Which of the following blood vessels in mammals normally carries the largest amount of urea?

The wall of the heart is made up of

$A$ man will be unconscious if the blood supply to the brain is stopped for more than

In which one of the following pairs do the two items mean one and the same thing?

$A$ specialised nodal tissue embedded in the lower corner of the right atrium,close to the atrioventricular septum,delays the spreading of impulses to the heart apex for about $0.1 \; sec$. This delay allows:

Heartbeat can be initiated by