Table of Contents

Many past paper SAQs have asked the candidates to identify some rash, pupuric blotching, gangrenous embolic phenomena or some other visually impressive manifestation of disease. Irritatingly, the college examiners tend to remove these images from their published papers, presumably because they plan to reuse them. Previous questions of this sort have included Question 25.1  from the first paper of 2011 (erythema multiforme), Question 20.2  from the second paper of 2008 (Stevens-Johnson syndrome) and Question 10 from the first paper of 2005 (Toxic Epidermal Necrolysis). Question 15.1 from the second paper of 2012 was more about the non-specific approach to the evaluation of a gross whole-body rash. This approach is discussed below.

Cardiac biomarkers some up  frequently, but to be honest these questions have generally been referring only to troponin. Only Question 27 from the second paper of 2010 takes a broad overview of the cardiac biomarkers. The college answer to that question is a table of advantages and disadvantages, comparing oldies like CRP and ESR with CK, troponin with some exciting novel biomarkers.  Since this 2010 paper, none of these exciting novel biomarkers have become commonplace.

The fraction of oxygenated haemoglobin is a parameter which is calculated from values directly measured by absorption spectrophotometry. It is expressed as FO₂Hb, and is otherwise known as "fractional saturation", which is distinct from "functional saturation". The latter corresponds to the sO₂  and refers to the saturation of the functional haemoglobin, i.e. the one which is capable of transporting oxygen.  The term "fractional saturation" refers to the oxygenated fraction of total haemoglobin.

The question, "does this patient need angiography", comes up frequently in the management of the post-cardiac arrest patient. Arguments can be made for and against. On one hand, coronary pathology may be revealed which needs to be dealt with, and which might have precipitated the arrest. On the other hand, the angiogram might be pointless (i.e. no lesion, or nothing stentable), or actually harmful (all that contrast). Lastly, one has to question the utility of an expensive intervention in a patient whose longevity will be determined by their neurological recovery, something more related to the duration of ischaemic downtime than to the patency of their coronaries  

The paediatric airway is mentioned in the Part One syllabus but does not appear in any of the past papers. In contrast, it contributes one-third of historical Part Two questions involving paediatrics. In summary, the airways of neonates and children are more difficult. Their tongues are larger their epiglotti (epiglottuses?) more floppy, their mandibles smaller, and their tracheas are shorter and more narrow.

The lower airways consist of the trachea and bronchi, i.e. everything below the larynx. These structures are lined with a pseudostratified ciliated columnar epithelium, and branch into successively narrowing generations which progressively lose their cartilage content, smooth muscle, and finally even their walls. Apart from conducting gases (and to some extent participating in gas exchange), these airways contribute to immunity by assisting the clearance of inhaled particles and pathogens by the"mucociliary escalator"

Conventionally, everything above the larynx is considered to be the upper airway. This includes the pharynx, the oral cavity, the nasal cavity, and the external nose. These structures and functions are much too complex to describe in any great detail; this chapter offers a brief point-form introduction to their structure and function

As the main substrate of the respiratory system are gases and vapours, it makes sense to start the discussion of respiratory physiology with this as a foundation. Humidification is discussed in greater detail in the chapters dealing with the normal physiological mechanisms of humidification and with the technological solutions used to replicate it for mechanical ventilation. For the purpose of this chapter, it will suffice to discuss the colligative properties of liquids which are relevant to the evaporation of water and anaesthetic gases.

Copious amounts of ketones which are generated in insulin-deficient or insulin-unresponsive patients will give rise to a high anion gap metabolic acidosis. Ketones are anions, and they form the high anion gap. Well, except for acetone, which does not dissociate at physiological pH.

Of the 20,000 currently US FDA-approved pharmaceutic products (which act through 324 distinct molecular drug targets), more than 50%  target only four cardinal receptor families: G-protein coupled receptors, nuclear receptors, ligand-gated ion channels and voltage-gated ion channels.

Ligands are usually small molecules, whereas receptors are usually large proteins with complex 3D structure. Receptors and ligands have molecular complimentarity: i.e. the shape and chemical properties of their binding sites are matching to permit high-affinity selective binding. The chemical bonds which mediate their interaction can be Van der Waals forces, hydrophobic attraction, hydrogen bonding, electrostatic attraction, π–π "stacking" interactions or even covalent bonding. The specificity of receptor and ligand binding forms one of the elements of a drug's pharmacophore - the "ensemble of steric and electronic features that is necessary to ensure the optimal supramolecular interactions with a specific biological target"

These are those properties of a solution which depend upon the number of molecules in it, rather than on what sort of molecules they are. It’s all determined by the ratio of number of solute particles to the number of solvent particles. There could be any particles whatsoever.

The historical eponymous gas laws as identified below have subsequently been combined into the unifying Ideal Gas Law, which is discussed last. A brief summary of the important features is available elsewhere, for the purposes of revision. This chapter is more of a reflective digression on the history of gas research, lingering delicately on the important roles played in it by lamb bladders and mobs of angry French villagers.

The principles governing the behaviour of gases in solution are fundamental to the understanding of gas exchange and gas transport in the blood. The major topics of this chapter are Dalton's and Henry's Laws, and the influence of temperature on the solubility of gases in body fluids.