Physiology of oxygen transport

Key points 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. 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). ### 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 …