133 votes
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Why is the heart not in the middle of the body?

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. ...
another 'Homo sapien''s user avatar
38 votes
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How did the cardiovascular system evolve?

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: ...
user151841's user avatar
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24 votes
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ECG wave names origin

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 ...
Bryan Krause's user avatar
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22 votes
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What is the speed of blood?

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/...
Chris's user avatar
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14 votes

What is the cause that angina pectoris is felt in your left arm?

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 ...
Giuseppe Biondi-Zoccai's user avatar
12 votes

How did the cardiovascular system evolve?

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 ...
gilleain's user avatar
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10 votes
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Can defibrillation be done with a car battery?

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. ...
10 votes
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Why is Heart Rate Recovery after exercise reasonably well described by a mono-exponential decay?

I think most people would take exponential decay in a circumstance like this to be the null hypothesis. That is, if you had something not exponential decay, that would be curious and interesting and ...
Bryan Krause's user avatar
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9 votes
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Is a one ventricle heart feasible?

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 ...
Bryan Krause's user avatar
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8 votes
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How does increased resistance to flow decrease blood pressure?

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 ...
Bryan Krause's user avatar
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7 votes
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What is a lethal dose of THC?

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'...
MattDMo's user avatar
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6 votes

How did the cardiovascular system evolve?

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 ...
Dan Bryant's user avatar
6 votes
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Why do people perceive blood pressure as the force that moves the blood forwards (see details)?

In the vascular system, pressure is what moves blood forwards, at least in an analogous manner to voltage...just like voltage, pressure itself doesn't move things, but a pressure gradient does. You ...
Bryan Krause's user avatar
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6 votes

ECG wave names origin

According to this site: http://www.ecglibrary.com/ecghist.html Originally the waves were designated as A,B,C& D but after correction they were termed as P,QRS, T. Why PQRST and not ABCDE? The ...
JM97's user avatar
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6 votes
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How can heart disease cause excessive sweating?

The answer lies in compensation. Take myocardial infarction, for starters. MI, if large enough, severely weakens the heart, and hence, at the same level of stimulation, it can no longer pump blood ...
stochastic13's user avatar
  • 4,679
6 votes

Why is the heart adversely impacted by chronic psychological stress, yet it benefits from routine physical exercise?

From the perspective of sympathetic nervous system Exercise induced adaptations of heart A common phenomenon in endurance athletes is the athlete's heart /athletic heart syndrome Once athletes stop ...
user 33690's user avatar
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6 votes
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Heart rate vs body size

The paper you link finds that there is not a significant correlation between body mass and resting heart rate in humans. While there is a well known negative correlation across mammals: This is the ...
kmm's user avatar
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6 votes

Does blood clot reduce blood flow?

A blood clot can nearly completely or completely block an artery, in which case the blood flow will be reduced or stopped. How do we know this? Pulmonary Embolism (Merck Manuals): Pulmonary ...
Jan's user avatar
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6 votes
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How are monocytes larger than capillaries?

They aren't completely rigid and can change shape to squeeze through (see Downey et al). If they are activated, monocytes can get stuck in capillaries and block them, which contributes to poor ...
Bryan Krause's user avatar
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5 votes

What is the cause that angina pectoris is felt in your left arm?

Our pain-sensing neurons work in useful ways only when they inform about skin areas or muscles. When nettles sting your left hand, you want to retract your left hand right away. This is in part an ...
nvja's user avatar
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5 votes
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Why is the current flow shown to be flowing from the negative area towards the positive area?

By convention, positive current is assumed to be the direction of flow of positive charges. The trouble is that in many common situations (like this one), the current is actually carried by electrons ...
Charles E. Grant's user avatar
5 votes
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Why does high blood pressure not damage the body during exercise?

Actually it can. See https://clinicalhypertension.biomedcentral.com/articles/10.1186/s40885-016-0052-y for instance: Deleterious effects of HRE [hypertensive response to exercise] on structure and ...
Dolphin 613 Motorboat's user avatar
5 votes
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How does the SNS increase the heart rate when it causes an increase in cellular uptake of potassium?

It's important to keep in mind that extracellular potassium concentration is normally very tightly regulated at 4.2 mEq/L (±0.3 mEq/L in nonpathological circumstances.) It's precisely because so many ...
anongoodnurse's user avatar
4 votes

How does sepsis affect heart function?

While the heart is affected during septic shock, it is the result of the chain of events that occur as a result of a systemic release of the pro-inflammatory cytokine Tumor Necrosis Factor alpha (TNF-$...
AMR's user avatar
  • 5,005
4 votes
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Isolating the vasculature of an organ?

The typical name for this technique is "corrosion casting" - if you search for literature on corrosion casting you will find many many papers detailing the technique. Another answer mentions "...
Bryan Krause's user avatar
  • 45.3k
4 votes

What prevents backflow of blood from right atrium to vena cava during atrial systole

Pressure differences. Atrial contractions are much more gentle than ventricular ones, and in normal circulation the venous pressure in the vena cava often stays higher than the right atrium, even ...
Bryan Krause's user avatar
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4 votes
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At what stage is the nervous system developed enough to interpret neuronal signals as 'pain'?

First, there is some confusion on your part about heart cells and pain perception. Heart cells generate an action potential intrinsically; they do not need the central nervous system to beat (your ...
anongoodnurse's user avatar
4 votes

Seizures and blood pressure

Yes, seizures can affect autonomic function including blood pressure. Such symptoms can even result in death. Note though that not all seizures are the same: there are many different types with many ...
Bryan Krause's user avatar
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4 votes

The 4-chambered heart

The short answer is crocodiles may be secondarily cold blooded, but the long answer is warm blooded and cold blooded is not a binary condition but a spectrum. It has to do with how much heat you ...
John's user avatar
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4 votes
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Can the heart generate its own rhythm independent to the SAN?

Your textbook and review guide are correct, but the missing details may be a little confusing. Yes, the heart has the property of automaticity, meaning action potentials fire on their own at a certain ...
De Novo's user avatar
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