130

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 ...


36

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 ...


22

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

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

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

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

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 ...


11

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

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 ...


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. ...


10

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

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 ...


8

There is not enough information in the question to solve it. The answer key from the original question makes a logical error: Viscosity is directly proportional to resistance. This is true. An increase in viscosity increases resistance. Flow and pressure do not matter for this statement to be true. You are correct to assume an increase in resistance. ...


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-...


7

This page (and many others) explain the idea rather well. This is more of a physics than a biology question, but the fundamental concepts are the same. In fact, contrary to what you wrote in the question, the measured blood pressure should be lower than expected if the arm is elevated above heart level. When you reduce the pressure on the bent pipe, the ...


7

According to the abstract from this paper, the intragastric LD50 of $\Delta^9THC$ (tetrahydrocannabinol) in sesame oil using Fischer rats was 1270 mg/kg. Assuming rats and humans are identical (they're not), for an average-sized adult human weighing 70 kg (~155 lb.), the median lethal dose would be 88.9 grams, or about 3.1 oz. Keep in mind that's 3.1 oz. of ...


6

To put it in very simple words the reason for isovolumetric contaction and relaxation is to make the necessary pressure changes that is necessary to allow blood to flow into or flow out of the ventricles. The basic formula you need to remember to understand this is:- Fluids flow from high pressure area to low pressure area along the pressure gradient (...


6

Both your linked fact from the University of Arkansas When you sneeze, the intrathoracic pressure in your body momentarily increases. This will decrease the blood flow back to the heart. The heart compensates for this by changing its regular heart beat momentarily to adjust. However, the electrical activity of the heart does not stop during the sneeze. ....


6

This is a good question, but it has a vast scope, as you're talking about the progression of millions of different living animals over hundreds of millions of years, none of which are still alive, so we have to make inferences based on what we observe in their surviving offspring. That means if you want to learn how 'intermediate' (say, not-quite-lungs, not-...


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