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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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26 votes
1 answer
29k 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?
Mohini Yadav's user avatar
11 votes
3 answers
9k views

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 ...
paracetamol's user avatar
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24 votes
1 answer
7k 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?
kiss my armpit's user avatar
48 votes
1 answer
8k 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 ...
Harini's user avatar
  • 615
18 votes
1 answer
4k 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 ...
HDE 226868's user avatar
  • 1,415
5 votes
2 answers
8k views

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?
Ram Manohar M's user avatar
27 votes
1 answer
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 ...
ringo's user avatar
  • 373
15 votes
2 answers
9k views

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 ...
Mesentery's user avatar
  • 3,293
14 votes
4 answers
46k views

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?
Shashank's user avatar
  • 577
10 votes
2 answers
11k 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 (...
L.B.'s user avatar
  • 1,122
6 votes
1 answer
544 views

Immune System - B-cell receptors

How do the B-cells, which are a part of our body, develop antibodies against antigens of the outside world (outside of our body), which they don't even know about? Is it just a random match?
Sandeep's user avatar
  • 335
6 votes
1 answer
4k 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'...
Harini's user avatar
  • 615
6 votes
1 answer
4k 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%) ...
AlexDeLarge's user avatar
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5 votes
1 answer
2k views

What is the function of the Hyoepiglottic ligament?

The hyoepiglottic ligament (ligamentum hyoepiglotticum) is an elastic band that connects the epiglottis to the hyoid bone. Although I can find information about the clinical significance of this ...
theforestecologist's user avatar
4 votes
2 answers
592 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. ...
Sudhanva's user avatar
  • 327
4 votes
2 answers
2k views

Why do humans lose subcutaneous fat tissue with age?

Why exactly do humans lose subcutaneous fat tissue with age? It appears that we either lose fat cell volume or we might actually be losing the number of fat cells with age. One hypothesis is that as ...
user45506's user avatar
3 votes
2 answers
4k views

Why is arterial pO2 normal in carbon monoxide poisoning?

Arterial blood gas measurements often show that pO2 is 'normal' even though haemoglobin is bound to carbon monoxide with high affinity. Is this because there is still oxygen bound to some subunits of ...
pincushion44's user avatar
3 votes
0 answers
127 views

How do we sneeze?

When a stimulus triggers the sneezing pathway, known as the trigenimal nerve network, how do the droplets from a sneeze get created within the nose? What affects the size of these droplets?
TanMath's user avatar
  • 3,079
2 votes
1 answer
919 views

Causes of Back Dimples

What are the causes of the dimples commonly found above the buttocks? They seem to be in line with the sacroiliac joints. Do the joints have anything to do with them?
Chris Rogers's user avatar
2 votes
2 answers
1k views

Why is the resting membrane potential of excitable tissue not affected by the extracellular sodium concentration?

I know that the resting membrane potential for excitable tissue (eg, nerve) is primarily determined by the electronegative difference between the inside and the outside of the membrane for potassium ...
Remoun's user avatar
  • 43
2 votes
0 answers
266 views

Does all CO2 from the blood leave the body through the respiratory system?

I know that the primary way that CO2 leaves a healthy human’s body from the blood is by diffusing into the lungs during gas exchange and then being exhaled. Is there any other way in which CO2 from ...
user avatar
2 votes
2 answers
968 views

Does every nerve ending send information to the brain separately?

Does every nerve ending send information to the brain separately? Is there a nerve path (I don't know their scientific name) from every nerve ending to the brain; or are they sent to brain from the ...
b.y's user avatar
  • 23
2 votes
3 answers
6k views

How does low cysteine conditions affect pheomelanin production?

So we were studying this amino acid called cysteine. Specifically we were studying it's effect on melanin genesis. Our teacher told us how excess of cysteine affects the melanin synthesis by ...
AScientist's user avatar
1 vote
0 answers
55 views

How do we sneeze? - Part 2

Here is the second part of my question about how we sneeze. How are the sneeze droplets propelled at such a fast speed? I have heard sneeze travels at 100 mph. How is this possible?
TanMath's user avatar
  • 3,079
1 vote
2 answers
6k views

Why do we urinate more often in winter compaired to summer?

I have been thinking of this question for a long time, but I do not seem to find an answer yet. Is there a hormonal change in our body during winter due to which we have to run to toilet often?
joydeep1993's user avatar