Fluid Movement

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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.


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


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

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Fluid Movement