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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.

23
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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?
21
votes
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?
10
votes
3answers
4k 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 ...
42
votes
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 ...
18
votes
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 ...
4
votes
2answers
7k 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?
0
votes
2answers
95 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 ...
-1
votes
1answer
99 views

Is there any way bicondylar/bigonial, bizygomatic or bitemporal breadth can change in adults?

Without cosmetic surgery or etc., are there any cases/example wherein a human adult has had a change in significance regarding these regions of the face? I have seen many anecdotes where people have ...
15
votes
2answers
5k 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 ...
6
votes
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'...
6
votes
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%) ...
25
votes
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 ...
15
votes
4answers
41k 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?
5
votes
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?
4
votes
1answer
389 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 ...
1
vote
2answers
5k 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?
3
votes
0answers
101 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?
3
votes
1answer
264 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?
2
votes
2answers
361 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 ...
2
votes
3answers
2k 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 ...
1
vote
0answers
41 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?