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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How large are medullary thymic epithelial cells in volume?

I'm looking for a rough average volume of medullary thymic epithelial cells (mTECs/MECs) in humans and mice. It would also help to know how they differ in form (are they spherical, long stretched, ...
6
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1answer
79 views

Why is there no symmetry in pigmentation when comparing people north and south of the equator?

If you are at the equator and start moving north, the further you travel, the lighter the skin of the indigenous peoples. Considering that we live on a ball, why do we not find the same traveling ...
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0answers
18 views

Relationship between Human Sleep Cycles & Sunlight

What is the relationship between the human sleep cycle and Sunlight? Why do humans tend to sleep for longer hours during the night than the day. Since we rely on Artificial lighting during the night ...
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0answers
45 views

Are all the atoms in your body replaced with others over a 30 year period?

I was reading Creation - Life and How to Make It by Steve Grand. (This is the book that inspired Jeff Bezos to start the AWS initiative. ) In it he makes the following statement: Anyhow, by now I ...
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2answers
966 views

What is the cause that angina pectoris is felt in your left arm?

When someone has heart problems sometimes they feel pain in their left arm. But why is the left arm painfull?
2
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1answer
72 views

Fasting gastric pH versus normal gastric pH

I want to know if someone is fasting (no food or drink for a whole day) will they have a higher or lower pH than a person who is eating regularly? If so what is an estimate of both of those pH's in ...
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0answers
16 views

Is it true that our tooth enamel shows a 7 days rhythm?

Is it true that in fossil remains of the Turkana Boy a kind of growth rings are found in tooth enamel which have a rhythm of a week? This also appears to apply to other primates? If so what is the ...
0
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1answer
172 views

If human proteins are synthesized from only 20 different amino acids, then how can there be such variety of proteins in human cells?

I know that human proteins are synthesized using only 20 different amino acids. However, how can there be thousands of different proteins in human cells, if we only use 20 amino acids to make them?
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0answers
26 views

Are there biological safeguards to compensate for male primate infertility?

I'm trying to understand human sexual selection, and the following question has been on my mind for some time. I don't know the exact terminology to do a quality scholarly search on the subject. Are ...
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3answers
2k views

What would happen if one eats silica gel?

What happens if one actually does go about eating the beads in those "do-not-eat" packets?
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1answer
44 views

Why does the blood not clump and result in death?

In this question's accepted answer, it is said that the blood type will slowly change to that of the donor's. When the blood in the person is about 50% his own and 50% that of the donor's. i.e, 50% A ...
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0answers
20 views

What kind of cell has the most different receptors?

All hormones and neurotransmittors has their own receptor. Now some of the cells has a few different receptors but others has many sorts of receptors. So what are the most receptive cells? Are that ...
8
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1answer
132 views

Does our immune system react on all bacteria?

In our body we carry a lot of bacteria. Some of them are bad for our health, but others are beneficial. For example bacteria may protect us against other pathogenic bacteria. But is our immune ...
12
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2answers
182 views

Can viruses be toxic?

Bacteria can produce toxins like endotoxins and exotoxins. In diseases like cholera or tetanus they can harm infected people due to these toxins. Now, although viruses are much smaller and are ...
4
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1answer
124 views

Which literature/study/myth spurred the idea that urine is sterile?

There is a seemingly unfounded mantra that a person's urine is sterile who is not suffering from a UTI. So far I have found convincing evidence to the contrary; urine is not sterile. This poster ...
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0answers
38 views

When touch and pain are caused by heat/cold or pressure how are the nerve cells triggered?

I suppose that when your skin is smoothly touched by any cold/heat or pressure we feel that because our AB cells notice this due to a kind of change in the nerve cell. But when you touch something ...
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0answers
14 views

Does the change in eye color (melanin concentration) affect the iris pattern?

In cases of acquired heterochromia, is there a quantifiable change in the iris pattern; the clefts , furrows, etc. If yes, what changes are observed? And if no, are there any diseases or acquired ...
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0answers
21 views

Anaerobic nutrient expenditure

Doing some research into different forms of exercise and energy systems and I realized something odd about the way we talk about energy. When we eat, we take on macronutrients that are broken down ...
5
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1answer
60 views

If our skin is burned by the sun what causes the red color of the skin?

Mostly it is not a good sign we are burned because too much UV light has damaged our skin and increases skincancers. But the red color we get after a few ours, what is the exact cause of it and why ...
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1answer
83 views

Corpus luteum during the luteal phase and gonadotropins

Does the corpus luteum operate independently of the hypothalamic-hypophyseal-ovarian axis? I know that hCG sustains the corpus luteum in the absence of FSH and LH, but in an ovarian cycle where there ...
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1answer
37 views

the evolution of the human brain size [closed]

I was thinking, as I know, sometimes the process of producing DNA did not work well(correct me if I'm wrong), so it gives us some changes in the object we gonna ...
0
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1answer
166 views

Is an athlete's heart rate after exercise greater than a non-athlete [closed]

I was just wondering And if it is greater or lower how does this benefit an athlete Also what is the averaged number of heart beats per minute
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2answers
120 views

Are humans evolving since their first appearance? [duplicate]

Is the evolution a very prolonged progress, or are we going to witness further evolution of the human species? If so, in which direction? Are there any widely predicted changes for humans?
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4answers
16k views

How many genes do we share with our mother?

Somewhere I have read we share more than 99% of our genes with every other other person and 98% of our genes with chimpanzees. What does this mean? Don't we share 50% of our genes with our mother and ...
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1answer
29 views

Can specific B-cells be created in a lab? [closed]

Instead of creating protein sequences, could that stepped be skipped and just have B-cells created to manufacture a particular type of immunity?
5
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2answers
6k views

How do we know that everybody's DNA fingerprint is unique?

How do we know that everybody's DNA fingerprint is unique? I know, I know, everybody's DNA is unique. But when we do DNA fingerprinting, we're looking at very specific regions of high variability. ...
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1answer
5k views

Why do sneezes come in pairs or more?

I very rarely sneeze just once, usually there's two coming in a row, and I've noticed the same thing in other people and even in animals. Is there any reason for this?
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5answers
17k views

Why is cold water more refreshing than warm water?

Obviously, the temperature of water does not affect its chemical composition. At least not in the ranges we are likely to drink it in. Yet it is clearly far more pleasant and refreshing to drink cool ...
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1answer
45 views

Does a zygote express all genes?

If a zygote has all the cytoplasmic determinants and all the specific transcription factors, does that mean that all genes in the genome are expressed?
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0answers
70 views

What Would Happen To a Human Who Died In Space And Stayed There For a Prolonged Period of Time? [closed]

Last night I was watching a documentary regarding the Apollo space program, and it spoke about how Apollo 8 orbited the moon 10 times then came back to Earth. It said that while the ship was in orbit ...
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0answers
41 views

Is the zygote the only totipotent cell?

I’ve been told that the unfertilized egg contains cytoplasmic determinants (e.g. proteins, transcription factors, mRNAs) that are divided unevenly during the early stages of cell division in an embryo....
10
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1answer
13k views

Will a bone marrow transplant change one's blood type?

Will a bone marrow transplant change one's blood type? Or is the donor blood type matched with the person before transplant?
5
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0answers
136 views

What will happen when humans are injected with plant growth hormones

Will plant growth hormones (PGHs), (let us consider auxins for example) poison our body or not? I do realise that when you eat a shoot, auxins get digested and are less likely to be poisonous but when ...
5
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0answers
56 views

Are high sounds worse for your hearing than low sounds?

From about 80 dB it is possible to suffer loss hearing after a couple of hours. But does it make a difference what frequencies those sound waves are or is it just the volume of the sound in dB that ...
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2answers
81 views

Do babies conceived naturally or artificially have any differences in long-term health?

Are there any long-term differences in children conceived via artificial insemination or sexual intercourse, pending that the mother successfully delivers the child?
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2answers
2k views

Why do we like salt?

A few friends of mine told me that salt provides zero nutritional value to us, and in fact can harm our bodies. Now, these guys are medical students, and being an engineering student myself, I decided ...
7
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1answer
2k views

What is Mendelian Randomization, and how is it used to infer causality in epidemiology?

Studies of human traits and diseases are inherently confined to observational studies, known as epidemiological studies. This can make it very hard to determine what actually causes a particular ...
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2answers
2k views

Why is it advised that infants are fed mother's milk?

I have heard that mother's milk is preferred over other baby foods, because it contains immunoglobulines (secretory IgA), and other essential nutrients. But why is mother's milk so special? Any ...
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3answers
430 views

During starvation, does the human body do anything to prioritize which organs receive nutrients?

When food is scarce, the body slows its metabolic rate to conserve energy. Are there any other systems or processes that prioritize which organs receive nutrients?
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1answer
223 views

Why are plants classified in living things? [closed]

@Volunteers Beware that I am none of the biological magnates. Nor a philosopher. This is just a sign of curiosity. And, I want only an intuition that enables me to see the difference. As far as I ...
10
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3answers
1k views

What is the purpose of gluconeogenesis?

The gluconeogenesis pathway seems quite pointless to me. I don't understand why an organism would want to spend energy to create a molecule that can then be metabolized again for less energy? The ...
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0answers
39 views

Do both the Sperm and Egg must be at exactly 7.4 pH for fertilization?

I suddenly came across this article and it says that for human conception to occur both the sperm and egg must be at exactly 7.4 pH - not 7.0, nor 7.7 but 7.4. If conception depended on such exact ...
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0answers
39 views

Are all genes transcribed in differentiated cells?

My textbook tells me that it’s specific transcription factors that allow for a different set of genes to be expressed in different cells (differential gene expression). My book gives the example of ...
2
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1answer
82 views

When you take a very cold or hot bath how is that influencing your breath?

It looks like when you take a cold shower or bath your veins get smaller and when you take hot shower your veins get wider. But is that right and do you need to breath more in both cases because you ...
6
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1answer
61 views

Is Zika suspected of causing birth defects only if contracted during pregnancy?

There seems to be growing evidence that a recently spreading strain of Zika virus is in fact linked to microencephaly and other birth defects in newborns (see here, here, and here for examples). I ...
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2answers
237 views

Why did women historically have such a high mortality rate during birth?

Historically women had a relatively high chance of dying while giving birth. At first thought it seems to me that this would be a disadvantage for the species for the obvious reason that a dead ...
5
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1answer
106 views

Why is it always Sodium that we talk of in blood pressure?

Why is that we emphasize so much on sodium in blood pressure? I understand that it is a major extracellular ion, but, it also is tightly regulated. So when something is that tightly regulated, won't ...
5
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1answer
716 views

What is the function of the polar bodies produced during oogenesis?

Why are polar bodies produced during oogenesis in human females? I read that polar bodies are produced during meiosis so that the oogonium (or gamete mother cell) can be converted into a haploid ...
5
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1answer
178 views

Do humans have skin cells that trigger oxytocin release in the brain?

I was reading an article by Montgomery on the therapeutic effect of pets (Boston Globe, January 12, 2015), and I found this quote: All animals appear to have cells directly under the skin that ...
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0answers
39 views

Why are oral cells (or tissues) more heat resistant? [closed]

When we are having meals, such as enjoying hot pot and drinking hot water, we only have a sense of "warm" in our mouth, or even along the organs in alimentary canal. But when we put our fingers into ...