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101

Apparently you're not the first person to notice this; in 1895, a German nose specialist called Richard Kayser found that we have tissue called erectile tissue in our noses (yes, it is very similar to the tissue found in a penis). This tissue swells in one nostril and shrinks in the other, creating an open airway via only one nostril. What's more, he found ...


41

This is natural phenomenon called the nasal cycle. It is discussed in this paper by Telles et al. (1994), among many others. The nostrils are used on an alternating cycle of about 2-3 hours, controlled by the autonomic nervous system. If you notice alternating congestion, that also seems to be coupled to the nasal cycle (Hasegawa and Kern 1977, 1978). ...


32

Humans can, to some extent, be scaled: While most humans are two meters tall; the human body essentially works throughout the entire range from around a meter to around two and a half meters, although you tend to run into problems at the extremes. However, outside of that range you run into the tyranny of the square-cube law: As you scale a creature (or, ...


13

Hemoglobin molecules used to manufacture these products are not contained by a red cell membrane, and when released into the vasculature, these molecules rapidly scavenge nitric oxide.This can result in systemic vasoconstriction, decreased blood flow, increased release of proinflammatory mediators and potent vasoconstrictors, and a loss of ...


12

As others have said, this phenomena is called the nasal cycle, a process controlled by the autonomic nervous system that alternants congestion between your nostrils. Mentalfloss of all places has an article about this that explains: ...it makes our sense of smell more complete. Different scent molecules degrade at different rates, and our scent ...


9

The female breast is composed primarily of fat and connective tissue plus lobules and ducts for milk production and delivery. The pectoralis muscles form a thin layer beneath the breast, as seen in the figure in the link. An athletic female can enlarge the size of the pectoralis muscle and the laterals muscles, just as male athletes can enlarge their "pecs" ...


8

Fracture healing occurrs in several steps: haemorrhage: blood and surrounding cells fill the space created by the fracture. fibrous callus: chondrocytes colonize the fracture space, with neovascularization. bony callus: osteocytes colonize the fracture space and rearrange in woven bone remodelling: in long bones, woven bone is remodelled into lamellar bone ...


6

This is a well worded question. There are more reasons than the following but the most apparent is hemoglobin production and its transport. The erythrocyte is a cell whose structure is optimal for its function-the production and transport of hemoglobin. It lacks a nucleus and organelles so that it can devote almost 100% of its energy to hemoglobin ...


5

As @WYSIWYG pointed, muscular atrophy is the main cause for height decrease. A spine injury leads to neural impairment and paresis / paralysis. This affects directly muscular trophism. It also limits physical activity, this being another favoring factor for muscular atrophy and overweight issues [1]. Association of bone degenerative processes (osteoporosis, ...


5

When you bend your fingers, they all arrive at the same height. I would tend to think that their lengths differ when you keep them straight because they need to have similar length when you bend them to grasp something. And I guess that there is some optimal length (when bended) for fingers to grasp things. It is nothing but a quick hypothesis. But it ...


5

Flexion: the movement that decreases the angle between two parts [1]. Examples: clenching the hand into fist, sitting down. Contraction: the property of muscle to generate tension when actin and myosin filaments are crossing. There are a few types of contractions. The isometric contraction is when the muscle generates tension but its length doesn't change ...


5

They don’t meet. Some framework: Spinal nerves contain motor, sensory, and autonomic fibers. Each of these have different pathways. Spinal nerves don’t go to the brain. Rather, they synapse in the spinal cord with other neurons which in turn go to the brain (sometimes requiring one more synapse). In the case of motor neurons, we talk about upper and ...


5

They would die. Let's imagine that we perfectly cut a person down the middle. That would mean cutting the spinal cord in half, probably damaging the tissue so much that the remaining half wouldn't work well. The liver would be gone. The intestines and bladder would just be open. The heart would have to be adjusted to the left. The surgery would probably ...


4

How humans evolved to have head / beard hair that continues to grow longer than other animals is a topic that many anthropologists & biologists are still not sure about & there is no general consensus as to "why" yet. The three main views that I am aware of however are : 1) Evolution of the "Aquatic Ape." (Ingram, 2000: Morgan 1997; 1982) ...


4

Orbitofrontal cortex: the area of the cerebral cortex located at the base of the frontal lobes above the orbits (or eye sockets), involved especially in social and emotional behaviour.


4

The main functional reason is we need to be able to grip things with our hands (and feet, which are also hairless), and hair would interfere with that. Physiologically, the epidermis in these parts of the body is very thick and highly keratinized, and when combined with the thick underlaying layer of dermis, this results in skin that does not support the ...


4

You cannot change the oxygen concentration of inhaled air in the absence of an external source of oxygen. However, you can use your lungs at their maximum capacity doing this: breathe deeply: =increase tidal volume. Your muscles will inflate your lungs as much as they are able to, inflating parts of the lungs that were not fully inflated (atelectases) in ...


4

This looks like a misinterpretation. Because collarbone is the only horizontal long bone of the human body [1], it is the first to fracture when falling on the shoulder. Its fracture can affect many structures: The muscles involved in clavicle fractures include the deltoid, trapezius, subclavius, sternocleidomastoid, sternohyoid and pectoralis major ...


4

They are actually different. INTERVERTEBRAL FORAMINA is actually spaces between adjacent vertebrae which gives passage for spinal nerves to exit. Whereas, VERTEBRAL FORAMINA forms vertebral canal. Source: Organization of the Nervous System: An introduction for students in the Human Anatomy Course


3

Inhalation and exhalation happen sequentially as Herman stated in the comments. Yes, your general understanding of inhalation is correct. After the air gets into the lungs, the oxygen is diffused into the capillaries covering the alveoli. The now oxygenated blood travels back to the heart to be circulated throughout the body. As this blood enters ...


3

In adult/pediatric humans, no they don't. A good figure to get everyone on the same page was made by Cleaver & Melton: It is important to note that: In fact, endothelial diversity is reflected by vessel size-specific, organ-specific and even age-specific differences. (1) Developing blood vessels in the fetus can be a bit of a different story, ...


3

Going on the abstract of a study by J.P. Pessan, et al., fluoride intake, as well as "the fact that toenails are less prone to environmental contamination," constitutes a lesser need for growth in toenails than that in fingernails. Also, fluorine being a crucial component in maintaining the solidity of bones, the body may redirect more fluorine that is ...


3

The fingers and toes (for example) ARE at lower temperatures than the interior of the torso. It's why it's so easy to get frostbite on the extremities. As for temperature regulation of the testes, you have to also consider that humans evolved without clothes...i.e. The testes just "hang out" and get lots of airflow, as opposed to modern times, when they are ...


3

Interesting question, I am not sure if I have a definite answer, but at least some ideas: The pigment in the hair is made by specialized cells, the melanocytes. The make the pigment (eumelanin=dark and pheomelanin=red/yellowish) which is then deposited into the growing hair. They are located at the bottom of hair bulb and usually die at the end of each hair ...


3

Myoepithelial cell contraction initiates glandular release from most exocrine glands developed from the ectoderm. These are the cells that exist in the glandular epithelium. At the distal end of the glanduar coil, an isotonic plasma filtrate gets actively transported into its lumen. As you move down the coil, close to where it connects to the duct, ...


3

I would write my answer in a comment but it doesn't fit! I guess there are two main solutions: 1) From the science of antropometry you might find some clues of the probability that you have of growing taller. For example, if your body (hairs and stuff) already look like an adult body, then you would probably not grow much more. See @MCM's answer who gives ...


3

Cortisol produced from the zona fasciculata of the adrenal cortex is directly caused by stress. According to http://en.wikipedia.org/wiki/Cortisol Cortisol stimulates gastric-acid secretion. Cortisol's only direct effect on the hydrogen ion excretion of the kidneys is to stimulate the excretion of ammonium ions by deactivating the renal glutaminase ...


3

Maintenance of Polymorphism and Mutation Load There are many possible reasons why some amount of deleterious alleles are maintained in the population. One of which is the mutation-selection-drift balance. In short: Because mutations always occur, there is continually an input of deleterious mutations in populations genome resulting in some fitness decay ...


3

Remi.b and Potterbond007 have put forward excellent answers. Would like to add something.. One of the reasons that Myopia (near sightedness) happens is because of use of eye in work like reading, which requires working with close objects. I don't think there was much working with close objects in the past. So very few people with myopia might have been ...


3

With nearly 40,000 years of natural selection on eyesight, prior to the invention of eye glasses, there needs to be a better explanation than the effects of 'modern' technology. There are two likely reasons for the persistence of "poor" eyesight in humans. First, humans are social animals and live in groups. Within groups there is frequently a division of ...



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