This tag is for questions about the general biological features of human beings (as opposed to the biology of non-humans).

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7
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2answers
152 views

How was the guided daily amount (GDA) calculated?

We are constantly shown nutritional information on food packaging stating this food contains "x" amount of your guided daily amount. A linked to the values is here. How were these values calculated? ...
5
votes
3answers
525 views

When to measure resting heart rate and blood pressure for following day-to-day trend?

I'd like monitor my resting heart rate and blood pressure to see how they are affected by regular cardiovascular training and other events in life. When should I take the measurements in order to ...
13
votes
2answers
13k views

Possible? When a pregnant woman suffers an organ damage, fetus would send stem cells to the damage organ to help repair it?

I am quite sure that there is this blood-placental barrier between the mother and the baby so that nothing (except a type of antibody) can pass through it. But I remember reading somewhere that when ...
7
votes
3answers
271 views

Weighing 2 vertical halves of the human body

I had this thought while bathing: Assume a perfectly developed physical human body and anatomy in terms of size, dimensions and proportions. In theory, if I cut the body vertically into two exact ...
15
votes
3answers
928 views

Do probiotics survive digestion?

Pretty much this. I've been wondering if any of the yogourt and other "health" foods containing living probiotic cultures survive digestion to populate our intestines? If so, is there peer-reviewed ...
21
votes
3answers
3k views

What actually happens when my leg 'falls asleep'?

Most people have experienced the temporary loss of feeling and tingling in their leg resulting from sitting in an abnormal position for a short while. Usually you get a loss of feeling in your leg ...
19
votes
2answers
660 views

Why is rabies incurable?

I'm still not sure about the mechanics that lead to rabies being incurable. I know that it can be treated before any symptoms show up, but why is it that once symptoms show the person is a dead man ...
10
votes
3answers
836 views

Why do people say that trans fatty acids are bad for your health?

I've heard from several sources that trans FAs are bad for you and their consumption will lead to cardiac problems, and that they are indigestible. But I also learned from biochemistry that they are ...
14
votes
3answers
1k views

What causes a 'stuffy' or 'runny' nose when you have a cold?

When humans get the common cold, a common symptom is a stuffy or runny nose. Is that the body's immune response or is that the virus's doing?
12
votes
2answers
473 views

Is the 'fluttering feeling' when under stress neurological or physical?

I'm sure that everyone is familiar with the sensation commonly known as "butterflies in the stomach". It is commonly experienced during periods of anxiety or stress (e.g. before high stakes job ...
8
votes
2answers
986 views

Why are goosebumps so ineffective at keeping us warm?

If the purpose of "goosebumps" is to keep us warm, why is it so ineffective? Or are the changes subtle, but important?
8
votes
2answers
346 views

Where do the bacteria within the vagina originate from?

I understand that it's feasible the bacteria within the gastrointestinal tract originate from the food we eat and air we breath, but where does this population of microbes originate from?
15
votes
5answers
7k views

Origin, or source, of rhesus negative in human blood

This is my first post here, so please be gentle. I recently learned that I have Rh- blood (I'm A-), and was idly looking into blood types on Wikipedia. I was surprised to find that relatively few ...
8
votes
1answer
518 views

What conditions are necessary for HPL (human pancreatic lipase) to activate?

What conditions are necessary for human pancreatic lipase to activate? Is there an optimal temperature or pH? How quickly does it take effect?
13
votes
2answers
630 views

Does testosterone increase female sexual behavior?

According to my lecture notes testosterone generally increases sexual behavior. Given that it's generally thought to be the male hormone I'm not quite sure whether they mean that it also increases ...
4
votes
2answers
130 views

Does age affect the frequency of flatus?

Is there any relation between age and the frequency of flatus? I often have this feeling that older people f*** more often than younger ones. Is this feeling scientifically correct?
13
votes
3answers
2k views

How does the human body metabolize gasoline?

A Chinese man has been drinking gasoline to relieve his pain for 25 years. How does the human body metabolize gasoline? Also, what are the side-affects to gasoline?
4
votes
1answer
2k views

What is the role of acetylcholine in blood pressure regulation?

What is the role of acetylcholine in the cardiac cycle and in blood pressure regulation?
6
votes
1answer
129 views

What is the number of cells in a line of a fingerprint?

I have been reading a little about the size of cells and was curious as to how small they really were. I have noticed that on my finger, the outlines of the fingerprint are made up of thin lines. In ...
7
votes
1answer
305 views

What causes light to be brighter in the corner of the eyes?

I have noticed when in a dark room light and color seem to be brighter and more intense in the corner of my eyes. For example the light that comes from my digital clock seems like a dark pink when I ...
9
votes
2answers
400 views

Does arterial blood always flow away from the heart?

Is there a negative net flow of blood in human arteries at any point of the cardiac cycle? I realise that blood flow can be turbulent, e.g. in the aorta or around stenotic arteries, but then the ...
12
votes
2answers
5k views

Do white Australians have a distinct look?

Background I've heard from many people working in tourism or similar industries that, white Australians can be recognized as Australian solely by their facial features. Being Australian myself I've ...
8
votes
1answer
1k views

What influences the timing of human bowel movements in the morning?

I'm trying to understand if the timing of human bowel movements in the morning is associated with the circadian rhythm, and can thus be used to make predictions about the circadian rhythm. What ...
4
votes
1answer
308 views

Human sleep cycles and dream times, what influences the timing and intensity? Sleep history included

I'm doing sleep and dreams research and have developed an iPhone application to help me track my bedtime, rise time, sleep onset and also mark dreams. The app also monitors overall activity overnight ...
8
votes
1answer
432 views

Which human body hormonal systems exhibit 24 hour diurnal cyclical activity?

I'm researching the possible connection between the dream content and the activity of various organ or hormonal systems within the human body. I'm looking for information on biological cycles within ...
6
votes
1answer
584 views

What forms the human amniotic sac?

I am trying to understand the formation of embryonic disc for human and chick so the following question is related to here about formation of embryonic disc. I had thought that the amniotic sac forms ...
5
votes
3answers
2k views

Fetal development, gastrulation and embryonic disc

I am completely confused by the images circulating on the internet of human gastrulation. First, lets see how it happens in deuterostomes. This image depicts the process: (image is from Wikipedia) ...
5
votes
1answer
816 views

Do eye muscles relax when you close your eyes?

I wonder whether the eyes muscle relax when you close them. Common knowledge told us the eyes muscle get tense when you stare at nearby object. If you close your eyes, you eye lids have 0 distance ...
22
votes
2answers
8k views

What causes fingerprints to form and why is the pattern formed unique?

I've found research that suggests that the reason we develop fingerprints is because they aid us with feeling surfaces (Scheibert, et al. 2008) and not to increase friction and help with the gripping ...
14
votes
4answers
2k views

Can two humans with 44 chromosomes produce viable offspring?

It is known that there are very few individuals having 44 chromosomes, not the usual 46 chromosomes. One example is a male in China: the first article, the second article. The other is a female in ...
19
votes
3answers
23k views

Why do mammalian red blood cells lack a nucleus?

How did the red blood cell in humans get to lose its nucleus (and other organelles)? Does the bone marrow just not put the nucleus in, or is it stripped out at some stage in the construction of the ...
7
votes
2answers
6k views

Mitosis in human body

I've heard that stomach lining has the fastest reproducing cells and the brain has the slowest. Where in the human body does mitosis occur and at what rates do these cell reproduce? Is there a chart ...
7
votes
1answer
520 views

Why do people look different after a long sleep?

What happens during a long sleep that makes people look odd when they have just woken up? Why doesn't the same phenomenon occur in the case of a person who lies down for an extended period of time, ...
4
votes
1answer
2k views

What are differences between formation of embryonic disc in chick and mammal embryo?

Exam question which got lowest average points in my university: 1/5 average. No markscheme available so my attempt below. I assume that embryonic disk prefers to germ disk such that Formation prefers ...
9
votes
1answer
78 views

Are homozygous carriers of the CCR5-Δ32 allele fully immune to all known strains of HIV?

Or is there documented evidence of even one homozygous carrier contracting HIV and staying infected?
7
votes
2answers
270 views

What is the eye muscle status when you stare at distant view through a glass wall?

The book said when you look at object close to you, the eye muscles contract and vice versa. I wonder what will be the status of the eye muscles when I stare at distance view (such as a mountain) ...
7
votes
1answer
5k views

Does consuming sodium benzoate (preservative E211) cause problems during pregnancy?

There seems to be strong evidence to support the claim that sodium benzoate (E211) causes hyperactivity in young children, e.g. Bateman et al. (2004) and McCann et al. (2007). This leads me to ...
12
votes
1answer
4k views

Why does scar tissue change color?

I was wondering why, when you are cold, scar tissue turns bluish or purple while original skin stays the same color. The only thing I can think of, is that maybe scar tissue gets less circulation ...
7
votes
1answer
221 views

Does cooking ginger reduce its anti-nausea effect?

There seems to be strong evidence to support the hypothesis that eating ginger helps reduce nausea e.g. during pregnancy (e.g. Vutyavanich et al.). It seems that gingerol is the active ingredient in ...
7
votes
1answer
131 views

How exactly does long-term tension (over months) build up in the ligaments, tendons, muscles?

And is there any basis for believing that massage relieves that tension?
5
votes
1answer
121 views

What evidence gives clues to the physiological basis for conversion disorder?

Conversion disorder has a set of DSM diagnosis criteria, which, among other things, includes ruling out all neurological disease. However, as the media has shown us (and one could argue a biased ...
39
votes
4answers
8k views

How does the brain's energy consumption depend on mental activity?

What is the impact of mental activity on the energy consumption of the human brain? I am most interested in intellectually demanding tasks (e.g., chess matches, solving a puzzle, taking a difficult ...
9
votes
2answers
2k views

Why would taking antibiotics increase stamina and energy?

I often hear that people who are taking antibiotics experience wild fluctuations between feeling full of energy and completely alert but soon after feeling impossibly fatigued and sick. Does this ...
10
votes
1answer
926 views

Is there a correlation between muscle fibers and body types?

I have been told the number of muscle fibers a particular muscle has varies from person to person. Unfortunately, the person who told me this did not know much more than this. Initial searching on the ...
5
votes
1answer
142 views

What are the constraints when growing an artificial brain?

Are there any experiments on growing artificial brains from brain tissue? What are the constraints? Will such tissue grown to the mass greater than that of human brain surpass it in intellect or it ...
6
votes
2answers
521 views

How are the gene sequences of individual sperm and egg cells “randomized”?

What I mean by "randomized" is, in the place where an egg cell or sperm cell is made, what is the mechanism by which each one is not made identically? Though I am a layman, I'm pretty sure that if the ...
10
votes
1answer
316 views

Can Naegleria fowleri enter through wounds into the bloodstream?

All the sources I've read said that Naegleria fowleri enters the brain through the nose. But lets say that someone had cuts on their arm or leg and they are swimming in water that is conducive to ...
12
votes
2answers
432 views

Could an “overactive” brain increase the chances of Alzheimer's Disease?

From Raichle ME. 2010. Two views of brain function. Trends in cognitive sciences 14: 180–90: Alzheimer’s disease (AD) is the most common cause of progressive cognitive decline and dementia in ...
18
votes
3answers
1k views

How and where, in the human brain, are memories stored?

Background I am a computer programmer who is fascinated by artificial intelligence and artificial neural networks, and I am becoming more curious about how biological neural networks work. Context ...
15
votes
3answers
400 views

Are human fetuses more likely to be male?

Question: From a physiological point of view, when sex is determined in a human fetus, is it equally likely to be male or female? Studies in this area typically measure age at birth, where the data ...