Question 31

[asfino12217]

All of the following are characteristics of the circulatory system of mammals EXCEPT:

A. return of lymph to the main circulation.[x]
B. muscular arterioles.[x]
C. elastic capillaries. [x]
D. functionally separate pumps for the systemic and pulmonary systems.

isn't the lymphatic system separate from the main circulatory system? it has its own vessels, ducts, etc so why wouldn't the answer be A.?

[jellywing_2058]

Yes the lymphatic system is its own system, however it is interconnected with the circulatory system.
In fact, the lymphatic system pours out the lymph into the circulatory system at specific locations.

[StoneColdPS14]

i was actually thinking that D. is the answer.

D. functionally separate pumps for the systemic and pulmonary systems

doesn't it sound like mammals have two hearts? or 'functionally separate' goes to the extend of Right Ventricle=Systemic, Left Ventricle=Pulmonary, thus heart has different ventricles for different functions?

[mcat_premed3832]

asfino12217: Please note that any definition of the circulatory system includes the lymphatic system: http://en.wikipedia.org/wiki/Circulatory_system

StoneColdPS14: functionally, indeed, mammals have 2 hearts. Pulmonary circulation begins with the right ventricle.

1) Pulmonary circulation (to expire waste and oxygenate blood): right ventricle, pulmonary artery-arterioles-capillaries-venules-veins, left atrium

2) Systemic circulation (to provide oxygen to the body's cells and remove waste): left ventricle, aorta-arteries-arterioles-capillaries-venules-veins-vena cavae, right atrium

There are some portal systems but that is not relevant to the MCAT.

[msamadia]

I chose D b/c the pulmonary shares the same blood vessels (like they are all connected, so how can they be separate pumps?)

Is this just the conceptual terminology that i have know?

Thanks!

[msamadia]

i was reading in wiki that anatomy of blood vessel... do capillaries get only the endothelial of the intima layer (elastica interna + endothelial)?

don't they have to be a little elastic to prevent easy ruptures?

Thanks!

[mcat_premed3832]

1) I do not know what you mean by this: "I chose D b/c the pulmonary shares the same blood vessels (like they are all connected, so how can they be separate pumps?) "

There are 2 functionally separate pumps: pulmonary and systemic as described above. It is not the case that the 2 separate pumps share "the same blood vessels" (except in disease or exceptional cases).

2) "do capillaries get only the endothelial of the intima layer (elastica interna + endothelial)?"

The capillary wall does include an endothelial (cell) layer that sits on a basal lamina. There is no elastica layer.

Your question "don't they have to be a little elastic to prevent easy ruptures? "; it's like comparing a rubber ball with a metal pipe. The truth is, even a metal pipe is "a little" elastic but it is relatively inelastic. Arteries are very elastic, veins have little elasticity and capillaries are relatively inelastic. There are many reasons regarding fluid shifts and waste exchange which depends on this feature of capillaries.