2.5.1 The Heart Chambers

Introduction

The human heart is a four-chambered muscular pump. Internally, it is divided into two halves by a vertical partition called the septum. Each half contains two chambers: an upper chamber (atrium) that receives blood and a lower chamber (ventricle) that pumps blood out. This topic explains the structure and function of the four heart chambers.

Definition

The heart chambers are the four hollow spaces within the heart that receive and pump blood. They are:

• Right atrium — receives deoxygenated blood from the body
• Right ventricle — pumps deoxygenated blood to the lungs
• Left atrium — receives oxygenated blood from the lungs
• Left ventricle — pumps oxygenated blood to the body

Main Idea

Internally, the heart is divided by a vertical portion into two halves, the right and the left. The vertical partition is called the septum. The heart consists of four chambers, two on the top and two on the bottom.

• The two bottom chambers are called the right ventricle and the left ventricle. They pump blood out of the heart.
• The two top chambers are the right atrium and the left atrium (plural: atria). They receive the blood entering the heart.

The thickness of the walls of each chamber is different:

• Atria have comparatively thin walls as they have to force blood into the ventricles, which does not require much power.
• Ventricles have to force blood out of the heart, hence they have relatively thick walls, especially the left ventricle, which has to pump blood around the whole body.
• The right ventricle has thinner walls than the left ventricle in a ratio of 1:3; it pumps blood to the lungs, which are at a short distance from the heart.

The human heart is myogenic (a heart that does not require neural input to beat is called a myogenic heart).

Core Concept

The Four Chambers of the Heart

Detailed Explanation

1. Septum

Internally, the heart is divided by a vertical portion into two halves, the right and the left.

What is the septum?

• The vertical partition that divides the heart into right and left halves.
• It prevents the mixing of oxygenated and deoxygenated blood.

Simple explanation: The septum is like a wall that separates the right side of the heart from the left side. This ensures that oxygenated and deoxygenated blood do not mix.

Why this is important:

• Mixing of oxygenated and deoxygenated blood would reduce the efficiency of oxygen delivery to tissues.
• The septum keeps the two circuits (pulmonary and systemic) separate.

2. Atria (Upper Chambers)

The two top chambers are the right atrium and the left atrium (plural: atria).

Function: They receive the blood entering the heart.

Right atrium:

• Receives deoxygenated blood from the superior and inferior vena cava.
• Blood from the head, neck, and arms is returned to the right atrium by the superior vena cava.
• Blood from lower parts of the body is brought back by the inferior vena cava to the right atrium.

Left atrium:

- Receives oxygenated blood from the lungs via the pulmonary veins.

Wall thickness:

• The atria have comparatively thin walls.
• They only have to force blood into the ventricles, which does not require much power.

Simple explanation: The atria are like waiting rooms. They collect blood and then push it into the ventricles.

3. Ventricles (Lower Chambers)

The two bottom chambers are called the right ventricle and the left ventricle.

Function: They pump blood out of the heart.

Right ventricle:

• Pumps deoxygenated blood to the lungs via the pulmonary trunk.
• The pulmonary trunk divides into two pulmonary arteries, one to each lung.
• The right ventricle has thinner walls than the left ventricle in a ratio of 1:3.
• It pumps blood to the lungs, which are at a short distance from the heart.

Left ventricle:

• Pumps oxygenated blood to the whole body via the aorta.
• The left ventricle has the thickest wall because it has to pump blood around the whole body.
• It must overcome resistance from muscles and other body tissues.

Wall thickness:

• The ventricles have relatively thick walls because they have to force blood out of the heart.
• The left ventricle is especially thick because it pumps blood to the entire body.

Simple explanation: The ventricles are like pumping stations. They push blood out of the heart with great force. The left ventricle is the strongest because it pumps blood to the whole body.

4. Comparison of Wall Thickness

Simple explanation: The left ventricle has the thickest wall because it has the hardest job — pumping blood to the entire body. The right ventricle has a thinner wall because it only pumps blood to the lungs, which are close by.

5. Myogenic Heart

The human heart is myogenic.

What does myogenic mean?

• A heart that does not require neural input to beat is called a myogenic heart.
• The heartbeat originates from within the heart muscle itself.
• The sinoatrial (SA) node acts as the pacemaker.

Simple explanation: The heart can beat on its own without signals from the brain. It has its own built-in pacemaker.

Why this is important:

• The heart continues to beat even if nerve connections are damaged.
• This ensures a constant blood supply to the body.

Intermediate Level

The heart has four chambers separated by the septum:

Key points:

• Atria receive blood; ventricles pump blood out.
• Atria have thin walls; ventricles have thick walls.
• Left ventricle has the thickest wall because it pumps blood to the whole body.
• Right ventricle has thinner walls because it pumps blood only to the lungs.
• The septum prevents mixing of oxygenated and deoxygenated blood.
• The heart is myogenic.

Important Points

• - Internally, the heart is divided by a vertical portion into two halves, the right and the left.
• - The vertical partition is called the septum.
• - The heart consists of four chambers: two atria and two ventricles.
• - The two bottom chambers are the right ventricle and the left ventricle. They pump blood out of the heart.
• - The two top chambers are the right atrium and the left atrium. They receive blood entering the heart.
• - The thickness of the walls of each chamber is different.
• - The atria have comparatively thin walls.
• - The ventricles have relatively thick walls.
• - The left ventricle has the thickest wall because it pumps blood around the whole body.
• - The right ventricle has thinner walls than the left ventricle in a ratio of 1:3.
• - The right ventricle pumps blood to the lungs, which are at a short distance from the heart.
• - The human heart is myogenic.

Remember

• - Septum = divides right and left halves
• - Atria = upper chambers, receive blood, thin walls
• - Ventricles = lower chambers, pump blood out, thick walls
• - Right atrium = receives deoxygenated blood from body
• - Right ventricle = pumps deoxygenated blood to lungs
• - Left atrium = receives oxygenated blood from lungs
• - Left ventricle = pumps oxygenated blood to body
• - Left ventricle = thickest wall
• - Right ventricle = thinner wall (1:3)
• - Myogenic = heart beats without neural input

Common Mistakes

• 1. Confusing atria and ventricles.
• - Atria = upper chambers, receive blood.
• - Ventricles = lower chambers, pump blood out.
• 2. Thinking the right ventricle has the thickest wall.
• - The left ventricle has the thickest wall because it pumps blood to the whole body.
• 3. Forgetting the role of the septum.
• - The septum prevents mixing of oxygenated and deoxygenated blood.
• 4. Thinking the heart is neurogenic.
• - The human heart is myogenic. It does not require neural input to beat.
• 5. Mixing up the right and left sides of the heart.
• - Right side = deoxygenated blood.
• - Left side = oxygenated blood.
• 6. Believing all heart chambers have the same wall thickness.
• - Atria have thin walls; ventricles have thick walls; left ventricle is the thickest.
• 7. Confusing the pulmonary artery and pulmonary vein.
• - Pulmonary artery = carries deoxygenated blood from right ventricle to lungs.
• - Pulmonary vein = carries oxygenated blood from lungs to left atrium.

Quick Revision

60-Second Revision

• Septum = divides right and left halves
• Atria = upper chambers, receive blood, thin walls
• Ventricles = lower chambers, pump blood out, thick walls
• Right atrium = receives deoxygenated blood from body
• Right ventricle = pumps deoxygenated blood to lungs (thinner wall, 1:3)
• Left atrium = receives oxygenated blood from lungs
• Left ventricle = pumps oxygenated blood to body (thickest wall)
• Myogenic = heart beats without neural input
• Warning: Do not confuse atria (upper, receive blood) with ventricles (lower, pump blood out). The left ventricle has the thickest wall.