Blood Circulatory System

Blood Circulatory System

The human circulatory system, also known as the blood vascular system, is made up of a muscle-chambered heart, a network of closed branching blood arteries, and blood, which is the fluid that circulates.Alternatively, the circulatory system is in charge of collecting metabolic waste and toxins from cells and tissues so that they can be cleansed or evacuated from the body.

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Organs of the Circulatory System

Our heart is the only circulatory system organ.


The mesodermally derived organ, the heart, is located in the thoracic cavity, between the two lungs, and is slightly inclined to the left. It is around the size of a clenched hand. The pericardium, a double-walled membranous sac that encloses the pericardial fluid, protects it.

Our heart is divided into four chambers − two small upper chambers called atria and two bigger lower chambers called ventricles. The right and left atria are separated by a thin, muscular wall called the interatrial septum, whereas the left and right ventricles are separated by a thicker wall called the interventricular septum.

The atrio-ventricular septum is a thick fibrous structure that separates the atrium and ventricle on the same side. Each of these septa, however, has an entrance through which the two chambers on the same side are joined.

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  • The tricuspid valve, which is made up of three muscular flaps or cusps, protects the opening between the right atrium and the right ventricle, whereas a bicuspid or mitral valve guards the entrance between the left atrium and the left ventricle.

  • Semilunar valves are located at the entrances of the right and left ventricles into the pulmonary artery and aorta, respectively. The heart's valves only allow blood to flow in one way, from the atria to the ventricles, and from the ventricles to the pulmonary artery or aorta. Backward flow is prevented by these valves.

  • The cardiac muscles make up the complete heart. The walls of the ventricles are much thicker than those of the atria. The heart also contains specialized cardiac muscles known as nodal tissue.

    The sino-atrial node is a piece of this tissue located in the right upper corner of the right atrium (SAN). The atrioventricular node is another mass of similar tissue found in the bottom left corner of the right atrium, next to the atrioventricular septum (AVN).

Cardiac Cycle Phases

Following are the different phases that occur in a cardiac cycle −

Atrial Diastole

The heart's chambers are calmed at this period. When the aortic and pulmonary arteries close and the atrioventricular valves open, the chambers of the heart relax.

Atrial Systole

During this phase, blood cells travel from the atrium to the ventricle and the atrium contracts.

Isovolumic Contraction

The ventricles begin to contract at this stage. The atrioventricular, valve, and pulmonary artery valves all close, but there is no volume change.

Ventricular Ejection

Ventricular Ejection occurs when the ventricles contract and empty. Both the pulmonary artery and the aortic valve shut.

Isovolumic Relaxation

During this phase, no blood enters the ventricles, lowering pressure and causing the ventricles to cease contracting and relax. Because of the aortic pressure, the pulmonary artery and aortic valve have closed.

Ventricular Filling Stage

Blood moves from the atria into the ventricles during this stage. It is referred to as a single-stage (first and second stage). Following that, there are three steps that involve the movement of blood from the ventricles to the pulmonary artery.

Duration of Cardiac Cycle

A normal person's heartbeat is 72 beats per minute. As a result, the length of one cardiac cycle may be estimated as follows

1/72 minutes/beat =.0139 minutes/beat

Each cardiac cycle will last 0.8 seconds at a heart rate of 72 beats per minute.

The following pointers show the duration of the various phases of the cardiac cycle −

  • Atrial systole lasts roughly 0.1 seconds.

  • Ventricular systole lasts roughly 0.3 seconds.

  • Atrial diastole lasts around 0.7 seconds.

  • Ventricular diastole lasts roughly 0.5 seconds.

Double Circulation

Blood travels in a straight line via Blood Vessels—the arteries and the veins. Each artery and vein has the following three layers −

  • an inner lining of the squamous endothelium called the tunica intima,

  • a middle layer of smooth muscle and elastic fibres called the tunica media, and

  • an outside layer of fibrous connective tissue with collagen fibres called the tunica externa.

The tunica intima is made up of squamous endothelium, the tunica medium is made up of smooth muscle and elastic fibres, and the tunica externa is made up of fibrous connective tissue with collagen fibres.

The oxygenated blood enters the aorta and travels to the tissues via a network of arteries, arterioles, and capillaries, where it is collected by a system of venules, veins, and the vena cava, and discharged into the right atrium. This is the circulatory system.

The systemic circulation delivers nutrition, oxygen, and other vital elements to tissues while also transporting CO2 and other toxic compounds for removal. The hepatic portal system is a unique circulatory link between the digestive tract and the liver. The hepatic portal vein transports blood from the colon to the liver before it is circulated throughout the body.

Disorders of the Circulatory System

  • Coronary Artery Disease (CAD) − It is a condition that affects the veins that feed blood to the heart muscle. It is also known as atherosclerosis.

  • Angina − It is also known as 'angina pectoris.' A sign of acute chest discomfort occurs when the heart muscle does not receive enough oxygen.

  • Heart Failure − Heart failure occurs when the heart is unable to pump blood efficiently enough to satisfy the body's demands

  • Hypertension − Hypertension (high blood pressure) is the medical term for blood pressure that is higher than normal (120/80).


Q1. What are the three types of circulation?


  • Pulmonary Circulation

  • Systemic Circulation

  • Coronary Circulation

Q2. Is the circulatory system of humans open or closed?

Ans. Blood is pumped through a network of arteries and veins in the human circulatory system, which is a closed system. All vertebrates and certain invertebrates have this sort of circulation.

Q3. What are the benefits of having a closed circulatory system?

Ans. More pressure is available with a closed circulatory system, and blood may reach the bodily extremities much more quickly. In species with closed circulatory systems, this leads to a substantially higher metabolism and movement rate.

Q4. How did the first circulatory system work?

Ans.The circulatory system developed as a cost-effective way to transport vital nutrients and waste products throughout the body. Blood flowed in a hollow enclosed chamber in the oldest circulatory system, which was similar to today's open circulatory system. Closed circulation appeared considerably later invertebrate ancestors.


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