# Tag Info

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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 ...

14

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

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 ...

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

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. ...

12

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 ...

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

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 ...

9

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 ...

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

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 ...

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

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 ...

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-...

6

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.

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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 ...

6

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, ...

6

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 ...

5

Insects primarily get oxygen through diffusion of air through their skin. I doubt the antennae need hemolymph circulation.

5

Because of reflected pressure waves and the stiffness of the blood vessel. The forward pressure wave from the heart travels much faster than the blood itself and is reflected at areas of tapering and branching. This backward wave slows the forward flow of blood, and at the same time, when it meets the next forward pressure wave, that forward pressure wave ...

5

I would be very surprised if the time of day made a difference. I've personally never heard mention of such a phenomenon in discussions with intensive care practitioners (where of course HR and BP are measured constantly). However this is only the case during rest, this paper (on horses) suggests that there is some difference in HR and BP after exercise ...

5

I am not sure if I understand your question correct. What I can see here is a clear ST depression, that might be indicative of myocardial ischemia/infarction. The underlying mechanism is the shortage of oxygen in myocytes leading to elevation of resting potential and slowing of the depolarization -- this accounts for the elevated baseline after T. I am not ...

5

In terms of cell bodies? Zero. There are autonomic projections from the spinal cord (sympathetic) and vagus nerve (parasympathetic) to the sinoatrial node, the atrioventricular node, and at discrete points in the atria and ventricles.

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I recognize this was asked like 7 months ago, but in case you're still looking for a good resource: I used a CD of heart sounds that is called something like "Harvey Heart Sounds," which I got with the purchase of my stethoscope. If you can find a copy of this, I found it an excellent tool when training to recognize the differences. These are good heart ...

5

The parasympathetic supply to the heart is by nerves and that is truncated during surgery as pointed out. The sympathetic supply to the heart is by two means: Through sympathetic nerves from the sympathetic trunk From the adrenal medulla which secretes both adrenaline and nor-adrenaline directly into the blood stream The heart contains the beta ...

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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 ...

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