56 Questions
What is the approximate oxygen content in normal arterial blood with a PO2 of 100 mm Hg?
0.003 mL O2/mL of blood
What would the cardiac output need to be if the tissues were able to remove the entire 0.3 mL O2/100 mL of blood flow they receive?
83.3 L/min
What is the resting oxygen consumption of an adult approximately?
250 to 300 mL O2/min
At normal FIO2 and barometric pressure, is the physically dissolved oxygen in the blood sufficient to fulfill the body’s oxygen demand?
No, it is not sufficient
During severe exercise, how much can the oxygen demand increase as compared to resting oxygen consumption?
Sixteen-fold
What does Henry’s law state in relation to oxygen dissolved in plasma?
1 mL of plasma contains 0.00003 mL O2/mm Hg PO2 at 37°C
Which component is necessary for the chemical reaction with oxygen to take place?
Both globin and heme in proper spatial orientation
Which type of hemoglobin has a higher affinity for oxygen than adult hemoglobin?
Fetal hemoglobin (HbF)
How many iron atoms are there in each heme group?
1
What does methemoglobin contain that limits its capacity to bind oxygen?
Iron atom in the ferric state
What is the oxygen-carrying capacity of hemoglobin per gram?
1.34 mL
If a person has 20 g Hb/100 mL of blood, what would be their oxygen-carrying capacity in mL O2/100 mL of blood?
26.8 mL
What determines the amount of oxygen that binds to hemoglobin in erythrocytes?
PO2 of the plasma
What does 'percent saturation' in hemoglobin represent?
Percentage of hemoglobin bound to oxygen
Why is the oxyhemoglobin dissociation curve S-shaped and not linear?
It is a result of positive cooperativity between hemoglobin subunits
How does the dissociation curve for a single monomer of hemoglobin compare to that for the tetramer?
Single monomer curve is steeper than the tetramer curve
'Oxygen content' in blood is influenced by which factors?
Hemoglobin concentration and PO2 in the plasma
What is the influence of pH and PCO2 on the oxyhemoglobin dissociation curve referred to as?
Bohr effect
How does high blood temperature affect the oxyhemoglobin dissociation curve?
Shifts it to the right
What happens to the oxyhemoglobin dissociation curve at very low blood temperatures?
It shifts to the left
What is the role of 2,3-BPG in hemoglobin's affinity for oxygen?
Decreases affinity for oxygen
During chronic hypoxic conditions, what happens to the oxyhemoglobin dissociation curve due to 2,3-BPG production?
Shifts to the right
Why is it important to restore normal levels of 2,3-BPG in banked blood before transfusion?
To decrease oxygen unloading
What happens to the P50 value of normal human blood if the oxyhemoglobin dissociation curve is shifted to the right?
Increases
How does carbon monoxide affect the oxyhemoglobin dissociation curve?
Shifts it to the left
How do low pH, high PCO2, increased 2,3-BPG, and higher temperature collectively affect the oxyhemoglobin dissociation curve?
Shift it to the right
In what way does anemia secondary to blood loss affect oxygen transport in the body?
Reduces arterial PO2
What is the effect of pH, PCO2, and temperature on enhancing or interfering with oxygen unloading?
More pronounced at lower PO2s
What happens to the oxyhemoglobin dissociation curve when venous blood returns to the lung and CO2 leaves the blood?
Shifts to the left
Which of the following is a common cause of methemoglobin?
Nitrite poisoning
What is the effect of iron atoms in the Fe3+ state on oxygen?
They do not combine with oxygen
How does fetal hemoglobin's affinity for oxygen compare to that of maternal hemoglobin?
Fetal hemoglobin has higher affinity for oxygen
In what way does myoglobin differ from normal adult hemoglobin?
It binds more oxygen at higher partial pressures
Which of the following statements describes the dissociation curve of myoglobin compared to normal adult hemoglobin?
Myoglobin's dissociation curve is far to the left of normal adult hemoglobin
How do abnormal hemoglobins typically affect their affinity for oxygen?
They usually decrease their affinity for oxygen
At a PO2 of 40 mm Hg, hemoglobin is approximately what percentage saturated with oxygen?
75%
What happens to the oxyhemoglobin dissociation curve when the PO2 is greater than approximately 70 mm Hg?
It flattens out
What effect does elevated levels of 2,3-BPG have on the oxyhemoglobin dissociation curve?
Shifts it to the right
How does a high pH affect the oxyhemoglobin dissociation curve?
Shifts it to the left
'Shifting the oxyhemoglobin dissociation curve to the right' indicates what in terms of oxygen binding?
Decreased affinity for oxygen
At what partial pressure of CO2 (PCO2) in mm Hg does the arterial blood carry about 5% of the carbon dioxide in physical solution?
40
What chemical compounds are formed when carbon dioxide combines with the terminal amine groups in blood proteins?
Carbamino compounds
What happens when a carbamino compound is formed in blood proteins?
A hydrogen ion is released
What is the primary role of hydrogen ions in the context of hemoglobin and oxygen transport?
Facilitating the release of oxygen from hemoglobin
How is electrical neutrality maintained in erythrocytes during the exchange of ions?
Through the exchange of chloride ions for bicarbonate ions
What happens to bicarbonate ions as the PO2 increases and the PCO2 decreases in the lungs?
They diffuse out of the red blood cells
During oxygen release, what is the role of hydrogen ions in combination with bicarbonate ions?
Conversion into carbon dioxide
In the context of hemoglobin and oxygen transport, what is the purpose of the chloride shift?
Maintain electrical neutrality in tissues
What is the main protein in the blood that transports carbon dioxide?
Globin of hemoglobin
How is most of the carbon dioxide transported in the blood?
Bound to amino acids of hemoglobin
Which enzyme plays a crucial role in the conversion of carbon dioxide to bicarbonate ions?
Carbonic anhydrase
What allows hemoglobin to accept hydrogen ions and continue the reaction during carbon dioxide transport?
Hemoglobin's ability to bind oxygen
In the carbon dioxide dissociation curve for whole blood, how does it compare to the oxygen dissociation curve?
It has a steeper slope
What effect does deoxyhemoglobin have on the pH and PCO2 levels during oxygen transport?
Decreases pH and PCO2 levels
How does deoxyhemoglobin affect oxygen binding at low pHs or high PCO2s?
It decreases oxygen binding
What allows more carbon dioxide to be transported in bicarbonate ion form by deoxyhemoglobin?
Higher affinity for hydrogen ions than oxyhemoglobin.
Study Notes
Transport of Oxygen and Carbon Dioxide
- Physically dissolved oxygen in the blood is not sufficient to meet the body's oxygen demand, even at rest.
- The oxygen physically dissolved in the blood is about 0.003 mL O2/mL of blood, or 0.3 mL O2/100 mL of blood.
Structure of Hemoglobin
- Hemoglobin is a complex molecule with a molecular weight of about 64,500.
- It has a tetrameric structure consisting of four linked polypeptide chains, each attached to a protoporphyrin (heme) group.
- Each heme group has a ferrous (Fe2+) iron atom at its center, which binds to oxygen.
- Each of the four polypeptide chains can bind a molecule of oxygen (or carbon monoxide).
- The tetrameric hemoglobin molecule can combine chemically with four oxygen molecules (or eight oxygen atoms).
Chemical Reaction of Oxygen and Hemoglobin
- Hemoglobin rapidly combines reversibly with oxygen.
- The reaction is very fast, with a half-time of 0.01 seconds or less.
- Each gram of hemoglobin is capable of combining with about 1.39 mL of oxygen under optimal conditions.
- The oxygen-carrying capacity of hemoglobin is conventionally considered to be 1.34 mL O2/g Hb.
Oxyhemoglobin Dissociation Curve
- The oxyhemoglobin dissociation curve is a plot of the percentage of hemoglobin saturated with oxygen against the PO2 of the plasma.
- The curve is S-shaped, steep at lower PO2s and nearly flat when the PO2 is above 70 mm Hg.
- The curve is influenced by the availability of one of the reactants, oxygen (expressed as the PO2 of the plasma).
Loading Oxygen in the Lungs
- Mixed venous blood entering the pulmonary capillaries normally has a PO2 of about 40 mm Hg.
- At a PO2 of 40 mm Hg, hemoglobin is about 75% saturated with oxygen.
- The oxyhemoglobin dissociation curve is relatively flat when PO2 is greater than approximately 70 mm Hg.
Unloading Oxygen at the Tissues
- The PO2 in the capillaries varies from tissue to tissue, being very low in some (e.g., myocardium) and relatively higher in others (e.g., kidney).
- A small decrease in PO2 can result in a substantial further dissociation of oxygen and hemoglobin, unloading more oxygen for use by the tissues.
Influences on the Oxyhemoglobin Dissociation Curve
- High temperature, low pH, high PCO2, and elevated levels of 2,3-BPG all shift the oxyhemoglobin dissociation curve to the right.
- Effects of pH and PCO2 on the oxyhemoglobin dissociation curve are referred to as the Bohr effect.
- High temperatures shift the curve to the right; low temperatures shift the curve to the left.
- 2,3-BPG binds to hemoglobin in erythrocytes, decreasing the affinity of hemoglobin for oxygen.### Factors Affecting Oxygen Transport
- pH of 7.4, temperature of 37°C, P50 of 26-27 mmHg for normal human blood
- P50 increases when oxyhemoglobin dissociation curve shifts to the right
- P50 decreases when oxyhemoglobin dissociation curve shifts to the left
Anemia's Effect on Oxygen Transport
- Most forms of anemia do not affect oxyhemoglobin dissociation curve
- Anemia decreases amount of hemoglobin, but not percent saturation or arterial PO2
- Arterial oxygen content is reduced due to decreased hemoglobin
Carbon Monoxide's Effect on Oxygen Transport
- Carbon monoxide has a higher affinity for hemoglobin than oxygen
- Carbon monoxide shifts oxyhemoglobin dissociation curve to the left
- Carbon monoxide can prevent loading of oxygen in the lungs and unloading of oxygen at tissues
Nitric Oxide's Effect on Oxygen Transport
- Nitric oxide reacts with oxyhemoglobin to form methemoglobin and nitrate
- Nitric oxide can react with deoxyhemoglobin to form a hemoglobin-nitric oxide complex
- Nitric oxide may play a role in hypoxia-induced vasodilation
Methemoglobin
- Hemoglobin with iron in the ferric (Fe3+) state
- Does not combine with oxygen
- Can be caused by nitrite poisoning, oxidant drugs, or congenital hemoglobin M
Other Hemoglobins
- Fetal hemoglobin (HbF) has a higher affinity for oxygen than adult hemoglobin (HbA)
- Abnormal hemoglobins can have increased or decreased affinities for oxygen
Myoglobin
- A heme protein found in muscle cells
- Can combine with a single molecule of oxygen
- Has a hyperbolic dissociation curve far to the left of HbA
- Can store and transport oxygen in skeletal muscle
Artificial Blood
- Fluorocarbon emulsions can carry oxygen reversibly
- Can carry significantly more oxygen than plasma
- May be useful as emergency blood substitutes, for transfusions, and in anemic patients or during surgery
Cyanosis
- A sign of poor oxygen transport
- Occurs when more than 5 g Hb/100 mL of arterial blood is in the deoxy state
- Can appear bluish-purple discoloration of skin, nail beds, and mucous membranes
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