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Internal RespirationInternal respiration is the diffusion of O2 from systemic capillaries into tissues

and CO2 from tissue fluid into systemic capillaries.

Oxyhemoglobin gives up O2, which diffuses out of the blood and into the tissues because the partial pressure of O2 of tissues fluid is lower than that of the blood.

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- About 9% of CO2 molecules end up dissolving in blood plasma and hitch a ride in the plasma back up to the lungs.

- About 27% of CO2 molecules attach themselves onto Hemoglobin (Hb) to form a new combined form of Hemoglobin called CARBAMINOHEMOGLOBIN (HbCO2)

- The majority (64%) of CO2 given off by cells must undergo a chemical reaction. This chemical reaction occurs inside Red Blood Cells (erythrocytes). The end product is BICARBONATE IONS.CO2 + H2O H2CO3 H+ + HCO3

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Carbonic Acid Hydrogen Bicarbonate Ion Ion

An enzyme called Carbonic Anhydrase found inside RBC’s, will run this reaction

Water Carbon DioxideCarbonic Acid

Bicarbonate Ion

Hydrogen Ion

Know It ! Live It ! BREATHE It ! - Become One with the REACTION !

Hemoglobin (Hb) – “MASTER CARRIER”

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Hemoglobin can alter shape to pick up and transport three key molecules/ions:1.OXYGEN – Oxyhemoglobin (HbO2)2.CARBON DIOXIDE – Carbaminohemoglobin (HbCO2)3.HYDROGEN IONS – Reduced Hemoglobin (HHb)

How Does Hemoglobin Do This ?

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Hemoglobin is a protein. What happens to proteins when we change the pH they are in or change the temperature of their environment?

Temperature around lungs is cooler, pH is slightly higher – 7.2

Temperature around bodily tissues is slightly warmer, and pH is slightly lower – 6.8

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Saturation of Hb relative to temperature

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Saturation of Hb relative to pH

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Binding Capacity of HemoglobinThe partial pressure of gases, temperature, and pH affect

binding capacity of hemoglobin. The high pressure of oxygen, the low temperature and low

pH aid the binding of oxygen to hemoglobin in the lungs; the opposite is true in the tissues.

In both cases, environmental conditions are favorable to the uptake of the appropriate gases.

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After CO2 diffuses from tissue cells into the blood, it enters red blood cells where a small amount is taken up by hemoglobin, forming carbaminohemoglobin – approx 25%-30% of CO2

Most of the CO2 combines with water to form carbonic acid (H2CO3), which dissociates to release hydrogen ions (H+) and bicarbonate ions (HCO3

-); the enzyme carbonic anhydrase speeds this reaction.

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The globin portion of hemoglobin combines with excess hydrogen ions to become reduced hemoglobin or HHb; this helps maintain a normal blood pH. So Hemoglobin acts as a BUFFER to help buffer blood.

Blood leaving capillaries is a dark maroon color because red blood cells contain reduced hemoglobin.

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External Respiration Individual gases exert pressure proportional to their portion

of the total in a mixture of gases; this is called “partial pressure”.

External respiration is the diffusion of CO2 from pulmonary capillaries into alveolar sacs and O2 from alveolar sacs into pulmonary capillaries.

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In both cases, diffusion occurs because the partial pressures are higher causing diffusion (from higher to lower concentrations) across the capillary wall.

Most CO2 is carried as bicarbonate ions. Approx 65%-70%The enzyme carbonic anhydrase, in red blood cells, speeds up the

conversion of bicarbonate and H+ to H2O and CO2; CO2 enters alveoli and is exhaled.

Hemoglobin (Hb) takes up oxygen from alveoli and becomes oxyhemoglobin (HbO2).

Because the lungs are cooler and the pH is higher, the reaction below runs to the left.

H2O + CO2 H2CO3 H+ + HCO3-

The reaction takes place inside erythrocytes and performed by the same enzyme – CARBONIC ANHYDRASE

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External and internal respiration