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8

There are two types of sweat glands: (1) eccrine sweat glands and (2) apocrine sweat glands. Eccrine sweat glands are present from birth in humans and secrete sweat that is mostly water and functions in evaporative cooling. Apocrine sweat glands are found in the armpits and groin regions and become active in humans at puberty (although the distribution ...


7

You are correct in that the neurons themselves do not sense pain. However, the brain contains layers of coverings, blood vessels, the scalp and some muscles. All of these other structures have pain receptors. The coverings of the brain are called meninges and consist of the dura, arachnoid and pia. The dura in particular has a lot of pain receptors and may ...


5

It's probably around 7 cm for men and 6 cm for women. The Evolution of Adult Height in Europe, which is a source for some of the statistics reported on that Wikipedia page, gives averages, standard deviations, and sample sizes for both sexes across 10 european countries (and across a number of different age cohorts). Taking their numbers for men and women ...


5

There is no direct link between the capillaries in the sinuses and the ear. The Eustachian tubes drain the middle ear (between the eardrum and the inner ear) into the nasopharynx, the part of the throat that is just behind the nose. The para-nasal sinuses drain into the nasal passages themselves at different points. The sinuses and middle ear constantly ...


4

Mechanical force can compress neurons and cause action potentials as you probably experienced in the form of hitting the funny bone. Strong enough acceleration of the brain tissue may be causing massive excitation of neurons as indicated by animal EEG study. It suggests that the loss of consciousness is due to generalized epileptic seizure. However, it is ...


3

The main functional reason is we need to be able to grip things with our hands (and feet, which are also hairless), and hair would interfere with that. Physiologically, the epidermis in these parts of the body is very thick and highly keratinized, and when combined with the thick underlaying layer of dermis, this results in skin that does not support the ...


3

Hands are complicated and the genetic machinery behind their shape doubly so. It's easier to figure out worm segments first, and then work up from there. An egg has head/tail information encoded in it even before fertilization: see here You can imagine the first or second cell division would give a 'head' cell with higher concentration of head polarity ...


3

The fingers and toes (for example) ARE at lower temperatures than the interior of the torso. It's why it's so easy to get frostbite on the extremities. As for temperature regulation of the testes, you have to also consider that humans evolved without clothes...i.e. The testes just "hang out" and get lots of airflow, as opposed to modern times, when they are ...


3

I would write my answer in a comment but it doesn't fit! I guess there are two main solutions: 1) From the science of antropometry you might find some clues of the probability that you have of growing taller. For example, if your body (hairs and stuff) already look like an adult body, then you would probably not grow much more. See @MCM's answer who gives ...


3

From the Smithsonian website: Humans are the only mammal that cannot breathe and swallow at the same time, and we are the only species that can choke on its own food. The reason? The lowering of the voice box in our throats (during infancy) enables us to create the enormous range of sounds used in producing language; but this lowering of the voice box comes ...


3

In adult/pediatric humans, no they don't. A good figure to get everyone on the same page was made by Cleaver & Melton: It is important to note that: In fact, endothelial diversity is reflected by vessel size-specific, organ-specific and even age-specific differences. (1) Developing blood vessels in the fetus can be a bit of a different story, ...


2

How humans evolved to have head / beard hair that continues to grow longer than other animals is a topic that many anthropologists & biologists are still not sure about & there is no general consensus as to "why" yet. The three main views that I am aware of however are : 1) Evolution of the "Aquatic Ape." (Ingram, 2000: Morgan 1997; 1982) ...


2

From a quick look at the paper @ChinmayKanchi links to (Palmer, 2004) it seems that: All living vertebrates possess a heart that is conspicuously asymmetrical and normally displaced toward the left (Fishman & Chien, 1997). So the heart orientation seems to be evolutionary conserved in vertebrates (as are many fundamental traits), and no specific ...


2

Going on the abstract of a study by J.P. Pessan, et al., fluoride intake, as well as "the fact that toenails are less prone to environmental contamination," constitutes a lesser need for growth in toenails than that in fingernails. Also, fluorine being a crucial component in maintaining the solidity of bones, the body may redirect more fluorine that is ...


2

Check out the muscle relaxant article on Wikipedia, it's pretty straight forward. In short, there are two main types: Neuromuscular blockers, than act at the junction between the neuron and the muscle; and spasmolytics/antispasmodics, which (mainly) act on the central nervous system to reduce excitation or increase inhibition. Most of the ones I've heard ...


2

The main reason why the anatomic position is supinated is because the radius and ulna are crossed when the arm is pronated and parallel when the arm is supinated. It doesn't have anything to do with the resting state of the arm, it's just the easiest way to arrange the bones neatly for description and analysis.


2

People of the same height can easily have different leg lengths. Think western women models - currently they are typically women with relatively long legs while ordinary people can easily have shorter legs for the same total height. There's even leg-to-body ration section in Body proportions Wikipedia article. This is why pedometers always require ...


2

First of all 'Testosterone' hormone controls the growth of hair on our body and also oil secretion. Depending up on the nature of a person's body, this hormone controls the growth of the hair. Why shaving facial hair leaves the skin dry ? First let me explain the reason behind the oiliness of the skin. Sebum is produced by the sebaceous glands and is a ...


2

The name of the instrument is ophthalmoscope. It is used to determine the health status of your retina. Retina is the one of the few places in the body where you can observe the blood vessels directly. The link also includes a picture of what your eye looks like from doctor's point of view.


2

Simpler answer (although I like Remi.b's): Probably. If you want to know for sure go to a doctor and have them look at your Epiphyseal Plates in your long bones (Femur, Tibula, Fibula). If they've fused, you won't grow anymore. If they're still distinct then you'll continue to grow until they fuse. For males that can happen as late as early-20's. ...


2

The boney component of the anatomical orbit*strong text* (in lay terms the eye socket) is the area bordered by the zygomatic, frontal, maxilla, sphenoid, palatine, lacrimal and ethmoid bones. The use of the word orbit (red) in orbitofrontal cortex refers to the positioning of this part of the frontal cortex (green) being directly behind the orbit: ...


2

I'm pretty sure this doesn't exist. If it did, that would be awesome. The following is 100% pure speculation with nothing to back this up at all (as a disclaimer). Phosphorus-31 (the stable isotope) is NMR active, which means that you could theoretically use an MRI machine to visualize phosphorus. A quick google search shows scientists attempting to use ...


2

Inhalation and exhalation happen sequentially as Herman stated in the comments. Yes, your general understanding of inhalation is correct. After the air gets into the lungs, the oxygen is diffused into the capillaries covering the alveoli. The now oxygenated blood travels back to the heart to be circulated throughout the body. As this blood enters ...


2

First of all: No, there is no connection between these two incidents, correlation does not imply a causation. Cold and flu viruses affect the respiratory system and the infection route goes via it. A cut is a local wound, which does not affect the respiratory tract. Then: Recovering from an infection is a task for the immune system (its both, the innate and ...


2

Humans do not have the ability to move their outer ear in response to sound. Many animals can do that, and use it to determine the source of the sound waves. Thus, human outer ears are equipped with many "hills and valleys". It does not provide amplification (because the waves can lose their energy bouncing around the ridges), but rather gives the brain more ...


2

The optic nerve fibers cross inside the optic chiasm sharing the same shell: The crossing fibers go ones between others, like on this classical picture -


1

I can't say anything for sure (and, with questions like this, it's rare that anyone can), but my guess would be that human nails grow constantly for the same reason as the (analogous) claws of most mammals do: to keep them from accumulating damage. Your bones, if they suffer mild to moderate damage, are capable of healing through the concerted action of ...


1

It didn't have to benefit them, evolution has no intent and not all traits are advantageous. Not every thing we have in our bodies is there "for a reason", some things are just there, others evolved, and some are vestigial (inherited from our ancestors). A whale can move his tail up-down only because he's a mammal and can't ever be anything else, while fish ...


1

We use central vision for a lot more things today than in the past. Peripheral vision is most important in navigation, so those who lose their central field retain the ability to navigate around objects. It is important that this is fast and sensitive in the dark as well as light. It isn't important for it to be in colour; this would mean it would be less ...


1

This question is for Doctor Frankenstein! I guess the answer would depend on what you would accept to consider being a human. Does it still need to be able to make simple calculation in order to be a human? Yes, because otherwise we would have lost some functions. But then you may askā€¦ Does it need to have big enough hands in order to fulfill the social ...



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