[Biology Class Notes] on Circulatory System Pdf

Human Circulatory System

• It is also known as the cardiovascular system or the vascular system. 

• It moves oxygen around the body and moves carbon dioxide out the body. It also circulates nutrients to the cells in the body.

• Before knowing the human circulatory system, we should be aware of the different types of circulatory systems. For example, insects and spiders do not have blood, instead they have hemolymph which is the mixture of blood and interstitial fluid. Fish have two chambered hearts for functioning inside the water. Land animals have a three chambered heart, example in bearded dragon. So, depending on the structure and kinds of heart they possess, there exists an open circulatory system and closed circulatory system. Humans (having four chambered hearts) and larger organisms like birds, mammals, fish, reptiles, amphibians and some invertebrates have a closed circulatory system whereas smaller organisms like mollusks, insects and spiders have open circulatory systems. 

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Circulatory System Meaning

As learnt from above, it can be said that the circulatory system is the system that circulates blood and lymph (hemolymph in insects) throughout the body, consisting of the heart, blood vessels, lymph, blood, and the lymphatic vessels and glands.

Components of Circulatory System 

Let’s know about various circulatory system parts and functions in this section.

The circulatory system comprises three independent parts working together that includes the heart, lungs and arteries, veins, coronary and portal vessels. These can be referred to as cardiovascular and pulmonary systems for heart and lungs, respectively and systemic for the rest. The circulatory system is responsible for the flow of blood, oxygen, nutrients and other gases, and as well as hormones to and from cells.

1. Heart

The heart is a major organ responsible for pumping blood to all parts of the body. Therefore the heart and circulatory system, together termed cardiovascular system is a network for delivering blood, oxygen, hormones and nutrients to the body’s tissues. With each heartbeat, the function is performed where all the cells are enriched with oxygen, blood and nutrients. Normally, it beats between 60 to 100 times per minute.

Blood takes entry to the heart through two large veins, the inferior and superior vena cava, and there it empties oxygen-poor blood from the body into the right atrium. When the ventricle contracts, blood leaves the heart through a valve called pulmonic valve into the pulmonary artery and to the lungs where it gets oxygenated. This process carries on in the body.

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2. Lungs

A pair of spongy and elastic organs that help us in breathing are called lungs. The human chest cavity is occupied mainly with the lungs as they are located just behind to either side of the heart. They can be seen extending down from the collarbone to the diaphragm which is the muscular wall between the abdominal cavity and the chest cavity). In adults, the human lung’s length is 25 to 30 cm.or 10-12 inch. These are roughly cone shaped and the right lung is slightly larger than the left lung as it has three lobes and on the other hand, the left lung has only two. Lungs function in inhalation and exhalation or breathing, external respiration (exchange of gases between the lungs and bloodstream) and internal respiration (exchange of gases between the bloodstream and body tissues).

The circulatory system of the lungs is also the portion of the cardiovascular system where oxygen-depleted blood is pumped away from the heart, via the pulmonary artery. It is taken to the lungs and then returned to the heart in the oxygenated form via the pulmonary vein. 

3. Systemic Circulation

The systemic circulation is responsible for the functional blood supply to all body tissues. It carries oxygen and nutrients to the cells and helps in removal of carbon dioxide and waste products. Systemic circulation carries oxygen rich blood from the left ventricle to the capillaries in the tissues of the body, through the arteries. It moves blood between the heart and the other parts of the body whereas pulmonary circulation is known to move blood between the heart and the lungs. Systemic circulation sends oxygenated blood to the cells as discussed above and also should be noted that it returns deoxygenated blood to the heart.