The circulatory system, or cardiovascular system, is a network in our body that moves blood, nutrients, oxygen, and waste materials around. It helps keep our body working well and balanced. It includes the heart, blood vessels, and blood itself. The heart pumps blood, the blood vessels are like roads for blood to travel on, and blood carries what our body needs to work properly.
Circulatory system are grouped into three major categories namely;
1.. Closed and open circulatory system
2.. Single and double circulatory system
3.. Pulmonary and systemic circulatory system
Blood in the closed circulatory system is contained within vessels. Blood vessels leading away from the heart are called Arteries, which branch and enters various tissues and organs. They further divide into smaller vessels called arterioles which branch again and again to form fine vessels called capillaries but eventually joins up with other vessels called veins that are connected to the heart. By this design, blood is always contained within the cavities of the vessels and the heart, and never comes into direct contact with the cells of the body.
Some invertebrates like annelids and all vertebrates have closed circulatory system.
In open circulatory system, the heart pumps out blood into a blood vessel which leads out of the heart, this vessel branches and opens space in the body cavity called haemocoels. The organs and tissues are bathed in blood and exchange of materials occurs between the body cells and blood . blood in the spaces eventually flow into vessels leading back to the heart . Valves in the heart only allows blood to flow in one direction which makes the distribution of blood to various part of the body to be poorly controlled.
Arthropods and some mollucs have open circulatory system.
In a single circulatory system, blood only passes the heart once every time it makes a complete movement round the body. This system is commonly found in animals with lower metabolic rates and less active lifestyles, such as most fish and some amphibians. These animals typically have simpler body structures and do not require as much oxygen to support their activities compared to more active animals like mammals and birds. The single circulatory system is sufficient for meeting their basic oxygen and nutrient needs.
In double circulatory system, blood passes through the heart twice every time it makes a complete movement round them body ensuring efficient oxygenation of blood and effective distribution of nutrients. Double circulation is a characteristic feature of mammals, birds, and some reptiles, enabling them to support higher metabolic rates and more active lifestyles.
Pulmonary circulation involves the movement of blood between the heart and lungs for oxygenation. In pulmonary circulation, blood travels from the heart to the lungs and back to the heart again.
Systemic circulation involves the movement of blood between the heart and all other parts of the body besides the lung. In one complete circulation, blood from any part of the body enters the heart for the first time, it is then sent to the lungs for oxygenation. From the lungs, it is transported back to the heart for the second time before it can be redistributed to all parts of the body.
Pulmonary and systemic circulation can be represented mathematically as;
Pulmonary circulation = heart + lungs
Systemic circulation = heart + all parts of the body.
In conclusion, the circulatory system is a remarkable team effort involving blood, vessels, and the heartbeat. This system moves important things around our body like nutrients, oxygen, and waste. Whether using closed or open paths, single or double circulation, or the pulmonary and systemic circulation, the system keeps us balanced and healthy. As we learn more, we realize how crucial it is for our life and well-being.
