Biology
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The Heart

The Heart

The heart is a powerful organ that pumps blood throughout your body. It's about the size of your fist and weighs around 300g. It's located in your chest, between your ribs and breastbone. The heart is surrounded by a special membrane that helps prevent it from getting too full with blood. The heart is made up of special muscle cells called cardiac muscle cells. These cells can keep working without getting tired. They don't need the nervous system to tell them what to do. If the heart muscles don't get enough oxygen, they can start to die off. This is what happens during a heart attack. It's important to take care of your heart by eating healthy, exercising, and getting enough rest.

What does the heart look like from the outside?

Let’s explore the heart from the outside first.

The two sides of the heart

This muscular organ is divided into two parts: the left side and the right side.

A model of the heart
A model of the heart

You might be wondering why the heart is split into two parts. Well, each side has a different job to do. The left side gets oxygen-rich blood from your lungs and pumps it out to the rest of your body. The right side gets oxygen-poor blood from your body and sends it to your lungs to get more oxygen.

But why can't the heart just have one pump? Well, when blood goes through the lungs, there's a big drop in pressure. So the heart needs to pump harder to get the blood flowing again. Having two pumps, one for each side, makes it easier for the heart to do its job.

Even though the heart has two pumps, they work together. Both sides of the heart squeeze and relax at the same time to keep your blood flowing smoothly. It's pretty amazing how the heart works, isn't it?

The heart pumping blood. Notice that both sides relax at the same time

Blood vessels of the heart

The heart is connected to four blood vessels - two veins (vena cava and pulmonary vein) and two arteries (aorta and pulmonary artery).

The heart labelled
The heart labelled

Veins carry blood back to the heart, while arteries carry blood away from the heart.

There are two main veins that connect to the heart. The vena cava brings deoxygenated blood from the upper and lower body, while the pulmonary vein brings oxygenated blood from the lungs.

Similarly, there are two main arteries that connect to the heart. The aorta is a large, arching artery that branches off into smaller arteries to bring oxygen-rich blood to the head and lower body. The pulmonary artery branches off into two smaller arteries to bring deoxygenated blood to the lungs.

Blood vessels are responsible for supplying the heart muscles with oxygen and nutrients. The coronary arteries branch off from the aorta and bring oxygenated blood to the heart muscles. Meanwhile, the cardiac veins bring deoxygenated blood with metabolic waste back to the vena cava.

Remember that the pulmonary artery carries deoxygenated blood, while the pulmonary vein carries oxygenated blood. This is different from all other arteries and veins in the body. Keep this in mind when studying for exams.

Four chambers of the heart

The human heart is made up of four chambers, divided by a muscular structure called the septum. The two upper chambers are called the atria, and the two lower chambers are called the ventricles.

The atria are smaller in size and have thin walls. They are connected to the veins, with the right atrium connected to the vena cava and the left atrium connected to the pulmonary vein. The atria pump blood into the ventricles, whose lower pumping pressure prevents them from bursting.

The ventricles are larger and have thicker walls than the atria. They are connected to the arteries, with the right ventricle connected to the pulmonary artery and the left ventricle connected to the aorta. The left ventricle has thicker walls than the right because it pumps oxygenated blood to the rest of the body, which requires a higher pressure to overcome the elastic recoil of arteries. The right ventricle has thinner walls because it pumps deoxygenated blood to the lungs, which are closer to the heart and have delicate capillaries.

A helpful acronym to remember where veins and arteries connect is AV – arteries are connected to ventricles, while atria are connected to veins.

In summary, the heart is divided into four chambers – two atria and two ventricles – by the septum. The atria have thin walls and are connected to veins, while the ventricles have thicker walls and are connected to arteries.

Heart valves

How the heart achieves a regular direction of blood flow across the different chambers?

Valves play an important role in regulating blood flow in the heart. The valves between the atria and ventricles are called atrioventricular valves. There is an atrioventricular valve on the left and right sides of the heart. The bicuspid (or mitral) valve is located on the left side, while the tricuspid valve is located on the right side.

The atrioventricular valves are supported by string-like tendons called chordae tendineae. These tendons prevent the backflow of blood into the atria when the ventricles contract. They act like anchors, keeping the valves in place and preventing them from turning inside out under the pressure of the blood flow.

The bicuspid valve has two flaps, or cusps, that open and close to regulate blood flow. The tricuspid valve has three cusps. When the ventricles contract, the pressure in the chambers increases, causing the cusps of the valves to close tightly. This prevents the blood from flowing back into the atria.

In summary, atrioventricular valves regulate blood flow between the atria and ventricles of the heart. They are supported by chordae tendineae, which prevent the valves from turning inside out under the pressure of the blood flow. The bicuspid valve has two cusps, while the tricuspid valve has three cusps. When the ventricles contract, the valves close tightly to prevent the backflow of blood.

Heart valves

In addition to atrioventricular valves, there are also semilunar valves located on the arteries connected to the heart. Semilunar valves include the aortic valve and the pulmonary valve. These valves are called semilunar because they have a crescent shape.

Both atrioventricular and semilunar valves have flaps that open and close to regulate blood flow. The key difference between bicuspid/tricuspid valves and semilunar valves is the number of flaps they have. Bicuspid valves have two flaps, tricuspid valves have three flaps, and semilunar valves also have three flaps.

Remembering which valve belongs to which side of the heart can be challenging. It may help to remember that the right ventricle is thinner and needs three flaps to compensate.

In summary, semilunar valves are located on the arteries connected to the heart and have a crescent shape. They have three flaps, just like the tricuspid valve. The number of flaps in a valve determines its name – bicuspid valves have two flaps, while tricuspid and semilunar valves have three flaps.

How does the heart function?

To summarize, the heart is responsible for circulating blood throughout the body. It accomplishes this by contracting and relaxing its muscles, which moves the blood through the four chambers and out to the rest of the body via blood vessels. The valves in the heart help ensure that blood flows in only one direction. The heart also helps maintain a constant blood pressure and transports important substances, such as hormones, to different parts of the body. Overall, the heart is a vital organ that works tirelessly to keep the body functioning properly.

The Heart - Key takeaways The heart is a ‘muscular bag’ filled with blood that contributes to the circulatory system by pumping blood around the body. It is divided into the left and right sides and connected to four blood vessels - two veins (vena cava and pulmonary vein) and two arteries (aorta and pulmonary artery).The heart is made up of four chambers - the right atrium and ventricle and the left atrium and ventricle. The veins connect to the atria, whereas the arteries connect to the ventricles. Heart muscles have coronary arteries and cardiac veins. Coronary arteries branch off from the aorta and supply the heart muscles with oxygenated blood, whereas cardiac veins bring deoxygenated blood containing metabolic waste into the vena cava. Valves are present in the heart to prevent backflow. Atrioventricular valves, between the atria and ventricles, include the tricuspid valve at the right side of the heart and the bicuspid valve at the left side of the heart.

The Heart

How does the heart work? 

The chambers of the heart regularly contract and relax to transport both oxygenated and deoxygenated blood around the body.  

What is the heart and its function? 

The heart is a bag of muscle that pumps blood around the body. 

What are the 4 main functions of the heart? 

These functions include:Pump oxygenated blood around the body.Receive and pump deoxygenated blood to the lungs for oxygenation.Transport hormones and other vital substances to different parts of the body.Maintain a constant blood pressure across the different vessels.

What happens during a heart attack? 

During a heart attack, the heart muscles die off due to a lack of oxygen supply to cardiac muscle tissues. 

What are the four parts of the heart? 

The four parts of the heart include the heart chambers, vessels, valves and septum.

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