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Why are the walls of the lower chambers of the heart thicker and more muscular than the walls of the upper chambers?
Some terminology first: The upper chambers = atria (singular atrium) The lower chambers = ventricles The atria are responsible for receiving blood: the right atrium receives deoxygenated blood from the body and the left atrium receives oxygenated blood from the lungs. The atria only pump this blood into the ventricles and therefore do not need particularly thick muscular walls. The ventricles on the other hand are responsible for pumping the blood received from the atria to the body. The right ventricle pumps the deoxygenated blood it receives from the right atrium out of the heart and into the lungs. On the other hand, the left ventricle is responsible for pumping the oxygenated blood received by the left atrium to the rest of the body. It is because of the this that the walls on the side of left ventricle are the thickest. The left ventricle requires "more muscle" than the right ventricle as the distance it has to pump the blood is far greater. So, SHORT ANSWER: The walls of the lower chambers/ventricles are thicker and more muscular than the walls of the upper chambers/atria because they have to pump blood out of the heart and to the body as opposed to the atria which only receive blood from the body and then pump into the ventricles.
Do the ventricles have thicker or thinner walls than the atria?
Usually small arterioles and capillaries have thin walls to facilitate air exchange and nutrient/waste diffusion across the vessel wall. Thick walls would reduce the efficiency of these processes. However, large arteries and veins such as the aorta and the superior and inferior vena cavae have thicker walls. The aortic wall is especially thick because it has to withstand the large changes in pressure between systole and diastole. A thin aortic wall would bulge under such pressures and result in what is called an aortic aneurysm.
Why are the atria smaller than the ventricles?
Because there is less blood regulating through the lungs and atria. The ventricles have to pump blood through the whole rest of your body.
Why do the ventricles have more muscle mass than the atria?
The ventricles are the lower chambers of the heart which pump blood around the body. They require more muscular walls to enable them to have enough power to pump the blood around the body effectively. The atria are the upper chambers in the heart and squeeze the blood returning from the lungs and body into the ventricles. Because this is such a short distance, they require a lot less strength to be able to do there job effectively than the ventricles do. The left ventricle has an even more muscular wall than the right ventricle, because the right ventricle pumps blood to the lungs only, whereas the left ventricle pumps blood to all the other organs and therefore has a further distance to cover.
Why does the QRS complex have the largest amplitude?
More cells depolarize during this QRS complex(ventricular contraction). The reason is because the muscle mass of the atria is small compared with that of the ventricles. The ventricles have a larger muscle mass. Therfore the electrical impulses within the atria are shorter and are less. The ventricles are larger so there is a larger deflection of the ECG when the ventricles are depolarised this is called the QRS complex
What is the medical term meaning surgical incision into an upper heart chamber?
The atrial septum divides the right from the left atrium. The atria are smaller, less muscular chambers of the heart that sit atop the powerful ventricles.
Why does atrial fibrlillation not cause immediate death but ventrucular fibrillation does?
The atria are like the heart's "turbochargers"...even if they are fibrillating, blood will still trickle into the ventricles by gravity but a lot less than normal. The ventricles then contract normally, delivering less blood to the body (decreased cardiac output) giving the symptoms of cyanosis and dyspnoea. If the ventricles are fibrillating, blood can't leave the heart in sufficient volumes to support life, simply put.
Why is the wall in the left ventricles thicker?
The left and right atria are thinner walled receiving chambers of the heart where blood returns to the heart via the great veins. The two inferior chambers, the left and right ventricles, are the pumps that eject the blood into the arteries and keep it flowing through the body. If you picture it like your hands it might help. Picture holding both hands out, and in one hand you have a cup of water (atria), and in the other hand you have a squeeze pump that you constantly have to squeeze to move that water (ventricles). That hand with the pump will eventually become stronger (and therefore bigger/thicker) than the hand that is simply holding the water because of the muscle activity. So it makes sense that the atrium has some muscle, but not nearly as much as ventricles because the ventricles are acting as the pump. :-)
Why does a infarction in the ventricular wal often leads to sudden death while an infarction in the atrial wall is less likely to cause death?
Think of the atria as like turbochargers. If you knock them out, blood will still fill the ventricles by gravity as if you were pouring water into a jug, but if the ventricles are infarcted and are not working, you can't pump the blood containing oxygen out to the body.
Ventricular contractions are larger because?
The ventricles are the part of the heart that are responsible for the pumping action to move blood throughout the body. Therefore, the muscles in the ventricles are much larger and thicker to do their job properly. The atrium only has to pump blood through an open valve (the tricuspid valve) into the right ventricle. There is much less resistance to this flow of blood so much less muscle is needed.
What is the Difference between the papillary muscle and the pectinate muscle?
The pectinate muscles are shaped a bit like brush bristles, and their function is to allow maxium contraction of the atria using the minimal muscle mass. Papillary muscles are connected to strong tendons in the ventricles called the chordae tendinae, which gives them a lot of strength. Their purpose is to prevent prolapse of the valves in the ventricles after the ventricles contract. Prolapse means that the valves fall inward, allowing backflow of blood back into the ventricles after they have contracted, which makes for a far less efficient action of the ventricles. Prolapsed valves and the blackflow of blood caused by the valves folding onto themselves is called a "heart murmur".
The ventricles should depolarize in?
less than 0.08 seconds
