The Circulatory System
ICSE Class 8 · Biology · Chapter 6
What this chapter covers
- A quick look back: heart, blood and blood vessels
- Internal structure of the heart
- Major blood vessels of the heart
- Double circulation
- Blood groups
- Conditions related to the heart
- The lymphatic system
Key definitions
Blood is a red, fluid connective tissue made up of a pale yellow liquid called plasma and the blood cells floating in it.
Haemoglobin is the iron-containing red pigment in red blood cells that picks up oxygen in the lungs and gives it up in the tissues.
Coronary arteries are the blood vessels that branch from the base of the aorta and supply oxygenated blood to the muscle of the heart itself.
Double circulation is the type of circulation in which blood passes through the heart twice in each complete round of the body: once on its way to the lungs and once on its way to the rest of the body.
Pulmonary circulation is the shorter loop, in which deoxygenated blood goes from the right ventricle to the lungs and comes back as oxygenated blood to the left atrium.
Antibodies are proteins in the plasma that attack anything the body treats as foreign.
Hypertension is a condition in which a person's blood pressure stays higher than normal over a long period.
Cardiac arrest is a sudden emergency in which the heart stops pumping blood effectively, usually because its electrical signals become badly disordered.
Lymph is the colourless fluid inside lymph vessels, formed from the tissue fluid, which contains many white blood cells but no red blood cells.
Key points
- The circulatory system is made up of the heart, blood and blood vessels; it carries food and oxygen to cells and takes wastes away.
- RBCs carry oxygen using haemoglobin, WBCs fight infection, and platelets help blood to clot.
- The heart has four chambers: two thin-walled atria above, which receive blood, and two thick-walled ventricles below, which pump it out.
- The septum keeps oxygenated blood (left side) and deoxygenated blood (right side) apart.
- Valves (tricuspid, bicuspid and the two semilunar valves) keep blood flowing one way; their closing makes the "lub-dub" sound.
- The pacemaker (SA node) in the right atrium starts every heartbeat with an electrical signal.
- The venae cavae bring body blood to the right atrium; the pulmonary trunk takes it to the lungs; the pulmonary veins return it to the left atrium; the aorta sends it to the body.
- Coronary arteries supply the heart muscle itself; coronary veins drain it; a blocked coronary artery causes a heart attack.
- In double circulation, blood passes through the heart twice per round: the pulmonary circulation and the systemic circulation.
- The four ABO blood groups are A, B, AB and O; group O is the universal donor and group AB the universal recipient (acceptor).
- Palpitation is an awareness of one's own heartbeat; hypertension is long-term high blood pressure; cardiac arrest is a sudden stop of effective pumping.
- The lymphatic system is a parallel circulatory system that returns tissue fluid to the blood, fights infection and carries absorbed fat.