Question

What is meant by human circulatory system? What is meant by the term"single circulation" and "double circulation "

Answer 1

Single circulation The type of circulatory system that occurs in fishes, in which the blood passes only once through the heart in each complete circuit of the body Compare double circulation.

Double circulation (double circulatory systems) are circulation systems in which blood flows through the heart twice.

In the case of double circulation, pulmonary circulation - i.e. blood flow between the heart and lungs, is separate from systemic circulation - i.e. movement of blood from the heart through the rest of the body (excluding the lungs), then back to the heart.

Difference

1. During one complete cycle of flow through the whole body (blood system), blood in a double circulatory system passes through the heart twice.Another way to say this is the blood passes through the heart twice during each cycle of the circulatory process.
2. In a double circulatory system there are two circuits for blood passing through the heart:

• Pulmonary CirculationDeoxygenated blood is pumped from the heart to the lungs, oxygenated blood returns to the heart from the lungs.
• Systemic Circulation

Oxygenated blood is pumped from the heart around the body (including all the organs). That blood returns to the heart deoxygenated (more accurately 'oxygen poor') because much of the oxygen it contained when it left the heart has been supplied to tissues in the body.

• In animals that have double circulation (blood circulation) systems, the animal's heart has more than two chambers, e.g.

Fish:Single Circulation:Two-chambered heart

Frogs, Lizards:Double Circulation:Three-chambered heart
Mammals, Birds:Double Circulation:Four-chambered heart

• The pressure of blood flowing through a double circulation system can be higher than that flowing through a single circulatory system because in the case of double circulation the blood is pressurized twice per cycle around the whole blood system. (However, the blood pressure in a double circulatory system isn't twice that in a single circulatory system - it is not that simple because blood pressure in different parts of the heart varies according to the cardiac cycle and blood pressure around the body also varies e.g. according to the type and location of the blood vessel, and with the general state of health of the person or animal.)The blood is pumped around the body after it has returned to the heart from the lungs. This is beneficial because blood pressure and flow rate is reduced as it passes through the lungs so if the blood wasn't returned to the heart and pumped onwards it would continue to the tissues of the body at much lower pressure and flow rate than it does in double circulation systems.
• The separation of oxygenated (more accurately 'oxygen-rich') and deoxygenated (more accurately 'oxygen-poor') blood is possible in the cases of double circulation systems that include a 'double pump', i.e. a four chamber, heart.

See for example the diagram of a human heart at the top of this page, which shows the separation of oxygenated and deoxygenated blood within a human heart. Specifically, it illustrates:
Oxygen-poor blood, which is often called deoxygenated blood - entering the right atrium of the heart via the inferior vena cava and the superior vena cava then leaving the right ventricle of the heart via the pulmonary artery shown in blue with blue arrows.
Oxygen-rich blood, which is often called oxygenated blood or 'reoxygenated blood' - entering the left atrium of the heart via the pulmonary veins then leaving the left ventricle of the heart via the aorta shown in pale red with red arrows.