Human body

Table of Contents

related humanbodybiology

[B] [2018-07-08] In novice strength trainers, the muscle's ability to generate force is most strongly limited by nerve’s ability to sustain a high-frequency signal humanbody

[2018-07-01] nervous system humanbody


  • sympathetic – short term survival (githg or flight) response
  • parasympathetic – long term syrvival 'background' activities

[2018-07-21] Leptin inhibits hunger. in obesity, decreased sensitive to leptin occurs so you're unable to detect hunger [wiki] humanbody

[2018-07-18] TLDR: serotonin and dopamine are just transmitters and have MANY functions humanbodyhormones

Some neurotransmitters almost always do one thing: GABA is almost always an inhibitor of some kind, kind of like how a green wire is almost always a ground. Glutamate is always an excitatory neurotransmitter, kind of like black wires are almost always the "hot" wire in home electrical wiring.
dopamine is more like a purple wire. used for various purposes. Saying dopamine is a reward neurotransmitter is like saying purple wires are for right-rear car speakers.

neither serotonin or dopamine are generally considered hormones
"Hormone" typically refers to a substance like cortisol or testosterone; substances that are released from one (or more) body areas and then just flow around in the bloodstream, acting at a bunch of different places in the body.
D and S, unlike hormones, aren't released into the whole body, but rather released by one cell (usually nerve) in very small amount and then immediately act on another nearby cell before being broken down or sucked back up by the neuron that released them.

- Dopamine:

serves many, many different functions in different parts of the brain. some of brain circuits use dopamine as a way of communicating between neurons and some of them don't. For example, there's one pathway in the brain that uses dopamine release to control lactation. But nobody calls dopamine "the lactation chemical." Part of the reason for that is that those circuits use MANY, MANY other neurotransmitter chemicals besides dopamine.

There IS a pathway in the brain that is involved in controlling attention and reward (or something LIKE reward; this is a controversial subject in neuroscience) that involves dopamine. But that pathway also involves glutamate, GABA, acetylcholine, and many other neurotransmitters and signalling molecules.

TL;DR: Dopamine is ONE of the neurotransmitters involved in what MIGHT be a reward pathway, but there are MANY other neurotransmitters involved in that pathway and MANY other unrelated pathways that dopamine is involved in. You should not call dopamine a "reward neurotransmitter" any more than you should say that all keys are used to start cars. It's wrong.

- Serotonin:

Serotonin-related drugs DO produce improvements in depressed patients SOMETIMES (and there is considerable evidence that this may be mostly a placebo effect), but this doesn't prove that depression is caused by a serotonin imbalance any more than the fact that aspirin helps headaches proves that headaches are caused by a lack of aspirin.
involved in a LOT of different functions: Serotonin is involved in regulating blood pressure, memory, vomiting, movement of food through the gut, bone density, pain, and yes, sometimes mood.
And again, there are MANY more neurotransmitters involved in regulating mood than serotonin. I would say it's even MORE wrong to call serotonin a "mood neurotransmitter" than it is to call dopamine a "reward neurotransmitter."
Neurotransmitters are NEVER connected to just one function, and most functions are NEVER controlled by just one neurotransmitter. The fact that people talk about dopamine in connection with reward and serotonin in connection with mood is PURELY due to dime-store psychology and misleading antidepressant commercials.

[2017-07-27] blood types humanbody

Apes and old-world monkeys have ABO blood types like us.
Other animals have blood types, but not the same ones as us. There are thirteen different dog blood types, but cats are categorised as A, B, or AB. Not the same as human A and B.

[2018-08-17] humanbody

sleep is a state required for nervous system plasticity. In other words, in order for the nervous system to grow and change, there must be down time of active behavior.

resynthesis of brain glycogen

higher amounts of prolactin makes women cry more often than men humanbody

implications: women might not be as sad as you think; men might be sad without you realizing

[2017-04-18] Cold shower burns fat? humanbody

The time you spent sitting in a cold shower will not burn as much energy as high-intensity physical activity performed for the same length of time.
TL:DR: Yes, it works. But it's extremely inefficient and your time is better spent on high-intensity physical activity if fat-loss is your goal. /r/fitness and /r/loseit are your friends.

right, only brown adipose tissue produces heat (it contains many more mitochondria to do work)
But there isn't that much of it really. reserves are stored in white adipose tissue

[2015-03-05] How morning after pills work? humanbody

Progestin? Birth control pills

[2015-03-05] Do men have significant hormonal cycles? humanbodyhormones

[2018-04-11] Why we have hangovers? humanbodyalcohol

acetaldehyde humanbodyalcohol

Part of it may be attributed to acetaldehyde but there is clearly more to it. The liver enzyme alcohol dehydrogenase 1 (ADH1) produces acetaldehyde from ethanol, and aldehyde dehydrogenase 2 (ALDH2) makes acetate from that, so the aldehyde does not exist for a long time, and is rather responsible for short-term illnesses.

ADH and diuresis humanbodyalcohol

Hangover severity is proportional to antidiuretic hormone concentration (46). Alcohol inhibits the effect of antidiuretic hormone on the kidneys, thereby inducing diuresis that is out of proportion to the volume of fluid ingested. As blood alcohol concentration decreases and dehydration persists, the serum level of antidiuretic hormone increases, maintaining water retention in dehydrated patients with hangover. In our clinical experience, hydration attenuates but does not completely relieve hangover symptoms.

cytokines humanbodyalcohol

The constellation of hangover symptoms (nausea, headache, diarrhea) resembles that seen in conditions related to dysregulated cytokine pathways (for example, in viral infections and after administration of interferon-alpha). Alcohol alters cytokine production through a thromboxane pathway. Levels of thromboxane B2 are elevated during experimentally induced alcohol hangover (42), and the administration of tolfenamic acid, a prostaglandin inhibitor, at the time of alcohol consumption has a small prophylactic effect in reducing hangover severity (9).

further substances humanbodyalcohol

Congeners, the byproducts of individual alcohol preparations (which are found primarily in brandy, wine, tequila, whiskey, and other dark liquors), increase the frequency and severity of hangover (24, 39, 40). Clear liquors, such as rum, vodka, and gin, tend to cause hangover less frequently.
So there are factors that aren't even identified exactly, and these could fit the mixing of drinks observation.

[2015-06-19] impact of radiation humanbody

Gamma rays excite electrons and eject them from the atom, causing ionization
Ionization breaks chemical bonds, and produces new.

Ionizes water, producing harmful free radicals H+, OH-

In general, the radiation sensitivity of a tissue is:

proportional to the rate of proliferation of its cells
inversely proportional to the degree of cell differentiation
For example, the following tissues and organs are listed from most radiosensitive to least radiosensitive:

Most Sensitive: Blood-forming organs
Reproductive organs
Bone and teeth
Least sensitive: Nervous system

This also means that a developing embryo is most sensitive to radiation during the early stages of differentiation, and an embryo/fetus is more sensitive to radiation exposure in the first trimester than in later trimesters

[2018-07-02] Fat soluble vitamins are stockpiled in the body in fatty tissue and the liver humanbodymetabolism

[2018-09-04] What happens to veins when an arm or leg gets amputated? (x-post from AskReddit) /r/askscience humanbody

The blood in your arteries enters capillaries(about the diameter of one red blood cell). The blood leaves the capillaries and is absorbed into venules that carry the blood into veins back to your heart. Think of it as a highway system. Your vein is the highway and the venules are the 'on ramps'. After surgery the vein is simply cut off and shut after the point of amputation. This doesn't stop the vein from collecting blood through the venules closer than your forearm.

[2018-09-04] When a human limb is amputated, how does the circulatory system redirect blood flow? /r/askscience humanbody

This was asked a few months ago, here's my answer:

>Yes, blood vessels reorganize themselves to ensure healthy blood flow to tissues. The process is called vascular remodeling and it begins almost immediately through a variety of mechanisms. Larger scale vessels change their diameter quickly using vasomotor responses, while smaller vessels undergo longer-term diameter changes in response to blood flow rates, oxygen demands, and other biological growth factors. However, there is still a lot we don't know about how blood vessels self-organize and it is a very hot area of research. In addition to wound healing, it has huge implications in tumor research because new cancer drugs can target vessel formation in tumors, essentially cutting off blood flow.

I would also like to add that new blood vessels can sprout off from the remaining vessels through a process known as angiogenesis. These new vessels can fuse back onto existing vessels, creating new network connections.

TODO [C] Tweet from Massimo (@Rainmaker1973) humanbodyviz

CREATED: [2019-08-13]
Massimo (@Rainmaker1973) Tweeted:
CGI animated graphic of the human heart, sectioned, with motions and timing synced with the Wiggers diagram. The section shows the opened ventricles contracting once per heartbeat, or once per each cardiac cycle (link:

[2020-12-20] Muscular Homeostasis | Anatomy and Physiology I humanbody

Skeletal muscles contribute to maintaining temperature homeostasis in the body by generating heat. Muscle contraction requires energy and produces heat as a byproduct of metabolism. All types of muscle produce heat, but because of the large amount of skeletal muscle present in the body, skeletal muscle contributes most greatly to heat production. This is very noticeable during exercise, when sustained muscle movement causes body temperature to rise.
In cases of extreme cold, shivering produces random skeletal muscle contractions to generate heat as part of the negative feedback mechanism of maintaining body temperature.

[2020-12-20] What Causes Sore Muscles? | Why Am I So Sore? humanbodyexercise

Aching muscles after a workout, otherwise known as delayed onset muscle soreness (DOMS), are due to micro-tears in your muscles that occur when you put stress on them, says Schoenfeld. Usually, you’ll begin to feel sore 24 to 48 hours after a workout—that’s how long it takes for your body to produce inflammation as a result of that injury, which is responsible for your muscle pain.

[2019-03-27] If darker skin colors absorb more heat energy and have a higher resistance to cancer then why did humans who live in snowy/colder climates develop fare skin? /r/askscience humanbody

[C] [2018-08-04] nkukushkin humanbody

. В результате этого в митохондриях нервных клеток Потапа некуда стало девать электроны, вырабатываемые при переработке питательных веществ и в норме сбрасываемые на кислород. Из-за этого основной путь переработки питательных веществ – окислительное фосфорилирование – застрял. Переработка пошла через другой, в десять-пятнадцать раз менее эффективный бескислородный процесс с выработкой молочной кислоты. Молочная кислота стала повреждать мозг Потапа, но куда серьёзнее его повредила другая проблема: недостаток энергии, добытой из питательных веществ. Нервным клеткам энергия нужна постоянно для поддержания заряда на мембране.

[2019-08-27] Baby born inside of amniotic sac. Also called an en caul birth, it occurs approximately 1 in every 80,000 births. Various famous figures in history are alleged to have been born this wa. /r/interestingasfuck humanbody

[2019-12-13] Why isn't blood attracted to magnets? /r/biology humanbodyblood

There is an educational video on Youtube which shows blood being repelled by a powerful magnet. 
The video is called: "Monster magnet meets blood"

[2019-12-13] Why isn't blood attracted to magnets? /r/biology humanbodyblood

Because it's one iron atom surrounded by a huge hydrogen and carbon matrix... the iron's electrons are dedicated to bonds, and not free to be magnetized.

[C] [2019-06-20] What's the most amazing thing the human body does that people have no idea about? /r/AskReddit humanbody

Look at an object on the wall across the room.  Now keep looking at it while you move your head back and forth, up and down.  Your eyes stay pointed at that spot.  Not hard to do, is it?
For that to happen, you brain needs to calculate the direction and rate of change your head is moving in 3 dimensional space and then send corresponding signals to the muscles in your eyes to **exactly** counter match the rotation and speed in order to keep them pointed at that spot.  And not only that, the muscles that have to be moved (and the rate at which they move) are different for *each* eye, since if you turn your head quickly right, you R eye contracts the muscles on the nose side to compensate, and the L eye contracts the muscles on the temple side.
It's an absolutely amazing, fine-tuned process involving incredible spacial calculations and microsecond signaling and adjusting that we do all the time and take completely for granted.

why do people black out on alcohol? humanbodyalcohol

CREATED: [2021-01-14]
We sort of know: alcohol makes neurons in the hippocampus stop talking to each other properly, which prevents the formation (encoding) of longer-term memory, which means that by the next morning, you don't remember what happened the previous night.
Rapidly increasing BAC (like binge-drinking) seems to cause more memory problems. Some people are simply more susceptible to alcohol-related memory impairment than others, and no one is entirely sure why that is.
Be careful with black out-level drinking. Short-term, it can put you in dangerous situations. Long-term, it may not be very good for your brain's health.

All that really happens is that your GABA receptors stop working, which causes you to be unable to encode new memories. While you're in the moment, you're as much in control as you were five minutes before, you'll just suddenly have great difficulty remembering the conversation you're in, and you'll often find yourself getting tunnel vision. You can walk yourself home, you can brush your teeth, take a shower; hell, even play a video game for a few hours. You just won't remember it in the morning.
The reason blacking out is considered to be scary is that you could have done more-or-less anything during that time, since drinking reduces inhibitions.

[B] [2018-07-17] about 7-10% of fat can be converted to glucose humanbodymetabolism

This is because triglyceride is made up of one 3-carbon glycerol molecule and three 16- or 18-carbon fatty acids. The glycerol (3/51-to-57 = 5.2–5.9%) can be converted to glucose in the liver by gluconeogenesis (after conversion to dihydroxyacetone phosphate).

process: humanbodymetabolism

The FA chains are cleaved off of the glycerol backbone. The 3 FA chains are oxidized and you get some Acetyl-CoA to use in the Krebs cycle. You also are left with the glycerol backbone. It was the 3 carbon chain holding these FAs together. Remember pyruvate from before? Well, it's also a 3 carbon molecule and glycerol is converted to pyruvate, which then is converted to Acetyl-CoA. A perfect design! Now you can put all that Acetyl-CoA into the Krebs cycle.

[C] [2018-07-07] glucose vs fructose humanbodymetabolism

Another thing to consider: Not all types of carbohydrates end up the same way when digested. Glucose, as said earlier, can be stored in the form of glycogen in the body. Fructose, on the other hand, cannot do the same and is directly converted into fat if it cannot be used immediately. This means that if you eat a lot of carbohydrates in the form of fructose (white sugar, corn syrup, fruits) many of it will be converted into fat without any opportunity to be used. This is also why since low-fat food arrived everywhere, the obesity epidemic started. Fat has been replaced by sugar and corn syrup, and voilà. Same result, but since it says "no fat" on the product we think we can eat all we want. Hope I have been some help.

hm, or is it?

This is a common misconception. Fructose and glucose are both broken down to the same triose sugars and can both therefore enter the gluconeogenic pathway.
De Novo lipogenesis from carbs is fairly uncommon because it is metabolically ludicrously inefficient. You have to massively overfeed on carbs.

[B] [2021-03-14] > Each time you view something new, your brain gives a hit of dopamine. Oh… | Hacker News humanbody

Oh dear god. That is not how dopamine works. Dopamine is a chemical that your brain secretes when you are trying to get something, not once you get it - so when you're hungry, for example, you'll have higher dopamine levels.
Then when you eat, they go back down. The actual sensation of higher dopamine levels is stress and anxiousness - it actually doesn't feel good at all.

[C] [2021-03-14] I'm kind of shocked no one seems to have researched the authors of Your Brain on… | Hacker News humanbody

I'm kind of shocked no one seems to have researched the authors of Your Brain on Porn. While I think their stuff is interesting, I am very skeptical, especially considering their past work and their general views on sexuality. I read their Cupid's Poison Arrow book and it's not just porn they think is bad for you, it's orgasm in general. Their book teachers a method of orgasm-free sex and sexuality that is supposed to improve the longevity of your relationship. I don't really think Marnia or Gary have much qualifications in the science of sex or addiction, but they wrap up their arguments in scientific-sounding language. I am familiar with such things because I grew up Evangelical and they used the same type of arguments for their views on sexuality.

For a better perspective on issues relating to having an addictive personality, I recommend The Compass of Pleasure by neuroscientist David J. Linden for understanding reward-theory that dominates the psychology research now.

I don't doubt that some people have legitimate problems worsened by pornography use, but I would say that they would benefit highly from seeing a therapist rather than following some of these more shaky theories. I've known young men who are thinking they have issues with dopamine, when in reality many of them have issues with shame, anxiety, and communication. I do believe porn addicts exist, but I think it is worth getting diagnosed by a professional who can rule out other causes.

[C] [2020-03-19] When you have an illness (flu, throat infection etc) does your immune system weaken since it is busy fighting or actually improves since it is active? Or none of the above? Thank you /r/askscience humanbodyimmunity

I see some people saying yes and this is not a supported statement. Your immune system is activated upon interaction with a pathogen or with the recognition of a non-self antigen. This means your entire immune system begins to rapidly expand and proliferate. At the beginning of an infection this is dominated by your innate immune system (complement, macrophages, dendritic cells, neutrophils, natural killer cells, ect). At this same time this is occuring T and B cells are interacting with antigen presenting cells in your lymphatic system. When a T or B cell interacts with its cognate antigen (the antigen that corresponds to its T-cell receptor or B-cell receptor) it undergoes a proliferative burst. B cells will create plasma cells and undergo somatic hyper-mutation. At this point the adaptive response overtakes the innate response and remains the primary response until; containment, clearance or host death.
So no, your immune system is not weakened as a whole. What does happen is the survival cytokines and other survival signals are sequestered by cells who have an advantage, such as the T or B cells who recognize the pathogen. HOWEVER other cells are still around and if you had your immune system recognize multiple antigens at a given time, they would all receive the same signal and compete for resources.
Interestingly, this is why the theory that you can develop an allergy during an immune response exist and why some researchers are looking into using broad immune system activating events to combat cancers.
TLDR; When fighting off an infection your entire immune system goes into overdrive. Once the adaptive immune system is fully operational it sequesters energy from other parts because it has so many things pushing its activation.
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