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Respiratory systemL4

Faisal I. Mohammed, MD, PhD

University of Jordan

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Transport of Oxygen and Carbon Dioxide Oxygen transport

Only about 1.5% dissolved in plasma 98.5% bound to hemoglobin in red blood cells

Heme portion of hemoglobin contains 4 iron atoms – each can bind one O2 molecule

Oxyhemoglobin Only dissolved portion can diffuse out of blood into

cells Oxygen must be able to bind and dissociate from

heme

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OXYGEN IN THE BLOOD in Milliliters: 200 ml in 1litre arterial blood.

Oxygen in blood:Blood of a normal person contains about 15 gm of Hb in each 100 ml of blood.

Each gram of Hb can bind with a maximum of 1.34 ml of O2

98.50%

1.50%

Oxygen Hb Oxygen in soln.

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Relationship between Hemoglobin and Oxygen Partial Pressure Higher the PO2, More O2 combines with Hb Fully saturated – completely converted to oxyhemoglobin Percent saturation expresses average saturation of

hemoglobin with oxygen Oxygen-hemoglobin dissociation curve

In pulmonary capillaries, O2 loads onto Hb

In tissues, O2 is not held and unloaded 75% may still remain in deoxygenated blood

(reserve)

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Hemoglobin and Oxygen

Other factors affecting affinity of Hemoglobin for oxygen

Each makes sense if you keep in mind that metabolically active tissues need O2, and produce acids, CO2, and heat as wastes Acidity (pH) PCO2

Temperature

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Hemoglobin and 02 Transport

280 million hemoglobin/RBC.

Each hemoglobin has 4 polypeptide chains and 4 hemes.

In the center of each heme group is 1 atom of iron that can combine with 1 molecule 02.

Insert fig. 16.32

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Hemoglobin

How does Hemoglobin carry Oxygen?

Hemoglobin exists in two forms:Oxyhemoglobin: HbO2

O2 + Hb HbO2

Iron in Hb binds to O2

4 O2 molecules per Hb molecule

Deoxyhemoglobin The fraction of all the Hemoglobin in the form of

Oxyhemoglobin is expressed as Hemoglobin saturation.

Hemoglobin (continued)

Methemoglobin: Has iron in the oxidized form (Fe3+).

Lacks electrons and cannot bind with 02. Blood normally contains a small amount.

Carboxyhemoglobin: The reduced heme is combined with carbon

monoxide. The bond with carbon monoxide is 210 times

stronger than the bond with oxygen. Transport of 02 to tissues is impaired.

Hemoglobin (continued) Oxygen-carrying capacity of blood determined by its

[hemoglobin]. Anemia:

[Hemoglobin] below normal. Polycythemia:

[Hemoglobin] above normal. Hemoglobin production controlled by erythropoietin.

Production stimulated by PC02 delivery to kidneys. Loading/unloading depends:

P02 of environment. Affinity between hemoglobin and 02.

Oxyhemoglobin Dissociation Curve Graphic illustration of the % oxyhemoglobin saturation at

different values of P02.

Loading and unloading of 02.

Steep portion of the sigmoidal curve, small changes in P02 produce large differences in % saturation (unload more 02).

Decreased pH, increased temperature, and increased 2,3 DPG: Affinity of hemoglobin for 02 decreases.

Greater unloading of 02: Shift to the curve to the right.

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Oxygen-hemoglobin Dissociation Curve

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Oxyhemoglobin Dissociation Curve

Insert fig.16.34

Effects of pH and Temperature The loading and

unloading of O2 influenced by the affinity of hemoglobin for 02.

Affinity is decreased when pH is decreased.

Increased temperature and 2,3-DPG: Shift the curve to the

right.

Insert fig. 16.35

Effect of 2,3 DPG on 02 Transport

Anemia: RBCs total blood [hemoglobin] falls, each RBC

produces greater amount of 2,3 DPG. Since RBCs lack both nuclei and mitochondria,

produce ATP through anaerobic metabolism. Fetal hemoglobin (hemoglobin f):

Has 2 -chains in place of the -chains. Hemoglobin f cannot bind to 2,3 DPG.

Has a higher affinity for 02.

Inherited Defects in Hemoglobin Structure and Function

Sickle-cell anemia: Hemoglobin S differs in that valine is substituted for

glutamic acid on position 6 of the b chains. Cross links form a “paracrystalline gel” within the

RBCs. Makes the RBCs less flexible and more fragile.

Thalassemia: Decreased synthesis of a or b chains, increased

synthesis of g chains.

Muscle Myoglobin Red pigment found exclusively

in striated muscle. Slow-twitch skeletal fibers

and cardiac muscle cells are rich in myoglobin. Have a higher affinity for

02 than hemoglobin. May act as a “go-between”

in the transfer of 02 from blood to the mitochondria within muscle cells.

Insert fig. 13.37

May also have an 02 storage function in cardiac muscles.

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Bohr Effect As acidity increases (pH

decreases), affinity of Hb for O2 decreases

Increasing acidity enhances unloading

Shifts curve to right PCO2

Also shifts curve to right As PCO2 rises, Hb unloads

oxygen more easily Low blood pH can result

from high PCO2

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Temperature Changes

Within limits, as temperature increases, more oxygen is released from Hb

During hypothermia, more oxygen remains bound

2,3-bisphosphoglycerate BPG formed by red

blood cells during glycolysis

Helps unload oxygen by binding with Hb

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Fetal and Maternal Hemoglobin Fetal hemoglobin has a

higher affinity for oxygen than adult hemoglobin

Hb-F can carry up to 30% more oxygen

Maternal blood’s oxygen readily transferred to fetal blood

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CO2 produced by cells is carried by the blood in three forms In physical solution Plasma/Erythrocyte: 7% As Carbamino-Hemoglobin : 23%

CO2 + Hb HbCO2

As Bicarbonate ions: 70% Mostly in the Erythrocyte which has the enzyme, Carbonic

anhydrase (Catalyses the formation of Carbonic acid 5000 times.)

CO2 + H2O H2 CO3 [H+] + [HCO3-]

Carbon dioxide in blood

7%

23%

70%

Phy. Soln. CarbaminoHb Bicarbonate

Carbon dioxide in blood

transported from the body cells back to the lungs (Tidal Co2) as:

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Chloride shift HCO3

- accumulates inside RBCs as they pick up carbon dioxide

Some diffuses out into plasma To balance the loss of negative ions, chloride (Cl-)

moves into RBCs from plasma Reverse happens in lungs – Cl- moves out as moves

back into RBCs

CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-

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Thank YouThank You

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