Energy Transfer in Cell During Exercise and Oxygen Metabolism and Transport - Palak

7/30/2019 Energy Transfer in Cell During Exercise and Oxygen Metabolism and Transport - Palak

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Compiled By:

Palak Brahmbhatt


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Laws of Thermodynamics and its relation to energy balance

and work within biologic systems

Potential Energy And Kinetic Energy

Energy-Releasing and Energy-Conserving Processes

Interconversions of Energy

Forms of Energy

Biologic work in Humans


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The capacity to extract energy from food

macronutrients and transfer it at a high rate to the

contractile elements of skeletal muscle largely

determines ones capacity for swimming, running, or

skiing long distance.

All forms of biologic work require power generated

from the direct transfer of chemical energy.


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Extracting energy from the stored nutrients and transferringit to the contractile proteins of skeletal muscle greatlyinfluences exercise performance.

We can not define energy in concrete terms of size, shape,or mass.

Rather the term Energy suggests a dynamic state related tochange; thus the presence of energy emerges when a changeoccurs.

Within this context, energy relates to the performance ofwork- as work increases so does energy transfer, thusproducing a change.


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It describes one of the most important principles related

to biologic work.

The basic tenet states that energy cannot be created or

destroyed but, instead, transforms from one form to

another without being depleted.

This law describes the immutable principle of the

conservation of energy that applied to both living and

nonliving systems.

In the body, chemical energy stored within the bonds ofmacronutrients does not immediately dissipate as heat

during energy metabolism; instead a large portion

remains as chemical energy, which the musculoskeletal

system then changes in to mechanical energy.


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Potential and kinetic energy together constitutes the total

energy of a system. Releasing potential energy transforms in to kinetic energy

of motion. In some cases, bound energy of one substance directly

transfers to other substance to increase their potential

energy. This type provide necessary energy for bodys chemical

work of biosynthesis. BIOSYNTHESIS is a process, where specific building

block atoms of carbon, hydrogen, oxygen, and nitrogen

become activated and join other atoms and molecules tosynthesize important biologic compounds and tissues.

Other synthesized compounds such as adenosinetriphosphate (ATP) and phosphocreatine (PCr) serve thecells energy requirements.


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Exergonic energy reactions results In a transfer of energy to thesurroundings. Such reactions represent Downhill process.

Endergonic energy results in the storage conservation orincrease in the free energy. This reaction represents Uphill

process.

In some instances Exergonic process link or couple withEndergonic reaction to transfer some energy to Endergonicprocess.

In the body, such coupled reactions conserved in a unstable formof a large portion of chemical energy stored within themacronutrients.


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Energy transfer in cells follow the same principle in the

Waterfall-Waterwheel.

Carbohydrate, lipids, proteins, macronutrient have potential energy

Formation of product substances progressively reduces the nutrient molecules, original potential energy

which corresponds increase in the kinetic energy

Enzyme regulated transfer systems conserve a portion of the chemical energy in new compounds for use in

biologic work

Leaving cell act as a transducer and had a capacity to extract and use chemical energy stored within a

compound atomic structure

Also bond atoms and molecules together, raising the level of potential energy


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Transfer of potential energy in any spontaneous research

always proceed in a direction that decreases capacity toperform work.

The tendency of potential energy to degrade to kineticenergy of motion which a lower capacity of work called

second law of thermodynamics.

E.g. Flash light battery, electrochemical energy storedwithin its cells slowly dissipates, even if the battery remains

unused.

The energy from sunlight also continually degrades to heatenergy when light strikes and becomes absorbed by asurface.


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Food and other chemicals represent excellent stores of

potential energy, yet this energy continually decreases

as the compounds decompose through normal oxidative

processes.

Energy, like water, always runs downhill, so potential

energy decreases.

Ultimately, all of the potential energy in a system

degrades to the unusable form of kinetic or heat energy.


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Because the total energy in an isolated system remains

constant, a decrease in one form of energy is matchedby an equivalent increase in other form.

During energy conversions, a loss of potential energy

from one source often produces a temporary increase inthe potential energy of another source.

In this way, nature harnesses vast quantities of potential

energy for useful purposes. But even under suchfavorable conditions, the net flow of energy in thebiologic world moves toward entropy, which ultimatelyresults in the loss of potential energy.


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Entropy reflects the continual process of energy change.

All chemical and physical processes in a direction in which

total randomness or disorder increases and the energyavailable for work decreases.

In coupled reactions during biosynthesis, part of a systemmay show a decrease in entropy while another part shows

an increase.

However, no way exists to circumvent the second law- theentire system always shows a net increase in entropy.

In a more global sense, the biochemical reactions within thebodys trillions of cells tilt in the direction of spontaneitythat favors disorder and randomness. ( i.e. entropy)


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Energy is categorized into one of six forms :

Chemical

Mechanical

HeatLight

Electric

Nuclear


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The conversion of energy from one form to another occurs

readily in the inanimate and animate worlds.

Photosynthesis and Respiration represent the most

fundamental examples of energy conversions in living cells.

PHOTOSYNTHESIS

In the sun, with a temperature of several million degrees

Fahrenheit, nuclear fusion releases part of the potential

energy stored in the nucleus of the hydrogen atom. This energy, in the form of gamma radiation, then converts

to radiant energy.


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CELLULAR RESPIRATION

The reactions of respiration are the reverse of those of

photosynthesis as the plants stored energy is recovered for

use in biologic work. A portion of the energy released during cellular respirations

becomes conserved in other chemical compounds for use in

energy requiring processes; the remaining energy flows to

the environment as heat.


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Biologic work takes one of three forms:

Mechanical work of muscle contraction

Chemical work that synthesize cellular molecules

Transport work that concentrates various

substances in the intracellular and extra cellularfluids


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It generated by muscle contraction andsubsequent movement provides the most

obvious example of energytransformation.

The molecular motors in a muscle fibersprotein filaments directly convert

chemical energy into mechanical energy.

However, this does not represent thebodys only form of mechanical work.

In the cell nucleus, for example,

contractile elements literally tug at thechromosomes to facilitate cell division.

Specialized structures such as cilia alsoperform mechanical work in many cells.


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All cells perform chemical

work for maintenance andgrowth.

Continuous synthesis ofcellular components takesplace as other componentsbreak down.

The extreme muscle tissue

synthesis that occurs inresponse to chronic overloadin resistance training vividlyillustrates chemical work.


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The biologic work of concentrating substances in the

body progresses much less conspicuously thanmechanical or chemical work.

Cellular materials normally flow from an area of

high concentration to one of lower concentration.

This passive process of diffusion requires no energy.

For proper physiologic functioning, certain

chemicals require transport uphill, against their

normal concentration gradients from an area of lowerto one of higher concentration.

Active transport describes this energy-requiring

process.


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Secretions and reabsorptions in the kidney tubules

use active transport mechanisms, as does neural

tissue in establishing the proper electrochemical

gradients about its plasma membranes.

These quiet forms of biologic work require a

continual expenditure of stored chemical energy.


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The limits of exercise intensity ultimately depend on

the rate that cells extract, conserve, and transfer thechemical energy in the food nutrients to the contractilefilaments of skeletal muscle.

The sustained pace of marathon runner at close to 90%of maximum aerobic capacity, or the rapid speedachieved by the sprinter in all-out exercises, directlyreflects thebodys capacity to transfer chemical energy

into mechanical work.

Enzymes and coenzymes significantly affect the rate ofenergy release during chemical reactions.


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An enzyme, a highly specific and large protein

catalyst, accelerates the forward and reverse rates of

chemical reactions within the body without being

consumed or changed in the reaction.

Enzymes only govern reactions that would normallytake place but at a much slower rate.

In a way, enzyme reduces the required activation

energy.

An enzyme-catalyzed reaction proceeds in onedirection so that all substrate molecules convert into

product molecules with the help of enzyme.


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The enzyme first combines with its substrate to form an enzyme-

substrate complex

This complex then converts in to an enzyme-intermediate

complex

It further changes to an enzyme-product complex that quickly

dissociates into free product and the enzyme released

unchanged


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Enzymes possess the unique property of not being readilyaltered by the reactions they affect.

Consequently, enzyme turnover in the body remains relativelyslow, and the specific enzymes are continually reused.

A typical mitochondrion may contain up to 10 billion enzymemolecules, each carrying out millions of operations within a

brief time.

During strenuous exercise, the rate of enzyme activityincreases tremendously within the cell, as energy demandsincrease some 100 times above the resting level.

A single cell contains thousands of different enzymes, eachwith a specific functions that catalyzes a distinct cellularreaction.


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Enzymes usually take the names of the functions they

perform.

The suffixase appended to the enzyme whose prefix

often indicates its mode of operation or the substance

with which it interacts.

For example, hydrolase adds water during hydrolysis

reactions, protease interacts with protein, oxidase

adds oxygen to a substance.


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Enzymes do not all operate at the same rate; some operate slowly,

others much more rapidly.

Enzymes often work cooperatively among their binding sites. Whileone substance turnson at a particular site, its neighbor turnsoff

until the process completes.

Enzymes also can act along small regions of the substrate, each time

working at a different rate than previously. Some enzymes delay initiating their work.

For some enzymes, peak activity requires relatively high acidity,

while others function optionally on the alkaline side of neutrality.

This pH effect on enzyme dynamics takes place because changingfluids hydrogen ion concentration alters the balance between

positively and negatively changed charged complexes in the

enzymes amino acids.Increase in temperature generally accelerate

enzyme reactivity.


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Step 1 : The active site of the enzyme and substrate

line up to achieve a perfect fit, forming an enzyme-substrate complex.

Step 2 : The enzyme catalyzes(greatly speeds up) the

chemical reaction with the substrate. Note that the

hydrolysis reaction adds a water molecule.

Step 3 : An end-product (two glucose molecules)forms releasing the enzyme to act on another

substrate.


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Lock and key mechanism


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Lock and key mechanism

This interactive process ensures that the correct

enzyme mates with its specific substrate to perform

a particular function. Once the enzyme and substrate join, a conformational

change in enzyme shape takes place as it molds to the

substrate.

Even if an enzyme links with a substrate, unless thespecific conformational change occurs in the shape of

the enzyme, it will not interact chemically with the

substrate.

The lock and key mechanism serves a protective

function so only the correct enzymes activates a given

substrate.


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Some enzymes remain totally dormant without activation by

additional substances termed coenzymes.

The metallic ions iron and zinc play coenzyme roles, as do the Bvitamins or their derivatives.

Oxidation-reduction reactions use the B vitamins riboflavin andniacin, while other vitamins serves as transfer agents.

Some advertisements for vitamins imply that taking vitamin

supplements provide immediate usable energy for exercise.

A coenzyme requires less specificity in its action than an enzymebecause the coenzyme affects a number of different reactions.


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ENZYME INHIBITION

Competitive inhibitors Closely resemble the structure of the normal substrate for an

enzyme, so they bind to the enzymes active site but cannot bechanged by the enzyme.

The inhibitor repetitively occupies the active site and blunts theenzymes ability to interact with its substrate.

Noncompetitive inhibitors Do not resemble the enzymes substrate and do not bind to its

active sites.

Instead, they bind to the enzyme at a site other than the active

site, which cause a change in the enzymes structure and abilityto catalyze the reaction because of the presence of the boundinhibitor.

Many drugs act as noncompetitive enzyme inhibitors.


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Hydrolysis Reactions

Hydrolysis catabolizes complex organic moleculescarbohydrates, lipids, and proteins- into simpler forms thebody easily absorbs and assimilates.

This basic decomposition process splits chemical bonds byadding H+ and OH- to the reaction by products.

Example of hydrolytic reactions include digestion ofstarches and disaccharides to monosaccharides, proteins toamino acids, and lipids to glycerol and fatty acids.

AB + HOH AH + B - OH


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Condensation Reactions

The reactions illustrated for hydrolysis can occur in

the opposite direction.

In the reverse reactions, the compound AB is

synthesized from AH and B OH, and a water

molecule forms in the building, or anabolic, processof condensation.

The structural components of the nutrients bind

together in condensation reactions to form more-complex molecules and compounds.


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Literally thousands of simultaneous chemical reactions occurin the body that involves the transfer of electrons from onesubstance to another.

Oxidation reactions transfer either oxygen atoms, hydrogenatoms, or electrons.

A loss of electrons always occurs in oxidative reactions,with a corresponding gain in valence.

For example, removing hydrogen from a substance yields anet gain of valence electrons.

Reduction involves any process in which the atoms in anelement gain electrons, with a corresponding decrease invalence.

Th t d i t d ib th b t th t d t l


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The term reducing agent describes the substance that donates or loses

electrons as it oxidizes.

The substance being reduced or gaining electrons is called theelectron acceptor or oxidizing agent.

Electron transfer requires both an oxidizing agent and a reducing

agent.

Oxidation and Reduction reactions become characteristically coupled.

Whenever oxidation occurs, the reverse reduction also takes place;when one substance loses electrons, the other substance gains them.

The Redox reaction commonly describes an oxidation-reduction

reaction.


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The effect of the concentration of chemicals in solution on the

occurrence of a particular chemical reaction embodies the law of

mass action, often referred to as the mass action effect.

In essence, a chemical reaction progresses to the right with the

addition of reactants and to the left with the addition of byproducts.

In a simple chemical reaction, the formation of product increases

linearly with the concentration of chemicals available to enter the

reaction.

In an enzyme-mediated reaction, however, the rate of product

formation increases dramatically with a small change in substrate

concentration, which generally produces a relatively large effect on

product formation.


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Certain substances in the body frequently link to several

reaction; thus, the products of one reactions become reactant

substances for other reactions.

Simply changing the concentration of one substance

profoundly affects a number of different reactions.

Also some molecules play key roles in a whole chain ofchemical events.

Oxygen, for example, exerts a significant mass action effect on

reactions required for energy transfer. If oxygen supply totissue diminishes, several chemical processes cease, and the

net energy available for biologic work decreases dramatically.


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The gain or loss of heat in the biologic system provide asimple way to determine the energy dynamics of any

chemical process.

For example, in food catabolism, within the body, a humancalorimeter measures the energy change directly as heat(kcal) liberated from the reactions.

Because complete combustion of food takes place at theexpense of molecular oxygen, the heat generated in theseexergonic reactions can readily be determined frommeasurements of oxygen consumption.

Oxygen consumption measurement forms the basis ofindirect calorimetry and enables one to infer the energymetabolism of humans during rest and diverse physicalactivities.


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Gases moves from one point to another by diffusion & the cause ofthis movement is always a Pressure difference from the first pointto the next.

Alveoli

[O2 diffusion]

Pulmonary capillary blood

Conversely, when oxygen is metabolized in the cells to form CO2 ,the PCO2 rises to a high value, which causes CO2 to diffuse into thetissue capillaries.

Pulmonary capillary blood

[CO2 diifusion]

Alveoli


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During strenuous Ex. A persons body may require asmuch as 20 times the amount of oxygen.

Also, because of the increased Cardiac Output, the time

that blood remains in the pulmonary capillary maybe

reduced to less than one-half normal.

O2 diffusion capacity increases almost threefold during

Ex. Due to

1. Increased surface area of capillaries participating inthe diffusion

2. More nearly ideal Ventilation-Perfusion ratio in the

upper part of the lungs.


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The blood becomes more saturated with oxygen by the

time it has passed through 1/3 of the pulmonary

capillary and little additional Oxygen normally enters

the blood during the latter 2/3 of its transit.

The blood normally stays in the lung capillaries about

3 times as long as necessary to cause full oxygenation.

Therefore, In Exercise, even with the shortened time of

exposure in the capillaries, the blood can become fully

oxygenated or nearly so.


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About 98% of blood the blood that enters the left

atrium from the lungs has passed through the alveolar

capillaries and has become oxygenated up to a PO2 of

about 104 mmHg.

Another 2% of the blood has passed directly from the

Aorta through the bronchial circulation, which suppliesmainly the deep tissues of the lungs and is not exposed

to the pulmonary air.

This blood flow represents shunt flow , meaningblood that is shunted past the gas exchange areas.


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On leaving the lungs, the PO2 of the shunt blood is

about that of normal venous blood, about 40mmHg.

This blood combines in the Pulmonary veins with the

oxygenated blood from alveolar capillaries This

mixing of the blood is called Venous Admixture of

blood.

It causes the PO2 of the blood pumped by the left side

of the heart into the aorta to fall to about 95 mmHg.


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When the arterial blood reaches the peripheral tissues,

its PO2 in the capillaries is still 95 mmHg.Yet, the PO2

in the interstitial fluid that surrounds the tissue cellsaverage only 40 mmHg.

Thus, There is a tremendous initial pressure difference

that causes oxygen to diffuse rapidly from the bloodinto the tissues, so rapidly that the capillary PO2 falls

almost to equal the 40 mmHg pressure in the

interstitium.

Therefore, the PO2 of the blood leaving the tissue

capillaries and entering the veins is also about 40

mmHg.


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EFFECT OF RATE OF BLOOD FLOW ON INTERSTITIAL

FLUID PO2

If the blood flow through a particular tissue becomes

increased, greater quantities of oxygen are transported into the

tissues in a given period and the tissue PO2 becomes

correspondingly increased.

EFFECT OF RATE OF TISSUE METABOLISM ON

INTERSTITIAL FLUID PO 2

If the cells use more O2 for metabolism than normally , this

tends to reduce the interstitial fluid PO2.


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1. The rate of oxygen transport to the tissues in the blood

2. The rate at which the oxygen is used by the tissues.


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Oxygen is always used by the cells. Therefore the Intracellular PO2

in the peripheral tissue cells remains lower than the Po2 in theperipheral capillaries. Also, there is considerable distance between

the capillaries and the cells.

The Normal intracellular Po2 ranges from As low as 5 mmHg to as high as 40 mmHg

Averaging 23 mmHg

Because only 1 to 3 mmHg of Oxygen Pressure is normallyrequired for full support of the chemical processes that use oxygen

in the cell. So even this low intracellular Po2 of 23mmHg is more

than adequate and provides a large safety factor.


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When O2 is used by the cells

CO2

increases the intracellular Pco2.

[CO2 diffuses]

Cells

Tissue Capillaries

[By blood]

Lungs

Pulmonary Capillaries

Alveoli


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At each point in the gas transport chain, CO2 diffuses in a

direction exactly opposite that of O2 diffusion.

Major difference between diffusion of O2 and CO2 :

CO2 can diffuse about 20 times as rapidly as O2.

Therefore, The Pressure differences required to cause CO2

diffusion are far less than the pressure differences required to

cause O2 diffusion.


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[UPTAKE OF CO2 BY THE BLOOD IN THE TISSUE CAPILLARIES]

1. Intracellular Pco2 about 46 mmHg & Interstitial Pco2 -

about 45 mmHg.

2. Pco2 of arterial blood entering the tissue40 mmHg &Pco2 of venous blood leaving the tissue - about 45 mmHg


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DIFFUSION OF CARBON DIOXIDE FROM THE PULMONARY BLOOD INTO THEALVEOLUS


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Exactly opposite from the ways in which they affect tissue

Po2.


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1. A decrease in blood flow

from Normal (Point A) one quarter normal (Point B)

increases the tissue Pco2

from the normal value of 45 mmHg Elevated level of 60mmHg

Conversely,

Increasing the blood flow to 6 times normal (Point C)

Decreases the Pco2

from the normal value of 45 mmHg 41 mmHg

2 10 f ld i i b li


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2. 10- fold increase in metabolic rate

greatly elevates the interstitial fluid Pco2 at all levels of blood

flow

Decreasing the Metabolism to one quarter normal

Interstitial fluid Pco2 to fall to about 41 mmHg.

Closely approaching that of the arterial blood , 40 mmHg.

ll b 9 % f h d f


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Normally, about 97% of the oxygen transported from

the lungs to the tissues is carried in chemical

combination with hemoglobin in RBC.

The remaining 3% is transported in the dissolved

state in the water of the plasma and cells.

Thus, under normal conditions, oxygen is carried to

the tissues almost entirely by Hemoglobin.


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The Oxygen molecules combine loosely and

reversibly with the heme portion of the hemoglobin.

When Po2 is high, as in the Pulmonary capillaries

O2 binds with the hemoglobin

When Po2 is low, as in the tissue capillaries

O2 is released from the hemoglobin


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The blood of a normal person contains about 15

grams of hemoglobin in each 100 ml of blood andeach gram of hemoglobin can bind with a maximum

of 1.34 ml of oxygen.

15 * 1.34 = 20.1 which means on an average, The

hemoglobin in 100 ml of blood can combine with a

total of almost Exactly 20 ml of O2, when the

hemoglobin is 100% saturated, usually expressed as20 volumes percent.


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During heavy Exercise, the muscle cells use O2 at a rapid

rate, which , in extreme cases, can cause the interstitial fluid

Po2 to fall to as 15 mmHg.

At this pressure only 4.4 ml of O2 remain bound with the

hemoglobin in each 100 ml of blood. Thus, 19.4- 4.4=15h ml,

is the quantity actually delivered to the tissues by each 100 ml

of blood.

3 times as much as O2 as normal is delivered in each volume

of blood that passes through the tissues & Cardiac Output canincrease to 6 to 7 times normal in well-trained Marathon

runner


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The percentage of the blood that gives up its oxygen as it

passes through the tissue capillaries is called the utilization

coefficient.

The normal value for this is about 25%, i.e 25% of the

oxygenated hemoglobin gives its oxygen to the tissues.

During strenuous Exercise, the Utilization coefficient in the

entire body can increase to 75 to 85 percent.

And in the local tissue areas where the blood flow is extremelyslow or the metabolic rate high, utilization coefficients

approaching 100% have been recorded i.e. essentially all the

oxygen is given to the tissues.


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Another major function essential to lifeas a tissue

Oxygen buffer system. i.e. the Hemoglobin in theblood is mainly responsible for stabilizing the

oxygen pressure in the tissues.

Role of hemoglobin in maintaining Constant Po2 in

the tissues

The hemoglobin in the blood automatically deliversO2 to the tissues at a pressure that is held rather

tightly between about 15 and 40 mmHg.


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A shift of the Oxygen hemoglobin dissociationcurve in response to changes in the blood CO2 and

Hydrogen ions has a significant effect in enhancing

oxygenation of the blood in the lungs and then again

in enhancing release of O2 from the blood in thetissues .

Blood passes through the lungs


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p g g

Co2 diffuses : From the blood Alveoli

Reduces the blood Pco2 and Decreases the H+ ion Concentration

[because of the decrease in blood carbonic acid]

Shift of Oxygen-Hemoglobin dissociation curve to the left & upwards

Therefore, the quantity of the Oxygen that binds with hemoglobin atany given alveolar Po2 now becomes considerably increased. Allowsgreater O2 transport to the tissues.


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The normal DPG in the blood keeps the Oxygen-Hemoglobin

dissociation curve shifted slightly to the right all the time.

In Hypoxic conditions, that last longer than a few hours, the

quantity of DPG in the blood increases considerably. That

shifts Oxygen Hemoglobin dissociation curve even farther to

the right.

This causes oxygen to be released to the tissues at as much as

10 mmHg higher tissue oxygen pressure than would be the

case without this increased DPG.

DPG mechanism important for adaptation to hypoxia,

especially caused by poor tissue blood flow.


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In exercise, several factors shift the dissociation curve to the right,delivering extra amounts of Oxygen to the active , exercising muscle

fibers.

The exercising muscle release large quantities of CO2, also severalother acids released by the muscles, increases the hydrogen ionconcentration in the muscle capillary blood.

Increase in Muscle Temp. to 2 to 3 degreesincreases O2 delivery tomuscle fibers.

This right hand shift of the curve allows oxygen to be released to the

muscle at Po2 levels as great as 40 mmHg, even after removing 75-80% of O2 from the Hemoglobin.

Then, in the lungs, the shift occurs in the opposite direction , allowingpickup of extra amounts of O2 from the Alveoli.


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EFFECT OF INTRACELLULAR Po2 ON RATE OF

OXYGEN USAGE : Only a minute level of oxygen pressure is required in the

cells for normal intracellular cellular chemical reactions to

take place

The reason : The respiratory enzyme systems of the cell, are

generated so that when cellular Po2 is >1 mmHg, O2

availability is no longer a limiting factor in the rates of

chemical reactions, Instead the main limiting factor is the

concentration of (ADP) in the cells.


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[Effect of intracellular po2 on rate of oxygen usage by the cells ]

Note : Increasing the intracellular concentration of Adenosinediphosphate(ADP) increases the rate of oxygen usage.

ATP used in the cells to provide energy


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p gy

ADP

Increase in concentration of ADP

Increases the metabolic usage of both oxygen andvarious nutrients that combine with the Oxygen to

release energy

This energy used to convert ADP ATP

U d N l ti diti th t f


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Under Normal operating conditions, the rate of

oxygen usage by the cells is controlled ultimately by

the rate of energy expenditure within the cells

i.e.by the rate at which ADP is formed from ATP.

Only at very low intracellular Po2 (


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Tissue cells are seldom more than 50 mm away from a

capillary & O2 normally can diffuse readily enough from thecells to supply all the required amounts of oxygen formetabolism.

Occasionally, cells are located farther from the capillaries -

rate of O2 diffusion to these cells becomes so low Intracellular Po2 falls below the critical level of 1 mmHg i.e.required to maintain maximal intracellular metabolism.

Under these conditions, O2 usage by cells is said to bediffusion limited and is no longer determined by the amountof ADP formed in the cells.

Almost never occurs in Pathological states.


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The total amount of O2 available each minute for use in any

given tissue is determined by :1. The quantity of O2 transported in each 100 ml of blood

2. The rate of blood flow

If the rate of blood flowfalls to 0

Amount of available O2 - falls to 0

There are times when the rate of blood flow through a tissue

can be so low that the tissue Po2 falls below the critical 1

mmHg required for maximal intracellular metabolism. Under these conditions, The rate of tissue usage of O2 is

Blood flow limited


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At the normal arterial Po2 of 95 mmHg, about 0.29 ml of O2is dissolved in every 100 ml of water in the blood.

When the Po2 of the blood falls to 40 mmHg in the tissuecapillariesonly 0.12 ml of O2 remains dissolved.

In other words : ).17 ml of O2 is normally transported in thedissolved state to the tissues by each 100 ml of blood.

During Strenuous Exercise -

Hemoglobin release of O2 to the tissuesIncreases Threefold

The relative quantity of O2 Transported in the dissolved statefalls to as little as 1.5 %

B t if P b th O2 t hi h l l P 2 l l


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But if a Person breathes O2 at very high alveolar Po2 levels

The amount transported in the dissolved state czan becomemuch greater

Sometimes so much so that serious excesses of O2 occur in

the tissues and Oxygen Poisoning ensues.

Seizures and Death

In relation to High Pressure breathing of O2, as occurs in

deep-sea divers


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Thank you!!

Documents

Energy Transfer in Cell During Exercise and Oxygen Metabolism and Transport - Palak