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Question 1
Correct
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Using a negative feedback loop, Haem production is controlled by which of these enzymes?
Your Answer: ALA synthetase
Explanation:Heme a exists in cytochrome a and heme c in cytochrome c; they are both involved in the process of oxidative phosphorylation. 5′-Aminolevulinic acid synthase (ALA-S) is the regulated enzyme for heme synthesis in the liver and erythroid cells.
There are two forms of ALA Synthase, ALAS1, and ALAS2.
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This question is part of the following fields:
- Physiology
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Question 2
Incorrect
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A 27-year-old woman is admitted to the emergency room with an ectopic pregnancy that has ruptured. The following is a description of the clinical examination: Anxious, Capillary refill time of 3 seconds, Cool peripheries, Pulse 120 beats per minute, Blood pressure 120/95 mmHg, Respiratory rate 22 breaths per minute. Which of the following is the most likely explanation for these clinical findings?
Your Answer: Reduction in blood volume of 30-40%
Correct Answer: Reduction in blood volume of 15-30%
Explanation:The following is the Advanced Trauma Life Support (ATLS) classification of haemorrhagic shock:
Class I haemorrhage:
It has blood loss up to 15%. There is very less tachycardia, and no changes in blood pressure, RR or pulse pressure. Usually, fluid replacement is not required.Class II haemorrhage:
It has 15-30% blood loss, equivalent to 750 – 1500 ml. There is tachycardia, tachypnoea and a decrease in pulse pressure. Patient may be frightened, hostile and anxious. It can be stabilised by crystalloid and blood transfusion.Class III haemorrhage:
There is 30-40% blood loss. It portrays inadequate perfusion, marked tachycardia, tachypnoea, altered mental state and fall in systolic pressure. It requires blood transfusion.Class IV haemorrhage:
There is > 40% blood volume loss. It is a preterminal event, and the patient will die in minutes. It portrays tachycardia, significant depression in systolic pressure and pulse pressure, altered mental state, and cold clammy skin. There is need for rapid transfusion and surgical intervention. -
This question is part of the following fields:
- Physiology
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Question 3
Correct
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An 81-year old man was admitted to the Pulmonology Ward due to chronic obstructive airway disease (COPD) exacerbation. Upon physical examination, he was hypertensive at 140/90 mmHg, tachycardic at 114 beats per minute, and tachypnoeic at 33 breaths per minute. Arterial blood gas analysis was obtained and showed the following results: pH: 7.25 (Reference range: 7.35-7.45), PaO2: 73 mmHg (9.7 kPa) (Reference range: 11.3-12.6 kPa), PaCO2: 56 mmHg (7.5 kPa) (Reference range: 4.7-6.0 kPa), SaO2: 90%, Standard bicarbonate: 29 mmol/L (Reference range: 20-28), BE: +4 mmol/L (± 2). Which of the following options has the most significant impact on his respiratory rate?
Your Answer: CSF pH
Explanation:The arterial blood gas analysis indicates presence of acute respiratory acidosis.
Central chemoreceptors are located in the ventral medulla and respond directly to presence of hydrogen ions in the CSF. When stimulated, it causes an increase in respiratory rate.
It is believed that hydrogen ions may be the only important direct stimulus for these neurons, however, CO2 is believed to stimulate these neurons secondarily by changing the hydrogen ion concentration.
Changes in O2 concentration have virtually no direct effect on the respiratory centre itself to alter respiratory drive. Although, O2 changes do have an indirect effect by acting through the peripheral chemoreceptors.
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This question is part of the following fields:
- Pathophysiology
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Question 4
Correct
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Which of the following statements is true with regards to the Krebs' cycle (also known as the tricarboxylic acid cycle or citric acid cycle)?
Your Answer: Alpha-ketoglutarate is a five carbon molecule
Explanation:Krebs’ cycle (tricarboxylic acid cycle or citric acid cycle) is a sequence of reactions in which acetyl coenzyme A (acetyl-CoA) is metabolised and this results in carbon dioxide and hydrogen atoms production.
This series of reactions occur in the mitochondria of eukaryotic cells, not the cytoplasm. The cycle requires oxygen and so, cannot function under anaerobic conditions.
It is the common pathway for carbohydrate, fat and some amino acids oxidation and is required for high energy phosphate bond formation in adenosine triphosphate (ATP).
When pyruvate enters the mitochondria, it is converted into acetyl-CoA. This represents the formation of a 2 carbon molecule from a 3 carbon molecule. There is loss of one CO2 but formation of one NADH molecule. Acetyl-CoA is condensed with oxaloacetate, the anion of a 4 carbon acid, to form citrate which is a 6 carbon molecule.
Citrate is then converted into isocitrate, alpha-ketoglutarate, succinyl-CoA, succinate, fumarate, malate and finally oxaloacetate.
The only 5 carbon molecule in the cycle is alpha-ketoglutarate.
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This question is part of the following fields:
- Physiology
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Question 5
Correct
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Arterial pressure waveforms give an indication of the operation of the heart and the patient's clinical state. Which of the following listed characteristics of arterial waveforms is most indicative of myocardial contractility?
Your Answer: Slope of the upstroke of the curve.
Explanation:Arterial pressure waveforms is an invasive form of monitoring cardiac parameters. It provides a lot of information on the performance of the heart from different sections, including:
Cardiac measurements:
Heart rate
Systolic pressure
Diastolic pressure
Mean arterial pressure
Pulse pressure
Change in pulse amplitude corresponding to respiratory changes
Slope of anacrotic limb associated with aortic stenosisFrom the shape of the arterial waveform displayed:
Slope of anacrotic limb represents aortic valve and LVOT flow
Indications of aortic stenosis (AS): Slurred wave, collapsing wave
Rapid systolic decline in LVOTO
Bisferiens wave in HOCM
Low dicrotic notch in states with poor peripheral resistance
Position and quality of dicrotic notch as a reflection of the damping coefficientFor this question, the upstroke slope of the pressure wave is indicative of myocardial contractility and is mathematically represented as:
dP/dt, which represents a change of pressure with regards to time.
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This question is part of the following fields:
- Clinical Measurement
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Question 6
Correct
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A 78-year-old man with a previous history of ischaemic heart disease is admitted to hospital. He is scheduled for a cardiopulmonary exercise test (CPX) before he undergoes an elective abdominal aneurysm repair. What measurement obtained during a CPX test alone provides the best indication for postoperative mortality?
Your Answer: Anaerobic threshold
Explanation:Cardiopulmonary exercise testing (CPX, CPEX, CPET) is a non-invasive testing method used to determine the performance of the heart, lungs and skeletal muscle. It measures the exercise tolerance of the patient.
The parameters measured include:
ECG and ST-segment analysis and blood pressure
Oxygen consumption (VO2)
Carbon dioxide production (VCO2)
Gas flows and volumes
Respiratory exchange ratio (RER)
Respiratory rate
Anaerobic threshold (AT)The anaerobic threshold (AT) is an estimate of exercise ability. Any measurement below 11 ml/kg/min is usually related with an increase in mortality, especially when there is a background of myocardial ischaemia occurring during the test.
Peak VO2 <20 mL/kg with a low AT have a correlation with postoperative complications and a 30 day mortality. The CPX test is used for risk-testing patients prior to surgery to determine the appropriate postoperative care facilities.
The V slope measured in CPX testing represents VO2 versus VCO2 relationship.
During AT, the ramp of V slope increases, but does not provide a picture of postoperative mortality.
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This question is part of the following fields:
- Clinical Measurement
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Question 7
Incorrect
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Regarding the anatomical relations of the first rib, one of the following is right
Your Answer: The costoclavicular ligament attaches to the tubercle
Correct Answer: The subclavius muscle attaches to the upper surface
Explanation:The first rib is an atypical rib. It is short, wide, and flattened and lies in an oblique plane.
It has a small scalene tubercle on its medial border which marks the point of attachment of scalenus anterior. The lower surface lies on the pleura and is smooth.
The tubercle on the upper surface separates an anterior groove for the subclavian vein and a posterior groove for the subclavian artery and lower trunk of the brachial plexus.
Scalenus medius is attached to a roughened area posterior to the groove for the subclavian artery.
The upper surface gives attachment anteriorly to the subclavius muscle and costoclavicular ligament.
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This question is part of the following fields:
- Anatomy
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Question 8
Correct
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A double-blinded randomised controlled trial is proposed to assess the effectiveness of a new blood pressure medication. Which type of bias can be avoided by ensuring the patient and doctor are blinded?
Your Answer: Expectation bias
Explanation:Observers may subconsciously measure or report data in a way that favours the expected study outcome. Therefore, by blinding the study we can eliminate expectation bias.
Recall bias is a systematic error that occurs when the study participants omit details or do not remember previous events or experiences accurately.
Verification can occur during investigations when there is a difference in testing strategy between groups of individuals, which might lead to biasness due to differing ways of verifying the disease of interest.
Nonresponse bias is the bias that occurs when the people who respond to a survey differ significantly from the people who do not respond to the survey.
A distortion that modifies an association between an exposure and an outcome because a factor is independently associated with the exposure and the outcome. Randomization is the best way to reduce the risk of confounding.
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This question is part of the following fields:
- Statistical Methods
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Question 9
Correct
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You performed pelvic ultrasound of Mrs Aciman as she had pelvic bloating and intermittent pain. The ultrasound shows a complex ovarian cyst and the radiologist who reported the results has advised urgent consultation with a gynaecologist. Upon breaking the news to Mrs Aciman you learn that she recently had a blood test done that was normal. You explain it to her that the test performed (Ca-125) is not always perfect and is only able to detect 80% of the cancer cases while the remaining 20% go undetected. Which statistical term appropriately explains the 80% in this example.
Your Answer: Sensitivity
Explanation:Tests are used to confirm the presence of a particular disease. However the results can be misleading at times since most of the tests have some limitations associated with them.
Sensitivity is the correct term that refers to the probability of a positive test. The others are explained below:False Positive rates refer to the proportion of the patients who don’t have the condition being detected as positive.
False Negative rates refer to the proportion of the patients who have the condition being detected as negative (like the 20% of the patients that went undetected by the Ca-125 test).
Specificity describes the ability of a test to detect and pick up people without the disease. Absolute risk ratio compares the rate of two separate outcomes.
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This question is part of the following fields:
- Statistical Methods
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Question 10
Correct
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A 61-year-old woman, present to her general practitioner. She complains of a severe lancinating pain in her forehead that only last a few seconds, possibly triggered by washing her face, occurring over the previous six weeks. On examination, she is normal with no other signs or symptoms. Which nerve is the most likely cause of her pain?
Your Answer: Sensory branches of the ophthalmic division of the trigeminal nerve
Explanation:Her symptoms are suggestive of trigeminal neuralgia which is a short, sudden, severe sharp unilateral pain in the facial region. The pain often follows the sensory distribution of the trigeminal nerve (CN V).
The trigeminal nerve gives rise to 3 sensory and 1 motor nuclei. Neuralgia can arise from any of the 3 sensory divisions.
The ophthalmic division gives rise to 3 further sensory branches, which are the frontal, lacrimal and nasociliary.
The frontal branch of the ophthalmic division of the trigeminal nerve is responsible for the innervation of the area in question.
The superior alveolar dental, zygomatic and sphenopalatine nerves are all branches arising from the maxillary division of the trigeminal nerve.
The mandibular division of the trigeminal nerve provides sensory and motor innervation. The sensory innervation is carried out by the auriculotemporal nerve which supplies the lower third of the face, while the motor fibres are responsible for controlling the muscles of mastication.
The somatic sensory branches of the vagus nerve are responsible for sensory innervation of the external acoustic meatus and tympanic membrane.
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This question is part of the following fields:
- Pathophysiology
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