Pbl 9 a Matter of Opinion

PBL 9 – A MATTER OF OPINION

1999 Paper 2, Part A: Q11

Question 11. It is common practice to divide the abdomen into nine divisions by using vertical lines and horizontal planes. On the diagram below, draw and label these lines and planes, including the nine (9) abdominal divisions.

Question 3. (4 marks) The rate of protein breakdown accelerates for the first few days of fasting, but slows again after 3-4 days of fasting.

(a) Why does protein breakdown increase in the early stages of fasting? (2 marks)

Protein breakdown increases in the early stages of fasting because amino acids are needed for gluconeogenesis. Glucose is required in higher amounts in this early stage of fasting as the brain still utilises it as its primary energy source.

(b) Why does protein breakdown slow later in the fast? (2 marks)

After 3-4 days, the brain switches its energy requirements to 25% glucose and 75% ketone bodies. Also, the body wishes to preserve its skeletal muscle as much as possible and high protein turnover would result in large muscle degradation. So the body uses its adipose stores to produce ketones instead. 2001 Paper 1, Part D

Rob de Castella is about to run the Olympic Marathon in Atlanta in August, 1996. The average temperature in Atlanta at the time of the marathon is expected to be 30oC and 90% humidity. He is expecting to lose up to six kilograms in body weight.

Question 1. (5 marks) Outline the mechanisms by which loss of water and other substances leads to weight loss.

Loss of water in the airways and through sweat would be the main source for water loss. Urine loss would be minimal because the blood to the muscles is being increased and therefore the blood supply to the kidneys decreases.

Question 2. (5 marks) Outline the key pathophysiological events leading to collapse of a marathon runner.

Collapse in a marathon runner is due to a combination of: . Hypervolemia due to dehydration  decreased perfusion of the brain . Hypoglycaemia due to the excessive consumption of rapidly mobilised energy sources, ie. glycogen . Metabolic acidosis due to excessive lactic acid production directly affecting loss of consciousness

Question 3. (6 marks) List the major fuels that are used by muscle cells to provide energy during a marathon run. Briefly outline how each fuel is metabolised (details of metabolic pathways are not required).

Glucose either is directly available or is mobilised from glycogen. It is an easily mobilised store for energy. Glucose is taken into the cell and then is metabolised in the TCA cycle to ATP, NADH and FADH. These highly reduced species undergo oxidative phosphorylation to give ATP in the mitochondria. Amino acids from the circulating pool enter the TCA cycle or the gluconeogenic pathway to make glucose. This then undergoes the process described above.

Question 4. (5 marks) The respiratory rate of an athlete competing in a marathon is much faster than his resting rate. Describe the molecular events in muscle cells that are responsible for this increase in respiratory rate.

Increasing the anaerobic metabolism of pyruvate  lactic acid to regenerate NADH to NAD+ to continue the TCA operation  lactic acidosis and increased H+ (CO2 + H2O ↔ H+ + HCO3-) = LEFT SHUNT  increased PCO2 in the blood stimulates central and peripheral chemoreceptors. The increased CO2 generated from metabolism also increases the PCO2. Increased H+ and PCO2 stimulates the dorsal respiratory group of the respiratory rhythmicity centre of the medulla which increases the respiratory rate Question 5. (10 marks) Endurance competition at high altitude is assisted by adaptive changes to the capacity of the blood to deliver oxygen to muscles, apart from any changes to the blood acid-base balance. What are these changes, what are the underlying mechanisms, and what period of time is required to effect each change?

The problem is there is less oxygen in inspired air at high altitudes, so there is less haemoglobin saturation at the alveolar membrane. Adaptation to these condition is immediate to weeks to months: . Immediately hypoxia causes an increase in respiratory rate and heart rate to match the ventilation-perfusion mismatch and to maintain oxygen supply to the tissues . Continued hypoxia is sensed by the juxtaglomerular apparatus in the kidney which increases erythropoietin. This stimulates RBC production to increase the oxygen carrying capacity of the blood. This process takes weeks to months

2003 Paper 1: Q8

Question 8. (5 marks) A 19 year-old man involved in purchasing drugs was knifed in the left hypochondrium of the abdomen. On examination in the emergency department, it was difficult to determine whether the knife had penetrated into the peritoneal cavity. The doctor in charge decided to do a midline peritoneal lavage below the umbilicus to see if there was any free blood in the peritoneal cavity.

(a) Mark the area of the left hypochondrium on the diagram above. (1 mark) (b) List the layers of tissue, from superficial to deep that a cannula would penetrate in order to enter the peritoneal cavity in the midline below the umbilicus. (4 marks)

Phillipa M, a 25 year-old hockey player, has been losing weight recently. Her weight has fallen from 65 kg to 58 kg over two months. She is 170 cm tall (BMI = 20).

Question 1. (12 marks) List three (3) broad hypotheses that might explain Phillipa’s weight loss. Detailed mechanisms and specific diagnoses are not required. For each hypothesis, indicate two clinical features which you might seek either from history or physical examination of the patient that would help to support or oppose your hypotheses .

Excess Exercise – how much she exercises, state of muscles Cancer – Unusual Lumps, Eating pattern Eating Disorder – Muscle mass, Eating patterns

2005 Paper 1, Part A: Q1, 2

Phillipa Morris, a 25 year-old hockey player, has been losing weight recently. Her weight has fallen from 65 kg to 58 kg over two months. She is 170 cm tall.

Question 1. (3 marks) a) What do the initials “BMI” represent? (1 mark)

Body Mass Index b) Define the formula for BMI (including units of measurement). (2 marks)

Weight (kg) / Height2 (m) Question 2. (15 marks) List three (3) broad hypotheses that might explain Phillipa’s weight loss. Detailed mechanisms and specific diagnoses are not required. For each hypothesis, indicate two clinical features which you might seek either from history or physical examination of the patient that would help to support or oppose your hypotheses .

Excess Exercise – how much she exercises, state of muscles Cancer – Unusual Lumps, Eating pattern Eating Disorder – Muscle mass, Eating patterns