2.6 Circulation of Blood

Introduction

The circulatory system provides blood to all the body's tissues so they can function. Blood circulates through the heart and through a network of blood vessels in a continuous pattern. This continuous movement of blood is called circulation. The circulatory system has three circuits: pulmonary, systemic, and coronary. This topic explains how blood circulates through these circuits.

Definition

Circulation of blood is the continuous movement of blood through the heart and blood vessels, delivering oxygen and nutrients to tissues and removing carbon dioxide and waste products.

The circulatory system has three circuits:

• Pulmonary circuit — heart to lungs and back
• Systemic circuit — heart to body and back
• Coronary circuit — heart to heart muscle and back

Main Idea

The circulatory system provides blood to all the body's tissues so they can function. The circulatory system has three circuits. Blood circulates through the heart and through these circuits in a continuous pattern.

Core Concept

The Three Circuits of Circulation

Detailed Explanation

1. Pulmonary Circuit

What it is: This circuit carries deoxygenated blood (blood without oxygen) from the heart to the lungs.

What happens:

• Deoxygenated blood is pumped from the right ventricle to the lungs via the pulmonary arteries.
• In the lungs, blood receives oxygen and releases carbon dioxide.
• The pulmonary veins return oxygenated blood to the heart (left atrium).

Simple explanation: The pulmonary circuit is the journey of blood from the heart to the lungs and back. Its main job is to pick up oxygen.

Why this is important:

• It oxygenates the blood.
• It removes carbon dioxide from the blood.
• It is essential for cellular respiration in all body cells.

Pathway:

Right ventricle → Pulmonary arteries → Lungs → Pulmonary veins → Left atrium

2. Systemic Circuit

What it is: In this circuit, oxygenated blood (blood with oxygen) travels from the heart to the rest of the body.

What happens:

• Oxygenated blood is pumped from the left ventricle to the body via the aorta.
• The aorta branches into arteries that lead to all body organs.
• In the capillaries, oxygen and nutrients are delivered to tissues.
• Carbon dioxide and other waste products are picked up.
• The veins bring the deoxygenated blood back to the heart (right atrium).

Simple explanation: The systemic circuit is the journey of blood from the heart to the body and back. Its main job is to deliver oxygen and nutrients to all body cells and remove waste.

Why this is important:

• It delivers oxygen and nutrients to all body tissues.
• It removes carbon dioxide and waste products from tissues.
• It maintains the internal environment of the body.

Pathway:

Left ventricle → Aorta → Body tissues → Vena cava → Right atrium

3. Coronary Circuit

What it is: Coronary refers to the arteries of the heart. This circuit provides the heart muscle with oxygenated blood.

What happens:

• The coronary arteries branch off from the aorta.
• They supply oxygenated blood to the heart muscle (myocardium).
• The coronary veins collect deoxygenated blood from the heart muscle.
• The coronary sinus returns this blood to the right atrium.

Simple explanation: The coronary circuit is the journey of blood from the heart to the heart muscle itself and back. Its main job is to supply the heart muscle with oxygen and nutrients.

Why this is important:

• The heart muscle needs a constant supply of oxygen and nutrients.
• Without coronary circulation, the heart muscle cannot function.
• Blockage of coronary arteries can cause a heart attack (myocardial infarction).

Pathway:

Aorta → Coronary arteries → Heart muscle → Coronary veins → Coronary sinus → Right atrium

Intermediate Level

The circulatory system has three circuits:

Key points:

• Pulmonary circuit carries deoxygenated blood to the lungs and returns oxygenated blood.
• Systemic circuit carries oxygenated blood to the body and returns deoxygenated blood.
• Coronary circuit supplies the heart muscle with oxygenated blood.
• All three circuits work together to maintain circulation.

Important Points

• - The circulatory system provides blood to all the body's tissues so they can function.
• - The circulatory system has three circuits.
• - Blood circulates through the heart and through these circuits in a continuous pattern.
• - The pulmonary circuit carries deoxygenated blood from the heart to the lungs.
• - The pulmonary veins return oxygenated blood to the heart.
• - The systemic circuit carries oxygenated blood from the heart to the rest of the body.
• - In the veins, blood picks up carbon dioxide and other waste products.
• - The veins bring the blood back to the heart.
• - Coronary refers to the arteries of the heart.
• - The coronary circuit provides the heart muscle with oxygenated blood.
• - The coronary circuit returns deoxygenated blood to the heart's right upper chamber (atrium) to send to the lungs for oxygen.

Remember

• - Pulmonary circuit = heart → lungs → heart (oxygenates blood)
• - Systemic circuit = heart → body → heart (delivers O₂ and nutrients)
• - Coronary circuit = heart → heart muscle → heart (supplies heart muscle)
• - Pulmonary circuit = low pressure
• - Systemic circuit = high pressure
• - Coronary circuit = high pressure (branches from aorta)
• - All three circuits work together

Common Mistakes

• 1. Thinking there are only two circuits.
• - There are three circuits: pulmonary, systemic, and coronary.
• 2. Confusing pulmonary and systemic circuits.
• - Pulmonary = heart → lungs → heart.
• - Systemic = heart → body → heart.
• 3. Forgetting the coronary circuit.
• - The coronary circuit supplies the heart muscle itself. It is essential for heart function.
• 4. Thinking the pulmonary circuit is high pressure.
• - The pulmonary circuit is low pressure because the lungs offer little resistance.
• 5. Believing the coronary circuit is separate from the systemic circuit.
• - The coronary circuit is a branch of the systemic circuit.
• 6. Mixing up the direction of blood flow.
• - Pulmonary circuit: right ventricle → lungs → left atrium.
• - Systemic circuit: left ventricle → body → right atrium.
• 7. Thinking the heart muscle gets oxygen from the blood inside its chambers.
• - The heart muscle gets oxygen from the coronary arteries, not from the blood inside its chambers.

Quick Revision

60-Second Revision

• Pulmonary circuit = heart → lungs → heart (oxygenates blood; low pressure)
• Systemic circuit = heart → body → heart (delivers O₂ and nutrients; high pressure)
• Coronary circuit = heart → heart muscle → heart (supplies heart muscle; high pressure)
• All three circuits = work together to maintain circulation
• Coronary arteries = branch from the aorta
• Warning: Do not confuse pulmonary (heart → lungs → heart) with systemic (heart → body → heart). The coronary circuit is a branch of the systemic circuit.