Summary
The heart, blood vessels and blood that transport materials around the body.
In depth
Double circulation: the pulmonary circuit carries blood to the lungs and back; systemic delivers it to the body. This keeps oxygenated and deoxygenated blood separate, giving high pressure to tissues.
Blood flows in one direction because of valves. The lymphatic system returns fluid. Circulation delivers oxygen, nutrients and hormones, removes wastes.
Key idea: a double circulation keeps pressures appropriate for lungs and body.
The heart pumps about 5 litres per minute at rest, and 20 or more during exercise, and 100,000 times a day. Blood vessels total roughly 100,000 km. Systemic circulation delivers oxygenated blood from the left ventricle via the aorta to organs, with the coronary arteries feeding the heart itself. The hepatic portal vein takes nutrient-rich blood from the gut to the liver. Capillary beds exchange gases, nutrients and wastes.
Blood flow is controlled by constriction and dilation of arterioles, which direct blood to active organs. Disorders include hypertension, atherosclerosis, heart attack (myocardial infarction), stroke and heart failure. William Harvey described circulation in 1628, before capillaries were seen by Malpighi.
Example: during exercise blood flow to muscles rises from about 20 percent to 80 percent of cardiac output.
Frequently asked questions
What is Circulatory System?
The heart, blood vessels and blood that transport materials around the body.
Which area of biology covers Circulatory System, and how advanced is it?
Circulatory System is one of the 51 topics in Human Physiology. It is rated Beginner, so it suits learners who are starting out in biology. Related topics in this area include Heart Structure, Blood Vessels, Excretory System.
Can you give an example of Circulatory System?
The heart beats about 100,000 times a day.
What should I learn before Circulatory System?
Circulatory System is a Beginner topic, so no earlier topic is required. Other Beginner topics in Human Physiology that pair well with it include Homeostasis, Tissues and Organs, Skeletal System.
What topics are related to Circulatory System?
The closest topics to Circulatory System are Heart Structure, Blood Vessels, Excretory System, Cardiovascular Disease Mechanisms. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Circulatory System?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Circulatory System. To practise the whole of Human Physiology, use the Human Physiology quiz.
How is Circulatory System different from Heart Structure?
Circulatory System: The heart, blood vessels and blood that transport materials around the body. Heart Structure: A four-chambered muscular pump with atria, ventricles and valves that keep blood flowing one way. Read both side by side and note what each one explains.
How should I study Circulatory System step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Heart Structure and explain the difference aloud. Finally, take the Human Physiology quiz and come back to this page for any question you miss.