Section 6 Flashcards
What is the PO2 of arterial blood, and why is oxygen considered to be poorly soluble in liquid such as plasma?
The PO2 of arterial blood is 100 mmHg, representing around 200 ml O2/L. Oxygen is considered poorly soluble in liquids like plasma, with only about 3 ml O2 able to physically dissolve into 1 L.
What is the solution to the limited solubility of oxygen in plasma, and how does it address the supply of oxygen for the body’s metabolic needs?
The solution is haemoglobin (Hb). Once bound to Hb, oxygen no longer contributes to the PO2, and the Hb-bound oxygen acts as a reserve, addressing the limited solubility of oxygen in plasma.
What is the critical concept in understanding the difference between saturation and content in the context of oxygen transport in the blood?
The critical concept is that once oxygen is bound to Hb, it no longer contributes to the PO2, and the PO2 only represents the freely dissolved oxygen in the plasma. This understanding is crucial for differentiating between saturation and content.
Describe the structure of human hemoglobin (Hb) and its composition.
Human hemoglobin is an assembly of four protein subunits. Each subunit consists of a protein chain and a heme group, which contains the iron molecules to which oxygen binds.
What percentage of circulating oxygen is bound to hemoglobin (Hb)?
98.5% of circulating oxygen is bound to hemoglobin (Hb).
Describe the process by which each iron atom in a hemoglobin (Hb) molecule can bind an oxygen molecule.
Each iron atom in a hemoglobin (Hb) molecule can bind an oxygen molecule, leading to the formation of HbO2, Hb(O2)2, Hb(O2)3, and Hb(O2)4, as represented by the equation: Hb + O2 ↔ Hb O2 ↔ Hb(O2)2 ↔ Hb(O2)3 ↔ Hb(O2)4.
The double arrows indicate that each reaction is fully reversible, allowing Hb to bind oxygen for transport and unbind oxygen for delivery.
What does it mean for hemoglobin (Hb) to be fully saturated, and how is Hb saturation expressed?
Hemoglobin (Hb) is fully saturated when all Hb present is carrying its maximum oxygen load. Hb saturation is expressed as a percentage.
According to the chemistry law of mass action, how does the concentration of a substance, such as PO2, affect a reversible reaction like Hb binding to oxygen?
According to the law of mass action, if you increase the concentration of one substance involved in a reversible reaction (such as increasing PO2), the reaction is driven to the other side. The opposite is also true.
What is the oxygen dissociation curve, and what does it describe?
The oxygen dissociation curve describes the relationship between PO2 and % Hb saturation.
How is the oxygen dissociation curve shaped, and what is notable about the steep slope and plateau regions?
The oxygen dissociation curve is sigmoidal, with a steep slope between 0 and 60 mmHg and a plateau beyond 60 mmHg as it approaches 100 mmHg. The steep slope below 60 mmHg indicates that a small change in PO2 can have a large effect on % Hb saturation.
What does the plateau region of the oxygen dissociation curve represent, and in which PO2 range is it found?
The plateau region of the curve, from 60 mmHg to 100 mmHg, represents the PO2 range found in the pulmonary capillaries where hemoglobin (Hb) is collecting oxygen.
What percentage of saturation does the dissociation curve indicate for hemoglobin (Hb) when the blood is leaving the lungs with a PO2 of 100 mmHg?
The dissociation curve shows that hemoglobin (Hb) is 97.5% saturated when the blood is leaving the lungs with a PO2 of 100 mmHg.
Why is the plateau phase of the curve considered a margin of safety, and how does it benefit individuals with pulmonary disease or those in specific circumstances?
The plateau phase represents a margin of safety because even if there is a drop in PO2 to 60 mmHg, hemoglobin (Hb) would still be 90% saturated. This is crucial for individuals with pulmonary disease and for normal healthy persons in situations like high altitudes or oxygen-deprived environments, providing a safety buffer for oxygen transport to the tissues until arterial PO2 drops below 60 mmHg.
What does the steep portion of the oxygen dissociation curve correspond to, and in which PO2 range is it found?
The steep portion of the curve, between 0 and 60 mmHg, corresponds to the range of PO2 found in the systemic capillaries.
Describe the change in oxygen saturation from the arrival of blood in the systemic capillaries (PO2 of 100 mmHg) to its departure (PO2 of 40 mmHg).
Blood arrives in the systemic capillaries with a PO2 of 100 mmHg and is 97.5% saturated. By the time it leaves the systemic capillaries, the PO2 has dropped to 40 mmHg, and the blood is now 75% saturated, indicating that 25% of the oxygen has been unloaded to support metabolism at rest.
How does the steep portion of the oxygen dissociation curve facilitate oxygen unloading in metabolically active tissues?
In metabolically active tissues where more oxygen is needed, a drop in PO2 to 20 mmHg can release an additional 45% of the total oxygen. The steep portion of the curve allows for larger amounts of oxygen dissociation for small decreases in PO2.
How does the steep portion of the curve benefit individuals breathing at altitude, and what happens to alveolar PO2 and arterial PO2 at high altitudes?
At altitude, decreased atmospheric pressure leads to a decrease in alveolar PO2 and arterial PO2. The decrease in arterial PO2 activates carotid chemoreceptors, increasing ventilation. If the person is at rest, this increased ventilation results in a small decrease in arterial PCO2, leading to a small increase in alveolar PO2. On the steep portion of the curve, this small increase in alveolar PO2 can greatly increase % Hb saturation.
Which of the following resonate with the plateau phase of the oxygen dissociation curve?
- in the alveoli
- in the tissues
- low O2 attached to Hb
- high O2 attached to Hb
- In the alveoli
- High O2 attached to Hb
Which of the following resonate with the steep portion of the oxygen dissociation curve?
- in the alveoli
- in the tissues
- low O2 attached to Hb
- high O2 attached to Hb
- In the tissues
- Low O2 attached to Hb
Why could the role of hemoglobin in gas exchange be initially ignored when discussing oxygen being driven from the alveoli to the blood?
The role of hemoglobin in gas exchange could be initially ignored because blood PO2 depends entirely on dissolved oxygen, allowing the discussion to focus on the oxygen driven from the alveoli to the blood by a PO2 gradient.
What crucial role does hemoglobin play in facilitating the exchange of oxygen between the alveoli and the lungs?
Hemoglobin plays a crucial role in permitting the transfer of large quantities of oxygen before blood equilibrates with the surrounding tissues.
Describe the hypothetical situation when no hemoglobin is present in the blood and its impact on the equilibrium between alveolar PO2 and pulmonary capillary blood PO2.
In the hypothetical situation with no hemoglobin, the alveolar PO2 and pulmonary capillary blood PO2 are at equilibrium.
How does the presence of partially saturated hemoglobin impact blood PO2, and what is the role of dissolved oxygen in this scenario?
As hemoglobin starts to bind with oxygen, it removes oxygen from solution. Because only dissolved oxygen contributes to blood PO2, the blood PO2 remains below that of the alveoli, favoring the net diffusion of more oxygen down its partial pressure gradient from the alveoli to the blood.
What happens when hemoglobin is fully saturated with oxygen, and how does this affect the equilibrium between alveolar and blood PO2?
When hemoglobin is fully saturated with oxygen, the alveolar and blood PO2 are at equilibrium again. The blood PO2 resulting from dissolved oxygen is equal to the alveolar PO2, despite the total oxygen content in the blood being much greater than in the case of no hemoglobin.