This tag is for questions about the general anatomical features of human beings as opposed to the anatomy of non-human animals.

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175
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3answers
85k views

Why do I only breathe out of one nostril?

I was just sitting with my hand next to my nose and I realized that air was only coming out of the right nostril. Why is that? I would think I would use both, it seems much more efficient. Have I ...
28
votes
4answers
22k views

How does cerebrospinal fluid circulate in the central nervous system?

Cerebrospinal fluid (CSF) is produced in the choroid plexus of the lateral ventricles and in the 4th ventricle of the brain. CSF then circulates through the ventricles of the brain and the ...
27
votes
1answer
3k views

Is humans' height ideal?

More or less we humans are around 1.70 meters tall. My question is, would it be possible to scale us? that is, is it in principle possible having humans 1 cm tall, or 10 meters tall or is there some ...
26
votes
3answers
44k views

If the brain has no pain receptors, how come you can get a headache?

I've read many years ago in books, that the brain has no nerves on it, and if someone was touching your brain, you couldn't feel a thing. Just two days before now, I had a very bad migraine, due to a ...
24
votes
5answers
16k views

Does red light preserve your night vision?

A number of companies have started marketing LED lamps that can be switched to a red mode. The claim is that red light is less harmful to one's night vision. Given that our eyes are less sensitive to ...
22
votes
4answers
3k views

Why do we need red blood cells?

From what I know, the main function of red blood cells is hemoglobin transport. So, why do we need cells packed with hemoglobin: why can't it travel freely in the bloodstream? My own thoughts were: ...
22
votes
1answer
4k views

Why do stars disappear when I look at them?

I've noticed that when I'm out at night stars seem to vanish when I focus on them. I assume the reason is physiological and not astronomic. Why does this happen? I would expect that things would be ...
17
votes
3answers
468 views

Why would diffusion be faster across a non-specialised tissue?

The standard protocol for a person experiencing chest pains is to chew a 300mg aspirin tablet, the argument being that chewing rather than swallowing the tablet results in the aspirin entering the ...
16
votes
4answers
2k views

Could we transmit smells electronically?

We can encode sound and images in radio waves and send them, but presumably there's some physiological reason that we can't easily make a picture or video of a smell. Could we realistically break ...
15
votes
2answers
5k views

Will humans and animals be harmed by frequencies outside their hearing range?

The human ear (for example) is sensitive to frequencies from 20Hz to 20kHz. Any sound beyond that limit would not be heard by us naturally. Will it harm us (effect our ability to hear) when we hear ...
13
votes
2answers
2k views

The Uniqueness of DNA Paradox

How can everyone have unique iris and fingerprints? After a certain amount of human beings have lived on earth, wouldn't it be possible to exhaust all possible combinations? The same principle ...
12
votes
1answer
3k 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?
12
votes
2answers
3k views

How is eye color in humans inherited?

In high school we studied the inheritance of eye color, as it was explained to us in the most simple way: blue eye color is a recessive, monogenic, autosomal trait. Now I know that it is a bit more ...
11
votes
1answer
695 views

Average dimensions of the human back (anthropometry)

I am wondering if anyone can point me to (a scientific source that provides) the estimates of the dimensions (length x width) of the human back? I am specifically interested in the dimensions ...
11
votes
3answers
4k views

What is the evolutionary reason behind the fragility of teeth?

Almost all organs in the human body have a rather large threshold within which the organ or tissue is capable of repairing itself using materials supplied by the body, whether it's made from organic ...
10
votes
3answers
498 views

Why are the organs for reproduction and urinary excretion combined?

We eat food for getting energy to our body parts, and we excrete the wastes through urine, feces, and perspiration. Why has nature combined the urinary tract with the genital system (urogenital ...
10
votes
1answer
424 views

Foveal ganglion cell density (Tay-Sachs Disease)

I’m currently reading on Tay-Sachs disease and have stumbled upon something regarding the typical “cherry red” macula symptom. On the one hand it is mentioned that the macula is almost devoid of ...
10
votes
1answer
124 views

Unilateral damage to vagus nerve

Context: The vagus nerves supply the neck viscera, heart, lungs and gastrointestinal tract. They join around the oesophagus to form the oesophageal plexus. Question: Would damage to one vagus nerve ...
9
votes
2answers
3k views

How do the lungs act as a sieve to trap blood clots?

Does anyone know? I'm curious to find out as my human anatomy and physiology book doesn't go into much detail on how the lungs function as such
9
votes
1answer
916 views

Why are there nail growth differences between humans and other mammals?

When a cat is growing, his nails are growing with him to some extent. A grown cat has a fixed nail length that is not extending. By contrast, human finger nails just keep on growing, so we have to ...
9
votes
2answers
15k views

Why does human facial and head hair continue to grow?

Many people can grow extremely long head hair and facial hair. Are there evolutionary theories as to why this is the case? It seems like having long hair could be a disadvantage, and extremely long ...
9
votes
1answer
441 views

Coincidence that navel is near the womb?

The attachment point of the umbilical cord in a baby girl is very close to where her own baby would develop. Is there something in the evolutionary history of mammals that explains this, or some ...
9
votes
1answer
17k views

Why do toenails grow much slower than fingernails?

As the title suggests, I've noticed that my fingernail grow much faster than my toenails. For instance, I usually trim my fingernails every two week or so, but for toenails the number would be about 6 ...
8
votes
4answers
994 views

Is there any way a human could whistle and be unable to speak?

Is there any situation anatomically, where a human could understand the speech of others perfectly, without any capabilities of speech themselves, but would retain the ability to whistle with a tune? ...
8
votes
2answers
259 views

Which part of human body sustains most pressure when standing up straight?

Let's suppose a healthy fit barefoot young adult standing comfortably on a flat solid surface. A reasonable guess is somewhere around the foot. But is it the ankle, the heel, or the Metatarsus?
8
votes
1answer
539 views

What happens to bones that do not heal?

I would like to know the steps the body takes to heal a broken bone and what happens if it cannot heal properly. I am not looking for advice or explanations on resting and not doing activity, I am ...
8
votes
1answer
1k views

Do the right-handed people tend to use the right side teeth of their jaw to chew food more often than the left-handed people?

And vice versa, do the left-handed people tend to use the left side teeth of their jaw to chew food more often than the right-handed people?Or the frequency of food chewing distribute fairly to both ...
8
votes
1answer
163 views

Is it the sphincter that flexes when a human pushes a bowel movement?

Of course the sphincter muscle is at the exit point. To use a toothpaste tube analogy, if I want to squeeze out some toothpaste, it does me little to no good to jostle the nozzle; I need to squeeze ...
8
votes
1answer
248 views

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? ...
8
votes
1answer
271 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?
8
votes
2answers
38k views

What could cause hairs to gray at the tips but not the roots?

I have noticed that some of my sporadic gray hairs are gray at the tip side but oddly, not near the roots. Some are even only gray in the middle. I find all of this very counter intuitive, and I ...
8
votes
1answer
722 views

Why are we using upper teeth and lower lip on labiodental sounds?

I came to wonder this when studying language (as well as other same theme question posted just few ago). For example the word "fantastic" we use upper teeth and lower lip to produce F sound, instead ...
7
votes
3answers
358 views

Weighing 2 vertical halves of the human body

I had this thought while bathing: Assume a perfectly developed physical human body and anatomy in terms of size, dimensions and proportions. In theory, if I cut the body vertically into two exact ...
7
votes
3answers
4k views

Can any other animal choke on food?

I read somewhere (I think it was Bill Bryson's book on the origins of the English language) that of all animals, we are the only ones that can choke on food (having something to do with how our larynx ...
7
votes
1answer
4k views

Why does the sweat of children not smell like adults?

My kids sweat plenty in this hot heat, but they don't smell afterward. I on the other hand need all kinds of deodorant. Why doesn't kid sweat smell?
7
votes
2answers
157 views

Why are there no artificial wombs yet?

If the conditions within the womb are mimicked, and proper amniotic fluid with constantly recycling nutrients is maintained, is it not possible to obtain an artificial womb? Is there anything missing? ...
7
votes
2answers
86 views

What is the benefit of near-emptying the bloodstream in the mammalian kidney?

In the normal function of the kidney, the bloodstream is near emptied of fluids as it moves through the glomerulus, in which glomerular filtrate is formed. As it proceeds through the Nephron, a ...
7
votes
0answers
102 views

What is basis of multifunctionality of “master glands” in the endocrine system?

I have just started reading about the endocrine system and I am having some difficulty understanding the basis of distribution of glands and associated hormones. I am using multifuntionality to ...
6
votes
2answers
2k views

Why is the opposite of plantar flexion called “dorsiflexion”?

Why is the action of flexing the foot so that the toes move anteriorly/superiorly (i.e. in the direction opposite that which they move during plantar flexion) described as "dorsiflexion"? In the same ...
6
votes
1answer
124 views

What is the function of the human eye white?

If you have a look at the eyes of most animals, you never see the white part unless the eyes are averted. In contrast, humans always have the whites visible because the iris is quite small. The only ...
6
votes
1answer
1k views

Chest muscle and female breast size

Do female chest size have anything to do with muscle? I know many female athlete and their average breast size is much bigger than normal female that does not tend to play sports. Do this have any ...
6
votes
1answer
7k views

Is it biologically possible for an adult's eye color to change?

Can it be that the adult eye can change color? Specifically my question is about a unilateral color change, such that the color of one eye remains constant, while the other changes color over time. ...
6
votes
1answer
3k views

Why don't we have hair on palms?

We have hair all over the body except palms. What is the biological reason behind this? Thanks
6
votes
2answers
242 views

Why do we have two of some organs, but not all?

We have two eyes, but we don't have two hearts. Why do humans have two of some organs, but not all?
6
votes
1answer
1k views

How and why did mouth and nasal cavity evolve separate?

My initial objection is that nose filters air, mouth is for eating but is used for breathing also, plus they both are used to create sounds. What is the cause and reason in this case, why do we need ...
6
votes
3answers
3k views

3D models of adult male brain in the Blender software? Any open-sourced version for research?

I am trying to find 3D model of brains. I am particularly interested in adult-male -brains in Blender-model. I could find such 3D models of brains for sale here but because I am researching I would ...
6
votes
1answer
129 views

Reproduction and defecation

In mammals and birds the external reproductive organs and waste removal organs see to be the same. Is this always the case with other animals such as insects etc...? Are there any good reasons for it? ...
6
votes
1answer
616 views

Mechanism of Tear Gas (chloropicrin/Trichloro methane)

Tear gas (CCl3NO2) makes people cry, and crying doesn't seem to be a simple procedure. There has to be a triggering process somewhere. Can someone explain its mechanism / how it works?
6
votes
2answers
184 views

Are there nerves in the umbilical cord?

I have always imagined that cutting the umbilical cord after birth might be painful. But I have always been confused about who would feel the pain and why. It occurred to me that the mother or the ...
6
votes
1answer
166 views

Do people with congenital analgesia feel cold?

There are a few diseases that cause an insensitivity to pain. This question asks about the relationship between the cold and pain, which got me thinking: Is shivering a response driven by the ...