Exocrine Glands

∞ generated and posted on 2018.09.01 ∞

The skin possesses hair, glands, melanin, and keratin.

The skin possesses many aspects that are in addition to its serving simply as a covering of the body including coloration, waterproofing, hair, nails (collectively, skin appendages), and numerous exocrine glands.

This page contains the following terms: Keratinocytes, Melanocytes, Melanin, Arrector pili, Hair, Hair follicle, Nails, Exocrine gland, Sweat, Eccrine gland, Apocrine gland, Sebaceous gland, Sebum Acne vulgaris, Boil, Impetigo, Wart


Cells that are responsible for generating the primary protein constituent of the cornified layer of skin as well as of various skin appendages such as hair.
Keratinocytes form via mitosis from stem cells found within the basal stratum. They then undergo a process of cornification during which they accumulate keratin within their cytoplasms. This reaches a terminus with keratinocyte death and associated formation into corneocytes.

This process occurs for skin within the epidermis. For hair it occurs instead within hair follicles.

Links to terms of possible interest: Cornification, Keratinocytes, Melanocytes, Melanosome, Stratum basale, Stratum corneum, Stratum granulosum, Stratum spinosum

The above video goes into what keratinocytes are all about in some detail, with greater detail provided as the video progresses.

The above video goes over actinic keratosis, precancerous skin lesions that develop from keratinocytes.

The above video goes over squamous cell carcinoma, a type of skin cancer, which develops from actinic keratosis.


Cells responsible for producing the major pigment associated with skin and hair.
It is within melanocytes that melanin is produced, via a process known as melanogenesis. This production occurs at a genetically determined rate, or substantially less so in individuals who are deficient in their production of melanin, i.e., albinos.

Melanin production in the skin also is stimulated by exposure to UV radiation and the melanin itself is transferred from melanocytes to keratinocytes, serving there as a means of protecting the keratinocyte nucleus, whose DNA is among the most UV exposed of DNA within bodies (i.e., due to keratinocyte location within the epidermis). Melanocytes, however, actually are found in far more locations within the body than skin and hair, particularly where pigmentation occurs.

Links to terms of possible interest: Epithelial cell, Golgi apparatus, Keratinocytes, Melanocyte, Melanosomes, Nucleus

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, melanoma in situ, and invasive melanoma.

The above video goes over the basics of melanoma


Common pigment associated for example with skin, hair, and eyes which serves as an absorber of ultraviolet radiation.
Melanin is the coloration of tans as well as normal skin pigmentation. Melanin is common in animals, presumably serving generally as a means of protecting DNA from damaging UV radiation as supplied by the sun. Protection from UV is important since it is UV radiation that gives rise to both sunburns and skin cancers.

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 UV photons 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 pili

Smooth muscles attached to hair follicles.
Arrector pili muscles 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 pili muscles 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.

Links to terms of possible interest: Arrector pili, Hair follicle

The above video provides background on the utility of "goose bumps", which are the proximate result of the action of the arrector pili.

Though the video quality isn't great, you can sort of make out this kitten's hair standing on end (more or less) in this video.


Keratin-based skin appendage that is a defining characteristic of mammals.
Hair in mammals serves as insulation against cold, protection of the skin from the sun, decoration, and protection of the skin from friction. Hair also plays roles in the sense of touch.

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".

Links to terms of possible interest: Cortex, Cuticle, Hair, Hair shaft, Medulla

This video gets a bit weird towards the end but nonetheless is a good introduction to hair, particularly human hair.

Hair follicle

Source in mammals of defining keratinized skin appendages as well as the outlet for apocrine and sebaceous glands.
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.

It is within a specialized as well as well-vascularized indentation into the dermis that the hair-producing keratinocyte precursor cells are found and, just as is seen with the epidermis, undergo cornification. Meanwhile, dead melanocytes are found among the dead keratinocytes, making up the shaft, and providing much of the color of hair.

Note that shafts of hair are neither alive nor innervated. Instead it is the base of the hair, that is, the hair follicle that is alive and which can feel pain.

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.

Links to terms of possible interest: Bulge region, Connective tissue, Dermal papilla, Dermis, Epidermis, Epithelial tissue, Hair fiber, Hair follicle, Inner root sheath, Outer root sheath, Sebaceous gland, Subcutaneous fat

The above vide provides a nice overview of the anatomy of the hair follicle.


Hardened keratin-based structures found at the terminus of most primate digits.
Nails are described as being horny, which is appropriate as both nails and horns are keratin-based appendages. Nails are anatomically equivalent, in their embryonic origin, to claws as well as hooves.

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.

Links to terms of possible interest: Dermis, Epidermis, Eponychium, Lunula, Nail bed, Nail body, Nail cuticle, Nail root

This video provides a fascinating look at external nail anatomy from the perspective of manicures and application of nail extensions.

Exocrine gland

Means by which animals generate substances that are then released via ducts.
Examples of exocrine glands include eccrine glands, apocrine glands, and sebaceous glands. As derived sweat glands, mammary glands also are exocrine glands. All of these secrete substances to the surface of the skin.

Alternatively, the liver and pancreas serve also as exocrine glands, which secrete substances such as digestive enzymes via ducts to the small intestine. The prostate gland too secretes materials via a duct, in this case into semen.

Links to terms of possible interest: Compound acinar exocrine gland, Compound tubular exocrine gland, Compound tubuloacinar exocrine gland, Duct, Exocrine gland, Gland, Secretory cells, Simple acinar exocrine gland, Simple branched acinar exocrine gland, Simple coiled tubular exocrine gland, Simple tubular exocrine gland

The above video provides an effective comparison between the two basic gland types, exocrine glands and endocrine glands.

The above video compares exocrine glands with endocrine glands but with emphasis on exocrine glands.


Antimicrobial as well as cooling fluid released onto the skin by certain exocrine glands.
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.

This sweating in large amounts over much of the body is relatively unique to humans, though also is seen in horses. The principle sources of the cooling as well as antimicrobial components of sweat are our eccrine glands, a kind of exocrine gland.

Links to terms of possible interest: Apocrine gland, Eccrine gland, Hair follicle, Sweat, Sweat gland

Eccrine gland

Releaser, onto the skin, of sweat.
Eccrine glands, a.k.a., eccrine sweat glands, are found over most the skin surface of the human body, with the lips and genitals notable exceptions. Primarily they excrete sodium and chloride but eccrine glands in addition secrete various materials that represent either waste product from the blood (e.g., nitrogenous waste) or instead useful materials to place on the skin. These materials are released through sweat pores directly onto the skin's surface.

The salt that is released, i.e., sodium chloride, helps to limit the types of microorganisms that are capable of living on the skin as too does the antibacterial enzyme, lysozyme, which is also secreted by eccrine glands. The eccrine glands are found in particularly high numbers on our foreheads and also the palms of our hands and the soles of our feet.

Links to terms of possible interest: Apocrine, Apocrine sweat gland, Eccrine gland, Eccrine sweat gland, Hair follicle, Sweat pore

Apocrine gland

Releasers of non-sebum oily materials into hair follicles and from there to the surface of our bodies.
The apocrine glands, a.k.a., apocrine sweat glands, are found mostly under our arms (i.e., our arm pits), in our genital areas, and also in association with our anus. The substance secreted by these glands is very nutritive and therefore can support the growth of microorganisms, chiefly bacteria. Though the apocrine gland secretions themselves are not odorous, the materials secreted by these microorganisms, including their waste products, often are odorous.

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.

Links to terms of possible interest: Apocrine sweat gland, Arrector pili, Eccrine sweat gland, Sebaceous gland

Sebaceous gland

Releasers of water-proofing materials into hair follicles and from there to the surface of our bodies.
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.

Links to terms of possible interest: Dermis, Epidermis, Hair shaft, Hypodermis, Sebaceous gland, Sebum

Nice video that distinguishes among eccrine glands, apocrine glands, and sebaceous glands in terms of how their products are released.


Lubricating, waterproofing, and antimicrobial substance secreted onto the skin of mammals.
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 body cells that actually produce sebum are unable to release these oily substances while remaining intact but instead sacrifice (lyse) themselves to release the sebum.

Acne vulgaris

Skin condition associated with blockage of hair follicles and sebaceous glands.
Acne vulgaris strictly is not necessarily associated with bacterial infection though overgrowth of the bacterium Propionibacterium acnes nonetheless can exacerbate the condition.

Links to terms of possible interest: Acne vulgaris, Comedone, Inflammatory papule, Nodule cyst, Pustule

The above video discusses the pathophysiology of acne vulgaris.


Deep hair follicle infection.
Another name for boil is furuncle. They are caused predominantly by the bacterium, Staphylococcus aureus.

Links to terms of possible interest: Boil, Hair follicle, Infection, Skin infection

The above video nicely goes through the pathology of Staphylococcus aureus associated abscess formation, leading, e.g., to boils.


Contagious bacterial skin infection common especially among young children.
Impetigo is caused predominantly by the bacterium, Staphylococcus aureus.

Links to terms of possible interest: Bacteria, Impetigo, Infection

The above video considers impetigo mainly from a health and public health rather than mechanistic perspective.


Growth-like viral infection of the skin.
Warts are caused by the human papilloma viruses, a.k.a., HPV, which come in numerous different types. Certain types of HPV cause growths that are associated particularly with the genitals. Certain types of HPV also can give rise to cervical cancer as well as cancers of the penis, portions of the throat (oropharynx), etc.

Links to terms of possible interest: Blood supply, Mosaic wart, Plantar wart, Wart

The above video provides a nice overview of what warts are all about.