Circulatory System: Definition, Function, Diagram

What Is The Circulatory System?

The circulatory or cardiovascular system belongs to the indispensable set of vessels through which blood, and therefore nutrients, gases, and metabolic waste products, is transported to and from all cells of the entire body. The circulatory system consists of the heart, blood vessels, and blood, which provide the various tissues with all the necessary nutrients and oxygen and get rid of carbon dioxide and metabolic waste products. The system is very important in supporting homeostasis and other functions of the body, such as temperature regulation and some immune responses.

Components of the Circulatory System

The primary components or parts of the circulatory system are the heart, blood vessels, and blood. All these play crucial roles in the overall functioning and efficiency of the circulatory system.

Heart

The structure of the heart:

• Four chambers: two atria (upper chambers) and two ventricles (lower chambers)

• Valves: tricuspid, bicuspid (mitral), pulmonary, and aortic valves

• Walls: endocardium (the inner layer), myocardium (the muscle layer), epicardium (the outer layer)

The function of heart:

• A pump that provides a continuous circulation of blood throughout the body.

• Blood pressure maintenance and blood flow

• Carrying oxygen and nutrition, and carrying waste products to and from tissues, respectively.

Blood Vessels

• Types: Arteries, Veins, Capillaries

• Pulmonary Arteries and Veins: The arteries convey deoxygenated blood, while the veins convey oxygenated blood

• Capillaries: Microscopic blood vessels through which the exchange of nutrients and wastes between the blood and tissue fluid occurs

The structure and function of the blood vessels is discussed below:

• Arteries: These vessels are thick-walled and elastic which is necessary due to the high blood pressure

• Veins: The 'walls' of veins are much thinner, possessing valves to prevent backflow

• Capillaries: Thin-walled (one cell thick) to assist in the process of diffusion for substances.

Blood

• Composition: Plasma, Red Blood Cells, White Blood Cells, Platelets

• Plasma: Liquid component consisting of water, proteins, hormones, and waste products.

• Red Blood Cells (Erythrocytes): Contain haemoglobin, an oxygen-carrying pigment

• White Blood Cells (Leukocytes): Part of the immune system that fight infection

• Platelets (Thrombocytes): Involved in blood clotting and repair of wounds.

The functions of various components are:

• Plasma: Transports nutrients, hormones, and waste products

• Red Blood Cells: Transport oxygen from lungs to body tissues and back Carbon dioxide

• White Blood Cells: Defense against disease-causing microorganisms provides immunity

• Platelets: Involved in blood coagulation to arrest the loss of blood.

How Does the Circulatory System Work?

The human heart is a strong and muscular organ whose major function is to pump blood in the vascular system. This unending task involves sending oxygenated blood to several tissues of the body while deoxygenated blood is sent to the lungs.

Cardiac Cycle

• Phases: systole and diastole

• Systole: The contraction phase that results in blood being pumped out of the chambers.

• Diastole: The phase of the heartbeat when the chambers fill with blood.

Conduction System of Heart

• Electrical conduction system: SA Node, AV Node, Bundle of His, Purkinje Fibers.

• SA Node: A small mass of muscle tissue in the wall of the right atrium that initiates the heartbeat, acting as the heart's natural pacemaker.

• AV Node: Delays the impulse, allowing the atria to contract before the ventricles.

• Bundle of His and Purkinje Fibers: The impulses reach the ventricles and result in their contraction.

Circulation Pathways

The two most important pathways in the circulation of blood are systemic and pulmonary circulation. They both are very important in supplying oxygen and nutrients and removing waste.

Systemic Circulation

• Path of Heart to Body and the Heart back.

• Path: Left ventricle → Aorta → Arteries→ Capillaries→ Veins→ Right atrium

Functions

• Supplies body tissues with oxygen and nutrients

• Eliminates carbon dioxide and metabolic waste

Pulmonary Circulation

• Pathway from Heart to Lungs and Back

• Path: Right ventricle → Pulmonary artery→ Lungs →Pulmonary veins→ Left atrium

Functions

• Oxygenates deoxygenated blood

• Removes carbon dioxide from blood

Disorders of the Circulatory System

Diseases and disorders of the circulatory system can have a major impact on health, so early diagnosis and treatment are important to prevent serious complications.

Hypertension (High Blood Pressure)

• Signs and symptoms: Often has no symptoms but can lead to headaches, shortness of breath

• Causes: Genetic, poor diet, lack of exercise, stress

Atherosclerosis

• Symptoms: Chest pain, fatigue, shortness of breath

• Causes: High cholesterol, Smoking, hypertension, diabetes

Heart Attack (Myocardial Infarction)

• Symptoms: Chest pain, shortness of breath, sweating, nausea

• Causes: Blockage of coronary arteries

Stroke

• Symptoms: Sudden weakness, confusion, trouble speaking, vision problems.

• Causes: Blockage or rupture of blood vessels in the brain.

Diagnostic Techniques

• ECG (Electrocardiogram) records the electrical activity of the heart

• Echocardiogram is an ultrasonic test used to visualise the heart's structure and its functioning

• Angiography is a technique in which blood vessels are imaged in this technique.

Treatment and Prevention

• Medications: Blood pressure medicines cholesterol-lowering drugs and anticoagulants

• Lifestyle Changes: Good diet, regular exercise, quitting smoking, stress management

• Surgical Interventions: Angioplasty (a mechanical/wide-ranging intervention comprising inflating a balloon in a partially blocked artery, generally accompanied by the temporary insertion of a balloon or wire) and bypass surgery and placing a stent.

Circulatory System in Other Organisms

Different species have implemented circulatory systems in ways they have appropriate to their particular requirements and environments. In addition, circulatory systems also vary amongst other vertebrates.

Comparison with other Vertebrates

Invertebrate Circulatory Systems

• Insecta: Open circulatory system hemolymph instead of blood

• Mollusca: Some open circulatory systems, but others like the cephalopods are closed.

Circulatory System NEET MCQs (With Answers & Explanations)

Types of questions asked from this topic are:

• Cardiac cycle

• Disorders of the Circulatory System

Practice Questions for NEET

Q1. In most molluscs

1. Blood flows in larger blood vessels but at the tissue level vessels are absent

2. Blood flows in blood sinuses or lacunae or open spaces

3. The closed circulatory system is seen

4. Both a and c

Correct answer: 1) blood flows in larger blood vessels but at the tissue level vessels are absent

Explanation:

Generally in molluscs, it is larger blood vessels carrying blood, but at tissue levels, vessels are absent. Blood directly bathes tissues. This is characteristic of the open circulatory system with blood, known as hemolymph, flowing into opened spaces called sinuses where it supplies oxygen and nutrients to tissues. Exceptions in this regard are cephalopods, such as squids and octopuses, which have a closed system with capillaries of good blood flow.

Hence, the correct answer is option 1) blood flows in larger blood vessels but at the tissue level vessels are absent.

Q2. Choose the incorrect statement

1. The closed circulatory system increases the efficiency of circulation and regulates blood flow.

2. In the closed circulatory system, blood does not come in direct contact with tissue cells.

3. In the open circulatory system, the blood comes in direct contact with tissue cells.

4. The open circulatory system is found in annelids, echinoderms, some molluscs and all vertebrates

Correct answer: 4) The open circulatory system is found in annelids, echinoderms, some molluscs and all vertebrates

Explanation:

Types of the circulatory system

• The two basic types of circulatory systems that have evolved in animals are open circulatory system (in many invertebrates) and closed circulatory system (in vertebrates).

• These circulatory systems can be differentiated by the presence or absence of capillaries at tissue level

Open circulatory system

• In this system, the blood comes in direct contact with tissue cells.

• Blood may or may not flow in larger blood vessels

• When vessels are completely absent, blood flows in blood sinuses or lacunae or open spaces e.g arthropods

• In most molluscs, blood flows in larger blood vessels but at tissue level vessels are absent

Closed circulatory system

• In this system, blood does not come in direct contact with tissue cells.

• In this circulation, fine blood vessels called capillaries are present at the tissue level to prevent direct connectivity of tissue and blood, e.g. in annelids, echinoderms, some molluscs and all vertebrates

• The closed circulatory system increases the efficiency of circulation and regulates blood flow.

Hence, the correct answer is option 4) The open circulatory system is found in annelids, echinoderms, some molluscs and all vertebrates.

Q3. A single circulation circuit is seen in fish which have

1. One atrium and two ventricle

2. Two atrium and one ventricle

3. One atrium and one ventricle

4. Two atrium and two ventricle

Correct answer: 3) One atrium and one ventricle

Explanation:

The atrium is responsible for receiving deoxygenated blood from the body, while the ventricle functions to pump this blood towards the gills. Upon oxygenation at the gills, the oxygenated blood is directly distributed to the body tissues, circumventing the need for a pulmonary circuit. This configuration is denoted as single circulation due to the absence of a secondary loop, such as the pulmonary circulation present in higher vertebrates including amphibians, reptiles, birds, and mammals. This efficient mechanism facilitates the immediate delivery of oxygenated blood to the systemic circulation following the single passage through the heart.

Hence, the correct answer is option 3) One atrium and one ventricle.

Read more:

• MCQs on Circulatory System

• Cardiac Cycle

• Cardiac Output

Video Recommended on the Circulatory System