Transport of Blood Gases

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Questions and Answers

What is the primary reason for the sigmoidal shape of the oxygen-hemoglobin dissociation curve?

The Bohr effect

The quaternary structure of hemoglobin (correct)

The high affinity of oxygen for hemoglobin

The cooperative binding of oxygen molecules

What is the result of the binding of oxygen to the first heme group of hemoglobin?

An increase in the affinity of the second heme group for oxygen (correct)

No change in the affinity of the second heme group for oxygen

The release of oxygen from hemoglobin

A decrease in the affinity of the second heme group for oxygen

What is the primary mechanism of carbon dioxide transport in the blood?

Transport in red blood cells

Binding to hemoglobin

Dissolution in plasma

Conversion to bicarbonate (correct)

What is the effect of low partial pressure of oxygen on the oxygen-hemoglobin dissociation curve?

A shift to the right Signup and view all the answers

What is the percentage of oxygen that is transported in the dissolved state in the plasma?

3% Signup and view all the answers

What is the main reason for the sigmoid shape of the O2-Hb dissociation curve?

The quaternary structure of Hb Signup and view all the answers

What is the approximate PO2 at which the Hb is half saturated with O2?

P50, which varies depending on the individual Signup and view all the answers

What is the percentage of blood that gives off its O2 as it passes through the tissue capillaries in a normal individual?

25 % Signup and view all the answers

What is the maximum amount of O2 that can be bound to Hb in 100 ml of blood?

20 ml Signup and view all the answers

What is the O2 saturation of Hb in systemic arterial blood?

97 % Signup and view all the answers

What is the effect of an increase in blood CO2 on the oxygen-hemoglobin dissociation curve?

Shift to the right, decreasing oxygen saturation Signup and view all the answers

Which of the following factors does not shift the oxygen-hemoglobin dissociation curve to the right?

Presence of adult hemoglobin Signup and view all the answers

What is the effect of a decrease in pH on the oxygen-hemoglobin dissociation curve?

Shift to the right, decreasing oxygen saturation Signup and view all the answers

What is the role of the Bohr effect in oxygen transport?

It facilitates the release of oxygen from hemoglobin in the tissues Signup and view all the answers

What happens to the oxygen-hemoglobin dissociation curve in the lungs?

It shifts to the left, increasing oxygen saturation Signup and view all the answers

Study Notes

Transport of Oxygen

97% of oxygen is transported in blood in combination with hemoglobin (oxyhemoglobin; Hb-O2)
Remaining 3% is in the dissolved state in the plasma
Each of the 4 iron atoms in hemoglobin can bind one O2 molecule reversibly
Oxygen binding to hemoglobin is an oxygenation, not an oxidation reaction
Oxygenation and deoxygenation are very rapid processes, taking approximately 0.01 seconds

Quaternary Structure of Hemoglobin

Hemoglobin's quaternary structure is responsible for its sigmoid-shaped oxygen binding curve
The structure serves for its affinity for O2 by shifting the relationship of four components (polypeptide chains)
This helps in either O2 uptake or O2 delivery

Affinity

When hemoglobin takes up a small amount of O2, additional uptake of O2 is facilitated
The first heme binds with O2, increasing the affinity of the 2nd heme to combine with O2
Oxygenation of the 2nd heme increases the affinity of the 3rd, explaining the sigmoid shape of the O2-Hb dissociation curve

O2-Hb Dissociation Curve

The percentage of hemoglobin that is bound with O2 increases progressively as the PO2 increases
The curve is sigmoid-shaped, with saturation not differing much between 60-100 mm Hg
Below 60 mm Hg, the curve is very steep, with a larger release of O2 to the tissues

Myoglobin Curve

Myoglobin curve is hyperbolic, with only one O2 molecule per one myoglobin molecule

Binding/Releasing

Binding and releasing of O2 involves breaking or forming salt bridges between polypeptide chains
Upon oxygenation, 2 β chains move closer, while upon deoxygenation, they move apart

Maximum Amount of O2 that can be Bound to Hb

When blood is equilibrated with 100% oxygen, Hb is 100% saturated
Each gram of Hb can bind 1.34 ml of O2
Hb in 100 ml of blood can combine with nearly 20 ml of O2, when Hb is 100% saturated

O2 Saturation

In systemic arterial blood, PO2 is about 95 mm Hg, and O2 saturation is about 97%
In normal venous blood, PO2 is 40 mm Hg, and saturation is about 75%

Utilization Coefficient

The fraction of blood that gives off its O2 as it passes through the tissue capillaries
Normal utilization coefficient is 25% (1/4th), but it can rise to 75% to 85% during heavy exercise

P50 and Affinity

P50 is the PO2 at which the Hb is half saturated with O2
A higher P50 indicates lower affinity of Hb for O2
The Bohr effect: when the blood becomes slightly acidic, the affinity of Hb for O2 decreases, and O2 is released

Shift of OHDC by Changes in Blood CO2 and Hydrogen Ions

Shift of the OHDC to the right with an increase in CO2 and hydrogen ions, enhancing the release of O2 from the blood in the tissues

CO2 Transport

CO2 diffuses from the blood into the alveoli in the lungs, reducing PCO2 and decreasing H+ ion
This shift of the OHDC to the left and upward, allowing greater O2 transport to the tissues

Factors that Shift the Curve

Factors that shift the curve to the right: increased CO2 and decreased pH, increased blood temperature, and increased 2,3-diphosphoglycerate
Factors that shift the curve to the left: presence of large quantities of fetal Hb and low blood temperature

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Description

Understand how oxygen and carbon dioxide are carried in the blood, including the binding of oxygen with hemoglobin and the characteristics of oxygen-hemoglobin dissociation curve.