2023 Second Sitting SAQs

This question required candidates to identify that the measured arterial value (SaO2) was the gold standard to which the limitations of the pulse oximeter should be compared. A detailed description of the intrinsic and extrinsic factors of potential sources of difference of the SpO2 measurement was then expected. Intrinsic factors included wavelengths used, pulse added absorbance, derivation of the SpO2 value and time delays. Extrinsic factors where largely patient and environment related including light pollution, poor peripheral perfusion for various reasons, probe location variances and probe artefact.

This question expected an outline of the anatomy of the cardiac ventricles. Candidates that broke down the anatomy into subsections with correct and clear descriptions of each component were most successful. A potential structure to approach this question is included below; - position, orientation, relations and characteristics of the chambers including ventricular interdepence - internal ventricular structures including muscle type, septum, trabeculae, papillary muscules, infundibulum and moderator band - valves and valvular rings’ position, structure and attachments - conduction elements position and divisions - blood and nerve supply

This question required the identification of the components of the kidneys function that work to concentrate urine and a detailed description of how each of these components contribute to this. These components included the role of the loop of henle and vasa recta in the establishment and maintenance of the medullary osmotic gradient, the contribution of urea and urea cycling to this gradient and the subsequent contribution of antidiuretic hormone. A focus on not how urine is formed but how it is concentrated was expected.

The first part of this question required candidates to correlate the mechanism of action of anti epileptic drugs with atleast one example under each section. These included GABA potentiation (Barbiturates/Tiaganbine), reduction in excitory transmission (including NMDA/AMPA antagonists) and modification of ionic conductances (sodium channel blockade-Phenytoin, Calcium channel blockadeLamotrigine, Gabapentin, activation of potassium channels- Retigabine). The second part of this question involved an overview of gabapentin pharmacology. Gabapentin is an amino acid analogue of GABA utilised in neuropathic pain and epilepsy. There a multiple proposed mechanisms of action including Ca+ antagonism, inhibited glutamate release and anatagonism and increased GABA concentrations.. Important pharmacokinetic properties included dose dependent absorption, minimal protein binding, no metabolism with renal clearance and requirement for dose reduction in renal failure. It has largely central neurological side effects with a rare but important association with steven johnson syndrome or toxic epidermal necrolysis.

The first part of this question required the details of carbohydrate and lipid stores with their anatomical locations, biochemical forms, average amount of energy stored. Under the metabolic responses to starvation, a detailed description was expected of major sources of energy production, associated biochemical processes and their transition from one process to another or one source to another over time, and the hormonal influences that govern this. A more detailed answer would also include organ specific energy utilisation under a starved state. Overall it was expected that a transition of glycogenolysis to gluconeogenesis to ketogenesis would be described. It would also be important to highlight how an initial protein conservation strategy transitions to eventual protein catabolism and how muscle glycogen, an important store of glucose is unavailable to maintain blood glucose concentrations in starvation.

This question required an explanation of the factors that influence perfusion and diffusion and a detailed description of the behaviour of specific gases including perfusion limited oxygen and carbon dioxide and diffusion limited carbon monoxide. Factors influencing perfusion include flow/cardiac output, resistance (radius and length) and viscosity whereas diffusion is influenced by the characteristics of the gas (MW and solubility), surface area of diffusing surface and the pressure/concentration gradient. Perfusion and/or diffusion limited characteristics of different gases included how quickly if at all equilibrium is reached and why this occurs with each specific gas.

This question was asked in a specific way to provide candidates with a template for their answer. The classification most commonly used for opioid receptors (μ(MOP), δ(DOP), k(KOP) & NOP) and a description of the important characteristics or differences between them was expected. A description of their central and peripheral distribution was required including specific central nervous system sites such as pre and post synaptic locations in the brain (ie. the periaqueductal gray, locus ceruleus and amygdala) and spinal cord (ie. primary afferent neurons in the dorsal horn). Opioid receptors as a class are transmembrane spanning G protein receptors that have significant downstream effects including presynaptic inhibition of neurotransmitters of primary afferent neurons such as noradrenaline and substance P, and postsynaptic inhibition of membrane depolarization of dorsal horn nociceptive neurons. Specifity of detail in descriptions of these actions was expected.

The first part of the question required candidates to outline the impact of sedatives on the interthreshold range with an explanation of what this is, how heat is lost, how heat generation is impaired and the mechanism by which these occur (ie. radiation/conduction/convection via vasodilation, with absence of vasoconstriction/heat generation strategies). The second part of the question required a systems based approach with an outline of the perturbation as a result of the low body temperature. Temperature thresholds for certain physiological effects ie. loss of consciousness or arrhythmia was also expected for an overall thorough answer to this question.

This question required a list of effects of the stimulation of adrenoreceptors, thus detailed description of downstream effects and exact mechanisms was not required. Using a systems based structure with a subdivision into each receptor (or vice versa) meant that important GIT, GUT, endocrine and metabolic effects were not omitted. Given the need for little depth, this part of the question required breadth particularly within cardiovascular effects. Venoconstriction, dromotropy and lusitropic effects should also be covered. The second part of the question required a detailed description of the mechanism of action and pharmacokinetics only, thus dose, pharmaceutics and pharmacodynamic information was not required. Here it would be important to elaborate on the downstream effects of blocking the beta adrenergic receptors as compared with the information required in the first part of the question.

This question was best answered under the headings distribution, clearance and physiologic functions. Distribution involved intracellular vs extracellular concentrations, the spread amongst organ systems and state of ionisation and protein binding. Clearance of magnesium required an accurate description of its renal filtration and sites and proportion of reabsorption and secretion along the nephron. The regulatory factors and factors that influence this clearance should also be outlined. This included; Mg plasma concentrations, other cations, ECF volume and PTH. Physiologic functions should cover its role as a cofactor of metabolism and enzyme systems with some examples, the role and mechanism in the musculoskeletal system as a calcium antagonist and inhibitory action in the nervous system including the action against Ach, nerves and NMDA activity.

Cerebral Blood Flow is result of CPP/CVR. The brain defends a relatively constant high blood flow via multiple auto-regulatory processes that influence cerebral vascular resistance. This question required an in detail description of the physiological factors that alter CBF. Autoregulation via the myogenic and metabolic mechanisms, the difference between grey and white matter due to metabolic variation, the role of pCO2 and O2, sympathetic nervous system and temperature was expected. A "describe" question requires not only the factors that influence CBF but how and why, so detail is required. Whilst the monroe kellie doctrine does describe changes in blood flow this is only important at extremes of intracranial pressure when these normal autoregulatory mechanisms are exceeded, as such it was not part of the answer to this question.

ased on the question stem answers should have been structured to address the components of the complement system as well as the role, activation and regulatory mechanisms. A description of the components should include the number and type of molecule highlighting the important combinations of complement to produce the membrane attack complex. A description regarding the role in the innate immune response against bacterial infections was then required with a detailed description regarding the many ways this is achieved including opsonisation, phagocytosis, chemotaxis, mast cell/basophil activiation, lysis of cells and clearance of immune complexes. Information about the 3 pathways of activation where expected; classic, alternate and lectin pathyway, with some detail regarding the downstream effect of each that would take into account for the amplication of the response. The cessation of complement response is largely due to the limitatations of the half lives of the particular complement glycol-proteins or presence of specific inactivators.

This question required candidates to address the following relevant to the anatomy of the larynx - it's location and extent; relations; structure (paired and unpaired cartilages; major ligaments; intrinsic and extrinsic muscles); nerve supply (sensory and motor); and blood supply (and venous darinage). There were some marks allocated for other correct information relevant to the anatomy of the larynx (e.g. epithelium; differences in age; lymphatic drainage). This was a purely anatomy question so functions of the larynx was not required.

This question expected a detailed description of the effect of afterload on the left ventricle. This should cover the acute effect of increased afterload on left ventricular end systolic (and diastolic) pressure and volume, contractility, work and oxygen consumption, coronary perfusion pressure and baroreceptor responses. “Sustained” implied more longer term left ventricular exposure which would include the ventricular cellular response, concentric hypertrophy and the subsequent effects on diastolic and elevations of left atrial pressure. Definitions of afterload, cardiac output equations, vascular function curves and LV/PV loops are not required if the above concepts are described in adequate detail. The use of a diagram can assist in explaining concepts however should be linked back to the question in order to demonstrate the candidates understanding of the question being asked.

The vagus nerve anatomy was best broken down into a description of the fibers it carries (visceral, parasympathetic and somatic sensory fibres) and then origin and course from the parasympathetic, sensory and motor nuclei in the medulla as the tenth cranial nerve to its branches; the pharyngeal, cardiac, pulmonary and laryngeal branches. Pre and post-ganglionic physiology involved a detailed description of the Muscarinic Ach receptor and events. This would also include the 5 subtypes of the muscarinic receptor, with the locations and downstream effects of the M1-M3 locations being the most important to note.