They are the oil-secreting tissue in the skin of mammals.
When a piece of the epidermis is examined under a microscope, we see a hair follicle that crosses the surface of the skin into the subcutaneous layer. Inside lies the secretory sebaceous tissue.
The waxy oil that is secreted in the hair follicles is called sebum. This oil lubricates the skin and scalp of mammals. Since the sebaceous glands secrete their oil into the ducts before reaching the surface of the skin, they are considered exocrine glands.
Sebum is a mixture of fats (triglycerides, cholesterol, squalene, wax esters), detritus, and keratin. This forms the light film of oil on the surface of our skin. If you’ve ever taken a photo of yourself and you appear bright in the frame, it’s the sebum that has done it.
We may better recognize sebum as the waxy substance on our face and scalp before jumping into the shower. But in reality, sebaceous glands are found in every part of the skin except for the lower lip, the palms of the hands, and the soles of the feet.
There are two types of sebaceous glands: those that connect to a hair follicle and those that do not. Those linked to the hair follicles deposit sebum in the hair, which carries it along the follicle. Those that exist in the hairless areas of the skin are found on the inside of the nose, penis, and labia minora.
Similarly, the meibomia glands populate our eyelids and secrete sebum in tears for added weight and lubrication. The areolar glands surround the nipples and prevent the skin from drying out or drying out.
At the base of any of the pores is the sebaceous gland. It has an acinar structure as the acinar glands appear as berry lobes. These lobes, or sacs, secrete the oily suspension.
Development of the sebaceous glands
The sebaceous gland is formed during late to early life embryogenesis. It usually begins its journey during the fourth month of pregnancy. Stem cells begin to differentiate within the outer root sheath (or ORS), and appear as bumps, or small pockets, outside the hair shaft.
When these cells disintegrate, they release their oily secretion. The genetic factor in whether or not a sebaceous gland appears as well. In fact, the clear, waxy substance that lines the skin of newborn babies after birth is the secretion of a type of sebaceous gland.
However, after birth, the sebaceous glands shrink until there is almost no activity. This changes after age six, reaching the pinnacle of activity at puberty. The gland’s activity is closely related to the levels of the male hormone, testosterone.
The main function of the fatty sebaceous gland is to lubricate the skin. This prevents moisture loss. In turn, the skin remains hydrated and flexible. Without sebum, the skin would be easily dry and lacerated.
Dry patches are more prone to infection, as pathogens can penetrate through broken skin. This shows the importance of sebum to keep the skin intact.
The sebum in our hair strands, on the other hand, makes our hair waterproof. As mentioned above, an important component of sebum (and hair) is keratin.
Water cannot penetrate or break the threads. Without sebum, the hair would have no protective barrier against brittleness or even evaporation. On an evolutionary basis, of course, hair protects the skin from environmental damage.
Sebaceous gland problems
Underproduction of sebum or overproduction creates some complications. Like most processes, homeostatic control balances this delicate line. Byproduct glands will lead to breakage and infection of the skin.
Overproducing oil glands are involved in the very common skin affliction, acne vulgaris. Papules form when a sebaceous gland becomes clogged, allowing sebum to accumulate in the follicle and duct.
The eventual bacterial breakdown of triglycerides in the sebum will release fatty acids that trigger inflammatory lesions or “pimples.” Similarly, overactive glands can cause sebaceous cysts. These are painful pockets of pus that form inside the sebaceous ducts when they become clogged.
Unlike acne papules that are close to the surface of the skin, cysts will be deeper in the skin and painful to the touch due to their proximity to the dermal nerves.
Overactive sebaceous glands are also associated with more serious conditions, hyperplasia, and sebaceous adenoma. Hyperplasia refers to the rapid growth of tissue that can indicate the early stage of cancer.
Similarly, adenomas are lumps of cells in the sebaceous duct that can be a sign of internal disease. Sebaceous carcinoma is a rare but fatal skin tumor that originates in the gland.