127

First of all, let me make it clear that the heart is at the vertical centre of the body -- it is not shifted towards left (or right). However, it is slightly tilted towards the left in most cases. In some cases, it is tilted towards the right, and the condition is called Dextrocardia. For why it is so, lets look at what the heart does. Below is a diagram ...


35

While others have addressed the big picture aspects of your question, I think it would be useful to look at the specifics. Have a look at the heart (or more accurately, the hearts) of the earthworm: They're nothing more than veins with some pumping muscles wrapped around them. It seems almost a stretch to call them hearts, they are shaped so different ...


25

Red blood cells are not equipped with a motor system to propel them through the blood stream. Instead, they are passively transported through the vasculature by the the pumping action of the heart. The effects of dangerous situations on the skin have to do with hormonal effects on the blood vasculature, and not with direct effects on red blood cells. ...


24

Interesting question! I searched briefly and came up with an answer from this short paper. I won't repeat all the details of the paper, but to be not a completely link-only answer I will give a brief summary: The technology used at the time was a lot different than modern ECG leads: it used a Lippman capillary electrometer that used moving mercury to ...


23

Interestingly there is a inverse negative correlation between heart rate and life span, meaning the faster your heart rate is, the shorter is your lifespan. See this figure (from the paper 2 cited below): When the authors plotted the approximately total heartbeats vs. the lifespan, the amount of total heartbeats was in a pretty narrow corridor: So it seems ...


23

Short version The heart has the ability to beat independently of the brain as long as it has oxygen. The heart will eventually stop beating as all bodily systems begin to stop working shortly after brain death. Remember the heart can beat, but your diaphragm and lungs wont. hence the cardiac muscles undergo asphyxiation and die off. However, immediately ...


22

As you note yourself, this depends strongly on the vessel that you are studying. I found this table in reference 1: It lists speeds between 34 and 45 cm/sec for the inferior vena cava and 12 to 16 cm/sec for the superior vena cava. For the capillaries I found this table in reference 2, which measured the blood velocity in cats. Nevertheless I think this ...


15

The basic reason is osmosis, the tendency of solutes to move from an area of high concentration to one of low concentration across a permeable barrier. So, ingesting large amounts of salt results in a high sodium concentration in the blood stream. This in turn causes water to enter the blood vessels by osmosis. More water in the blood means a greater volume ...


14

Polynomial gives a good hint. By adding in a known tracer of known amount that should only circulate in the blood stream, the concentration of the tracer when completely distributed will give the volume of distribution. If the tracer only stays in the bloodstream (and that's a fairly large IF), then the VD will be equal to the VBlood. However, as many ...


13

The normal cardiac cycle is comprised of two distinct phases: the systolic phase in which the heart contracts, ejecting the blood, followed by the the diastolic phase when the cardiac muscle relaxes, refilling the heart with blood. This cycle is assured by specialised cardiomyocytes (Cardiac muscle cells) that conduct electrical impulses through the heart. ...


13

In layman's terms: an Asystole is not affected by the electric shocks of a defibrillator. A defibrillator is used when the heart goes in fibrillations because it actually CAUSES an asystole. The idea is that you basically reset the heart to a blank state so you can start normal CPR procedure to help the heart go back to a normal rythm. That's why you see ...


13

It has mainly to do with the embryonic origin of organs, with the heart being a typically left sided organ, it develops sharing some nerves with the left thorax and left arm. There is however high variability, typically among patients but also among coronary vessels. For instance, right coronary stenosis may lead to abdominal pain, whereas left circumflex ...


12

It is easy. Method A, simple, is based on "counting the fish in the pond" method. Make rough estimate of amount of blood in the organism. Choose a component of blood that is replenished slowly [from liver or marrow etc]. That takes time to replenish. Red blood cells are probably OK. Some easily measurable and slowly replenished component of blood. Let's ...


12

This kind of question was raised in a book called "Darwin's Black Box" by Michael Behe, who is a biochemistry professor in the U.S. - he calls this 'irreducible complexity' (IC). For example, the blood clotting cascade system where you have a large number of components that are all apparently essential for the process. Now I have to say I find the idea that ...


10

Trans fatty acids are digestible, but they cause an increase in LDL and a decrease in HDL, which is the leading mechanism for atherosclerosis. So, they increase the risk of a cardiac infarct. LDL means Low Density Lipoprotein, it's one of the 5 major lipoprotein groups. Lipoproteins carries the fatty acids and cholesterol which were absorbed from ...


10

Lipids require more oxygen to burn, but also they are cheaper to store (since they have great calorific power than carbohydrates and they're hydrophobic, thus not requiring water for their storage). The body can store so much lipids that it becomes an almost everlasting energy source (A normal adult have enough energy stored as fat to allow basal metabolism ...


10

This is a specific version of the great cancer question: "Why are some cancers more common than others?" The answer is either "Some have more common causes", and (or) "Some are cured spontaneously more often". So now all you are asking is "What causes cancer?" and "How do we cure it?" Given that, I don't expect a general definitive answer will be ...


10

Dizziness after eating, which can lead to falls and passing out, is called postprandial hypotension, and as the heart is indeed responsible for responding to hypotension by increasing it's rate - which can be seen in any number of clinical scenarios from blood loss to standing up too suddenly - failure to do so, for any reason including heart disease, can ...


10

Sydney Ringer showed in 1882 that when the heart, when separated from the body and immersed in lactated Ringer's solution, or even isotonic saline solution, will beat because it has its own pacemaker systems at the level of the Sinoatrial node and Atrioventricular node. This activity will continue until there is insufficient ATP to support it energetically. ...


9

The heart has nerve cells which are supposed to fire synchronously. This is what allows the heart to pump effectively. Fibrillation is when nerve cells (or the cardiac cells themselves, which have some "pacemaker" activity) are firing asynchronously, which means blood isn't getting pumped. The shock causes all of the units to fire at once (which isn't ...


9

In general, no. Car batteries are designed to provide a large amount of amperage, to turn the starter with a high amount of torque via an electric motor. Generally this is done at 12 or 24 volts. The current recommendations for a defibrillator requires 200V, and a very small amount of amperage. This is one of three settings in a standard defib procedure. ...


9

Alternative Heart Morphologies Amphibians and some reptiles have a three-chambered heart, with 2 atria and a single ventricle. There are still separate circulatory pathways for the lungs and the rest of the body, but the oxygenated and oxygen-depleted blood mix in the ventricle, and are pushed at the same time to the lungs and body. The disadvantage of ...


8

Quick answer, no. Imagine a balloon; as you compress the balloon, there will be a lot of air that leaves it. But as you let it relax, the balloon pulls in surrounding air even as you fill it from another side. When the aortic and tricuspid valves are closed, there is blood flow forward but due to conservation of mass, the blood goes back to fill in the ...


8

According to the Wikipedia page on Supraventricular tachycardia the heart can go to a new faster rate in the space of a single beat, and then come down again just as quickly, as shown in this image taken from the Wikipedia page.


8

Very simply putting, irregular heat beat means that the pulse is not regular. It can be diagnosed by checking your pulse clinically. Irregularities are further classified as: Regularly Irregular: this occurs in heart blocks where every second or third beat is skipped regularly causing a pattern. Usually as time progresses the degree of block worsens and ...


8

Ewing's sarcoma is a bone cancer. As such, it does not arise as a primary tumor in the heart. Ewing's sarcoma does metastasize. Like any metastatic cancer, it seeds along it's venous return to the heart, "taking root" in suitable tissue. Cardiac metastases of Ewing's sarcoma are exceedingly rare, with only a few reported cases. Since all blood returns to ...


7

There are many reasons why the maximal heart rate decreases with age. The most prevalent is the heterogenous thickening of the walls of the heart. Cardiac output is stroke volume times heart rate. When the wall thickens, the heart needs more energy to achieve the same pumping (bigger stroke volume) or it needs to increase heart rate at rest. Because of ...


7

If there are no pacemaker cells active, no muscle contraction will occur. This condition is named asystole. It can be a temporary or definitive condition. Some would call it "extreme bradycardia" in temporary cases, but this is just an euphemism. Edit: Ok, so let's try to clear up the confusion a bit. Technically, there is no asystole involved here (not ...


7

To say that there is a cutoff of one minute at which time shocking becomes ineffective is incorrect. The best way to defibrillate a heart within one minute of VFib onset is with electric shock. In fact, short of certain drugs in certain instances, it's the only way to defibrillate Vfib, regardless of the amount of time that has passed. If the one minute cut-...


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