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Movement of high precision is possible for us humans because of the systematic layout of the motor neurons and their associated muscle units. Muscle contraction is an ascending activity as motors units are recruited in an ascending order for any desired movement; this means the units initially activated are resistant to fatigue but they do not produce a lot ...


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Probably, you can find this article (link to PDF) useful - I placed an excerpt, the following part in the PDF itself explains the theories. Also, in PubMed you can find a lot of explanations, for example (cited 225 times):


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Summary: A fall from "any height" may be survivable, depending on what you hit, but with an expectation of severe injuries. A water impact at terminal velocity will in all likelyhood result in immediate death. The Serbian Flight attendant Vesna Vulović holds the Guiness World Record for surviving a fall without a parchute with an estimated fall height ...


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The endothelial cells in small blood vessels take in more glucose even if insulin level is high (insulin level increases as a feedback reaction in type II diabetes or after treatment in type I diabetes), because they don't have insulin receptors. Thus they form surface glycoproteins which causes the basement membrane to become thicker yet less strong. This ...


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According to an article in Vision Research Volume 50 issue 2 : "The face’s vertical distance between the eyes and the mouth is approximately 36% of its length, and the horizontal distance between the eyes is approximately 46% of the face’s width." The article can be found at: http://www.sciencedirect.com/science/article/pii/S0042698909005045


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This is quite common. It is most likely dried rheum (also know by slang terms such as "sleep", "eye boogers", "eye crusties", etc.). Rheum is the result of dried mucus, tears (and the salt and minerals therein), as well as dead blood and skin cells. Essentially it is all the stuff that’s normally in your eye that eventually dries up making the contents ...


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At sea level, where atmospheric pressure is 1 atm and oxygen is about 21% the partial pressure of oxygen is enough to saturate hemoglobin. The lowest tolerable pressure of air is about 0.47 atm (475 millibars of atmospheric pressure) - recorded at 5950m altitude. At about 0.35 atm (less than 356 millibars at around 8000m) life is impossible. Pulmonary and ...


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One of the most used surgical technique is Roux en-Y where the small intestine is divided approximately 40-50 cm below the lower stomach outlet and is re-arranged into a Y-configuration. The portion of intestine (jejunum) from the upper stomach is called the "Roux limb". It has a total length of 80 - 150 cm. So the Roux en-Y technique "bypasses" only the ...


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Small or relatively small amounts of the antigen can cause an allergy, when you have IgE antibodies which fit to this antigen. They will then cause a local immune reaction and cause the secretion of histamine. For the desensitation therapy large amounts of antigen are given (which is not without risk). The mechanism behind this therapy is not completely ...


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In the context of evolution, the only "purpose" that a thing can serve is the role it plays in the process of reproduction, selection and mutation. So, "what purpose do feet serve"? Naively: the formation of part of the human body as feet serves to increase the likelihood of the survival and reproduction of humans, by supporting the way we move and stand. ...


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That all depends on the perspective from which you view the question. For example, from the perspective of a human being the purpose of human existence may be to make more humans. From the perspective of a herd of goats the purpose for human existence is for the humans to bring food and water, care for kids, shovel out the barn, talk nicely to them, scratch ...


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Our bodies work in cycles.. Circadian cycles that refer to our daily routines. We need sleep every night, eating at night affects us differently than if eating in the morning, etc... all because our bodies functions work in these 24 hour cycles... Now, beside the circadian cycles, our bodies also have circaceptan (or 7 day) rythms. For example, our immune ...


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Purpose requires a sentient being to have intent. There is no biological reason to suppose there is any purposeful intent behind life. If you hold otherwise, perhaps inquire of the fellow or lady or other you suppose is responsible. Just because a child can give an answer to a question doesn't mean that the answer is accurate, or that the question truly ...


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I will start with a quote from François Jacob, a French geneticist: The sole ambition of a bacterium is to make two bacteria. The same reasoning can be extended to all life on Earth, including humans. There is no purpose to human existence, in the same way that there is no purpose for life at all. Life is there because it can. It works, chemically, ...


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Actually, for your example it would be pretty easy to adapt. You just have a 25.5 hour day with 12.75 hours of day and 12.75 hours of night. Except you have a 4.25 hour period in the middle of the day where you stay inside and use lights (like in the evening for most people on Earth) and a 4.25 hour period at night where you make sure your eye mask is on. ...


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Humans have evolved for 24 hour days and our bodies would not adapt well to this short of sleep/wake cycles (whether or not they were born there, unless they have been there for many generations and have been able to evolve for the new time). Our bodies would still want to spend about the same amount of time sleeping and being awake. If we tried to adjust ...


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You may consider consulting the H2DB database. The database is quite new, so the number of heritability estimates is not very high at the moment (currently 225 estimates for human, 838 estimates in total), but it's a start. The database is described in a paper by Kaminuma et al.(2)


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I gather you are talking about anti-axiety drugs (anxiolytics). Benzodiazepines is one of the major groups of anxiolytics, and includes Xanax. Benzodiazepines are central nervous depressants, meaning that they reduce the activity of neurotransmitters in the brain. They do this by binding to the GABA-A receptor and enhancing the effect of the inhibitory ...


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There are regulatory mechanisms that may prevent moderate hypoglycemia to progress to a more severe state, however these mechanisms act before lack of conciousness sets in. The progression of hypoglycemia may depend on overall health and medical status and vary between healthy and diabetic persons, for example. Rosenthal et al. (1) write that The brain ...


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The dynamic-dominance hypothesis of handedness states that the essential factor that distinguishes dominant from nondominant arm performance is the facility governing the control of limb dynamics. Sainburg (1) writes that It should be noted that dominant arm advantages do not apply to all tasks, or all aspects of tasks. Healey et al. (1986) examined an ...


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In the developing embryo you have the three germ layers: Endoderm, mesoderm and ectoderm. From these layers all cell lineages of the body develop and can be traced back through their differentiation and migration to this three layers. Have a look on the image below, which illustrates this pretty nicely: The figure is part of this PhD thesis, which also ...


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What do you call an acquired trait? A trait acquired during the lifetime of the individual through its relationship with the environment (especially culture and traditions in humans)? If you take any population of living organisms, the variance of quantitative trait in this population, also called phenotypic variance and denoted $V_P$ is the result of the ...


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Look at this scheme - As I stated before, vitreous is 99% water and is not an organ itself, thus the "replacement of vitreous" is actually = 99% water re-production and the only organ inside the eye which can perform this - ciliary body. Consequently, if the vitreous was removed and replaced by gas or saline it will be replaced by aqueous which produced ...


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One example of an active selection pressure's effect on human phenotype is in areas where malaria is endemic, the prevalence of sickle cell anemia is higher. Sickle cell anemia is highly protective against malaria, and less people die from sickle cell than die from malaria, so you see a rise of sickle cell in the population. This is a small degree of ...


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First of all, I should quote the sentence from the MOST reliable ophthalmology sourcing in the world - American Academy of Ophthalmology: Section 11 - "Lens and Cataract" "The equatorial diameter of the unfixed human lens measures 2 mm at 12 weeks and 6 mm at 35 weeks. Both the growth and the maturation of lenticular fibers continue throughout life." The ...


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With age your eyeball, as everything else in your body with time, actually shrinks. In the developing stages I'm not sure when it reaches its full size though. So this is why elder often report far sightedness, when they need reading glasses. This is because the image no longer falls on the retina perfectly. When you are near sighted your eye is actually too ...


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The name used frequently for this phenomenon is "Post-lunch dip". "The post-lunch dip is a real phenomenon that can occur even when the individual has had no lunch and is unaware of the time of day. This dip has its roots in human biology, and may be linked to the size of the 12-hour harmonic in the circadian system. It is certainly exacerbated by a ...


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Source : Here Sugary foods lead to the production of insulin. Insulin stimulates cells to take up glucose from blood. It also mobilizes tryptophan to brain. Once in brain, tryptophan triggers formation of serotonin, a hormone involved in controlling mood and slumber.


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No. In fact the lens of the eye, which is nearly optically perfect in humans, does not change or grow after it is fully formed around week 26 of gestation. Interestingly this is why one of the cues for identifying young children is having small faces with large eyes. This also the case for puppies and cats and other animals, who are mostly cuter when they ...


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Background I'd like to start by saying that traits phenotypic (loosely speaking phenotypic mean morphological) traits evolve because their variance is correlated with some genetic variance. If most of the phenotypic variance is genetically coded, you'd expect that the trait will change through if different variant of the trait influence fitness (which is a ...


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To learn obstructive/restrictive lung diseases, I find it easiest to think in extremes at first, with vivid descriptions of why. So in obstructive lung diseases, like COPD/emphysema: Total volume increases because so many of the walls of the alveoli have been destroyed, they are like giant floppy bags instead of nice firm bubbles. There's more empty ...


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No, they are of course not there to cause allergies. It is thought (although not directly proven in human) that IgE is important to fight parasites and worms. They bind to antigens from the parasites, which leads to the secretion of histamines. This causes a local immune reaction (which also is a problem in allergies) which is helpful to fight the parasites. ...


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nuhcole is mostly correct. Airborne particles first pass through the nasal passageways and/or mouth and throat and many are caught, but those that enter the lungs become trapped in mucus. Your cilia act like a constant escalator, bringing up that mucus from your lungs 24/7. You reflexively swallow it without even realizing it. That is why when you are ...


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I wasn't sure when I first read this, but this is actually a very interesting question. Right now there seem to be two completely divorced lines of inquiry that researchers are pursuing with respect to the antimalarial drugs. One group of researchers is working on working out the mechanism by which say, chloroquine and its ilk bind to and interfere with ...


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Quoting a great biologist Peter Medawar : It is by no means difficult to imagine a genetic endowment which can favor young animals only at the expense of their elders; or rather at their own expense when they, themselves, grow old. A gene or combination of genes that promotes this state of affairs will, under certain numerically definable ...


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Your body knows it should die. Science discovered the details for us to understand. It is called apoptosis: pre-programmed cell death. The DNA in our cells is encoded to replicate only a certain number of times. Thus organs wear out as the cells are not being faithfully replaced (there are other factors to aging as well). [link] ...


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Human females have one of the worst chidbirth experiences. This is because of our extremely high cranial capacity compared to the apes. This had an obvious evolutionary advantage and made us what we are today. However this creates problems as the braincase has to pass the pelvic cavity during childbirth. The wider hips in women compensate for this but still ...


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Our respiratory tract is lined with cilia, which are hair-like structure that extend from the outside of the cells. They wave back and forth and act like brushes to catch dust particles before they enter the lungs. Some particles do get past these cilia and enter the lungs, however. The lungs will secrete mucus that collects the dust. You then cough up the ...


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That's an interesting question. And it is also a common misunderstanding of evolutionary processes. Thanks to @Chris comment, we know/can assume that high mortality rate is not a consequence of industrialization but has ever been before the era of modern medicine. Women don't let themselves die in order to improve the species. Those women that carry the ...


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In men, gout is associated with a higher risk of death from all causes. This would imply that their life expectancy is shorter. From a review by Kim et al. (1): Among men who did not have pre-existing coronary heart disease, the increased mortality risk is due primarily to an elevated risk of cardiovascular death, particularly from coronary heart ...


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I think CT is an abbreviation for connective tissue. Some examples of its use in that fashion: http://en.wikipedia.org/wiki/Connective_tissue http://www.vetmed.vt.edu/education/curriculum/vm8054/Labs/Lab5/Lab5.htm http://www.pitt.edu/~sshostak/biosci1450/hislec03.html


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Let us say this myopic patient has amplitude of accommodation of 8D. The patient accommodates 8D beyond far point, thus his near point is 1/6+8=0.07m (7.1cm). If we compare the case with emmetropic eye with accommodation amplitude of 8D, the near point is 1/8=0.12m (12cm). So, yes, near point of myopic person is different from an emmetropic one. But, you ...


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A Google search for "Huntingtons disease gene discovery" yielded this page at the Nature Education Scitable website. The following citations are provided regarding the molecular basis of HD: Huntingtin (HTT) was the first disease-associated gene to be molecularly mapped to a human chromosome (Gusella et al., 1983)2. Ten years later, scientists ...


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It was fascinating because Huntington himself described what we now call genetics before the field existed. Then to locate the gene scientists used essentially trial and error. They took enzymes that cut different parts of the DNA and looked at which of these were inherited. If it were inherited then there would be cuts made, otherwise not. Then they matched ...


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Here's an armchair evolutionary explanation. In nature, running water tends to be cold whereas tepid water tends to be lukewarm. And for reasons having nothing to do with temperature, running water tends to contain less harmful bacteria. Therefore, our ancestors who preferred to drink cold water over lukewarm had an evolutionary advantage over those who ...


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Yes a range of pain exists. This can be seen probably in your friends who all probably have a completely different threshold for pain. When doctors ask patients to rate their pain it's usually to establish a baseline so after treatment we can see if there's a decrease. The different thresholds have so many factors from general health to receptors to brain ...


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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 ...


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The main regulatory input into erythrocyte production is hypoxia. The response to elevated CO2 levels in the blood (hypercapnia) is mainly to increase ventilation (i.e. more and/or deeper breaths) so that the excess can be "blown off". I think that some carbon dioxide could pass into the bloodstream from the stomach since gases tend to be quite good at ...


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Answer: No. How should the CO$_2$ from you stomach get into your blood? And: Most of the CO$_2$ is removed (by burping) from the solution in your stomach anyway due to the conditions there.


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Question is two years old, and the answer is approx 20 yo, but I believe both are still pertinent: According to Jared Diamond on pg 12 of his Harper paper version (1993 -- but reissued in 2006) of The Third Chimpanzee, we replace intestinal lining epithelium every few days, urinary bladder lining every two months, and replace every red blood cell about every ...



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