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23

Humans can, to some extent, be scaled: While most humans are two meters tall; the human body essentially works throughout the entire range from around a meter to around two and a half meters, although you tend to run into problems at the extremes. However, outside of that range you run into the tyranny of the square-cube law: As you scale a creature (or, ...


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

As @WYSIWYG pointed, muscular atrophy is the main cause for height decrease. A spine injury leads to neural impairment and paresis / paralysis. This affects directly muscular trophism. It also limits physical activity, this being another favoring factor for muscular atrophy and overweight issues [1]. Association of bone degenerative processes (osteoporosis, ...


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 ...


5

When you bend your fingers, they all arrive at the same height. I would tend to think that their lengths differ when you keep them straight because they need to have similar length when you bend them to grasp something. And I guess that there is some optimal length (when bended) for fingers to grasp things. It is nothing but a quick hypothesis. But it ...


5

Flexion: the movement that decreases the angle between two parts [1]. Examples: clenching the hand into fist, sitting down. Contraction: the property of muscle to generate tension when actin and myosin filaments are crossing. There are a few types of contractions. The isometric contraction is when the muscle generates tension but its length doesn't change ...


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 ...


4

Orbitofrontal cortex: the area of the cerebral cortex located at the base of the frontal lobes above the orbits (or eye sockets), involved especially in social and emotional behaviour.


3

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 ...


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

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

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 ...


3

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) ...


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, ...


3

Cortisol produced from the zona fasciculata of the adrenal cortex is directly caused by stress. According to http://en.wikipedia.org/wiki/Cortisol Cortisol stimulates gastric-acid secretion. Cortisol's only direct effect on the hydrogen ion excretion of the kidneys is to stimulate the excretion of ammonium ions by deactivating the renal glutaminase ...


3

Maintenance of Polymorphism and Mutation Load There are many possible reasons why some amount of deleterious alleles are maintained in the population. One of which is the mutation-selection-drift balance. In short: Because mutations always occur, there is continually an input of deleterious mutations in populations genome resulting in some fitness decay ...


3

Remi.b and Potterbond007 have put forward excellent answers. Would like to add something.. One of the reasons that Myopia (near sightedness) happens is because of use of eye in work like reading, which requires working with close objects. I don't think there was much working with close objects in the past. So very few people with myopia might have been ...


3

With nearly 40,000 years of natural selection on eyesight, prior to the invention of eye glasses, there needs to be a better explanation than the effects of 'modern' technology. There are two likely reasons for the persistence of "poor" eyesight in humans. First, humans are social animals and live in groups. Within groups there is frequently a division of ...


3

The liver does quite a lot of "housekeeping". It is responsible for a lot of energy metabolism: Gluconeogenesis (the synthesis of glucose), Glycogenolysis (the breakdown of glycogen into glucose), Glycogenesis (the synthesis of glycogen from glucose). It is important for protein degradation as well as for amino acid synthesis, as well as in the lipid ...


3

This looks like a misinterpretation. Because collarbone is the only horizontal long bone of the human body [1], it is the first to fracture when falling on the shoulder. Its fracture can affect many structures: The muscles involved in clavicle fractures include the deltoid, trapezius, subclavius, sternocleidomastoid, sternohyoid and pectoralis major ...


2

Myoepithelial cell contraction initiates glandular release from most exocrine glands developed from the ectoderm. These are the cells that exist in the glandular epithelium. At the distal end of the glanduar coil, an isotonic plasma filtrate gets actively transported into its lumen. As you move down the coil, close to where it connects to the duct, ...


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

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

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. ...



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