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Physiology of oxygen transport

J-OC Dunn MB ChB BAO FRCA, MG Mythen MBBS MD FRCA FFICM FCAI (Hon), MP Grocott BSc MBBS MD FRCA FRCP FFICM
DOI: http://dx.doi.org/10.1093/bjaed/mkw012 341-348 First published online: 17 May 2016
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Key points

  • The transport of oxygen is fundamental to aerobic respiration.

  • Oxygen transport within the human body occurs through both convection and diffusion.

  • Within the pulmonary capillaries, one haemoglobin molecule binds up to four oxygen molecules in a cooperative manner.

  • Global oxygen delivery, or oxygen dispatch, describes the total amount of oxygen delivered to the tissues each minute, and is a product of the cardiac output and arterial oxygen content.

  • Oxygen diffuses from both the alveoli into the pulmonary capillaries and the systemic capillaries into the tissues, according to Fick's laws of diffusion and the random walk of the diffusing particles.

Oxygen is vital for life-sustaining aerobic respiration in humans and is arguably the most commonly administered drug in anaesthesia and critical care medicine. Within the mitochondrial inner membrane, oxygen acts as the terminal electron acceptor at the end of the electron transport chain whereby oxidative phosphorylation results in the synthesis of adenosine triphosphate (ATP), the coenzyme that supplies energy to all active metabolic processes. This article will discuss the key physiological concepts underpinning the movement of oxygen within the human body and also highlight some clinical applications that serve as examples of these concepts.

Convective vs diffusive oxygen transport14

With respect to human physiology, oxygen transport can be divided into that occurring through convection and that occurring by diffusion. In this context, convection describes the movement of oxygen within the circulation, occurring through bulk transport. This is an active process requiring energy, in this case derived from the pumping of the heart. On the other hand, diffusion describes the passive movement of oxygen down a concentration gradient, for example, from the microcirculation into the tissues (and ultimately the mitochondria).

Section 1: convective oxygen transport

Oxygen uptake into the blood

Deoxygenated venous blood becomes oxygenated in the pulmonary capillaries after diffusion down a concentration gradient across the alveolar capillary membrane (see Section 2: diffusive oxygen transport). The …

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