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      营养物

of which  an average adult...   这是一个定义从句， which 指 all of these 前面提到的 nutrients, hormones, waste

act as     作为。。。起作用 

capillary    毛细血管 

note      注意到

lay end-to-end      伸直 

 is closely linked to     与....紧密相关/相连 

via    经过