In this video, we're going to examine the various glands that are associated with the skin, and we'll begin our discussion by talking about two different types of sweat glands. So the first sweat gland is known as the eccrine sweat gland. So the eccrine sweat glands, these are mericrine glands, and if you recall the discussion about epithelial tissues, these are glands that secrete their substances via exocytosis, so the cells remain intact.
So eccrine sweat glands are the most numerous sweat glands in your body. They're involved primarily in thermal regulation, so the sweat evaporates and it has a cooling effect on the body. So it is most abundant on the palms, soles, and the forehead. And in fact, in most cases of thermal regulation, the forehead is where sweating begins, and then it progressively moves down in an inferior fashion.
So the sweat glands are very simple coiled glands that connect to ducts, and they are regulated by the sympathetic nervous system. So these are a type of... cell that will respond to sympathetic stimulation.
So we refer to these cells as myoepithelial. The myo part implies muscle and then epithelial is the origin. So the sympathetic nervous system will trigger the contraction of these cells that leads to the exocytosis of sweat. Now sweat is going to be hypotonic.
So overall it has less solutes than the rest of the fluids in the body. It's 99% water, but you do have some salts, vitamin C, antibodies, and then more importantly, you have compounds dermocidin. This is a microbe killing peptide. and you do have limited amount of metabolic waste such as urea.
So when you look at the composition with regards to salts and the metabolic waste, it's actually fairly similar to urine. But the antibodies and the dermocytin, those are going to be very important and that sort of explains why you have these types of sweat glands most abundant on the palms and the soles of the feet. So where you're more likely to interact with potential disease-causing pathogens. So here in the histological section, you see the very simple epithelia here, and in the center you have the duct network.
So again, coiled acrine gland. The second sweat gland that we're going to talk about are the apocrine sweat glands. And apocrine sweat glands are also... Despite what their name implies, they're also going to be merocrine glandular epithelia, but they're slightly modified compared to the eccrine. So when you look at the apocrine sweat glands, these are exclusively found in the axillary, so the armpit, and the anal or anogenital area, so around the anus and the external genitalia.
They are not responsible for thermal regulation. In fact, in humans, the function is sort of to be determined. They do secrete a sweaty substance, but the sweat is modified with more fats and proteins.
So it's a much thicker substance, viscous, sort of milky and slightly yellowish in hue, but it is odorless. However, the bacteria in these areas will metabolize the fats and the proteins, and that is what leads to body odor. So what could the potential function of this be if it's not thermal regulation? Well, it's very similar to other animals' sexual scent glands.
So the presumption is maybe this is some sort of pheromone-like secretion. secreting gland, although we are not as adept at picking up these subtle scents. Instead, we just pick up the body odors. So these apocrine sweat glands, they dump their secretions into and around the hair follicles. And we could look at sort of the side-by-side comparison between the eccrine sweat glands versus the apocrine sweat glands.
So apocrine towards hair, eccrine towards sort of the pores of the skin. So we also have modified apocrine glands. So the ceraminous glands, these are found that line the internal, excuse me, the external ear canal.
So the sweaty substance that we create is a little bit thicker. we call it cerumen or earwax. And then mammary glands, also sort of modified sweat glands that have sort of more fat, more protein, so it serves a nutritional value to offspring.
So if we look at more comparisons, eccrine glands tend to be significantly smaller than the apocrine glands. In fact, apocrine glands can sometimes go smaller. into the hypodermis.
Now in terms of similarity, they do both secrete into a duct. So you can see these cells are sort of cuboidal to columnular, so it's adapted for secretion. But when we look at the triggers, we already mentioned the trigger for eccrine sweat glands.
tends to be an elevated body temperature, sympathetic stimulation, then triggering sweating. But here, the triggers for apocrine sweat gland secretions are usually associated with either pain or stress. So this is sort of tied into the responses to sex hormones like androgens. to further stimulate the secretion from apocrine glands. So the last gland I want to focus on is the sebaceous or the oil glands.
So these are going to be widely distributed, although most of them are associated with hair follicles. You can have sebaceous glands that are independent of hair follicles. Functionally, they are there to secrete sebum.
to serve sort of a lubricating function, both lubricating the hair follicle, so it prevents the hair follicle from drying out in dry climates, as well as lubricating the surface of the skin. So sebaceous glands tend not to be found in the thick skin of the palms and the soles of the feet. For the most part, they are going to be somewhat inactive.
until puberty hits, but androgens will begin the secretion of sebum from the sebaceous glands. So sebum itself is sort of an oily substance. The sebaceous glands are holocrine in origin.
So remember, you have a central sort of cell that sort of explodes and releases all its contents. So the contents in the cellular debris be actually become the sebum. So not only does it serve to sort of lubricate, it helps to soften the hair and the skin.
And another very important property is that it contains antimicrobial peptides. So it's bacteriocidal in origin. However, when you have an overproduction of sebum and you start to clog up the ducts, that the sebaceous glands use, then you start to get white heads and if it gets clogged with dirt as well then you get black heads. Now if you look at the histological section of the sebaceous gland, you'll notice these sort of grape-like clusters.
So the organization is a simple alveolar tube. So it's a tube with a bunch of sort of these grape-like clusters like the alveoli that feed into the sebaceous gland duct.