodyinclude macrophages and
other types of white blood cellsthat help dispose of bacteriaand other foreign or damagedsubstances.
Most phagocytes move by aflowing of their protoplasm intoforming pseudopodia, amovement called amoeboidmotion. Macrophages freelyroam the tissues of the body insearch of potential pathogenicmaterials.
Fig. 4.13
Lab Activity 12
Macrophages of liver, Kupffer's cells
Kupffer's cells are
identified on this slidepreparation by the
presence of
phagocytized carbon
particles (particles
were injected into
blood).
Fig. 5.105
Fig. 5.106
Lab Activity 13
Amoeba - amoeboid movement
and phagocytosis. Amoebas are unicellular
organisms commonlyfound in freshwater pondsand streams. Observe forthe formation of cellextensions calledpseudopods.
Pseudopods allow for theamoebas slowmovement and for thephagocytosis of foodorganisms.
Observe the amoebas forphagocytosis of Euglena
Fig. 5.108
Lab Activity 14
Paramecia and phagocytosis.
Paramecium showing
food vacuoles
(phagosomes) containing
Congo Red stained yeast
(100x). Lysosomes fuse
with food vacuoles and
release powerful
hydrolytic enzymes. The
hydrolytic enzymes result
in a change of the color of
the yeast to blue.Fig. 5.110
PINOCYTOSIS
Pinocytosis (bulk-phase
endocytosis) is the
engulfment of
extracellular fluids.
This type of endocytosisis nonspecific and occurs
by the invagination of the
plasma membrane to
form a membranous
vesicle.
Fig. 5.111
RECEPTOR-MEDIATED
ENDOCYTOSIS Receptor-mediated
endocytosis specificallyengulfs substancesaccording to the
specificity of thereceptors. Membranereceptors becomeconcentrated in an areacalled a coated pit andbind only to their receptorspecific molecule.
Common receptorsinclude insulin and low-density lipoprotein (LDL)receptors.
Fig. 5.112