2.5.2 The Heart Valves

Introduction

The heart is a muscular pump that continuously pushes blood through the circulatory system. To ensure that blood flows in the correct direction and does not flow backwards, the heart has a set of valves. These valves open and close in response to pressure changes during the cardiac cycle. This topic explains the structure, location, and function of the four heart valves.

Definition

Heart valves are flap-like structures made of strong, flexible tissue that allow blood to flow in one direction only through the heart. They open and close in response to pressure changes during the cardiac cycle.

The heart has four valves:

• Tricuspid valve — between right atrium and right ventricle
• Bicuspid (mitral) valve — between left atrium and left ventricle
• Pulmonary semilunar valve — between right ventricle and pulmonary artery
• Aortic semilunar valve — between left ventricle and aorta

Main Idea

The heart has four valves, which separate the top chambers from the bottom chambers and also move blood. The valves ensure that blood flows in one direction and does not flow backwards.

Core Concept

The Four Heart Valves

Detailed Explanation

1. Atrioventricular Valves

Atrioventricular valves separate the atria from the ventricles. Each valve is composed of cusps or flaps.

There are two atrioventricular valves:

(a) Tricuspid valve:

• The valve between the right atrium and right ventricle.
• It has three cusps (flaps).
• It is called the tricuspid valve because "tri" means three.

(b) Bicuspid or mitral valve:

• The valve between the left atrium and left ventricle.
• It has two cusps (flaps).
• It is called the bicuspid valve because "bi" means two.
• It is also called the mitral valve.

Simple explanation: The atrioventricular valves are like doors between the upper and lower chambers of the heart. The tricuspid valve has three flaps, and the bicuspid valve has two flaps.

Function:

• They prevent the backflow of blood from the ventricles to the atria.
• When the ventricles contract, the valves close, preventing blood from going back into the atria.

2. Semilunar Valves

Two additional valves separate the ventricles from the large blood vessels that carry blood leaving the heart.

There are two semilunar valves:

(a) Pulmonary semilunar valve:

• It is between the right ventricle and pulmonary artery.
• It carries blood to the lungs.

(b) Aortic semilunar valve:

• It is between the left ventricle and the aorta.
• It carries blood to the body.

Simple explanation: The semilunar valves are like doors between the ventricles and the large arteries leaving the heart. They prevent blood from flowing back into the ventricles.

Function:

• They prevent the backflow of blood from the arteries to the ventricles.
• When the ventricles relax, the semilunar valves close, preventing blood from going back into the ventricles.

3. How Valves Work

During ventricular contraction (systole):

• The atrioventricular valves (tricuspid and bicuspid) close.
• This prevents blood from flowing back into the atria.
• The semilunar valves (pulmonary and aortic) open.
• Blood is pumped into the pulmonary artery and aorta.

During ventricular relaxation (diastole):

• The semilunar valves (pulmonary and aortic) close.
• This prevents blood from flowing back into the ventricles.
• The atrioventricular valves (tricuspid and bicuspid) open.
• Blood flows from the atria into the ventricles.

Simple explanation: The valves open and close like gates. They open to let blood through and close to stop it from going backwards. The pressure of blood pushing against them makes them open and close.

4. Summary of Blood Flow Through the Heart

Deoxygenated blood (right side):

• Blood from the body enters the right atrium via the superior and inferior vena cava.
• When the right atrium contracts, blood flows into the right ventricle through the tricuspid valve.
• When the right ventricle contracts, the tricuspid valve closes (preventing backflow).
• Blood leaves the right ventricle through the pulmonary semilunar valve into the pulmonary trunk.
• The pulmonary trunk divides into two pulmonary arteries, one to each lung.
• Return of blood into the ventricle is prevented by the pulmonary semilunar valve.

Oxygenated blood (left side):

• Oxygenated blood from the lungs is brought back to the heart by the pulmonary veins, which open into the left atrium.
• When the left atrium contracts, blood enters the left ventricle through the bicuspid valve.
• When the left ventricle contracts, the bicuspid valve closes (preventing backflow).
• Blood leaves the left ventricle through the aortic semilunar valve into the aorta.
• From the aorta, blood is distributed to all parts of the body except the lungs.
• The aorta also has the aortic semilunar valve to prevent backflow into the left ventricle.

Intermediate Level

The heart has four valves:

Function of valves:

• Atrioventricular valves prevent backflow from ventricles to atria.
• Semilunar valves prevent backflow from arteries to ventricles.

How they work:

• During ventricular contraction, AV valves close, semilunar valves open.
• During ventricular relaxation, semilunar valves close, AV valves open.

Important Points

• - The heart also has four valves, which separate the top chambers from the bottom chambers and also move blood.
• - Atrioventricular valves separate the atria from the ventricles.
• - Each valve is composed of cusps or flaps.
• - The valve between the right atrium and right ventricle has three cusps and is called the tricuspid valve.
• - The valve between left atrium and left ventricle has two cusps and is called the bicuspid or mitral valve.
• - Tricuspid valve separates the right side, and the bicuspid valve separates the left side.
• - Two additional valves separate the ventricles from the large blood vessels.
• - The pulmonary semilunar valve is between the right ventricle and pulmonary artery.
• - The aortic semilunar valve is between the left ventricle and the aorta.
• - The atria receive blood and the ventricles distribute it.
• - 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.
• - When the right atrium contracts, the blood flows into the right ventricle through the tricuspid valve.
• - When the right ventricle contracts, the blood pressure closes the tricuspid valve.
• - The blood leaves the right ventricle by the pulmonary trunk.
• - The pulmonary trunk divides into two pulmonary arteries, one to each lung.
• - Return of blood into the ventricle is prevented by semilunar valves in the pulmonary trunk.
• - Oxygenated blood from the lungs is brought back to the heart by the pulmonary veins, which open into the left atrium.
• - When the left atrium contracts, the blood enters the left ventricle through the bicuspid valve.
• - When the left ventricle contracts, blood leaves by the aorta.
• - Aorta also has semilunar valves to prevent backflow into the left ventricle.

Remember

• - Tricuspid valve = right atrium → right ventricle (3 cusps)
• - Bicuspid (mitral) valve = left atrium → left ventricle (2 cusps)
• - Pulmonary semilunar valve = right ventricle → pulmonary artery
• - Aortic semilunar valve = left ventricle → aorta
• - AV valves prevent backflow from ventricles to atria
• - Semilunar valves prevent backflow from arteries to ventricles
• - Valves open and close passively due to pressure changes

Common Mistakes

• 1. Confusing the tricuspid and bicuspid valves.
• - Tricuspid = right side, 3 cusps.
• - Bicuspid = left side, 2 cusps.
• 2. Mixing up the semilunar valves.
• - Pulmonary semilunar valve = right ventricle → pulmonary artery.
• - Aortic semilunar valve = left ventricle → aorta.
• 3. Thinking valves actively open and close.
• - Valves open and close passively in response to pressure changes.
• 4. Forgetting the role of chordae tendineae.
• - Chordae tendineae (heart strings) prevent AV valves from prolapsing.
• 5. Confusing the heart sounds.
• - "Lub" = closure of AV valves.
• - "Dub" = closure of semilunar valves.
• 6. Thinking the pulmonary artery carries oxygenated blood.
• - The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs.
• 7. Believing the aorta carries deoxygenated blood.
• - The aorta carries oxygenated blood from the left ventricle to the body.

Quick Revision

60-Second Revision

• Tricuspid valve = right atrium → right ventricle (3 cusps)
• Bicuspid (mitral) valve = left atrium → left ventricle (2 cusps)
• Pulmonary semilunar valve = right ventricle → pulmonary artery
• Aortic semilunar valve = left ventricle → aorta
• AV valves = prevent backflow from ventricles to atria
• Semilunar valves = prevent backflow from arteries to ventricles
• Valves = open and close passively due to pressure changes
• **"Lub"** = AV valves close
• "Dub" = semilunar valves close
• Warning: Do not confuse tricuspid (3 cusps, right side) with bicuspid (2 cusps, left side).