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5.3. The heart

The heart

In order for blood to travel through the circulatory system, it must be propelled by the heart. The heart is a hollow muscular organ, made up of thick walls of muscular tissue called the myocardium. Its interior is lined by a layer of cells (endocardium), and on the outside it is covered by a double membrane (pericardium).

The heart is divided by a septum into two parts that are not communicated, right and left. Each part has two cavities:

  • Auricle: in the upper part, small, and with thin walls. They receive the blood from the veins.
  • Ventricle: below the atrium, with thick walls. They expel blood through the arteries.

The atrium and ventricle on each side are communicated with each other by an atrio-ventricular valve that only allows the passage of blood from the atrium to the ventricle:

  • Mitral or bicuspid valvecommunicates the left atrium with the left ventricle.
  • Tricuspid valve: communicates the right atrium with the right ventricle.

Partes del corazón

By GarciaGerry (Own work) [GFDL, CC-BY-SA-3.0, GFDL or CC-BY-SA-3.0], via Wikimedia Commons

The heart is made up of cells that, like all cells, need nutrients and produce waste.

The cells that make up the heart, like all other cells, also need nutrients and produce waste. It is the coronary arteries and veins that provide the necessary blood to the heart muscle.

There are several blood vessels that enter or leave the heart :

  • Veins reaching the atria :
    • Right atrium : there are two caval veins coming from the whole body.
    • Left atrium : four pulmonary veins arrive.
  • Arteries leaving the ventricles :
    • Right ventricle : the pulmonary artery comes out.
    • Left ventricle : the aorta artery that carries blood to all cells of the body leaves .

At the exit of the ventricles there are other valves that prevent the blood that leaves the arteries from returning to the heart, they are the sigmoid valves.

The walls of the atria are thinner than those of the ventricles because they only have to push blood up to the ventricles, whereas the ventricles have to push it much further. The right ventricle, up to the lungs. And the left ventricle, which has the thickest walls, to the entire body.


File:Human heart beating at 61 bpm (Cc-by-3.0).ogg - Wikipedia, the free encyclopedia. (s. f.). Recuperado 11 de enero de 2014, a partir de

Corazón de cordero preparado para su disección

Lamb heart prepared for dissection

Answer in your notebook

5.3.- Briefly describe the structure of the heart, indicating the name of the cavities and valves it presents.

Answer in your notebook

5.4.- Why are the walls of the ventricles thicker than those of the atria? Why is the wall of the left ventricle thicker than the right?

Answer in your notebook

5.5.- What would happen if the blood from the left side of the heart mixed with that from the right side?

What is the heart of a giraffe like?

We will see, when we talk about evolution in 4th year of ESO, the advantage that giraffes have to be so tall. Having such long legs and neck allows it to reach heights of almost 6 meters, so it can get its food by eating the high parts of the trees, where other competitors cannot reach. Instead, to drink water they have to adopt very uncomfortable postures that makes them vulnerable. But now we are not on that topic.

Have you ever wondered what a giraffe's heart has to be so that it can pump blood to its brain?

The heart of a giraffe can weigh 11 kilos and is about 60 cm long, and it has to generate twice the blood pressure that humans need for blood to reach the brain, so the wall of the heart can have up to 7.5 cm thick. His heart rate is 160 beats per minute.

It also has a blood pressure regulation system in the neck that prevents excess blood from accumulating in the brain when the giraffe lowers its head. The blood vessels in the legs are under great pressure to prevent excess blood in the legs.


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