ABSTRACT
This chapter focuses mainly on internal respiration, identifying factors that affect tissue perfusion and oxygenation. It discusses the structure of haemoglobin and its effect on oxygen carriage and the oxygen saturation curve are identified. Gas transfers across semipermeable membranes from areas of greater to lesser pressure. Oxygen is not very soluble, so at normal atmospheric pressure 3 ml of oxygen dissolves in every litre of blood, insufficient to maintain life. Haemoglobin largely determines viscosity of blood. Less viscous blood flows more easily through small vessels, so optimum oxygen delivery to cells is a paradoxical balance between: high haemoglobin carries more oxygen, and low haemoglobin flows more easily through capillaries. Factors that can change oxyhaemoglobin dissociation include: temperature, pH, 2,3-diphosphoglycerate levels, and some haemoglobinopathies. Ventilation/perfusion ratio is the relationship between the volumes of air and blood reaching lungs.
