Sarah Izhar Content Writer
Content Writer
The circulatory system or cardiovascular system is crucial in the human body and animals. It is a network of blood vessels supplying the body with oxygen and nutrients while removing carbon dioxide and waste.
- It is known as the cardiovascular system because its essential components are the heart, lungs, and blood vessels which make this system work efficiently.
- The circulatory system is essential for the health of the organs, tissues, and vessels.
In this article, we will look into circulatory system definition, types of circulatory system, the anatomy of circulatory system, and its functions of circulatory system.
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Circulatory System Definition
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The Circulatory system is defined as a system that consists of the heart, lungs, and blood vessels involved in the transportation of blood, nutrients, and oxygen throughout the body. It helps tissues, cells, and organs to get sufficient oxygen, vitamins, and other nutrients to help our body get proper energy.
- This system is also called as cardiovascular system because in order to get oxygen, the system pumps blood from the heart to the lungs.
- The heart sends the oxygenated blood to other body parts via the arteries.
- The oxygen-depleted blood is sent back to the heart through the veins.
Circulatory System Diagram
The circulatory system diagram is shown below-
Circulatory System Diagram
Types of Circulatory System
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There are two types of circulatory systems: open circulatory system and closed circulatory system.
Open Circulatory System
The open circulatory system is mostly found in invertebrates like arthropods and mollusks. In this type of system, no blood vessels are present and the blood is pumped into the body's cavity called hemocoel.
- The blood is called hemolymph which is mixed with the fluids (interstitial fluids).
- This system does not utilize much energy to function or operate.
Open and Closed Circulatory System
Closed Circulatory System
The closed circulatory system is found in almost all vertebrates and a few invertebrates like mammals, fish, birds, reptiles, and amphibians. In this type of system, the blood is enclosed in blood vessels and flows in one direction.
- The blood flows from the heart surrounding the systematic circulatory route and then back to the heart.
- In simple terms, the blood is circulated through a closed network of blood vessels.
Anatomy of Circulatory System
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The circulatory system has three major parts: heart, blood, and blood vessels. In this section, we will discuss these parts in detail.
Heart
The human heart comprises two atria and two ventricles (left and right). The deoxygenated blood comes from the body into the right atrium as blood enters the heart through the inferior and superior vena cava.
- The contraction of the right atrium result makes the blood flow into the right ventricle via the tricuspid valve.
- This deoxygenated blood is pumped into the pulmonary arteries surrounding the lungs by the right chambers of the heart.
- Then the fresh oxygen enters the bloodstream, and the blood moves to the left side of the heart, where it is then pumped to the rest of the body.
Blood
Blood plays an important role in the circulatory system. It is a fluid connective tissue consisting of red blood cells, white blood cells, and plasma.
- The blood is responsible for carrying oxygen from the heart to all parts of the body.
Blood vessels
Blood vessels are mainly of three types: arteries, veins, and capillaries.
- Arteries are fine tubes that carry oxygenated blood away from the heart to the rest of the body. The largest artery present in the human body is the aorta.
- The veins carry oxygen-poor blood from the body to the heart so that it can be sent to the lungs.
- Capillaries are fine tubes that connect the veins and arteries. Because of the presence of thin walls, the nutrients, oxygen, and carbon dioxide pass to and fro of the cells.
Structure of Human Heart
Functions of Circulatory System
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The major role of the lungs is to convert deoxygenated blood from various organs in the body into oxygenated blood. Here the right chambers of the heart are responsible for pumping the deoxygenated blood to the lungs.
- The oxygenated blood from the lungs gets pumped into the left chambers of the heart.
- Finally, the left ventricle transports the oxygenated blood to the other parts of the body.
- The right atrium is a thin-walled chamber that receives deoxygenated- blood from body tissues and pumps it into the right ventricle.
Lungs
- Then, the right ventricle pumps blood from the right atrium to the pulmonary trunk and out to the lungs via the pulmonary arteries where blood gets oxygenated.
- Now, the left atrium receives oxygenated blood from the lungs and then pumps it to the left ventricle.
- Finally, the left ventricle of the heart pumps oxygenated blood throughout the entire body.
- The walls of this chamber are the thickest of all other chambers as it carries the most amount of blood to send to the other parts of the body.
Lymphatic System
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Lymph is a Latin word that originated from “lympha” which means “water”. The lymphatic system is a network of tissues and organs that consists of lymph vessels, lymph nodes, and lymph. In other words, it is a drainage system that helps to get rid of excess fluid from body tissues and returns it to the bloodstream.
- It helps in keeping the body healthy by eliminating infections and diseases.
- Lymph nodes are the bean-shaped structures found in the lymphatic system that consists of macrophages and dendritic cells.
- They help in swallowing up any pathogens to protect against infection.
Lymphatic System
Lymph Node
Functions of Lymphatic System
- It maintains the equilibrium of fluid between the blood and tissues, known as fluid homeostasis.
- It helps in fighting against bacteria and other foreign particles resulting in a healthy immune system.
- Tonsils, which are a part of the lymphatic system are responsible for blocking the ingested particles.
- Helps in antibody production to fight against pathogens.
Things to Remember
- The essential components of the circulatory system are the heart, lungs, and blood vessels.
- Erythrocytes, lymphocytes, monocytes, eosinophils, basophils, and platelets are the elements of blood.
- The human heart comprises 4 chambers which are: two atria; the left atrium & right atrium and two ventricles; the left ventricle & right ventricle.
- Pulmonary, systematic, and coronary are the three types of circuits present in the circulatory system.
- The thin muscular wall that separates the left and the right atria is called the interatrial septum.
- The interventricular septum is the wall separating the left and the right ventricles.
Sample Questions
Ques. Define the cardiac cycle? (1 mark)
Ans. The cardiac cycle is associated with the complete heartbeat from its production to the commencement of the next beat. It comprises diastole, the systole, and the intervening pause: the pause between the two.
Ques. Differentiate between the bicuspid valve and tricuspid valve. (2 marks)
Ans. Bicuspid valve- It has 2 flaps and is also known as a mitral valve.
It separates the left atria from the left ventricle.
Tricuspid valve- It has 3 flaps and is also known as the right atrioventricular valve.
It separates the right atria from the right ventricle.
Ques. Differentiate between lymph and blood. (2 marks)
Ans. Lymph- Found in the lymphatic system.
It is a connective tissue having WBC.
Blood- Found in blood vessels.
It is a connective tissue having leukocytes, erythrocytes, and platelets.
Ques. Why is the closed circulatory system considered advantageous over the open circulatory system? (1 mark)
Ans. Because it maintains high BP, allowing blood to flow at high velocity, speeding up the supply of essential supplies and eliminating the wastes easily.
Ques. Name the components of the formed elements in the blood and mention one major function of each of them. (2 marks)
Ans. Blood corpuscles are the formed elements in the blood, they constitute 45% of the blood. Formed elements are – (erythrocytes, RBCs or red blood corpuscles), (leucocytes, WBCs or white blood corpuscles) and throm¬bocytes or blood platelets. The major function of RBCs is to transport oxygen from the lungs to body tissues and CO2 from body tissues to the lungs. White blood cells provide immunity to the body. Blood platelets play an important role in blood clotting.
Ques. Why do we consider blood as a connective tissue? (2 marks)
Ans. Connective tissue connects different tissues or organs of the body. It consists of living cells and the extracellular matrix. Blood is vascular connective tissue, it is a mobile tissue consisting of fluid matrix and free cells. Blood transports materials from one place to the other and thereby establishes connectivity between different body parts.
Ques. What is meant by double circulation? What is its significance? (3 marks)
Ans. The type of blood circulation in which oxygenated blood and deoxygenated blood do not get mixed is termed double circulation. It includes systemic circulation and pulmonary circulation. The circulatory pathway of double circulation is given in the following flow chart.
Flow chart: Double blood circulation Double circulation or separation of systemic and pulmonary circulations provides a higher metabolic rate to the body and also allows the two circulations to have different blood pressures according to the need of the organs they supply.
Ques. Describe the evolutionary change in the pattern of the heart among the vertebrates. (4 marks)
Ans. Vertebrates have a single heart. It is a hollow, muscular organ composed of cardiac muscle fibres. Two types of chambers in the heart are the atria and ventricles. The heart of lower vertebrates has additional chambers, namely sinus venosus and conus arteriosus or bulbus arteriosus or truncus arteriosus. During the course of development, in higher vertebrates, the persistent portions viz, auricles and ventricles are retained. However, these get complicated by incorporating several valves inside them and becoming compartmentali sed.
In fishes, the heart is two-chambered (1 auricle and 1 ventricle). Both the accessory chambers, sinus venosus and conus arteriosus are present. The heart pumps out deoxygenated blood which is oxygenated by the gills and sent to the body parts from where deoxygenated blood is carried to the heart. It is called single circulation and the heart is called venous heart. Lungfish, amphibians and reptiles have a three-chambered heart, (2 auricles and 1 ventricle). The left atrium gets oxygenated blood from the gills/lungs/skin/buccopharyngeal cavity and the right atrium receives the deoxygenated blood from other body parts. But both oxygenated and deoxygenated blood gets mixed up in a single ventricle which pumps out mixed blood. This is called incomplete double circulation.
Crocodiles, birds and mammals have a complete four-chambered heart (right and left auricles; right and left ventricles). Oxygenated and deoxygenated blood never get mixed. The right parts of the heart receive deoxygenated blood from all other body parts and send it to the lungs for oxygenation whereas the left parts of the heart receive oxygenated blood from the lungs and send it to other body parts. This mode of circulation is termed as complete double circulation which includes systemic and pulmonary circulation. There are no accessory chambers in the hearts of birds and mammals.
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Ques. Sino-atrial node is called the pacemaker of our heart. Why? (1 mark)
Ans. Sino-atrial node (SAN) is a mass of neuromuscular tissue which lies in the wall of the right atrium. It is responsible for initiating and maintaining the rhythmic contractile activity of the heart. Therefore, it is called the pacemaker.
Ques. What is the significance of the atrioventricular node and atrioventricular bundle in the functioning of the heart? (2 marks)
Ans. The atrioventricular node (AVN) is a mass of neuromuscular tissue, which is situated in the wall of the right atrium, near the base of the interatrial septum. AV node is the pacesetter of the heart,- as it transmits the impulses initiated by the SA node to all parts of the ventricles. Atrio-ventricular bundle (A-V bundle) or bundle of His is a mass of specialised fibres which originates from the AVN. Within the myocardium of the ventricles, the branches of the bundle of His divide into a network of fine fibres called Purkinje fibres. The bundle of His and the Purkinje fibres convey the impulse of contraction from the AVN to the myocardium of the ventricles.
Ques. Define a cardiac cycle and the cardiac output. (2 marks)
Ans. The sequential events in the heart which are repeated cyclically are called the cardiac cycle and it consists of systole (contraction) and diastole (relaxation) of both the atria and ventricles. The duration of a cardiac cycle is 0.8 seconds. Periods of the cardiac cycle are atrial systole (0.1 seconds), ventricular systole (0.3 seconds) and complete cardiac diastole (0.4 seconds).
The amount of blood pumped by the heart per minute is called the cardiac output. It is calculated by multiplying stroke volume (volume of blood pumped by each ventricle per minute) with heart rate (number of beats per minute). The heart of a normal person beats 72 times per minute and pumps out about 70 mL of blood per beat. Therefore, cardiac output averages 5000 mL or 5 litres.
Ques. Explain heart sounds. (2 marks)
Ans. The beating of the heart produces characteristic sounds which can be heard by using a stethoscope. In a normal person, two sounds are produced per heartbeat. The first heart sound Tubb’ is low pitched, not very loud and of long duration. It is caused partly by the closure of the bicuspid and tricuspid valves and partly by the contraction of muscles in the ventricles.
The second heart sound ‘dubb’ is high pitched, louder, sharper and shorter in duration. It is caused by the closure of the semilunar valves and marks the end of ventricular systole.
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