Skin Glands

You learned back in chapter 5 about glands. You saw that you can distinguish glands based on their histological makeup. In that chapter it also describes that you can distinguish glands on the basis of what they secrete. We didn't discuss this in the web page back then, because it wouldn't have been very meaningful. But now, as we discuss skin glands, it should be more meaningful.

Sweat glands:

Sweat glands are coiled tubular glands that lie in the dermis (as far as their histological appearance). They fit into the category of merocrine glands based on what they secrete. Take a look at Figure 5.11 on page 143 to see this, because it is important that you understand this terminology since it gets confusing...

Merocrine glands secrete fluids with dissolved material in them. Sweat glands release water with salt and some metabolic wastes in them, so they fit this category. Urea and uric acid can be some of those wastes, and these molecules are "nitrogenous wastes." These wastes appear when we have to metabolize proteins for use in the production of energy.

The confusing part of this is that there are two types of sweat glands, depending on whether or not they also contain an odor in the sweat and on whether they secrete through a separate pore. Here are the two:

	eccrine sweat glands secrete odorless sweat through a separate pore.
	apocrine sweat glands secrete odorous sweat into a hair follicle.

Regardless of whether we are discussing an eccrine or an apocrine sweat gland, they are both merocrine glands on the basis of what they secrete. The confusing part about this is that "apocrine glands" is the name for the type of glands that secrete cell parts, wherease "merocrine glands" is the name for the type of gland that secretes dissoved materials. Therefore, one might think (incorrectly) that apocrine sweat glands are apocrine glands. They are not. Apocrine sweat glands are merocrine glands. It is one of those bad terminology problems.

Function of sweat glands:

The sweat glands normally release a little fluid all the time, and as this fluid evaporates, your body cools off. These glands can get stimulated to be more active, so that they secrete even more fluid and help us cool off more. The stimulus to the sweat glands occurs when our bodies recognize (through skin temperature nerve endings and/or blood temperature as it courses through our brains) that they are hot.

Sebaceous glands:

Sebaceous glands are compound alveolar glands based on their histology. Sebaceous glands are holocrine glands based on what they secrete, because they secrete entire cells! Once a cell is secreted, it finds itself in a pore, no longer surrounded by its normal environment. The new environment is disturbing to the cell, so it lyses and its contents leak out. This leaked out mixture of cell contents, cell membranes, and disruptive environment fluids (a fatty mixture) is then called sebum, and it is what gets to the surface of the skin.

Sebaceous glands secrete their sebum into hair follicles. The sebum then escapes to the surface of the skin through the same route that the hair uses-- out the follicle. This oily fluid on our skin helps to further protect our skin, coating it with a hydrophobic armor to keep out water and maintain our internal fluids.

Pimples and acne are troubles of the sebaceous glands. These occur when the sebaceous glands get clogged, by either sebum or cells, as too much secretion occurs.