In fact the cardiovascular system is not only responsible for delivering blood and oxygen, but also for transporting nutrients, hormones and waste throughout the body. All of these are carried in the blood, of which an average adult has about 5 liters. The heart acts as a pump which circulates the blood through the capillaries,arteries?and?veins. It is interesting to note that if these were laid end-to-end, the estimated length would be 100,000 KM.

Our next system, the digestive system is closely linked to the cardiovascular system as on the one hand it requires about 30% of all cardiac output. And on the other, the digestive system separates nutrients from food before they can be distributed via the cardiovascular system. Thus, as with the relationship between the CNS and the cardiovascular system, each system needs the other to work.

nutrient? ? ? 營養(yǎng)物

of which? an average adult...? ?這是一個定義從句， which 指 all of these 前面提到的 nutrients, hormones, waste

act as? ? ?作為。。。起作用?

capillary? ? 毛細(xì)血管?

note? ? ? 注意到

lay end-to-end? ? ? 伸直?

?is closely linked to? ? ?與....緊密相關(guān)/相連?

via? ? 經(jīng)過??