How Does The Circulatory System Work: Diagram, Steps, Function

What Is the Circulatory System?

The circulatory system is also called the cardiovascular system. It is a complex network of the heart, blood, and blood vessels. It aims to transport oxygen, nutrients, hormones, and cellular waste throughout the body. The circulatory system ensures the delivery of needs for every cell to live and function well and, ultimately, the removal of metabolic waste that may be detrimental to the then operation of a cell.

It regulates all human physiological functions such as body temperature, pH levels, and fluid balance in the body for homeostasis. The body is prone to diseases and other serious problems if the circulatory system fails. Since the normal function of the circulatory system is important for a human being's health, it is part of the immune response and aids in the repair of tissues and, in general, the vitality, and well-being of an individual.

Components of the Circulatory System

The vertebrate circulatory system is constituted by basically the main parts that provide for blood flow within the complete human body.

Heart

• The heart has four chambers, two atria (upper chambers) and two ventricles (lower chambers).

• These chambers provide space for four valves—the tricuspid, pulmonary, mitral, and aortic which are used to control the flow of blood.

• The heart is a pump that pushes blood into the circulatory system.

• The blood is pushed to transport oxygen and nutrients to the tissues and, in turn, remove waste products.

Blood Vessels

• Arteries carry oxygenated blood from the heart. Veins carry deoxygenated blood back to the heart.

• Capillaries allow gas exchange, the exchange of nutrients at the tissue level, and the elimination of wastes in the blood.

• The arteries are endowed with various muscles which can withstand high pressure.

• Veins have numerous valves to prevent backflow.

• Capillaries are thin-walled to allow easy exchange of substances.

Blood

• The four components of blood are red blood cells, white blood cells, platelets, and plasma.

• Red blood cells are known for the transport of oxygen,

• White blood cells act as infection-fighting agents.

• Platelets contain the clotting mechanism of blood, and plasma is for carrying nutrients, some hormones, and waste, alongside water.

Functions of the Circulatory System

The circulatory system performs activity through the interaction of many interwoven paths to move blood and, thus, oxygen from the lungs to the various tissues of the body.

Pulmonary Circulation

• Blood, which is deoxygenated, is pumped from the right ventricle into the lungs through the pulmonary arteries.

• In the lungs, blood is oxygenated, and from there, it enters the left atrium through the pulmonary veins.

• Carbon dioxide is exchanged for oxygen and this oxygen binds with the hemoglobin present in red blood cells.

Systemic Circulation

• The oxygen-rich blood from the left ventricle is pumped away through the aorta to the general body circulation, where the oxygen and nutrients are provided to cells.

• Deoxygenated blood, full of waste products, returns to the heart through veins, and the systemic circuit is completed.

Coronary Circulation

• The coronary arteries supply oxygenated blood to the heart muscle, which the heart cannot do without to work well.

• Adequate coronary circulation is thus needed to prevent ischemic conditions, such as those of heart attack.

Mechanisms Controlling Circulatory System

Several mechanisms take part in controlling the circulatory system so that it works properly or adjusts to the requirements of the body.

Heart Rate and Cardiac Output Regulation

• Stress, exercise, hormones, and autonomic nervous system inputs are a few stimuli that can increase or decrease heart rate.

• The volume of blood pumped by the heart in one minute is the cardiac output, and it is a key driver of the overall metabolic demand for oxygen from all the tissues in the body.

Blood Pressure Regulation

• The pressure exerted by blood on the walls of the arteries during systole is called systolic pressure, and the measure of the force when the heart relaxes is diastolic pressure.

• The autonomic nervous system is responsible for regulating the diameter of the blood vessels and the heart rate in response to appropriate stimuli to supply the heart with blood.

Homeostatic Mechanisms

• Regulation of blood volume and blood pressure is a function of the kidneys not independent of renal function.

• The long-term regulation of blood pressure is integrally related to the control of the balance of the body's fluids and electrolytes.

• Various sensors and effectors within the body affect the circulatory parameters, leading to homeostasis.

Why the Circulatory System Is Essential

The cells, tissues, organs, and organ systems make up the majority of the human body. All of them depend on specific vital elements and components, which are transported by the circulatory system, to continue their metabolic processes and maintain the health of our bodies.

Digestive System Link (Nutrient Transport)

Nutrients that have been broken down and absorbed from food molecules are transported to every body cell by the circulatory system.

Respiratory System Link (Gas Exchange)

The movement of oxygen from the lungs to every area of the body is facilitated by the circulatory system. Similar to this, carbon dioxide is drawn from the various cells and tissues and sent to the lungs, where it is expelled through the nostrils into the surrounding air.

Excretory System Link (Waste Transport)

All waste products generated by the cells, tissues, and other organs during their metabolic processes, including excess water, salts, nitrogenous wastes, urea, and others, are transported to the excretory system and expelled from the body via the appropriate excretory organs.

Endocrine System Link (Hormone Transport)

The specialised glands that produce hormones to control growth, development, metabolism, and other cellular processes are part of the endocrine system. Transporting released hormones throughout the body or to the intended locations is a function of the circulatory system.

Disorders of the Circulatory System

The derangements in the circulatory system may seriously impact overall health, so an apt approach to prevention and management is required.

Hypertension

Sustained higher-than-normal pressure, threatening damage to blood vessels and organs.

Atherosclerosis

Fatty plaque deposition within arteries, which leads to reduced blood supply.

Heart Attack

Obstruction of coronary arteries; subsequently, occlusion of the cardiac muscle.

Stroke

The interruption of blood flow to the brain resulting in neurological damage.

Prevention And Management

Disorders circulatory system can be managed by:

• Healthy eating, exercise, and abstaining from smoking and overconsumption of alcohol may prevent circulatory disorders.

• Medications to lower blood pressure and cholesterol, and surgical procedures such as angioplasty are used to treat and manage circulatory system disorders.

Circulatory System NEET MCQs (With Answers & Explanations)

Types of questions asked from this topic are:

• Functions of Circulatory System

• 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.

Also Read:

• MCQ Practice on Circulatory System

• Components of Blood

• Functions of Blood

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