chemistry

Oxygen–hemoglobin dissociation curve

Oxygen–hemoglobin dissociation curve is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Oxygen–hemoglobin dissociation curve rather than just read about it. In short: The oxygen–hemoglobin dissociation curve, also called the oxyhemoglobin dissociation curve or oxygen dissociation curve (ODC), is a curve that plots the proportion of hemoglobin in its saturated (oxygen-laden) form on the vertical axis against the prevailing oxygen tension on the horizontal axis. This curve is an important tool for understanding how our blood carries and releases oxygen.

Key takeaways

Oxygen–hemoglobin dissociation curve belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Oxygen–hemoglobin dissociation curve to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Oxygen–hemoglobin dissociation curve from memory before moving on to harder problems.

Reference excerpt

The oxygen–hemoglobin dissociation curve, also called the oxyhemoglobin dissociation curve or oxygen dissociation curve (ODC), is a curve that plots the proportion of hemoglobin in its saturated (oxygen-laden) form on the vertical axis against the prevailing oxygen tension on the horizontal axis. This curve is an important tool for understanding how our blood carries and releases oxygen. Specifically, the oxyhemoglobin dissociation curve relates oxygen saturation (SO2) and partial pressure of oxygen in the blood (PO2), and is determined by what is called "hemoglobin affinity for oxygen"; that is, how readily hemoglobin acquires and releases oxygen molecules into the fluid that surrounds it.

Background Hemoglobin (Hb) is the primary vehicle for transporting oxygen in the blood. Each hemoglobin molecule can carry four oxygen molecules. These molecules of oxygen bind to the globin chain of the heme prosthetic group. When hemoglobin has no bound oxygen, nor bound carbon dioxide, it has the unbound conformation (shape). The binding of the first oxygen molecule induces a change in the shape of the hemoglobin that increases its ability to bind to the other three oxygen molecules.This shape is called R-State or Relaxed State. In the presence of dissolved carbon dioxide, the pH of the blood changes; this causes another change in the shape of hemoglobin, which increases its ability to bind carbon dioxide and decreases its ability to bind oxygen. With the loss of the first oxygen molecule, and the binding of the first carbon dioxide molecule, yet another change in shape occurs, which further decreases the ability to bind oxygen, and increases the ability to bind carbon dioxide. The oxygen bound to the hemoglobin is released into the blood's plasma and absorbed into the tissues, and the carbon dioxide in the tissues is bound to the hemoglobin. In the lungs the reverse of this process takes place. With the loss of the first oxygen molecule, the shape again changes and makes it easier to release the other three bound oxygen molecules. This shape is called the T-State or Tense State. Oxygen is also carried dissolved in the blood's plasma, but to a much lesser degree. Hemoglobin is contained in red blood cells. Hemoglobin releases the bound oxygen when carbonic acid is present, as it is in the tissues. In the capillaries, where carbon dioxide is produced, oxygen bound to the hemoglobin is released into the blood's plasma and absorbed into the tissues. How much of that capacity is filled by oxygen at any time is called the oxygen saturation. Expressed as a percentage, the oxygen saturation is the ratio of the amount of oxygen bound to the hemoglobin, to the oxygen-carrying capacity of the hemoglobin. The oxygen-carrying capacity of hemoglobin is determined by the type of hemoglobin present in the blood. The amount of oxygen bound to the hemoglobin at any time is related, in large part, to the partial pressure of oxygen to which the hemoglobin is exposed. In the lungs, at the alveolar–capillary interface, the partial pressure of oxygen is typically high, and therefore the oxygen binds readily to hemoglobin that is present. As the blood circulates to other body tissues in which the partial pressure of oxygen is less, the hemoglobin releases the oxygen into the tissue because the hemoglobin cannot maintain its full bound capacity of oxygen in the presence of lower oxygen partial pressures.

Sigmoid shape

The curve is usually best described by a sigmoid plot, using a formula of the kind:

S ( t ) = 1 1 + e − t . {\displaystyle S(t)={\frac {1}{1+e^{-t}}}.}

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Oxygen–hemoglobin dissociation curve

Start with the simplest possible case. Write down what Oxygen–hemoglobin dissociation curve claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Oxygen–hemoglobin dissociation curve before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Oxygen–hemoglobin dissociation curve ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Oxygen–hemoglobin dissociation curve

In research: Oxygen–hemoglobin dissociation curve appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Oxygen–hemoglobin dissociation curve in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Oxygen–hemoglobin dissociation curve is common in secondary-school and first-year university syllabi. It links to neighbouring topics Clinical chemistry, Hematology, Oxygen, so understanding it makes those chapters shorter.
In everyday life: Look for Oxygen–hemoglobin dissociation curve outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Oxygen–hemoglobin dissociation curve in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Oxygen–hemoglobin dissociation curve means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Oxygen–hemoglobin dissociation curve out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Oxygen–hemoglobin dissociation curve in simple terms?

Why does Oxygen–hemoglobin dissociation curve matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Oxygen–hemoglobin dissociation curve?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Oxygen–hemoglobin dissociation curve.