100 votes
Accepted

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 ...
John's user avatar
  • 14.7k
55 votes
Accepted

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 ...
MattDMo's user avatar
  • 15.3k
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 ...
canadianer's user avatar
  • 17.7k
35 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 ...
hello_there_andy's user avatar
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 ...
Bryan Krause's user avatar
  • 45.7k
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 ...
kmm's user avatar
  • 12.3k
20 votes
Accepted

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 ...
Remi.b's user avatar
  • 68.1k
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 ...
kmm's user avatar
  • 12.3k
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 ...
theforestecologist's user avatar
13 votes
Accepted

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. ...
theforestecologist's user avatar
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 ...
theforestecologist's user avatar
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 ...
marsilt's user avatar
  • 131
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 ...
Remi.b's user avatar
  • 68.1k
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 ...
AlexDeLarge's user avatar
  • 2,868
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 ...
another 'Homo sapien''s user avatar
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). ...
cmungall's user avatar
  • 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 ...
et is's user avatar
  • 1,214
11 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 ...
anongoodnurse's user avatar
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 ...
Bilal's user avatar
  • 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

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 ...
Chimango Chisuwo's user avatar
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 ...
bandybabboon's user avatar
  • 10.4k
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 ...
Roland's user avatar
  • 5,705
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 ...
JM97's user avatar
  • 4,796
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, ...
JM97's user avatar
  • 4,796
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 ...
theforestecologist's user avatar
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 ...
theforestecologist's user avatar
8 votes
Accepted

Why the smell of sweat greatly varies across the body?

Sweat is actually odorless regardless of what type of sweat gland it comes from, of which there are two types - apocrine and eccrine. As suggested by canadianer, the odor comes from the mixture of ...
PreMedHopeful's user avatar
8 votes

Do women tend to have longer legs and shorter torsos than men?

We seem to have a preference for proportionally longer legs (see comment here for a good summary around that study). So when you are observing "pedestrians" they have probably tended to dress and ...
feetwet's user avatar
  • 795
8 votes
Accepted

Do breasts size depend solely on fat amounts?

You are asking two different, but related questions Does breast size depend solely on fat amounts? First, breasts are made up of skin, blood vessels, ducts, fibrous tissue, and fat. There is ...
De Novo's user avatar
  • 8,791

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