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Questions tagged [human-physiology]

For questions on the biochemical, physical, and mechanical functioning of humans in good health including their organs and cells.

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Why do children not have the Acid Mantle?

Post puberty humans begin to secrete a substance called Sebum which changes the neutral PH of our skin from ~7 to 4.5-5.5. This has that advantage of serving as a protective line against pathogens and ...
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What happens to apetite hormones like ghrelin and leptin when a person in coma?

Don't coma individuals feel hungry? If so, how does the brain senses this condition (as coma is caused by neural death or damage) and switches off gene expression of ghrelin and leptin. Is there any ...
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Does variation in human gut length vary predictably with diet of ancestors?

Background: Numerous online searches, textbooks and other sources seem to pin the average length of the human gut from mouth to anus (oroanal) between about 5-10m in length. To pick a reputable ...
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Empty room, Room full with stuffs & Auditory adaptation to reflection of sounds

Background When a room is full with stuffs like furniture, electronic utilities, books etc. it's hard to hear reflections of sounds made by us (talking, playing an instrument, sound from falling ...
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What is the average volume of the human Psychic tear? (“emotional tear”)

My goal is to find out the volume of the average human "emotional tear" (Psychic tear - sadness, happiness), specifically when crying. I found a lot of information about Basal tears (constant ...
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What's the ratio of saturated to unsaturated fatty acids in human cell membrane?

It's well established that the fluidity of a cell is largely dependent upon the ratio of saturated to unsaturated fatty acids that exist within the membrane, but, what exactly are the values for this ...
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237 views

Plant vs animal protein digestibility?

The protein scoring methodologies ( https://en.wikipedia.org/wiki/Protein_Digestibility_Corrected_Amino_Acid_Score) rate plant proteins of a lower quality than animal proteins. Now I can understand ...
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Pee Shiver: Any reliable research about this phenomenon?

I came across 2 webpages about the science of pee shiver. Link 1 Link 2 I wonder if there any reliable scientific research about this phenomenon. The 2 webpages I have hyperlinked attribute this to ...
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Physiological effects of electrical shocks on human body depending on the energy

When discussing safety of electricity, one usually considers a constant DC or AC current with constant amplitude over a longer time. It is easy to find tables in books or in the web which lists ...
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270 views

What is the lifespan of Skeletal Muscle Cells?

I have read that skeletal muscle cells cannot multiply and are generally not created after early development. However, I have also read that they have a "lifespan" of 10-15 years. Could this lifespan ...
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Changes in spongy urethra during tumescence

How does the columnar cells of spongy urethra expand during tumescence(erection of penis)? If we assume that the urethra has the length, long enough to sustain tumescence without expansion of cells, ...
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Sensing weather conditions through bodily reactions (e.g. dry hands, arthritic pains)

Two fairly known examples of the effect of certain weather conditions on the body are dry hands due to decreased air humidity around us (more commonly in the winter, as described here), and flaring of ...
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Why are adults so suceptible to dizziness?

I have a child and she, like pretty much all the others it seems, loves spinny rides in the park. Adults often can't stand them. In fact, I recall going from loving to hating dizziness over the space ...
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Coagulation of blood in small intestine due to trypsin

Trypsin is secreted in the small intestine to convert proteins into dipeptides i.e. to carry out digestion of proteins. However, it is also a coagulating agent which coagulates blood by hydrolysing ...
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Why is there a structural difference between the bicuspid and tricuspid valve?

There are three cusps in the tricuspid valve and only two in the bicuspid valve? Why is there such a structural difference? Does it have anything to do with that there is oxygenated blood on the left ...
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How do we sneeze?

When a stimulus triggers the sneezing pathway, known as the trigenimal nerve network, how do the droplets from a sneeze get created within the nose? What affects the size of these droplets?
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What is the evolutionary advantage of getting hard nipples when being aroused? Why can they even be stimulated sexually?

I try to understand the evolutionary advantages of the body reactions of nipples and penises/vaginas. I'm confused, because I can explain the evolutionary advantage in a logical & consistent way ...
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Why do I have super vision in purely red light?

I installed some RGBW led strips in my apartment recently.. by some I mean everything is now lit by led strips and there isn't a single light bulb left. One thing I've noticed over the last few days ...
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Why does the ova remain viable for only a day after ovulation?

The ova remains viable for approximately 24 hrs after ovulation to be fertilised by a sperm. ...chances of becoming pregnant increase dramatically if you have sex during the 5 days before ovulation ...
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Role of neuraminidase in preventing polyspermy in humans

Neuraminidase is a hydrolytic enzyme present in the acrosome of human sperm. It removes neuraminic acid (salic acid) from glycoproteins. I have read in a book that due to this reason it (the enzyme) ...
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221 views

Sex and human's sexual urge.

Why is it necessary for humans to feel pleasure while having sex? Why is it that other animals don't need to experience it? Is it evolutionary ? Why do we mate for pleasure when it's so energy wasting/...
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Does the humeroradial joint move medially/laterally?

The humeroradial joint is a ball-and-socket joint that, if unrestricted, would allow for movement around all possible axes. However (as succinctly stated from Wikipedia): the annular ligament, by ...
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Where can I find a list of medical conditions and their incidence rates?

Where can I find a list of diseases and their incidence rates? I'm giving a presentation on Long QT Syndrome, which affects 1 in 2000 people, or 50 per 100,000. I'm trying to find other, more well-...
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Portal Systems in Humans

I was reading about nephrons in my physiology book when i came across this- The efferent arterioles and peritubular capillaries technically constitute a portal system But according to Wikipedia, ...
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Why does rapid decompression make you lose useful conciousness so fast?

I was watching Smarter Every Day's episode on hypoxia, and it had an interesting chart that suggested that at 35kft, you have less than 10 seconds of useful consciousness. This number seemed low, and ...
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How to tell if something is an organ or apparatus?

An apparatus is defined as Physiology. a group of structurally different organs working together in the performance of a particular function. An organ is defined as: Biology. a grouping of ...
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Pressure produced by blowing with mouth

I need some figures on the pressure humans are capable blowing with their mouth with zero flow. I only need very approximate figures. I'm guessing around 500mm of water? I haven't got a tube handy to ...
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Why do workouts cause your muscles to feel heavy?

I know that muscle activity causes your muscles to build up lactic acid. Is this the specific reason that your muscles begin to feel heavy? How does this relate to the healing or inflammation process ...
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In oscillometric blood pressure measurement, why do we assume that highest oscillations correspond with mean arterial pressure?

As far as I've seen, the point on the oscillometric curve where there are greatest oscillations represents the mean arterial pressure (MAP). My question is - why? What is the logic behind this ...
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Contracting mouth muscles as reaction to taking in specific food items

When eating very specific food items, especially confectionery like (salty) liquorice, (it feels as if) the muscles of my mouth contract, right when it hits my tongue. Does anyone know why this ...
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Why do I feel nauseous at the sight of blood, despite not being afraid of it?

Every time I ask google this question, all it spits at me is info on blood phobias ^-^; basically, I've always been hugely interested in morbid stuff, but I noticed that I always feel sick when ...
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does being battered build muscle?

My crude understanding of how people normally go about building muscle is something like this following 2 step process: 1) a person can lift weights (for example), which tears muscle and stimulates ...
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Once neurotransmitters bind to its receptors, how does the post synaptic neuron “know” when to start a new action potential?

My textbook seems to gloss over this subject. Once the post-synaptic receptors are activated, do they cause particular ion channels to open, letting positive charge into the cell and inching the ...
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Why do humans lose subcutaneous fat from the extremities with age?

Why does fat tissue die and shrink on the hands, knees, and lower legs of most people as they age, even when they are overweight? In most people, their bone definition becomes much more visible around ...
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How does the stomach differentiate between liquids and solids to initiate churning?

Or maybe it doesn't at all. Can the stomach tell the difference between liquids and solids and change its churning process accordingly despite that it has no nerves? Because liquids don't need to be ...
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How to obtain normalised ECG given ECG readings across lead 1, 2, and 3?

I saw this youtube video on ECG readings and cardiac dipole vector locus of the heart across the three leads. Posting screenshots from it: My question is how to obtain the graph (2nd image) from the ...
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How do (commensal and mutualist) microorganisms colonize the seminal vesicles?

Human's seminal fluid has it's own microbiome (Javurek et al. 2016). How do species of this microbiome (bacteria and eukaryotes) colonize the seminal vesicles? It is possible that different species ...
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effect of arterial vasocontriction on the pressure in arteries

if experimentally one induces smooth muscle contraction on an artery and cause it to constrict, keeping the cardiac output same and also the arteriolar resistance(total peripheral resistance) the same ...
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108 views

Contribution of major nutrients to energy in the human body

What is the contribution of the major nutrients -- glucose, fat and protein -- to the human body's energy requirements, in normal conditions? For some tissues, the fuel preference is known ...
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Reference for most up to date sport physiology

I currently have Exercise Physiology Nutrition Energy And Human Performance, 7th Edition, 2012, McArdle et al. as my reference book for Exercise physiology. However, based on a question I ...
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What are the absolute facial features which features sexual dimorphism in humans?

Apart from beard and moustache, is there any facial feature that would help to distinguish between men and women? It is said that men have square, rectangular or oblong face and women have oval,...
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146 views

More *total* oxygen absorbed by breathing fast or slow?

I have heard that human lungs capture/absorb/process more oxygen by breathing slower. A) Is the above true? B) If so, if my primary concern was absorbing the most total oxygen (not most efficient), ...
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How is the Force of Contraction Applied to the Tendons by the Muscle's Individual Fibers?

Image and question have been updated for clarity! The image above is a side view of a semi-transparent skeletal muscle. The dark red lines represent individual fibers, the blue lines represent ...
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What is the lifespan of a human skeletal muscle cell (such as in the biceps)?

I have read that most human skeletal muscles (such as those in the biceps) cannot multiply after development (except for exceptional situations of severe damage that involve satellite cells) and that ...
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604 views

Fatty acid oxidation in adrenal medulla?

Why adrenal medulla can not utilise fatty acids for generation of energy? What could be the benefit for not having ability to use fatty acids? Refrence 1 Refrence 2
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What makes delayed onset muscle soreness stop occurring?

If someone lifts weights or takes a long jog after not doing it for a while, they can experience delayed onset muscle soreness (DOMS). However, when they return to the same exercise days afterwards, ...
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Thyroid transplanted to the abdomen

This question was posed in our endocrinology class, however I have no idea how to answer it: The thyroid gland of a 5-year old boy is transplanted from its normal position in the neck to the ...
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630 views

What makes the hepatic portal vein unique?

What makes the hepatic portal vein unique?, is it because it begins and ends with capillaries or because it carries digested food.
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How did we get self-aware?

Imagine being under a lot of stone age people and you are the only one who thinks something like "Hey I am a human being, and now I am thinking about this and that and maybe I change myself to become ...
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Why do I drop my pen in a drowsy lecture?

I know that there is loss of muscle tone during REM sleep. Is this loss in muscle tone the reason I generally drop my pen in a sleepy lecture? But we were taught that sleep has 4 stages and REM sleep ...