Anatomy & Physiology of Glands found in skin:
Glands found in skin include: eccrine and apocrine sweat glands (sudoriferous glands), sebaceous glands, ceruminous glands, and mammary glands. All of these are exocrine glands (they produce a product and deliver it to the surface of an epithelium– in this case the epidermis).
- Eccrine sweat glands: These are simple tubed glands that produce a very watery sweat. The major function of eccrine sweat glands is to help cool us down. The ducts of eccrine sweat glands lead to the surface of the skin. Eccrine sweat glands are found over most of the body, including the palms of our hands and soles of our feet. Eccrine sweat glands are merocrine glands in that the secretory cells release their product by exocytosis.
- What is sweat? Sweat from eccrine sweat glands is mostly water (around 99% water), but it also contains some sodium chloride, urea, ammonia, lactic acid, and other substances. Sweat is somewhat acidic (pH around 5) which contributes to our skin’s defense against bacteria (bacteria don’t like acidic conditions).
- Apocrine sweat glands: These sweat glands are larger than eccrine sweat glands, and they produce a more oily sweat into hair follicles. Apocrine sweat contains pheromones (scent molecules) and because they are secreted into a hair follicle and thus onto a hair the pheromones get out into the air more efficiently. Apocrine sweat glands are triggered to release sweat when we are emotionally excited, the firing of these glands is part of sexual arousal for example. In most people apocrine sweat glands are found in only a few regions including the groin and axillary regions. Apocrine glands secrete by apocrine secretion, meaning that a portion of the apical surface of the secreting cells actually pinch off in order to secrete the product, so part of the cell is actually lost in the process.
- Sebaceous glands: Sebaceous glands secrete an oily substance called sebum. The function of this substance is to condition skin and hair. When we bathe we remove sebum with soap and water and therefore often need to apply conditioner to our hair and lotion to our skin. Our skin and hair would probably be healthier if we only showered once or twice a week, but of course then we would smell more. Sebaceous glands secrete by holocrine secretion meaning that the secreting cells literally rupture in order to secrete the sebum, so the entire cell is lost in secretion (more cells are being made at the basal surface of the gland’s epithelium).
- Ceruminous glands: These glands are found in the outer ear canal and they produce cerumen or ear wax. Cerumen itself is mostly made of long chain fatty acids and cholesteral molecules (these are more solid and wax like at room temperatures). Cerumen functions to keep the tympanic membrane (ear drum) conditioned as well as the skin that lines the outer ear canal, it also has antibacterial properties. Ear wax is actually made up of cerumen, sebum, dead skin cells, and often also contains guard hairs released from the wall of the ear canal.
- Different people make different ear wax: Some people make a more soft/sticky ear wax (wet type) while others produce ear wax that is more crusty (dry type). People that produce the dry type of ear wax also sweat less. This may have developed as an adaptation to living in colder climates. If your ancestors came from East Asia you might be a dry type ear wax producer.
- Cerumen impaction: In many people ear wax accumulates faster then it drains and this can lead to a cerumen impaction, a build up that is great enough to block the ear canal and/or press on the tympanic membrane, interfering with hearing and possibly causing other discomfort. When I worked as a medical assistant I found the most effective way to deal with this was by using a large syringe (20 to 30cc) with an attached 1 to 1.5 cm rubber tube (usually from a butterfly needle). I used warm water in the syringe to irrigate the outer ear canal until the cerumen impaction washed out. If the impaction did not come out with several flushes I would very carefully use a plastic looped end probe to gently pull it out. I would only use warm water because cold water is uncomfortable and can cause acute dizzyness, and I would only use a looped end probe while also looking in the canal so that I could be absolutely sure not to touch the tympanic membrane (the ear drum is very sensitive and delicate).
- Mammary glands: These glands produce milk in order to feed our offspring. It may seem strange to discuss them when talking about skin, but there is a good reason for that. Evolutionarily speaking, mammary glands are modified sweat glands. These glands are also found in the hypodermal layer in both males and females in what is called the mammary fat pad (just superficial to the pectoral muscles). In females the mammary glands and nipples are more developed and only female humans develop more fat tissue in the mammary region (with the exception of human males with gynocomastia). Mammary glands secrete by apocrine secretion, meaning that a portion of the apical surface of the secreting cells actually pinch off in order to secrete the product, so part of the cell is actually lost in the process. I’ll discuss mammary glands more when I cover reproduction.
- Why do we think that mammary glands are modified sweat glands? One piece of evidence that mammary glands are modified sweat glands comes from our friend the platypus. This strange little creature does not have nipples and feeds its young from milk pads that consist of mammary glands with ducts leading to the skin surface (much like sweat glands). The milk is then lapped up off of mom’s skin by the baby platypus.
That’s it for glands found in and under the skin. Have any questions or comments? Please leave them below.