For each lipid-related topic A–E, select the most appropriate option from the following list.
1. Coronary artery disease risk factor.
2. Source of energy.
3. Cell membrane solubility.
4. Cell membrane structure.
5. Metabolic energy per unit mass.
6. Derived from cholesterol.
7. Body lipid stores.
8. Lipase.
9. Carbohydrate hormones.
10. Protein hormones
- When explorers were crossing Antarctica trailing all their food in a hand sleigh there was an advantage in taking a high proportion of fat rather than carbohydrate.
- Oestradiol, testosterone and aldosterone share a property which is not shared by insulin and vasopressin.
- In life-threatening acute inflammation of the pancreas (pancreatitis) considerable tissue damage is produced by a chemical which is detected in the bloodstream in large amounts.
- The interior of muscle fibres contains many glycogen granules and lipid droplets.
Medicine
A. Option 5 Metabolic energy per unit mass. Fat liberates just over twice the metabolic energy per unit mass that is liberated by metabolism of carbohydrates. The two substrates are both used by the body to provide energy especially in strenuous exercise. So by dragging relatively large amounts of fat the explorers were minimizing the load on their sleigh and maximizing the energy they obtained from their food.
B. Option 6 Derived from cholesterol. Oestradiol, testosterone and aldosterone are all derived in the body from cholesterol. Despite being a risk factor for arterial disease when present in excess in the blood, cholesterol is a precursor of vital hormones and is synthesized in the body. Insulin is a protein hormone and vasopressin a polypeptide hormone.
C. Option 8 Lipase. In acute pancreatitis large amounts of lipase escape into the blood and this leads to widespread fat necrosis as part of the life-threatening state when the pancreatic hormones enter the bloodstream.
D. Option 1 Coronary artery disease risk factor. Excessive lipids in the blood, including cholesterol, are a risk factor for coronary atheroma. The lipid profile may also be improved by moderate exercise and avoidance of obesity.
E. Option 2 Source of energy. During prolonged exercise energy is derived in approximately equal amounts from carbohydrate and fat. The glycogen granules in particular are a major source of energy. They become more prominent with physical training and are depleted after prolonged fasting exercise.
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