100
votes
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Why do we have two kidneys but one liver?
Your organs can be grouped into two categories.
The digestive tract organs, which are singular.
These form from the endoderm.
The liver and pancreases are all direct outgrowths from the digestive ...
- 14.3k
55
votes
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Why are the pulmonary vein and artery not like the rest of circulatory system?
It is true that nearly all arteries carry oxygenated blood and nearly all veins carry de-oxygenated blood, but that is not what defines them. Arteries are blood vessels that carry blood away from the ...
- 15.2k
37
votes
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How did the cardiovascular system evolve?
While others have addressed the big picture aspects of your question, I think it would be useful to look at the specifics.
Have a look at the heart (or more accurately, the hearts) of the earthworm: ...
- 1,387
37
votes
What is the function of epidermal ridges on human fingers (that produce fingerprints)?
I found many plausible claims that fingerprints increase friction. However, the following article claims, at least under their experimental conditions, that fingerprints actually decrease friction ...
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34
votes
What is the function of epidermal ridges on human fingers (that produce fingerprints)?
To balance the debate, from a neutralist evolutionary perspective...
There does NOT have to be a direct selective pressure for a trait's contribution to an organism's expressed phenotype.
Three ...
- 3,577
30
votes
Why do blood vessels in the eye not obstruct vision?
Avoid the fovea
Figure 2 from the same paper shows the distribution relative to the fovea:
As you can see, it's pretty much devoid of this superficial vasculature, so anything you are directly ...
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23
votes
Where can I find the list of all tendons in the human body?
Your best bet is the Terminologia Anatomica, which is the international standard for anatomical terminology.
The 1998 edition is freely available. It lists only a few named tendons though, which is ...
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20
votes
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Could a man be proved positive for a pregnancy test?
Pregnancy test, just like any test, has some non-zero false positive rate. So yes, of course a test could be positive when a man pees on it.
Pregnancy tests work by detecting the presence of a ...
- 68k
15
votes
Accepted
Human spine: Is the coccyx really fused?
The wikipedia article links to two papers. The first article has data for 120 pain-free and 51 affected patients with data on the number of coccygeal segments in each. We can back-calculate a ...
- 12.2k
14
votes
Accepted
Using anatomical terms for human organs and parts of plants
First, for reference, see here for a discussion about the difference in directional terms between bipeds and quadrupeds as well as a fairly complete explanation of word meanings/etymology.
The ...
- 29.7k
13
votes
Why do blood vessels in the eye not obstruct vision?
You CAN see your blood vessels!
Following-up from Bryan Krause's answer:
Bryan mentioned that the blood vessels are typically not visible partially because they are unchanging (i.e., static). In ...
- 29.7k
13
votes
Why does 360 degree rotation not seemed to ever have evolved?
Actually there are propeller like features called flagellum (3) evolved on many organisms like plants, animal sperms (4), bacteria (1) and flagellates (2). There are known only one macroscopic form of ...
- 131
12
votes
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What is the function of the human eye white?
Short answer
The relative large surface area of the white sclera in humans has been linked to an enhanced ability to detect eye gaze.
Background
The white of the eye is caused by the sclera. Human ...
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12
votes
Accepted
Are males taller than females in humans?
Are males taller than females?
Best data I could find come from the Statistical Abstract of the United States (1999) > Section 3. Here is a table reporting the percentage of the male and female ...
- 68k
12
votes
How did the cardiovascular system evolve?
This kind of question was raised in a book called "Darwin's Black Box" by Michael Behe, who is a biochemistry professor in the U.S. - he calls this 'irreducible complexity' (IC). For example, the ...
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12
votes
What makes humans omnivores, and not herbivores?
As the answers given already point out, humans are generally considered omnivores that are able to use food sources available to them opportunistically. Apart from that, there actually is not much to ...
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12
votes
Accepted
Why does the ring finger not move independently?
The reason for this phenomenon is in both the muscular structure and neural connections of the little and the ring finger. Lets start with the following diagram:
As you see (click on the image to see ...
- 14.1k
12
votes
Where can I find the list of all tendons in the human body?
The FMA lists 705 tendons, but note that it includes separate terms for left and right instances. As @kmm says, many of these simply shadow the list of skeletal muscles (and is likely incomplete).
...
- 291
11
votes
What is the evolutionary reason behind the fragility of teeth?
The evolutionary biologist in me would argue that, on average, teeth are exactly as strong as they need to be. In other words, the fitness cost of producing and maintaining teeth is balanced with the ...
- 1,204
11
votes
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Dorsal vs Posterior and Ventral vs Anterior
Short Answer
This page on wikipedia gives a good synopsis of these concepts.
The confusion lies in the fact that many websites on anatomy discuss/describe/define these terms in relation to humans. ...
- 29.7k
11
votes
Accepted
How can we move our lips even though they don't have any bones?
Because of the Orbicularis oris muscle, it's a complex of muscles in the lips that encircles the mouth, It forms the greater part of the substance of the lips, lying between the skin and the mucus ...
- 761
10
votes
Accepted
Can defibrillation be done with a car battery?
In general, no.
Car batteries are designed to provide a large amount of amperage, to turn the starter with a high amount of torque via an electric motor. Generally this is done at 12 or 24 volts.
...
10
votes
Accepted
What is the rest state for eyelids - Open or Closed?
This depends to some extent on how you define "resting state" (it matters).
Innervation of the eye occurs in the brainstem and upper spinal column, so is, like most brainstem functions, on autopilot ...
- 24.7k
10
votes
Why hand washing causes skin to dry?
I will assume the hand washing you speak of involves soap.
The human skin (which also covers hands) is a complex organ with an underlying system of glands.
One of these is the exocrine sebaceous ...
- 557
9
votes
Can any other animal choke on food?
There are different kinds of choking on food. All non-gilled animals also choke when they fall in the water. Drowning is choking. insects asphyxiate and fish asphyxiate in air but technically insects ...
- 10.3k
9
votes
Accepted
Why are the human knees and elbows bent in an opposite direction
I am no expert on comparative anatomy, but I will give this a shot. Please edit if you know more about this subject!
The configuration of opposing elbow and knee joints is a feature we humans share ...
- 5,675
9
votes
Accepted
Why do doctors use a new thread for each stitch?
Using a single thread for a suture also known as continuous stitching has a major con that it has higher risk of failing if the suture is cut in just one place. So it is generally avoided eventhough ...
- 4,786
9
votes
Accepted
Can you tell if a corpse was male or female by only examining its skull?
According to textbook of forensic medicine and toxicology by Ks Narayan reddy:
Qualitative differences are:
Male mandible has everted ramus, but female have inverted ramus.
Males have chin U shaped, ...
- 4,786
8
votes
Why is the opposite of plantar flexion called "dorsiflexion"?
Although the other 2 answers are accurate and well thought out, I just wanted to answer this with a bit different focused response.
Two things to note:
In general, one should think of flexion as ...
- 29.7k
8
votes
Accepted
When is an anatomic entity named "laterale" vs. "lateralis"?
This is actually much more of a lesson in Latin linguistics/grammar.
The root, Lateral, comes ultimately from latus meaning “side" or "flank” in Latin. [Source].
By adding one of these ...
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