64 votes
Accepted

Why don't we bleed interstitial fluid?

For fluid to flow from a wound there needs to be a significant pressure gradient between where it is now and the outside of the body. Your skin generally does not have a strong compressive effect, ...
TheChymera's user avatar
  • 1,316
55 votes
Accepted

Why are the pulmonary vein and artery not like the rest of circulatory system?

It is true that nearly all arteries carry oxygenated blood and nearly all veins carry de-oxygenated blood, but that is not what defines them. Arteries are blood vessels that carry blood away from the ...
MattDMo's user avatar
  • 15.3k
53 votes
Accepted

Why are bruises not lethal?

blood clots inside the body have an unfortunate tendency to get into the bloodstream and cause blockages, leading to severe problems such as strokes or heart attacks This statement is primarily true ...
Bryan Krause's user avatar
  • 45.3k
36 votes

Why are bruises not lethal?

@Bryan Krause's answer is quite correct. I just want to clarify what a bruise is, because I think you have a misconception of what happens. There are bruises (blood leakage into tissue because of ...
anongoodnurse's user avatar
22 votes
Accepted

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
  • 51.6k
13 votes

Why isn’t Haemoglobin a plasma protein, rather than being encompassed by the erythrocyte?

To the man with a hammer, everything looks like a nail. The poster’s hammer seems to be kidney function. Mine is the biochemistry of the erythrocyte (red blood cell). Others, no doubt will be able to ...
David's user avatar
  • 25.2k
12 votes

Why are bruises not lethal?

I would like to add a point which I feel others have missed: our body already has a safety system to prevent such a thing from happening, called fibrinolysis. Obviously, this system is not solely for ...
another 'Homo sapien''s user avatar
12 votes
Accepted

How do I calculate a "full-life" from a half-life of substance elimination?

There is no such thing as a "full-life", because in most relevant mathematical models (the simplest and most common being first-order exponential decay), the time required for all the the ...
electronpusher's user avatar
10 votes

Why isn’t Haemoglobin a plasma protein, rather than being encompassed by the erythrocyte?

An additional aspect is that the availability of iron usually constrains the growth of pathogens. Cassat and Skaar in "Iron in Infection and Immunity" state: Iron is an essential nutrient for both ...
mgkrebbs's user avatar
  • 9,044
10 votes

Why don't we bleed interstitial fluid?

Besides the answer by TheChymera, there's also the "problem" that interstitial fluid can't really flow freely. Blood runs in veins, allowing to quickly circulate through your entire body. And if you ...
Emil Bode's user avatar
  • 209
9 votes
Accepted

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
  • 45.3k
8 votes
Accepted

Why doesn't the rest of the body have something like the "blood-brain" barrier to protect itself from pathogens?

There can be many reasons to why BBB-like barrier is not present in all the capillaries of the body. Let's talk about them one at a time. Source Blood-brain barrier has its own side effects. Some ...
another 'Homo sapien''s user avatar
8 votes

Is there any justification for the claim that blood travels 12,000 miles per day?

A single erythrocite travelling from the heart via the aorta, a certain artery, capillary and vein back to the heart would make about 1 meter in average, I guess. If the blood volume of an adult is ~...
Jan's user avatar
  • 8,059
8 votes

How does blood reach skin cells and other closely packed cells?

The skin is highly vascularized up to the epidermis, with dense vessels right at the top of the dermis (your picture omits these, but you will find them in better diagrams like this one). The ...
Bryan Krause's user avatar
  • 45.3k
8 votes

How does blood reach skin cells and other closely packed cells?

It's also worth noting that the ~15-60 most superficial layers of keratinocytes (epidermal epithelial cells) are not metabolically active (i.e., "dead") and therefore do not need to receive ...
theforestecologist's user avatar
8 votes
Accepted

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
  • 45.3k
7 votes
Accepted

Why is it always Sodium that we talk of in blood pressure?

The key is in fluid compartments and osmotic activity. For the purposes of this discussion, let us say that there are two fluid compartments the ExtraCellular Fluid (ECF) and IntraCellular Fluid (ICF)....
Maljam's user avatar
  • 427
7 votes
Accepted

Do camels have nucleated RBCs or enucleated RBCs?

Camel RBCs are anucleate [1, 2]. The dark structure seen in microscopic images is not nuclei but a network of microtubules called the marginal bands. Marginal bands cause these RBCs to adopt an ...
WYSIWYG's user avatar
  • 35.5k
7 votes
Accepted

Why doesn't nitrogen diffuse into blood?

I like it that nitrogen came to your mind ;) I guess in school they didn't tell you about the nitrogen at all, for the matter of simplification, because it is of no function in the body and the $O_{...
mpribis's user avatar
  • 736
7 votes
Accepted

Why are veins not blocked by plaques?

Atherosclerosis can develop in high pressure systems, such as arteries, and not in low pressure systems, such as veins. It is high blood pressure that can damage the lining of the blood vessel and ...
Jan's user avatar
  • 8,059
6 votes

"Blood circulation". Why blood bleeds in atmosphere ?

That's actually the gauge pressure that we measure. Gauge pressure is the amount by which the pressure measured in a fluid exceeds that of the atmosphere. So, when we say that our blood pressure is ...
Sandeep's user avatar
  • 335
6 votes
Accepted

Why is urea not converted to ammonia in the body?

The answer to this question is quite simply this: The activation energy for the uncatalysed reaction is such that the amount of decomposition of urea in aqueous solution at blood temperature and ...
David's user avatar
  • 25.2k
6 votes
Accepted

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
  • 45.3k
6 votes
Accepted

why do our eyes not go red in response to body temperature?

Skin turns red when light skinned people flush because it contains few absorbers, so photons diffuse through it long distances. During this time green and blue light is absorbed as photons encounter ...
user1850479's user avatar
6 votes

How do physics notions of fluid dynamics relate to pressure gradients in circulation?

As far as we know so far, biology isn't able to break any laws of physics. However, biology isn't passive: biological systems react to changing environments to maintain some level of homeostasis. ...
Bryan Krause's user avatar
  • 45.3k
6 votes
Accepted

How to understand the biophysics and math behind a 0.2 second delay between the pulse in my arm and my ankle?

So it turns out that your estimate is not bad, by simple velocity calculation, I get it to be a little over 50% out (see below), but as you say, there is some error in your measurement. However, it ...
bob1's user avatar
  • 11.7k
6 votes
Accepted

Why does vasodilation increase blood flow in the capillaries, but decrease it in the chest during inspiration?

The passage isn't talking about a magical diameter increase in a physics problem. If negative outside pressure causes blood vessels to increase in diameter, something has to fill the vacated space ...
Bryan Krause's user avatar
  • 45.3k
5 votes
Accepted

How does alum help in blood coagulation?

I will answer the three questions one at a time. Lets begin with the first one: Do people actually use alum to stop bleeding, or only as a disinfectant? Does alum have any disinfectant effects? Yes, ...
another 'Homo sapien''s user avatar
5 votes

Why is urea not converted to ammonia in the body?

[Partial answer] [OP claim:] Urea in water can decompose into ammonia which is toxic. Probably not as easily as you think. If Wikipedia is correct: Urea alone is very stable due to the ...
Dolphin 613 Motorboat's user avatar
4 votes
Accepted

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

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