42 votes
Accepted

Why do the fastest runners tend to be black?

It's an interesting question and one that has been asked before. NPR did a story in 2013 on this topic, but their question was a bit more focused than just "why are so many black people good runners?" ...
  • 1,879
42 votes
Accepted

Why do human females have periods?

Short answer Shedding or reabsorbing the endometrial lining is energetically advantageous to the female.The advantage of shedding over re-absorption may be that sperm-born pathogens are removed from ...
  • 51.5k
25 votes
Accepted

Why is water flavorless?

Consumer water is not flavorless. Sources of flavor include (1) the chemical and microbial content, which is most influenced by geology and ecology; (2) chemicals added or removed during water ...
  • 51.5k
23 votes
Accepted

How fast can a human run?

An older answer that referred to the physiological feats of ancient humans, and why modern humans are wimps made me look up a couple of papers on running speeds a while ago. One of the examples used ...
22 votes
Accepted

Will the heart keep beating if it's separated from the body?

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 ...
  • 2,268
21 votes

Why does hair grow after trimming but remains at a constant length after a while?

Hair grows from the follicle; there is no way for the follicle to determine if the hair tip is trimmed or not. This is unlike plant shoot/root growth that happens at the tip. Also there is no ...
  • 35.1k
19 votes

What is the maximum altitude where humans can survive?

Short answer Between 62,000 and 63,500 feet (18,900 and 19,350 meters) blood begins to boil at body temperature. This altitude, referred to as the Armstrong limit, is generally considered to be the ...
  • 51.5k
15 votes
Accepted

How does aspirin "thin" blood?

Aspirine irreversibly inhibits the enzyme cyclooxygenase. This enzyme facilitates the reaction from arachidonic acid to prostaglandin G2/H2. The further reaction leads to the generation of Thromboxane ...
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12 votes
Accepted

Can you bleed from your bones?

Yes, bones too bleed if they get damaged (break or bruise). This is because bones are highly vascularised organs and breaking of bones will indeed rupture the blood vessels causing bleeding. Main ...
  • 4,726
11 votes

Will the heart keep beating if it's separated from the body?

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 ...
  • 5,630
11 votes

Why do the fastest runners tend to be black?

Take a look at Will Grover's answer here, I will cite the genetic diveristy explantion here, I think that sounds the most logical: Genetic Diversity This is my favorite answer, and the one that ...
  • 2,340
11 votes
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How can we move our lips even though they don't have any bones?

Because of the Orbicularis oris muscle, it's a complex of muscles in the lips that encircles the mouth, It forms the greater part of the substance of the lips, lying between the skin and the mucus ...
  • 761
11 votes

Pathogens vs Microbes and the Immune System

Not all microorganisms are pathogens Firstly, not all microorganisms are pathogens - some can be harmless and some can be even essential for the host organism functioning (e.g., many microorganisms ...
  • 3,792
10 votes
Accepted

How is vitamin B12 stored in the body although it is water-soluble?

Vitamin B12 (cobalamin) is a cofactor required by the enzymes methionine synthase (MTR) and methylmalonyl-CoA mutase (MUT). These are the only known enzymes that use B12 in humans, and are abundant in ...
  • 5,605
9 votes
Accepted

What creates the feeling of 'excess' blood pressure to an area of the body?

Arterial Baroreceptors felling the pressure. Arterial blood pressure is normally regulated within a narrow range, with a mean arterial pressure typically ranging from 85 to 100 mmHg in adults. It is ...
  • 1,442
9 votes
Accepted

Do human anal glands have any function?

They are vital if not incredibly useful in many other mammals but not humans. People have tried to look for a role and seen that they activate in times of stress or anxiety. However this probably only ...
9 votes

Why do we get sleeply after we eat?

After we have eaten... the maximum blood supply is transferred towards the digestive system so that digestion is done, and therefore the brain to does not get adequate blood supply. Am I right about ...
9 votes
Accepted

Why don't we feel hungry after waking up?

I will try to keep the answer as simple as possible, but feel free to point out if I make this too simple. Well, you are not alone with this observation. This is quite a common, but rather complex, ...
8 votes

Will a 0.2g/mL sugar concentration cause vomiting in humans?

Sugar (be it sucrose, glucose, fructose or honey) does not have emetic properties in any concentration, unless there is a personal (and highly individual) psychological adverse reaction to sweet ...
8 votes
Accepted

Besides hemoglobin, what proteins are present in red blood cells?

Reticulocyte stage is when the ribosomes are still present and after that no new protein synthesis occurs. However RBCs have a lot of proteins and major proteins other than haemoglobin are ...
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8 votes
Accepted

Do spinal cord reflexes (such as the knee-jerk reflex) continue to function under general anaesthesia?

The issue is complicated. In general it depends on the specific spinal reflex and on the specific anaesthetic. But it seems that the modern general anaesthetics usually do NOT block monosynaptic ...
  • 301
8 votes
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Could a trans-female person ever become pregnant?

Medical science has reached the point where it is able to consider performing uterine transplants in genetically female (cis-female) patients born without a uterus. In the MedlinePlus report, First ...
  • 4,945
8 votes

Why do the fastest runners tend to be black?

I also found this hypothesis from a scientific paper which suggests that asian and white people have a lower center of gravity than black people. See the general explanation: Blacks tend to have ...
8 votes
Accepted

Why are we able to differentiate between colored objects without the presence of light?

You seem to have many misconceptions about how we see and how that relates to light. I'll address them one sentence at a time: Why are we able to differentiate between colored objects without the ...
  • 3,190
8 votes
Accepted

Are 'homeothermic' and 'endothermic' synonymous?

[D]o homeothermic and poikilothermic have the same meaning as endothermic and ectothermic respectively[?] No. Once you are referring to the source of the heat, while the other time you are referring ...
  • 67.7k
8 votes
Accepted

Immune System - B-cell receptors

This is an excellent question. You are on the right track with the random match idea. B-cells (as a group) develop receptors that bind every possible antigen and then get rid of the receptors that ...
  • 8,721
8 votes
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Does LSD "stay" in your fat storage and then "returns" back?

I've heard this rumor for years, both from pro- and anti-drug people, and it is not true. According to this review of LSD's pharmacology, its half-life in the body is about 5 hours, with it being ...
  • 14.9k
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 ...
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