Hemoglobin Oxygen Saturation Simulation

The Effects of Altitude

Structure and Functions of Oxygen and Hemoglobin

Table of Contents

Table of Contents ►

Oxygen Molecules and Their Function
Hemoglobin Molecules and Their Function
Primary Factor Affecting Oxygen Binding to Hemoglobin

Atmospheric pO₂
Lung (Alveolar) pO₂
Arterial pO₂

Assessment
Terms of Use
References and Attributions

Structure and Function of Oxygen Molecules

Oxygen molecules (O₂) inhaled from the atmosphere are transported to tissue cells by the bloodstream, where they are used to convert the energy in food into a more readily accessible form of energy.

A diffusion gradient between the lung alveoli and nearby capillaries enables the first step in transporting O₂ to the tissues. The partial pressure of O₂ in the alveoli (pO₂) at sea level is approximately 100 mmHg, while it is about 40 mmHg in the blood entering the lung capillaries from the tissues. The O₂ molecules move along the gradient, from the lungs to the capillaries.

Gas Exchange Between the Lung Alveoli and Capillaries

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After diffusing from the lungs into the surrounding capillaries, oxygen molecules (O₂) are transported to the heart through the pulmonary veins. The heart’s left ventricle pumps this oxygen-rich blood into a network of arteries, arterioles, and capillaries, which carry it to the tissues.

The pO₂ of blood entering the tissue capillaries from the lungs is approximately 100 mmHg, and in the surrounding tissue cells, it is approximately 40 mmHg. The pressure difference causes O₂ molecules to enter the cells, where they enter organelles known as mitochondria.

Gas Exchange Between the Capillaries and Tissue Cells

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The mitochondria of cells utilize oxygen to transfer energy from nutrient molecules to ATP (adenosine triphosphate) through a series of reactions known as aerobic respiration. Water and carbon dioxide (CO₂) are produced as by-products of the reaction. The energy stored in ATP powers various chemical reactions necessary for normal cell function.

The Role of Oxygen in the Production of Cellular Energy

Without oxygen, cells can resort to anaerobic respiration. However, this chemical process is less efficient and generates significantly less ATP. Therefore, a lack of oxygen can lead to cellular dysfunction and cell death.

Structure and Function of Hemoglobin Molecules

Only a small percentage (1% to 2%) of O₂ molecules are carried in the blood plasma as they are nonpolar and do not dissolve easily in water, the primary component of plasma. Instead, most O₂ molecules (98% to 99%) travel through the bloodstream reversibly bound to the 270 to 300 million hemoglobin molecules found in each red blood cell (erythrocyte).

hemoglobin molecule showing alpha and beta chains, heme groups, and oxygen molecules

A hemoglobin (Hb) molecule is a highly folded protein consisting of two alpha and two beta subunits. Within each subunit is a central heme group containing iron, which can bind one oxygen molecule. Therefore, each hemoglobin molecule can bind up to four oxygen molecules.

Primary Factor Affecting Oxygen Binding to Hemoglobin

The primary factor affecting hemoglobin’s ability to bind with oxygen (O₂) molecules is the partial pressure of oxygen in the blood plasma (pO₂). In turn, the plasma pO₂ is influenced by the amount of O₂ present in the inhaled air and the rate of oxygen consumption by tissues.

:: Atmospheric pO₂

The atmospheric air is a mixture of gases, primarily consisting of nitrogen (~78%) and oxygen (~21%). At sea level, the total atmospheric pressure is about 760 mmHg, and the partial pressure of oxygen (pO₂) is roughly 160 mmHg.

Atmospheric pO₂ = 760 mmHg * 0.21 ≈ 160 mmHg

:: Lung (Alveolar) pO₂

While the atmospheric pO₂ is approximately 160 mmHg, the pO₂ in the alveoli is typically around 100 mmHg. This difference results from several factors: (a) Inhaled air is humidified in the respiratory tract, reducing its oxygen concentration. (b) It then mixes with residual air remaining in the lungs from the previous exhalation, which has a lower pO₂. (c) Finally, oxygen diffuses into the surrounding capillary blood, further reducing alveolar pO₂.

:: Arterial pO₂

The gases dissolved in arterial blood plasma (O₂, CO₂, and N₂) each exert a partial pressure. The arterial partial pressure of oxygen (PaO₂) represents the pressure exerted by dissolved oxygen molecules in the blood plasma, and it is the primary factor determining how effectively O₂ binds to hemoglobin.

A higher PaO₂ drives more O₂to bind with hemoglobin, increasing hemoglobin’s O₂saturation. In contrast, lower PaO₂ drives less O₂to bind with hemoglobin, lowering hemoglobin’s O₂saturation.

Assessment

Explain how O₂ molecules enter the circulatory system from the lungs.
Explain how O₂ molecules enter tissue cells from the circulatory system.
Explain why oxygen is essential for proper cell function.
What organelle is involved?
Describe why only a small percentage of oxygen molecules are transported in blood plasma.
What molecule transports the majority of inhaled O₂ molecules?
Describe a hemoglobin molecule’s structure and the heme group’s function.
How many oxygen molecules can one hemoglobin molecule bind?
What are the primary gases that make up atmospheric air, and what is the approximate percentage of oxygen?
What is meant by the term partial pressure?
What is the approximate total atmospheric pressure at sea level, and what is the partial pressure of oxygen (pO₂)?
Explain why the partial pressure of oxygen in the lungs’ alveoli is lower than the atmospheric partial pressure of oxygen. What factors contribute to this difference?
How does PaO₂ influence oxygen binding to hemoglobin?
What is the relationship between PaO₂ and hemoglobin oxygen saturation?

Terms of Use

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