Question

If a wound overwhelms the clotting mechanism and leads to serious hemorrhage and drop in blood pressure, what compensations does the body have to defend cardiac output?

Answer 1

Baroreflex, Circle of willies, you only need 30-40% of maximum potential blood output to the brain inorder for it to have enough.
.....this must be the 5'th time i answer this question so forgive my scarse answer.

Any of these terms unfamiliar to you? In which case which and i'll describe them more indepth. Also make an effort of googling before asking so you have some understand on the system as a whole before i explain the details limited to this particular circumstance.

Answer 2

Circle of willies in a region in the brain where pretty much all the Carotid arteries combines into one circular region. Basically put, let's say you've a clot in 1 of the (5? 3 posterior 2 anterior? i could use a second opinion here @Blues) major arteries, blood still flows through the regions of the brain that artery that clotted was previously supplying. Imagine 5 pipes leading toward a buffer with a continous intermittens preasure. If you shut one of the valves off somewhere in it's region you'd still have a circulation before the cloosing of the valve and after the closing of the valve due to the intermittens preasure of the other 4 valves.

Does any of this make any sense to you?

Answer 3

So close: five arteries total, two anterior (anterior cerebral and anterior communicating), two posterior (posterior cerebral and posterior communicating) and the internal carotid artery. :D