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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2
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0answers
62 views

How does estrogen influence collagen synthesis?

Through what mechanisms does estrogen interact with collagen synthesis? Especially in the context of elevated estrogen levels and genesis of purpura simplex .
2
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1answer
50 views

Why does uterus have to be prepared every month for fertilization?

I'm just curious why it has to happen every month when the uterus could have been prepared from the beginning and kept that way throughout life or till a certain point. But why make and break it every ...
6
votes
1answer
1k views

Name (and meaning of the absence) of the white semicircle at the base of the fingernail?

At the base of fingernail, there is a white semicircle (see on the first picture). But sometimes there isn't one. My questions are: what is this white semicircle on the fingernail, and what causes ...
-3
votes
1answer
64 views

Human Species of Males/Females [closed]

Why is it that when there is discussion about Race/Subspecies it is never about the genetic/physical differences between males and females. So every argument has been about physical and geographic ...
9
votes
1answer
573 views

What senses are active while sleeping?

During sleep, our body activity decreases. I am wondering on the extent of the lowering of this activity regarding our five senses. Clearly, the sense of touch is still very efficient since shaking a ...
5
votes
1answer
413 views

Why do we get 'bags under our eyes'?

Why do these circles form around the eyes if somebody is tired? And why does fatigue express itself around the eyes this way? Can I get eye bags very quickly in another way? ...
13
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2answers
2k views

Why I have to pee more often in low temperature? [closed]

I realised that I have to pee more often in winter or simply the temperature is low. Is there any scientific explanation, or just simply psychology?
3
votes
1answer
268 views

Why are sperm cells not attacked by the female immune system? [duplicate]

Whenever a foreign particle enters into someone's body, it is attacked by the white blood cells. I just want how it is that, when sperms enter the female body, they are not attacked by the the woman's ...
6
votes
2answers
65 views

SNPs and locations

I am new to reading raw DNA. When comparing two people's raw data, why does one person have a different SNP than the other, at the same location, on specific chromosome? But on a different chromosome ...
8
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2answers
2k views

Why don't breast enlargements leave any marks of surgery on breasts?

If we get stitches, we get marks left on the skin, but there are no marks for breast enlargements. I saw a YouTube video about a breast enlargement wherein a doctor makes a cut. Where does the cut ...
4
votes
1answer
96 views

Length of sleep time

Why do we wake up after 6-8 hours of sleep ? Why don't we sleep for lets say 20-30 hours ? What mechanism is it that controls when to wake us up and how does it determine the moment that we should ...
4
votes
1answer
115 views

What kinds of cells does human saliva contain?

I have heard that our saliva contains cells. What cell types can be found in human saliva?
0
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0answers
15 views

Swellings with Variegated consistency

I am interested in knowing the names of all swellings with variegated consistency. I have come across the following: Malignant swelling with partial necrosis Caseated tuberculous lymph nodes ...
1
vote
1answer
36 views

Dehydration from caffeine, alcohol and other

Tea, Coffee, Beer, Coke etc… I wonder if the benefit from amount of fluid we get from them is bigger or smaller then the handicap of dehydration. In other words it is worth to drink them if we want ...
5
votes
3answers
193 views

How does menstruation proceed during one period?

I'm simplifying things here: A. Does a woman bleed constantly, like a drop every 10 minutes? Two hours without pad or tampon and your underwear is dirty? or B. Does a woman bleed suddenly a ...
3
votes
1answer
83 views

Dehydration by a tea, coffee, beer etc

For the long time I am trying to find out if the following is truth: They say that some beverages dehydrates. I heard that about tea (sometimes green, sometimes black, sometimes both), coffee, beer ...
1
vote
2answers
161 views

What are the differences between a benign tumor and swelling?

What are the differences between a benign tumor and an injury related swelling? And can swellings due to injury turn into a benign tumor?
3
votes
1answer
165 views

Are nutrients absorbed in human esophagus?

Following this question regarding absorption in human oral cavity (sadly not yet fully answered), I'm curious if any nutrient absorption occurs during the descent of food through the esophagus. And ...
9
votes
1answer
149 views

Can people with paralyzed eye muscles see?

As far as I am aware, the saccades of the eye are central to visual perception. If the eye is held still, the human stops seeing, even if light is reaching the retina and the visual pathway is intact. ...
2
votes
1answer
40 views

Is it possible to estimate how much variation in common phenotypes is predicted by genetics?

Phenotypes such as; skin color, eye color, nose shape, lip size, limb proportions, and skull shape. Im trying to find a source for this quote. "If you ask what percentage of your genes is reflected ...
-3
votes
1answer
61 views

Could we engineer humans to behave like insects? [closed]

First off, though complex, I'm assuming insects are at an earlier evolutionary stage than humans. That being said, could humans be genetically engineered to behave like insects? I'm not talking about ...
2
votes
1answer
32 views

Are there any generic (not dependent on symptoms) ways to find parasite infections?

Are there any generic ways to determine if a person is infected with a parasite? With "generic ways" I mean ways that do not rely on symptoms caused by a particular parasite. Also I am mainly ...
1
vote
1answer
105 views

Pituitary giants - is the fusing of growth plates dependent on amount of growth hormone in blood?

I wanted to ask a couple questions related to pituitary giants (people who are giants because of some anomaly, such as a tumor, in their pituitary gland). Some of these giants seem to keep growing ...
1
vote
1answer
51 views

What is the biological basis for tiredness after eating? [duplicate]

I can sometimes feel quite drowsy after some "meals" (e.g. a cold cut & cheese sandwich with juice on the side) and less drowsy (or maybe less often) after others (such as a salad). This ...
3
votes
1answer
130 views

What’s the reason for isovolumic contraction and isovolumic relaxation?

During cardiac cycle, there are two periods in which the heart volume doesn’t change, but there is a change in tension/pressure. It takes about 0.25-0.35 second to achieve this change. I searched in ...
0
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0answers
24 views

Why after physical activity I see flickering concentric circles? [duplicate]

After prolonged hard physical exercise such as running uphill I sometimes experience rapidly vibrating black-and-white concentric circles for a few minutes, looking like a sinusoidal zone plate, small ...
0
votes
1answer
63 views

How much of the human body is processed sunlight?

So I believe (and correct me if I'm wrong--it's logic, not research) that the human body is pretty much all just processed sunlight based on the food chain. How much, if any, of the human body is ...
0
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1answer
108 views

Is it true that some organs “sleep” at certain times of the day and does this affect dieting or when to take medicine?

Is it true that some organs (such as the liver or the intestines) are less active at certain times of the day, regardless of whether the individual is awake or not?
3
votes
2answers
119 views

Why can't we defibrillate the heart within 1 minute after ventricular fibrillation by electroshock?

We mostly can defibrillate the heart before 1 min of ventricular fibrillation by electroshock.Then we often can't do defibrillate it with electroshock. What's the reason and What's the best way to ...
4
votes
2answers
753 views

What effect does the Barr body have, in relation to female Turner syndrome?

Why do persons with Turner syndrome have developmental abnormalities, when normal XX-females do not, even though they only have 1 active X chromosome? From what I know, one X-chromosome is ...
3
votes
1answer
45 views

Why do the size of the phase 1 notch vary among cardiac cells?

The size of the phase 1 notch varies among cardiac cells. It is prominent in myocytes in the epicardial and midmyocardial regions of the left ventricular wall and in ventricular Purkinje fibers. ...
4
votes
1answer
148 views

How can we measure cardiac output?

I could find a way which could find it by body oxygen consumption and there is another way to measure it by injecting drugs — measuring cardiac output by the so-called “indicator dilution method,” a ...
8
votes
2answers
388 views

What is the human ear's temporal resolution?

What is the smallest sound duration that the human can hear? In other words, what is the lower duration limit for a sound to be translated into electrical signals by the ear? Suppose the human ear ...
4
votes
1answer
69 views

What happens when someone is stung by a jellyfish?

What happens in the human body when someone is stung by a jellyfish; namely a box jelly. Judging by what I have heard about the stings I'm guessing that they involve a neurotoxin. But what is ...
2
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0answers
48 views

Why does human hair grow and behave differently depending on its location?

Why does human hair behave differently depending on its location? For instance, head hair grows to an indefinite length, but eyebrows maintain a particular length and appearance. Head hair and ...
7
votes
2answers
269 views

Why do we have more male infant born?

For every 104 male babies,we have 100 female babies and there is a Statistics which is more reliable (we have 997 female infant born per 1000 male infant born). what's the reason? why do we have male ...
1
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0answers
25 views

Is this description of etiology of celiac disease correct?

There is a detailed and, to my inexpert eyes, plausible description of the etiology of celiac disease and other autoimmune disorders posted here: http://no-gluten.org/CeliacDisease.htm Is it is at ...
2
votes
1answer
34 views

Is there any disadvantage to having a really low adipocyte count in our times?

The key feature of adipocytes seems to be energy storage. Today humans in Western countries don't have to hunger and have therefore less need to store energy in fat cells. Do adipocytes have ...
0
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0answers
16 views

Retinal eccentricity to colour sensitivity [duplicate]

Colour perception goes out to 50 degrees but is the sensitivity to RGB. Question is it the same in the four quadrants of the retinal field? That is if the red colour sensitivity eg is 30 temporal ...
0
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0answers
54 views

If what we eat can be seen in our hair, then to what degree can our food affect the “look and feel” of our hair?

It looks like most things (or everything?) that we consume, whether it is a food, drink, or something we smoke (like e.g. some drug like marijuana) ends up in some amounts in our hair. If this is the ...
5
votes
1answer
154 views

Is there any scientific evidence that a human has ever grown a third set of teeth?

This is about the possibility (or lack thereof) for a person to re-grow a new "permanent tooth" or set of teeth, to replace the teeth that grew after their milk teeth fell out. I had earlier seen ...
4
votes
2answers
222 views

Why do skin and nail go blue in cyanosis?

I have learned that Cyanosis presents with blue skin and nails. What is the reason for the blue coloration of the skin and nails? Why wont the skin and nails turn another color in the visible spectrum ...
10
votes
1answer
245 views

Why doesn't HDL cause diseases like LDL? [duplicate]

LDL particles pose a risk for cardiovascular disease when they invade the endothelium and become oxidized, since the oxidized forms are more easily retained by the proteoglycans. A complex set of ...
0
votes
1answer
50 views

How is oxygen and carbon dioxide exchange mediated by hemoglobin? [closed]

Oxygen is transferred by hemoglobin from the lungs to tissues, while carbon dioxide is transferred by hemoglobin from tissues to lungs. How is this regulated bidirectional transfer mediated?
5
votes
2answers
2k views

Why do men have a higher hematocrit (red blood cell count) than women?

The hematocrit, also known as packed cell volume (PCV) or erythrocyte volume fraction (EVF), is the volume percentage (%) of red blood cells in blood. It is normally 45% for men and 40% for women. ...
13
votes
0answers
2k views

Why do we experience temperatures below 37 degrees Celsius as 'hot'? [duplicate]

We always prefer to be in 20-25° C, although our core temperature is about 37°? Why is our skin temperature lower than our core temperature?
7
votes
1answer
145 views

Can humans live without their right atrium?

The right atrium is one of four chambers (two atria and two ventricles) in the hearts of mammals (including humans) and archosaurs (which include birds and crocodilians). It receives deoxygenated ...
13
votes
3answers
2k views

Why does hair grow after trimming but remains at a constant length after a while?

Some hair especially body hair regrows after trimming but stops growing after a while. What is the mechanism behind control of hair growth and how is the length limit determined?
4
votes
2answers
259 views

What do biologists mean when they use the term “biological distance”?

Here is its usage. "there is sufficient genetic control to make nonmetric traits useful in anthropological work, and such variables have successfully assigned individuals from distinct geographic ...
9
votes
3answers
352 views

Why did humans become bipedal?

Somewhere in evolutionary history homo started walking upright and became bipedal. You hear these hypotheses that, by walking upright, they could see better across the grassy savannas to escape ...