Oxygen Transport and Dissociation Curve

Oxygen is carried from the lungs to the tissues in the bloodstream.

Oxygen is transported in the blood in two ways: bound to hemoglobin and dissolved in solution.

The amount of oxygen dissolved in blood is determined by its partial pressure; a small component of overall transport but essential for diffusion.

Hemoglobin carries most of the oxygen in the blood; each hemoglobin molecule can bind four O2 molecules.

The amount of oxygen bound to hemoglobin in the blood (mL/dL of blood).

A measure of how much oxygen hemoglobin is carrying. Percentage how oxygen binds to hemoglobin.

A graph showing the relationship between oxygen partial pressure and hemoglobin saturation.

A condition where tissues don't receive enough oxygen; different types of hypoxia exist

1 gram of hemoglobin can carry 1.34 mL of oxygen. 100 mL of blood contains ~15 grams of hemoglobin, thus carrying about 20 mL of oxygen.

The amount of oxygen released by hemoglobin to the tissues. Specifically, a 100ml of arterial blood loses 5ml of oxygen as it becomes venous blood.

The curve is S-shaped due to the cooperative binding of oxygen molecules to hemoglobin. This means binding of the first O2 molecule increases the affinity for the next.

The binding of one oxygen molecule to hemoglobin increases hemoglobin’s affinity for binding additional oxygen molecules.

The flat part of the oxygen dissociation curve, where there is a high level of oxygen loading onto hemoglobin in the lungs (high PO2).

The steep part of the oxygen dissociation curve, where there is a high level of oxygen unloading from hemoglobin into the tissues (low PO2).

At 80 mmHg O2 tension, Hb is 95% saturated; at 60 mmHg, 90%. This indicates that even significant drops in alveolar O2, the blood's oxygen-carrying capacity remains relatively stable.

During intense exercise blood oxygen tension is as low as 15-30 mmHg, causing a dramatic decrease in Hb saturation (by 60%). This allows more oxygen to be delivered to muscles in need.

Increased temperature, CO2, H+ (lower pH), and 2,3-DPG decrease the affinity of Hemoglobin for oxygen; this means more oxygen is released to tissues.

Decreased temperature, CO2, H+ (higher pH), and 2,3-DPG increase the affinity of Hemoglobin for oxygen; reducing the release of oxygen to tissues.

2,3-DPG is a molecule produced by red blood cells that binds to hemoglobin, reducing its oxygen affinity. Higher levels are commonly found under low oxygen conditions.

The Bohr effect describes how increased CO2 and H+ levels (lower pH) shift the oxygen dissociation curve to the right, increasing oxygen delivery to tissues.

A graphical representation of the relationship between the partial pressure of oxygen and the saturation of hemoglobin with oxygen.

Even a slight drop in blood Po2 triggers a significant release of oxygen. This flat part of the curve, essential at the lungs, ensures relatively stable oxygen delivery to tissues while small variations in blood oxygen pressure are tolerated.

Tissue hypoxia occurs when there is a decrease in blood flow, meaning less oxygen reaches the cells. This can be either generalized affecting the whole body, like in heart failure, or localized affecting a specific area, like in cold exposure.

Histotoxic hypoxia occurs when the cells' ability to use oxygen is impaired. This is due to the damage or inhibition of enzymes involved in oxygen transport within the cells.

Cyanosis is a bluish discoloration of the skin and mucous membranes due to an excess of deoxygenated hemoglobin in the blood.

Central cyanosis indicates a problem with oxygenation of the blood itself. It involves areas with high blood flow like the lips, tongue, and mucous membranes.

Peripheral cyanosis results from increased oxygen extraction from the blood in the extremities, typically due to sluggish blood flow.

When the oxygen-hemoglobin dissociation curve shifts to the left, it indicates that hemoglobin has a higher affinity for oxygen, meaning it binds more readily to oxygen and releases it less easily. This occurs in situations where there's higher oxygen pressure (like in the lungs), promoting oxygen uptake from the lungs.

The oxygen-hemoglobin dissociation curve shifting to the right indicates that hemoglobin has a lower affinity for oxygen, meaning it releases oxygen more readily. This happens in tissues where oxygen demand is high, facilitating oxygen delivery to cells.

Several factors can cause the oxygen-hemoglobin dissociation curve to shift to the right, enhancing oxygen release to tissues. These include:

• Increased CO2 levels
• Increased acidity (lower pH)
• Higher temperatures
• Increased 2,3-diphosphoglycerate (2,3-DPG)

Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin. This allows the fetus to efficiently extract oxygen from the maternal blood in the placenta, despite lower oxygen pressure compared to adults.

Myoglobin, a protein in muscle fibers, has a higher oxygen affinity and different binding properties than hemoglobin. Its distinctive sigmoidal shape reflects its ability to bind and release oxygen at low oxygen tension, providing an oxygen reserve for muscle activity.

Carbon monoxide (CO) binds to hemoglobin with a much higher affinity than oxygen, preventing oxygen transport. This leads to hypoxia and can be fatal.

Carbon monoxide not only displaces oxygen from hemoglobin but also shifts the oxygen-hemoglobin dissociation curve to the left, hindering oxygen release to tissues.

Carbon monoxide is highly toxic due to its strong affinity for hemoglobin, blocking oxygen binding and causing hypoxia. Additionally, it prevents oxygen release from hemoglobin to tissues.

Low oxygen levels in arterial blood due to reduced oxygen partial pressure (PO2). This leads to decreased hemoglobin saturation and lower venous PO2.

Normal arterial oxygen partial pressure (PaO2) and saturation, but impaired blood flow leads to reduced oxygen delivery to tissues.

Normal oxygen delivery but cells can't utilize oxygen due to cellular poisoning.

Hypoxic hypoxia can be caused by various factors like high altitude, breathing low oxygen concentrations, shallow and rapid breathing, depressed respiratory centers, and lung diseases.

Carbon monoxide (CO) binds to hemoglobin with a much stronger affinity than oxygen, preventing oxygen transport. Though arterial PaO2 may be normal, oxygen content is reduced due to CO binding to hemoglobin.

Carbon monoxide binding to hemoglobin shifts the oxygen dissociation curve to the left, making it harder for remaining hemoglobin to release oxygen to tissues.

The bond between hemoglobin and carbon monoxide (Hb-CO) is extremely stable and breaks down very slowly, leading to prolonged hypoxia.