John has taught college science courses face-to-face and online since 1994 and has a doctorate in physiology.
Hemoglobin and Oxygen Transport
As you know, we breathe to get oxygen into our body. Specifically, our cells need the oxygen to make ATP, which then provides energy for work: for example, muscular contraction. Our red blood cells contain hemoglobin, which is a complex protein that carries the oxygen from our lungs to the metabolizing tissues.
As blood flows through the lungs, oxygen is loaded onto hemoglobin, and that forms what we call oxyhemoglobin. Oxyhemoglobin is like a delivery truck that will transport the oxygen to the tissues. As blood flows through the metabolizing tissues, oxygen is unloaded from the oxyhemoglobin, forming what we call deoxyhemoglobin.
Have you ever wondered what causes the oxygen to be unloaded? In this lesson, we will discuss the physiological factors that help hemoglobin unload oxygen as it goes through our metabolizing tissues.
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Effect of Temperature on Hemoglobin
Most people consider normal body temperature to be 37 degrees Celsius. While this may be accurate, body temperature is not the same everywhere in our body. For example, temperature can increase a few degrees in our metabolizing tissues as heat is released from the cells when they work.
Okay, so temperature increases in our tissues, but what does this have to do with oxygen transport? As it turns out, temperature affects the affinity, or binding strength, of hemoglobin for oxygen. Specifically, increased temperature decreases the affinity of hemoglobin for oxygen. As oxyhemoglobin is exposed to higher temperatures in the metabolizing tissues, affinity decreases and hemoglobin unloads oxygen. This is very important, as only free oxygen can enter the cells. In other words, it has to be released from the hemoglobin before it can get into our cells.
Here's a question for you: does increased temperature alone release enough oxygen to meet our metabolic needs? As it turns out, other factors are needed to unload oxygen from hemoglobin in our metabolizing tissues.
Let's take a look at how carbon dioxide and acid help us out. Cellular metabolism produces carbon dioxide and lactic acid, which lowers pH to about 7.2 - now that's compared with a pH of 7.4 in the lungs. While this may seem like a small decrease, it represents a relatively large increase in acidity.
Carbon dioxide and decreased pH decrease the affinity of hemoglobin for oxygen. This phenomenon is referred to as the Bohr effect. The Bohr effect favors unloading of hemoglobin in our metabolizing tissues. Once again, unloading makes the oxygen available for our cells.
Red blood cells, like any other cell in our body, metabolize food to make ATP. In the process of making this ATP, red blood cells make 2,3-bisphosphoglycerate, abbreviated 2,3-BPG. (That's how I'll refer to it.) While it seems the cell is mainly interested in making ATP, 2,3-BPG serves a purpose as well. 2,3-BPG binds to deoxygenated hemoglobin more readily than it binds to oxyhemoglobin.
Additionally, 2,3-BPG decreases the affinity of hemoglobin for oxygen. As hemoglobin is unloaded in our tissues, 2,3-BPG binds to the hemoglobin and thus favors unloading of oxygen. Once again, this decrease in hemoglobin affinity for oxygen in our tissues frees up oxygen so it can be used by our cells.
In summary, hemoglobin is the oxygen-carrying molecule that transports most of the oxygen in our body. Hemoglobin is loaded with oxygen in the lungs and unloaded of oxygen in the metabolizing tissues. Unloading is necessary to make oxygen available for our cells.
The affinity of hemoglobin for oxygen is decreased in our tissues by several physiological factors. Increased temperature, carbon dioxide, acid and 2,3-BPG all serve to decrease hemoglobin's affinity for oxygen, thus favoring unloading and making oxygen available for our cells.
At the end of this lesson, you will be able to:
- Explain the importance and function of hemoglobin
- Describe how several factors affect hemoglobin's affinity for oxygen: temperature, carbon dioxide, acid and 2,3-BPG
- Summarize the purpose of unloading oxygen from hemoglobin
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Gas Transport: Effect of Temperature, pH & Metabolism
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