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Questions tagged [human-physiology]

For questions on the biochemical, physical, and mechanical functioning of humans in good health including their organs and cells.

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Why do the fastest runners tend to be black?

If you watched the last Olympics like me you probably also observed that most medallists in running events were black. Why is that? I discussed this with university grad friends and researchers and we ...
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1answer
7k views

Why do human females have periods?

Why do human women have periods when most animals don't? It is known that the unfertilized egg needs to be shed from the uterus. But why shed the whole endometrium? Why didn't evolution put ...
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2answers
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Why don't chilli peppers taste as hot in space?

The following commentator writes: Chili peppers don’t taste as hot in space as they do on Earth. Nobody knows why. We know that the 'hot' feeling of chilli peppers is caused by Capsaicin. We read: ...
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1answer
4k views

Why is water flavorless?

I read recently that humans have an innate preference for sweet-tasting foods. That seems feasible since carbohydrates are necessary for cells to undergo cellular respiration, but why then is water ...
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5answers
22k views

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

Some hair especially body hair regrows after trimming but stops growing after a while. What is the mechanism behind control of hair growth and how is the length limit determined?
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1answer
6k views

Why can hair grow without limit while eyebrow cannot?

I cut my eyebrow and it grows until reach a certain length. Hair can grow without limit. Why can hair grow without limit while eyebrow cannot?
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1answer
2k views

How fast can a human run?

I'm a runner (cross country) and I'm always amazed at how fast Olympic sprinters are. There's a lot of hype about those in the 100-meter dash being the fastest in the world, and we're constantly ...
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4answers
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Will the heart keep beating if it's separated from the body?

The heart is a vital organ in our body, as it drives blood circulation. I was wondering if a heart keeps beating if it is separated from the body? If yes, then why?
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2answers
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Are 'homeothermic' and 'endothermic' synonymous?

I got this question from the comments below this answer. So, do homeothermic and poikilothermic have the same meaning as endothermic and ectothermic, respectively? A user also suggested that the ...
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1answer
2k views

Can you bleed from your bones?

I was talking to my science teacher about the body specifically the red bone marrow. She said that blood is created in the red bone marrow. Does that mean that if you were to cut a fresh bone open ...
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1answer
2k views

Why don't we feel hungry after waking up?

Yesterday, I was fasting (drinking only water until I had dinner at 9 pm). After dinner, I went back to my lab (I am a Master's student) and worked till 1:30 AM. By 1 o' clock, I was feeling quite ...
11
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1answer
239 views

What is the connection between sleep requirement and age?

By this question: Is the human biological clock genetically programmed or learnt? we discussed that the sleep requirement depends on the age of the individual. - Figure 1. - Sleep requirements by age ...
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3answers
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Do spinal cord reflexes (such as the knee-jerk reflex) continue to function under general anaesthesia?

The knee-jerk reflex (patellar reflex) is an example of a stretch reflex (myotatic reflex). Stretch reflexes are monosynaptic reflexes happening in the spinal cord without involvement of the brain. ...
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3answers
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Do humans produce rennin?

At school, we've been taught that human infants produce rennin/chymosin (which aids in the digestion of milk). More specifically, it is the peptic cells in the stomach which secrete prorennin, the ...
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1answer
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What creates the feeling of 'excess' blood pressure to an area of the body?

If I hang upside down, and feel blood rushing to my head, what structures are actually responsible for me "feeling" this excess flow of blood? Baroreceptors? Mechanoreceptors? Something else? ...
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1answer
4k views

Why some parts of the human body have immune privilege?

Why have the eye and CNS have immune privilege? Why does the body not develop tolerance against their tissue and instead risk their damage in case an accidental immune cell infiltration? Wiki: ......
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1answer
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What is the maximum altitude where humans can survive?

What is the highest altitude that a human can survive without being pressurized? Let's assume that oxygen and heat/insulation are not the limiting factors? Why I asked.
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1answer
701 views

How fast is the blood flow in various vessels?

How fast is the blood flow in different blood vessels, such as the aorta and capillaries?
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3answers
29k views

What is the function of the polar bodies produced during oogenesis?

Why are polar bodies produced during oogenesis in human females? I read that polar bodies are produced during meiosis so that the oogonium (or gamete mother cell) can be converted into a haploid ...
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2answers
4k views

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

Vitamin B12 is stored in the liver for a long time. How is it stored?
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1answer
9k views

How does aspirin “thin” blood?

As we all know, aspirin doesn't actually thin the blood, as it has been explained to me, it makes it "slippery". Slippery blood doesn't stick to itself hence this helps prevent internal blood clots (...
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2answers
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Why is there smooth muscle in our bronchioles?

Having muscle tissue in our bronchioles that can constrict seems like a poor choice for tissue. Why would our airway want to ever close up? Wouldn't it be more beneficial for our bronchioles to just ...
7
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1answer
371 views

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

Rods help us to see during the dark. We can see colour of the object when it reflects light. But in a dark room(room of any color but the light is switched off and it is night),we still can ...
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1answer
553 views

Why clotting does not occur during Menstruation

As we know when we get injured our body's clotting systems stop the bleeding. So why does it take days for menstruation to stop ?
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1answer
1k views

Why antipyretics do not bring the body-temperature below normal?

Antipyretics like paracetamol are used to decrease the body-temperature in fever patients. But some of them are also used as pain-killers in sprain or other injuries (where there's no fever). In ...
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1answer
19k views

Do human anal glands have any function?

Anal glands in all kinds of animals play a range of diverse functions - providing fat for preening feathers or waterproofing fur, generating distinct scent, even repelling predators. None of the ...
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1answer
656 views

When did our ancestors switch to a menstrual cycle instead of the estrous cycle?

The Wikipedia page on the Estrous cycle says: Humans have menstrual cycles instead of estrous cycles. They shed their endometrium instead of reabsorbing it. Unlike animals with estrous cycles, ...
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1answer
297 views

Why does eating saturated fat increase blood cholesterol?

I am interested in the biochemistry of diet and the way we have been advised to eat for the past forty years. In researching an explanation for the relationship between dietary fat and blood ...
7
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1answer
532 views

Can one eye affect the other eye's low-light adaption?

This previous question addresses how long eyes need to adapt to darkness and reach full contrast. My question is how does one eye affect the "transition" and/or efficacy of this "night vision" of the ...
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0answers
89 views

Why do we fear the night? [duplicate]

I always feel more afraid in the dark than in light conditions. Is this a common phenomenon in all the people? Does it have biological underpinnings?
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1answer
2k views

Do human populations differ in core body temperature?

Human body temperature is a very complex and tightly regulated system. Hypothermia or fever of only 1-2K (i.e. changes of about 5%) already cause major symptoms and changes of 3-4K (i.e. about 10%) ...
6
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1answer
248 views

How can ingesting a prion “infect” someone?

That's something that's been bugging me for a while... Our gastrointestinal tract produces proteases that degrade proteins. Prions are proteins. Shouldn't they be broken by proteases? Also, how can ...
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1answer
2k views

Digestion of milk in humans

The intial step in the digestion of milk in humans is carried out by which of the following enzymes? A) lipase. B) trypsin. C) rennin. D) pepsin. I'm confused between the C and D option. as it'...
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1answer
175 views

What is the biochemistry of love?

How is love induced between humans? (e.g. between mother and child,couples,etc)? Does the phenomenon of love exist in other mammals, too?
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1answer
404 views

Normal ECG/EKG Measurement?

I'm getting started using ECG using a 3 lead system by iWorx. I have place the leads on my two wrists and the ground on my ankle and have recorded some data into the provided LabScribe 3 software ...
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1answer
135 views

Why some tissues like small intestine epithelium are able to be replaced so often, yet they are not one of the most common cancers?

My small intestine epithelium cells are replaced thousands times more than my prostate. Yet I'm much more likely of getting a prostate cancer than cancer on my intestine epithelium. Is there a known ...
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2answers
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Cooperativity of haemoglobin and oxygen dissociation curve of haemoglobin

Haemoglobin shows positive cooperativity with oxygen. When an oxygen atom binds to one of hemoglobin's four binding sites, the affinity to oxygen of the three remaining available binding sites ...
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1answer
7k views

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

I knew that mature red blood cells (RBCs) lacked nuclei, but I wasn't aware until just now that they also lacked ribosomes and mitochondria. Most cells in the human body all contain a common laundry ...
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2answers
142 views

Why is urea not converted to ammonia in the body?

After the liver processes metabolites to produce urea and other by-products, these travel in the blood to the heart, then they are oxygenated, and some travel through the renal artery to the kidneys. ...
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1answer
294 views

Immune System - B-cell receptors

How do the B-cells, which are a part of our body, develop antibodies against antigens of outside world (outside of our body), which they don't even know about? Is it just a random match?
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1answer
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How can heart disease cause excessive sweating?

According to google: What can cause sudden sweating? Excessive Sweating. A person with excessive sweating has a condition called hyperhidrosis. ... In adults, the most common cause of ...
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1answer
60 views

Do fat people have more chances of developing nitrogen bends?

I was reading some text on deep sea physiology. I got to know that solubility of nitrogen in fat is five times that in water. The exact text from the book animal physiology adaptation and environment ...
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1answer
134 views

Do bile salts enter into enterocytes?

Wikipedia says : The contents of these micelles (but not the bile salts) enter the enterocytes (epithelial cells lining the small intestine) ..... So, where do the bile salts go? Additionally, ...
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1answer
1k views

How does vitamin C increase iron uptake?

I've read that vitamin C increases the iron uptake in the human body. How does that work, physiologically?
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2answers
721 views

Can you eat enough to make your stomach explode?

Background After eating a large meal last night, I noticed that my tummy had significantly enlarged. After that, I started wondering if eating too much could cause a stomach to explode. Could this ...
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1answer
81 views

Can nociceptors die because of too much mechanical stress?

In martial art people hit their body (e.g., with small bean bags) to become more insensitive to pain. Can the sensory neurons die during this procedure? I think this is just an urban legend. Instead, ...
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1answer
780 views

Fats as energy source

As we know that the preferred source of energy for our body (source) are carbohydrates but heart muscle is an exception and need some explanation for this exception, that why the preferred source of ...
5
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1answer
367 views

Are there neuron mediated reactions faster than reflexes?

I'm interested in how fast the human body can respond to a stimulus. I know the fastest reflex, the blink reflex, operates around 100ms from stimulus to reaction. I also know that the blink reflex ...
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0answers
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Why do children not have the Acid Mantle?

Post puberty humans begin to secrete a substance called Sebum which changes the neutral PH of our skin from ~7 to 4.5-5.5. This has that advantage of serving as a protective line against pathogens and ...
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2answers
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Can food swallowed when a person is upside down reach the stomach?

If a person positions him/herself upside down and swallows food, will it reach the stomach against gravity? If so how?