The Mammalian Heart

Mammalian Transport Systems

What are the two main learning objectives for the mammalian heart?

Relate the structure and operation of the mammalian heart, including the major blood vessels, to its function; and know the cardiac cycle.

What is the main function of the mammalian heart?

To pump blood around the body.

How many chambers does the mammalian heart have?

Four: two atria and two ventricles.

Why can the mammalian heart be described as two pumps working together?

The right side pumps blood to the lungs while the left side pumps blood around the rest of the body.

What does the right side of the heart do?

It receives deoxygenated blood from the body and pumps it to the lungs.

What does the left side of the heart do?

It receives oxygenated blood from the lungs and pumps it around the body.

What prevents oxygenated and deoxygenated blood from mixing in the heart?

The septum separates the right and left sides of the heart.

What is the septum?

A thick muscular wall separating the left and right sides of the heart.

Why is preventing oxygenated and deoxygenated blood from mixing important?

It ensures that blood pumped to body tissues has a high oxygen concentration.

What type of muscle makes up the heart?

Cardiac muscle.

What is cardiac muscle?

Specialised muscle tissue in the heart that contracts rhythmically and does not fatigue easily.

Why must cardiac muscle resist fatigue?

The heart must continue contracting throughout an animal's life to maintain circulation.

How is the cardiac muscle supplied with oxygen and nutrients?

By the coronary arteries.

What are coronary arteries?

Blood vessels that supply the heart muscle with oxygenated blood.

Why does cardiac muscle require a good blood supply?

It is continuously active and requires oxygen and respiratory substrates for aerobic respiration and ATP production.

What is myoglobin?

A respiratory pigment found in muscle that has a higher affinity for oxygen than haemoglobin.

Why does cardiac muscle contain lots of myoglobin?

Myoglobin stores oxygen for aerobic respiration, helping provide energy for continuous heart contractions.

What does the superior vena cava carry?

Deoxygenated blood from the upper parts of the body to the right atrium.

What does the inferior vena cava carry?

Deoxygenated blood from the lower parts of the body to the right atrium.

Which chamber receives deoxygenated blood from the venae cavae?

The right atrium.

What does the right atrium do?

It receives deoxygenated blood from the body and contracts to push it into the right ventricle.

Which valve separates the right atrium from the right ventricle?

The tricuspid valve.

What type of valve is the tricuspid valve?

An atrioventricular valve.

Why is the tricuspid valve called an atrioventricular valve?

It is located between an atrium and a ventricle.

How many flaps does the tricuspid valve have?

Three.

What is the function of the tricuspid valve?

It prevents blood flowing backwards from the right ventricle into the right atrium during ventricular contraction.

Which chamber receives deoxygenated blood from the right atrium?

The right ventricle.

What does the right ventricle do?

It pumps deoxygenated blood to the lungs through the pulmonary arteries.

Which vessels carry blood from the right ventricle to the lungs?

The pulmonary arteries.

What type of blood is carried by the pulmonary arteries?

Deoxygenated blood.

What prevents blood flowing from the pulmonary artery back into the right ventricle?

A semilunar valve.

Where does gas exchange occur after blood leaves the right ventricle?

In the capillaries of the lungs.

What happens to blood in the lungs?

It gains oxygen and loses carbon dioxide.

Which vessels carry blood from the lungs back to the heart?

The pulmonary veins.

What type of blood do the pulmonary veins carry?

Oxygenated blood.

Which chamber receives oxygenated blood from the pulmonary veins?

The left atrium.

What does the left atrium do?

It receives oxygenated blood from the lungs and contracts to push it into the left ventricle.

Which valve separates the left atrium from the left ventricle?

The bicuspid valve.

What is another name for the bicuspid valve?

The left atrioventricular valve.

How many flaps does the bicuspid valve have?

Two.

What is the function of the bicuspid valve?

It prevents blood flowing backwards from the left ventricle into the left atrium during ventricular contraction.

Which chamber receives oxygenated blood from the left atrium?

The left ventricle.

What does the left ventricle do?

It pumps oxygenated blood through the aorta and around the body.

Which blood vessel carries oxygenated blood away from the left ventricle?

The aorta.

What is the aorta?

The main artery carrying oxygenated blood from the left ventricle around the body.

What prevents blood flowing from the aorta back into the left ventricle?

A semilunar valve.

What is the complete pathway of blood through the heart and circulation?

Body → venae cavae → right atrium → tricuspid valve → right ventricle → semilunar valve → pulmonary arteries → lungs → pulmonary veins → left atrium → bicuspid valve → left ventricle → semilunar valve → aorta → body.

What is the pathway of deoxygenated blood through the heart?

Venae cavae → right atrium → tricuspid valve → right ventricle → pulmonary artery → lungs.

What is the pathway of oxygenated blood through the heart?

Pulmonary veins → left atrium → bicuspid valve → left ventricle → aorta → body.

Do the right and left sides of the heart pump at different times?

No. Both sides pump simultaneously.

What happens to both atria during atrial systole?

Both atria contract at the same time.

What happens to both ventricles during ventricular systole?

Both ventricles contract at the same time.

Why do the atria have relatively thin muscular walls?

They only need to generate enough pressure to move blood a short distance into the ventricles.

Why do ventricles have thicker muscular walls than atria?

They need to generate greater pressure to pump blood out of the heart.

Which ventricle has the thickest muscular wall?

The left ventricle.

Why is the wall of the left ventricle thicker than the right ventricle?

It must generate much higher pressure to pump blood around the entire body.

Why does the right ventricle have a thinner wall than the left ventricle?

It only pumps blood to the nearby lungs and therefore requires less pressure.

Why must blood entering the lungs be at relatively low pressure?

The delicate lung capillaries could be damaged by excessively high pressure.

Why must blood leaving the left ventricle be at high pressure?

It must travel around the entire body and overcome resistance in the systemic circulation.

What are tendinous cords?

Cord-like tendons attached to the atrioventricular valves.

What is another name for tendinous cords?

Valve tendons or heartstrings.

What is the function of tendinous cords?

They prevent the atrioventricular valves from turning inside out when ventricular pressure rises.

Do tendinous cords open and close the valves?

No. Valves open and close because of pressure differences.

What causes heart valves to open?

A valve opens when pressure behind it is greater than pressure in front of it.

What causes heart valves to close?

A valve closes when pressure in front of it becomes greater than pressure behind it, preventing backflow.

What is the main function of all heart valves?

To ensure one-way blood flow through the heart by preventing backflow.

What are semilunar valves?

Valves at the exits of the ventricles that prevent blood flowing back from the arteries into the ventricles.

Where are the semilunar valves located?

At the bases of the pulmonary artery and aorta.

What happens to the atrioventricular valves when atrial pressure exceeds ventricular pressure?

They open, allowing blood to flow from the atria into the ventricles.

What happens to the atrioventricular valves when ventricular pressure exceeds atrial pressure?

They close, preventing blood from flowing back into the atria.

What happens to the semilunar valves when ventricular pressure exceeds arterial pressure?

They open, allowing blood to leave the ventricles.

What happens to the semilunar valves when arterial pressure exceeds ventricular pressure?

They close, preventing blood from flowing back into the ventricles.

What is systole?

The contraction phase of the heart.

What is diastole?

The phase when the heart relaxes and fills with blood.

What is the cardiac cycle?

One complete cycle of contraction (systole) and relaxation (diastole) of the heart.

What are the three main stages of the cardiac cycle?

Diastole, atrial systole and ventricular systole.

What happens during diastole?

The heart muscle is relaxed, blood returns to the atria and flows into the ventricles.

What is the state of the atrioventricular valves during diastole?

They are open.

What is the state of the semilunar valves during diastole?

They are closed.

Why are the atrioventricular valves open during diastole?

Atrial pressure is greater than ventricular pressure, allowing blood to flow into the ventricles.

Why are the semilunar valves closed during diastole?

Pressure in the arteries is greater than pressure in the relaxed ventricles, preventing backflow.

What is atrial systole?

The stage of the cardiac cycle when both atria contract.

What happens during atrial systole?

The atria contract and force the remaining blood into the ventricles.

What is the state of the atrioventricular valves during atrial systole?

They are open.

What happens immediately after atrial systole?

Ventricular systole begins.

What is ventricular systole?

The stage of the cardiac cycle when both ventricles contract.

What happens to ventricular pressure during ventricular systole?

It rises rapidly as the ventricles contract.

What causes the atrioventricular valves to close during ventricular systole?

Ventricular pressure becomes greater than atrial pressure.

What causes the semilunar valves to open during ventricular systole?

Ventricular pressure becomes greater than the pressure in the pulmonary artery and aorta.

What happens to blood during ventricular systole?

Blood is forced from the right ventricle into the pulmonary artery and from the left ventricle into the aorta.

What happens after ventricular systole?

The ventricles relax, ventricular pressure falls and the heart enters diastole.

What happens to the semilunar valves when the ventricles relax?

They close as arterial pressure becomes greater than ventricular pressure.

What happens to the atrioventricular valves as the ventricles continue to relax?

They open when ventricular pressure falls below atrial pressure.

Approximately how long does ventricular systole last?

About 0.13 seconds.

Approximately how long does one complete cardiac cycle last at rest?

About 0.8 seconds.

What produces the sounds of a heartbeat?

The closing of the heart valves.

What causes the first heart sound, "lub"?

The atrioventricular valves closing as the ventricles contract.

What causes the second heart sound, "dub"?

The semilunar valves closing as the ventricles relax.

Does contraction of cardiac muscle directly produce the "lub-dub" sounds?

No. The sounds are mainly produced by the closing of the valves.

What does heart rate describe?

The number of times the heart beats per unit time, usually measured in beats per minute.