Questions tagged [human-anatomy]
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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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 ...
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What is the function of epidermal ridges on human fingers (that produce fingerprints)?
What function is served by the epidermal or capillary ridges on human fingers, the supposedly unique impressions of which are known as fingerprints?
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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 ...
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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 ...
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Why do we have two kidneys but one liver?
Both the liver and the kidneys are involved in "cleaning" our blood. But why we have one liver and two kidneys? I can just as well imagine that we have two livers and one kidney. Is this ...
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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 ...
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Why do we need red blood cells?
From what I know, the main function of red blood cells (RBCs) is hemoglobin transport. So, why do we need cells packed with hemoglobin: why can't it travel freely in the bloodstream?
My own thoughts ...
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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 ...
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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 ...
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What are the side-effects of long-term liquid breathing?
I just saw a recent Physics question that mentioned liquid breathing (which I had never heard of before) and I started to wonder about its long-term effects. Let's imagine a person underwent liquid ...
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Why do blood vessels in the eye not obstruct vision?
As light enters the eye, it reaches the photoreceptors at the "base" of the retina, which then pass that signal to the bipolar and ganglionic neurons -- the latter of which send the signal ...
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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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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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Why are the pulmonary vein and artery not like the rest of circulatory system?
I'm learning anatomy. What I learnt is that we have arteries that have oxygenated blood which appears red in color, and branch blood to arterioles to deliver blood to cells via capillaries from where ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 (...
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Do patella bones form in people born with the inability to walk?
The patella is a sesamoid bone that typically doesn't completely from and ossify until ~3-6 years of age (e.g., Source). My long-standing understanding (supported by a claim in Saladin's college A&...
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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 ...
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Human spine: Is the coccyx really fused?
Prologue: This post is about the adult (say, a 20 year old) human skeleton; I'm not particularly interested in infant skeletons.
The human spine has is composed of cervical, thoracic, lumbar, sacral ...
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Using anatomical terms for human organs and parts of plants
I know how to apply anatomical directional terms (e.g., dorsal/ventral, anterior/posterior, etc.) for animals as a whole (bipeds and quadrupeds).
Recently, I've been studying plant physiology, and I ...
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What is the standard deviation of adult human heights for males and females?
The wikipedia article on human height reports mean height for many different countries by sex but it does not report standard deviations.
What is the standard deviation of adult human heights within ...
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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?
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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 ...
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Are there certain symmetric-pair muscles that are slightly bigger and NOT due to handedness?
Ok, hear me out, I was just thinking about an article in Nature I read in the past titled "Scrotal asymmetry in man and in ancient sculpture"$^{\dagger}$ and more recently an entire medical textbook ...
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Why does the ring finger not move independently?
Why is it that we need to move little finger in order to move ring finger with it? For example, put your palm on a table and fold your middle finger inside. You won't be able to move your ring finger ...
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Dorsal vs Posterior and Ventral vs Anterior
From prior reading, I thought that Dorsal is the same as Posterior and Ventral is the same as Anterior. However, when I checked in google images for these anatomical terms for a horse (just to ...
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Anatomical Angle Made by the Fingers of an Extended Palm
Does the angle made by the fingers (excluding the thumb) of an extended palm (as shown in the figure below) have a name (such as the Lovibond or Cobb angle, for instance) ?
I have already checked ...
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What makes humans omnivores, and not herbivores?
Some vegans claim that humans are herbivores, not omnivores, and that we are not physiologically designed to eat meat (see here: http://www.peta.org/living/food/natural-human-diet/).
"According to ...
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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 ...
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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 ...
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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 ...
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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 ...
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Where can I find the list of all tendons in the human body?
https://www.healthcentral.com/article/aging-can-take-major-toll-on-womens-tendons (mirror) claims that:
There are about 4,000 tendons throughout the body.
This claim is echoed by a fair amount of ...
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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 ...
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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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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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Does the oxygen concentration equilibrate between red blood cells in the liver sinusoids?
In the sinusoids of the liver, venous blood from the hepatic portal system mixes with arterial blood from the hepatic arteries.
Do oxygen molecules move between oxygenated RBCs and non-oxygenated ...
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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 ...
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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
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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 ...
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Did human hairs actually evolve from scales?
What is the evolution of hairs? Did they evolve from scales?