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					Royal Free and University College Medical School

Phase 1 Year 1: May 2005
Copyright © 2005, Royal Free and University College Medical School

Objective Structured Practical Examination (OSPE) paper
2 hours are allowed for this assessment – you may not leave before the end. There are 12 stations in this OSPE, which accounts for 75% of the mark for the practical examination. The remaining 25% comes from the spotter exam in the Dissection Room. • You start at the same station as your ABC group number. Stations 1 – 6 are in lab 3, stations 7 – 12 in lab 4. After you have completed the first 6 stations you will move to the other lab and start at the station that is 6 greater than your group number (in lab 4) or 6 less than your group number (in lab 3). The questions and the cards or forms on which to answer each question are at the station. Every 8 minutes the bell will sound, and you must move to the next station. When you reach station 6 (in lab 3), go to station 1; when you reach station 12 (in lab 4), go to station 7, so that you complete all stations in each lab. As you leave each station, place your answer for that station face downwards in the box provided. Make sure you have placed a bar-code label on your answer and do not remove the picture (if any) from the station. For stations 1, 7 and 10 the images and questions appear on the computer only. o You must transfer your answers to the computer-readable card that is provided at the station. Make sure you use the card labeled for that station. o You must place a bar code label in the space indicated at the top of the card for each of these stations o The images for station 10 are not available in this document The relative value of each part question is shown. The mark for each station will be scaled to be of equal value before calculating the mark for this part of the examination. Negative marking is used for the computer-marked stations, but a negative mark for the station will count as zero – a negative mark for one station will not affect your marks for other stations.

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station 1

gam05b.jpg 1) Mark the following statements concerning these two stages in meiosis true or false: A) The green and blue parts of chromosome A indicate derivation from different genetic lineages. B) The two small black structures arrowed at B were formed by division of a single centromere. C) Cell C is in metaphase I. D) In the female germ line, stage D is reached before ovulation. E) The two chromosomes arrowed at E contain different alleles of the same genes.

dte06a.jpg 2) Mark the following statements about neurulation true or false: A) Midline structure A is the neural fold. B) Region B will form part of the brain. C) Structure C secretes molecules needed for normal nervous system development. D) Aperture D is normally closed by day 22. E) Folic acid in the diet can help to ensure that aperture D closes normally.

cav09a.jpg 3) Mark the following statements concerning the developing diaphragm and its nerve supply true or false: A) Nerve bundle A is one of the two phrenic nerves. B) The migrating cells marked B will form the fibrous pericardium. C) The somites marked C will form thoracic vertebrae and ribs. D) The structure marked D is an essential component of the diaphragm. E) The structure marked D is the main source of muscle precursor cells for the diaphragm.

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gut06a.jpg 4) Mark the following statements concerning these developing foregut structures true or false: A) Organ A contains many cells derived from ectoderm. B) Duct B lies within the ventral mesogastrium. C) Duct C usually survives into adulthood. D) In some normal people, structure D contains splenic tissue. E) Structure E originates from the ventral wall of the foregut.

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Station 2 The photograph provided shows the results of a blood group determination performed by the gelsedimentation technique. The plastic card contains six moulded minitest tubes. Each tube contains a plug of polyacrylamide beads. Starting from the left, tube 1 contains anti-A, tube 2 anti-B, tube 3 antiD, tube 4 inert solution (control), tube 5 known A cells, tube 6 known B cells. Patient cells are added to tubes 1, 2, 3 and 4, patient plasma to tubes 5 and 6. The card is then incubated, centrifuged and read. Agglutinated cells stay on top of the plug of beads, non-agglutinated cells fall to the bottom of the tube. a) What is the red cell group of this patient? (2 marks)

b) What is the plasma (reverse group) of this patient?

(2 marks)

c) In haemorrhagic emergency, would it be safe to transfuse this patient with group O Rhesus negative red cells? Explain your answer. (2 marks)

d) In haemorrhagic emergency, would it be safe to transfuse this patient with group B Rhesus negative red cells? Explain your answer. (2 marks)

e) What would it mean if tube 4 showed agglutination?

(4 marks)

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Station 3 Answer this question on lines 1 – 7 of the card provided. There is one correct answer for each question. Negative marking does not apply, but you will score zero if you mark more than one answer on a line. The diagram shows three idealised human ECG recordings. Each was recorded using a different Lead; I, II or III as indicated. 1) What voltage does the calibration pulse indicate? A) 0.1 mV B) 1.0 mV C) 10 mV D) 70 uV E) 10 uv F) 1.0 V 2) What time period does the calibration pulse indicate? A) 200 ms B) 20 ms C) 100 ms D) 50 ms E) 1 s F) 500 ms 3) From the Lead I ECG record calculate the duration of the PQ interval. A) 600 ms B) 400 ms C) 200 ms D) 100 ms E) 500 ms F) 300 ms 4) Which event underlies the T-wave? A) atrial depolarization B) ventricular repolarization C) ventricular contraction D) depolarization of the sinoatrial node E) ventricular depolarization F) atrial contraction 5) A Lead II ECG involves recording from which limb or limbs? A) right leg/right arm B) left leg/left arm C) right arm/left arm D) right arm/left leg E) left leg only F) right arm only 6) Calculate the patient’s heart rate in beats per min. A) 60 B) 50 C) 85 D) 75 E) 90 F) 70 7) Which axis (in degrees) does Lead I define in the frontal plane? A) 0 B) 60 C) 90 D) 120 E) -150 F) -30

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Station 4 The figure shows a trace taken from a spirometer for a young male subject whereby volume is plotted against time. The subject took 2 normal breaths and then a deep breath in with maximum effort. He then breathed out with maximal effort, followed by another 2 normal breaths. The lung volumes labelled W and X measured 0.55 litres and 4.2 litres respectively and the time between a and b was 5 sec. His anatomical dead space was measured as 140 ml. a) Name the phases of respiration labelled with the following letters (1 mark each) and state which muscles or groups of muscles (if any) are active (1 mark each)? Phase of respiration E F G H Muscles Place your barcode label here

b) Name the lung volumes labelled with the following letters: W X Y Z

(1 mark each)

c) What was his respiratory rate at rest? Give the units.

(1 mark)

d) What was his minute alveolar ventilation at rest? Show your calculations and give the units. (4 marks)

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400 300 200 N balance, mg N per day 100 0 -100 -200 -300 -400 -500
1 2 3 4

Experiment 1

Experiment 2

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6

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9

10

1

2

3

4

5

6

7

8

9

10

-600

Week of experiment 1

Week of experiment 2

OSPE.ppt 103

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Station 5 The figure shows two experiments studying nitrogen balance in a group of 25-year old men. a) Explain what is meant by nitrogen balance. (2 marks)

Place your barcode label here

In experiment 1 the subjects’ total protein intake (grams per day) was varied as follows: week protein 1 60 2 50 3 0 4 40 5 50 6 60 7 60 8 50 9 40 10 50 (4 marks)

b) What is their average protein requirement (grams /day)? Explain your answer.

c) Explain what is occurring in week 3 of experiment 1

(2 marks)

d) Explain what is occurring in weeks 5, 6 and 7 of experiment 1

(2 marks)

Week 6 Alanine Arginine Asparagine Aspartate Cysteine Glutamate Glutamine Glycine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Proline Serine Threonine Tryptophan Tyrosine Valine

Week 7

In experiment 2 the subjects were fed a mixture of amino acids, equivalent to 75 grams of protein per day, but each week one amino acid was omitted from the mixture; all other amino acids were present in (more than) adequate amounts. In the table on the right tick the amino acids that might have been omitted from the mixture in each of weeks 6 and 7

(½ mark for each correct amino acid, -½ for each incorrect amino acid, maximum = 10)

OSPE.ppt-103

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Station 6 The diagram shows oxygen electrode traces for mitochondria incubated with malate or succinate, and compounds X and Y; ADP and the substrates and other compounds were added at the point marked with an arrow on each trace. a) Explain why there is a difference between the traces for incubation with malate and succinate. (4 marks)

Place your barcode label here

b) What is the likely mechanism and site of action of compound X? Explain your answer. (4 marks)

c) What is the likely mechanism of action of compound Y? Explain your answer.

(4 marks)

substrate oxidation CO2 substrate oxidation CO2

NADH, H+ NAD+ flavinH2 flavin flavoprotein ADP + Pi ATP ubiquinone ADP + Pi ATP cytochrome b cytochrome c1 cytochrome c

½O2 H2O

cytochrome oxidase (cytochromes a and a3)

ADP + Pi ATP

OSPE.ppt-104

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Incubations with malate No other additions
% oxygen saturation
% oxygen saturation

+ compound X
% oxygen saturation

+ compounds X + Y

time

time

time

Incubations with succinate No other additions
% oxygen saturation % oxygen saturation

+ compound X
% oxygen saturation
time

+ compounds X + Y

time

time

OSPE.ppt 104

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Station 7

1 The green arrows point to: A) hepatocytes B) fibroblast nuclei C) skeletal muscle nuclei D) neurons E) smooth muscle nuclei

2 The tissue circled in green is: A) connective tissue B) smooth muscle C) skeletal muscle D) glandular tissue E) lymphoid tissue

3 The tissue within the black arrows is: A) the external elastic lamina B) the internal elastic lamina C) smooth muscle cells D) nerve fibres E) lamina propria

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4 The structure between the black arrows is: A) a gland B) a small vein C) a nerve bundle D) a small artery E) a duct

5 The green arrows point to: A) smooth muscle cells B) nerve cell bodies C) podocytes D) enterocytes E) chondrocytes

6 The black arrows point to: A) a gastric pit B) the lamina propria C) a blood vessel lumen D) the crypt of Lieberkuhn E) Bowman’s space

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7 The green arrows point to: A) neurons B) skeletal muscle cells C) podocytes D) goblet cells E) adipocytes

8 The black arrows point to: A) lymphatic vessels B) glomeruli C) interlobular ducts D) intralobular ducts E) blood vessels

9 The black arrows point to: A) lumen of blood vessels B) gastric pits C) distal convoluted tubules D) Bowman’s space E) the space of Disse

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Station 8 Answer this question on lines 1 – 11 of the computer readable card supplied. The diagram shows the digestive tract. For each of the regions numbered 1 – 11 mark which of the processes A – P that normally occur in that region. Note that more than one process may occur in any one region, and the same process may occur in more than one region. 1 mark for each correct answer, -1 for each incorrect answer. The processes you may choose are: A) B) C) D) E) F) G) H) I) J) K) L) M) N) O) P) Absorption of water Bacterial fermentation of resistant starch Bile salt metabolism Bile salt synthesis Bile storage Disaccharide hydrolysis Protein hydrolysis Secretion of bicarbonate and/or amylase and/or proteases Secretion of hydrochloric acid Secretion of insulin Secretion of intrinsic factor Starch hydrolysis Synthesis of glycogen Triacylglycerol hydrolysis Triacylglycerol synthesis None of the above

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6 2 7 3 8 4 9 10 5
1OSPEm05
OSPE.ppt 7

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Station 9 The renal plasma flow of a healthy subject is 550 L /day and the filtration fraction is 0.20. The plasma concentrations of sodium, glucose and urea were found to be: Sodium: Glucose: Urea: 145 mmoles/L (atomic weight = 23) 8 mmoles/L (molecular weight = 180) 2.3 mmoles/L (molecular weight = 60) Place your barcode label here

a) Calculate the amounts (in both grams and moles) of sodium, glucose and urea filtered per day. (You must show your working, and enter your answer in the box below) (6 marks)

grams sodium glucose urea

Moles

b) Estimate the amounts per day (in moles) of sodium and glucose entering the loop of Henle. (You must show your working, and enter your answer in the box below) (4 marks)

moles /day sodium glucose

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Station 11 Ventilatory and blood gas data were obtained from seven adults (numbered 1 - 7): 1) A normal healthy individual breathing air at rest. 2) A normal healthy individual breathing room air during during moderate exercise. 3) A breathless patient with emphysema who is hypoventilating while breathing air at rest. 4) A patient with normal lungs but with a brain tumour depressing nervous output from the respiratory centre, who is breathing 100% oxygen at rest. 5) A patient with uncontrolled diabetes but normal lungs, breathing air at rest. 6) An anxious medical student, who is hyperventilating while breathing air at rest. 7) A patient with impaired pulmonary diffusion who continues to hyperventilate at rest when her hypoxia is relieved by breathing an enriched oxygen gas mixture.

Place your barcode label here

The following data were collected from the seven individuals:

VA L /min A B C D E F G 2.4 4.3 7.5 2.8 6.7 24.0 18.6

PaCO2 mmHg 69 40 23 62 30 18 39.5

PaO2 mmHg 67 104 122 630 250 125 98

SaO2 % 88 97.5 98.8 100 90 98.2 97

pH 7.24 7.40 7.56 7.33 7.51 7.10 7.39

FEV1/FVC % 47 85 88 80 72 82 86

Complete the table below indicating which data set corresponds to which subject (1 mark each). Also indicate whether or not there is an acid base disturbance and, if so, whether it is a respiratory acidosis, a respiratory alkalosis, a metabolic acidosis or metabolic alkalosis (1 mark each) subject 1 2 3 4 5 6 7 Data set Acid/base disturbance

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Station 12 Urine glucose was measured in nine people by two different methods: • an alkaline copper reagent • glucose oxidase linked to oxidation of ABTS to a blue dye (see the diagram provided): Place your barcode label here

A) A normal subject B) A normal subject taking supplements of 3 g of vitamin C per day C) A normal subject who has just eaten 3 pears, which are a rich source of pentose sugars D) A person with idiopathic pentosuria (excretion of 5-carbon sugars in the urine) E) A person with idiopathic pentosuria taking supplements of 3 g of vitamin C per day F) A person with well-controlled diabetes mellitus G) A person with poorly controlled diabetes mellitus H) A person with poorly controlled diabetes mellitus who has just eaten 3 pears, which are a rich source of pentose sugars I) A person with poorly controlled diabetes mellitus taking supplements of 3 g of vitamin C per day Tick the box(es) in the table below if you think that one or more of these subjects A – I might have given the results shown More than one subject may give any of the results; some results may not be given by any of these subjects (tick “none” in this case). (1 mark each, -1 for an incorrect answer) alkaline copper negative positive positive negative glucose oxidase negative negative positive positive A B C D subject E F G H I none

Explain briefly how differences between the two methods of determining urine glucose led you to give the answers above. (6 marks)

Measurement of plasma or urine glucose
Cu++ HC HC HO CH HC HC OH OH glucose oxidase O OH alkaline copper reagent HO Cu2O (red-brown ppt) COOH HC CH HC HC OH OH OH

CH2OH glucose OSPE.ppt slide 39

CH2OH gluconate

O2

H2O2

ABTS (colourless)

peroxidase oxidised ABTS (blue)
1OSPEm05

H2O
OSPE.ppt 39

ABTS = 2,2'-azo-di(3-ethylbenzothiazoyl-sulphonate)

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