The above video gets a bit technical, and to a large extent emphasizes melanoma rather than melanocytes, but does start out with great explanations and visuals about what melanocytes are all about. Note the terms, nevus (which is the technical name for a skin mole), atypical nevus, dysplastic nevus, melanomain situ, and invasive melanoma.
Where, one can ask, does the UV radiation that is absorbed by melanin go? The answer is that the energy associated with the absorption of UVphotons is converted to heat.
The above video goes way beyond what we are covering here, providing what essentially is the biochemistry of melanin production.
Arrector pilimuscles are responsible for causing hair to "stand on end", that is, to cause hair to become erect. For the majority of mammals – which possess abundant hair – this can serve to increase the air-trapping and therefore insulating ability of hair. In addition, it can cause bodies to appear larger since hair takes up a greater amount of volume when erect.
In humans, the action of the arrector pilimuscles results in goose bumps, which would be seen as the erection of our hair (and indeed does involve the erection of our hair), but we have so little hair that the gesture in fact is somewhat meaningless. Indeed, it may represent a vestigial response that we possess only because our ancestors also possessed it.
Hair tends be much less abundant in humans than most other mammals, though obviously is still very important to humans. Humans as well as other relatively hairless mammals (e.g., whales) still have plenty of hair; it just does not grow to great lengths over much of our bodies.
One can distinguish between hair and fur in terms of growth patterns, where hair tends to continuously grow before individually falling out after a certain span of time, whereas fur tends to grow to an only certain length before stopping growing but nonetheless not immediately shedding. Technically, however, fur is simply a form of hair and hair is a word we use to describe our own less abundant "fur".
A shaft of hair can be viewed as specialized epidermis that does not undergo desquamation. That is, the corneocyte equivalents are not lost from the closely associated pile but instead are retained to form a shaft.
As desquamation is an active process that involves the cleavage of bonds holding together corneocytes, it makes good sense that if those bonds are not actively broken then corneocytes can remain associated. Indeed, this is exactly what happens with reptile skin, where corneocytes persist until they are shed en masse, just as hair persists until individual hairs are shed as a single unit, that is, as a shaft of hair.
After a time, hair follicles enter a period of rest after which the hair shaft falls out, and then this is followed usually by a return to active growth of the hair shaft.
Unlike hooves, which serve to support the weight of an animal, and claws, which are employed as puncturing, scratching, or gripping devices (such as during climbing), nails instead serve as protective endings of digits, where those digits instead are employed in grasping.
We tend to view sweat and sweating over the bulk of our body such as in response to hot weather (though also in response to emotions). It is particularly noticeable when we are anxious and when the relative humidity is high.
Of interest, it is during puberty that the apocrine glands begin to function. We fight the odor that these glands can help to generate by either applying bacterial growth inhibitors, limiting the functioning of eccrine glands (since reducing water availability also serves to inhibit bacterial growth, i.e., as can be accomplished via the use of antiperspirants), and also by simply masking odors by applying strongly scented substances to our skin, all particularly under our arms.
Sebaceous glands are found over the body surface in large numbers except on the palms of our hands and the soles of our feet. They become more active with puberty, and the resulting excessive production of sebum can potentially lead to the formation of pimples.
When sebum is relatively lacking, such as due to excessive washing (e.g., of hands or hair), then the result can be excessive dryness, which in turn we can at least attempt to counter via the use of skin moisturizers or hair conditioning products.
Sebum is secreted by sebaceous glands. It provides not only lubrication and moistening action to skin but also to hair, and is a constituent of earwax. If you have oily hair then this likely is a consequence of "excessive" accumulation of sebum. Body odor in part is a consequence of bacterial consumption (breakdown) of sebum.
The bodycells that actually produce sebum are unable to release these oily substances while remaining intact but instead sacrifice (lyse) themselves to release the sebum.
