Posted by: Johnson Francis on: 10 Jun, 2010
All of the following molecules are involved in the antithrombotic mechanisms of the endothelial cell except:
A. Heparan sulphate
B. Thrombomodulin
C. t-PA
D. Lipoprotein (a)
Answer: D. Lipoprotein (a)
Heparan sulfate proteoglycan molecules on the surface of the endothelial cell act as a co-factor for antithrombin III.
Thrombomodulin binds thrombin molecules and exerts antithrombotic properties by activating proteins S and C. Tissue type plasminogen activator produced by endothelial cells can lyse thrombi as soon as they start forming. Lipoprotein (a) on the other hand promotes ahterothrombosis.
Posted by: Johnson Francis on: 10 Jun, 2010
All of the following are true of endothelium dependent hyperpolarizing factor (EDHF) except:
A. Hyperpolarizes vascular smooth muscle
B. Acts via nitric oxide
C. Metabolite of arachidonic acid
D. Produced by cytochrome P-450 epoxygenase pathway
Answer: B. Acts via nitric oxide
Endothelium-dependent hyperpolarizing factor (EDHF) hyperpolarizes vascular smooth muscle and dilates arteries by opening calcium-activated potassium channels. The exact biochemical nature of EDHF is to be determined. The possible candidates are epoxyeicosatienoic acid and endothelium-derived hydrogen peroxide.
Posted by: Johnson Francis on: 10 Jun, 2010
All of the following are determinants of myocardial oxygen consumption except:
A. Systolic pressure
B. Diastolic pressure
C. Heart rate
D. Left ventricular contractility
Answer: B. Diastolic pressure
The major determinants of myocardial oxygen consumption are heart rate, systolic pressure and left ventricular contractility. The product of systolic pressure and heart rate is known as double product. The product of double product and left ventricular ejection time is sometimes called the triple product. The double product is a commonly measured indicator of myocardial oxygen consumption. The summary report of the treadmill exercise test displays the double product in each stage.
Posted by: Johnson Francis on: 10 Jun, 2010
Mechanisms of chronic preconditioning include all the following except:
A. Downregulation of iNOS
B. Upregulation of COX-2
C. Opening of mitochondrial K+ATP channels
D. Involves protein synthesis
Answer: A. Downregulation of iNOS
Chronic or delayed preconditioning involves protein synthesis with upregulation of iNOS (inducible nitric oxide synthase), cyclooxygenase (COX-2) and opening of mitochondrial K+ATP channels. It can persist up to 4 days.
Posted by: Johnson Francis on: 10 Jun, 2010
Extravascular compressive component of coronary vascular resistance is:
A. R1
B. R2
C. R3
D. R4
Answer: C. R3
R1 is the epicardial conduit resistance, which is negligible unless the obstruction is more than 50% of luminal diameter. R2 is the microcirculatory resistance in the small arteries and arterioles. R3 is compressive resistance and is related to the cardiac contraction and the systolic pressure developed in the left ventricle.
