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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59
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5answers
1k views

Is there a reason why human eyesight and plants make use of the same wavelength of light?

The accepted range for the wavelengths of light that the human eye can detect is roughly between 400nm and 700nm. Is it a co-incidence that these wavelengths are identical to those in the ...
12
votes
2answers
177 views

Why is the microbial ecosystem of the gut so susceptible to disruption by pathogens?

From all accounts, it seems as if the Escherichia, Enterobacter, etc. that live and thrive in the human gut are pretty well entrenched. I know that these microbial populations are often analyzed as ...
14
votes
4answers
2k views

Height and natural selection in humans?

I watched the documentary "Evolve" recently and in the segment on "size" Scott V. Edwards, Harvard evolutionary biologist mentioned the idea that humans might evolve to be 7' tall in 'hundreds of ...
17
votes
2answers
4k views

What is the mechanism behind “acquired” alcohol tolerance?

I can understand natural variation in alcohol dehydrogenase (ADH) in a population leading to variation in rate of inebriation (after controlling for other variables -- e.g., mass, food consumption, ...
14
votes
1answer
898 views

Why do we get runny noses in the cold?

The most annoying thing for me about being cold is a runny nose. Is there an advantage to having a runny nose when cold? What does having a runny nose achieve?
10
votes
1answer
196 views

What would be the conduction speed of A-alpha fibers, were they unmyelinated?

It's known (Hursh 1939) that myelinated axons exhibit the behavior $v = 6d$, where $v$ is the propagation speed [m/s] and $d$ is the axon diameter [μm]. A related relation for unmyelinated axons is ...
14
votes
2answers
1k views

What causes REM atonia to be lost in sleepwalking?

I understand that in normal REM sleep the voluntary muscles are in effect paralysed in order to prevent an individual acting out their dreams. This paper indicates that there are likley to be ...
38
votes
1answer
8k views

Why do Humans not produce Vitamin C like other mammals?

Why do most mammals produce their own Vitamin C? Why do Humans not?
7
votes
1answer
162 views

Can oxygen diffuse out through the lungs?

Let's say you accidentally walk into a room pressurized with pure nitrogen (or you're jettisoned into space). Within a couple of seconds, the partial pressure of oxygen within your lungs drops to 0. ...
17
votes
2answers
465 views

How is temperature sensed?

Can anyone summarize the mechanism by which when an object of a given temperature is placed in contact with, say, the skin on a human fingertip, the average speed of the particles of the object is ...
16
votes
2answers
354 views

Why would diffusion be faster across a non-specialised tissue?

The standard protocol for a person experiencing chest pains is to chew a 300mg aspirin tablet, the argument being that chewing rather than swallowing the tablet results in the aspirin entering the ...
24
votes
5answers
779 views

Why do we age? or Do we have a theory of senescence?

There seem to be a number of ideas about why we age. Hypotheses include the gradual accumulation of cell metabolic products affecting organism function and the reduction of telomere length during cell ...
8
votes
1answer
2k views

Effects of Polyphasic vs Monophasic sleep in humans

Why do humans practice monophasic sleep cycles? When altering one's circadian rhythm to a Polyphasic sleep schedule, how much would that affect development? Is Monophasic sleep (once per day) ...
4
votes
1answer
149 views

Is a raised baseline between T and QRS normal in any ECG lead?

Here are excerpts from an unknown ECG lead. I find it weird that the "baseline" changes after the T wave and doesn't return until after the following QRS complex. Is that normal/expected for any lead? ...
8
votes
1answer
86 views

Which aspects of renal physiology are standing in the way of an artificial (mechanical) kidney?

Scientists have been able to create artificial organs with varying degrees of success. The mechanical heart (in its various forms, e.g. ventricular assist) is able to sustain life for some period of ...
7
votes
1answer
230 views

Mechanism of syndesmophyte growth in AS

Ankylosing Spondylitis (AS) causes inflammation around joints and the growth of syndesmophytes that may eventually fuse vertebrae. I'm familiar with the genetics (HLA-B27, IL1A) related to the ...
7
votes
2answers
500 views

Where does vasoconstriction occur in limbs?

When cold or in shock a person's blood vessels constrict in order to preserve heat or to move blood flow to protect vital organs. I am interested in the mechanism by which this is achieved. Does ...
33
votes
1answer
15k views

Why Does Salt Water Help Sore Throats?

I am having some trouble understanding how salt water, a simple solution, could so effectively remove the pains of a sore throat. I do believe that the answer is closely related to hypo/hyper-tonic ...
25
votes
3answers
404 views

Is telomere length a reliable measure of health/lifespan?

Several companies are commercializing tests for telomere length such as this one here. I understand the basic mechanism for why telomeres shorten during DNA replication, but how good is the evidence ...
8
votes
1answer
191 views

Does the oxygen concentration equilibrate between red blood cells in the liver sinusoids?

In the sinusoids of the liver, venous blood from the hepatic portal system mixes with arterial blood from the hepatic arteries. Do oxygen molecules move between oxygenated RBCs and non-oxygenated ...
9
votes
1answer
109 views

Why is there an extended delay before G.M. liver cells are attacked by the immune system?

In this BBC article a trial is described where patients with B-Haemophillia are infected with modified Adeno-associated Virus 8 which contained the genes for Factor IX clotting protein. Trials seemed ...
6
votes
1answer
117 views

Latency to audition in human beings?

On average, in a human being with no neurological deficits, how long does it take for a sound which is sensed in the ear to reach the cortex? Which brainstem structures are most responsible for the ...
9
votes
1answer
188 views

What are the clotting factors' effect on avascular necrosis development?

Do clotting factors tpa and pai-1 lead to degenerative osteoarthritis in the same way that lupus anticoagulant and prothrombin might? Is one of these pathways particularly detrimental during formation ...
18
votes
2answers
325 views

Can an adult without genetic lactase persistence still develop a tolerance for dairy foods?

While investigating the rise of adult lactose tolerance, I came across the news that China has been encouraging its citizens to drink more milk, even though most of the Asian population lacks the SNP ...
16
votes
2answers
5k views

How do the brain and nerves create electrical pulses?

I have heard that information is sent between the brain and peripheral nerves via electrical pulses or signals, but I don't understand how they create them in the first place.
10
votes
2answers
1k views

Do human beings have pheromone receptors?

What is the current consensus on whether or not humans have receptors that detect pheromones? If there are purported receptors, in what anatomical areas are they located? With what organ systems do ...
21
votes
1answer
3k views

How long do your eyes need to adapt to darkness and reach full contrast?

I heard you should wait some time until your eyes adapt to darkness and are able to see smallest luminosity differences, otherwise you might overlook faint objects in the ocular. Are there any rules ...
13
votes
1answer
1k views

Why does looking at bright light trigger sneezing in some people?

Why does looking at bright light trigger sneezing in some people? Are there any recent studies that have found a cause for this Photic sneeze reflex? The Wikipedia article only references studies ...