USMLE Step 1- Review- 21

Q- In which one of the following locations a mural thrombus commonly occurs following myocardial infarction?

A- Left atrium

B- Left ventricle

C- Right atrium

D- Right ventricle

E- Thoracic aorta

B- Left ventricle- Ischemic heart disease commonly affects the left ventricle. Mural thrombi develop due to damage of the left ventricle. They are common in the right atrium in cases of mitral stenosis.

Q- Bones of calvarium and facial bones are formed by which one of the following types of ossification?

A- Endochondral ossification

B- Membranous ossification

B- Membranous ossification- These bones are woven bones which are formed directly without cartilage while bones of axial skeleton and base of the skull are made by chondrocytes replaced later by osteoblasts (endochondral ossification).

Q- If the half-life of a certain drug is 5 hours, how long it takes until the drug level reaches 25% of the initial dose?

A-5 hours

B- 7.5 hours

C- 10 hours

D- 15 hours

C- 10 hours- One half-life = 50%- two half-lives = 25%- three half-lives = 12.5% and so on.

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