 This video will cover part 3 of an introduction to the Integumentary System. As we go, we'll cover the following objective, describe the structure and function of the following accessory structures, hair follicles, erector pili, hair follicle receptors, pasinian corpuscles, myzner corpuscles, merkle cells, sebaceous glands, echorin glands, and nails. Hairs are composed primarily of keratin, growing out of the epidermis. Dead keratinized cells form the structure of the hair. The hair originates from modified epidermal tissue that folds deep into the dermis as a structure called the hair follicle. The hair shaft is the exposed part of the hair that's not anchored to the follicle, whereas the rest of the hair, which is deep underneath the skin anchored into the follicle, is known as the hair root. The deep enlargement of the hair follicle is called the hair bulb, and within the hair bulb is a layer of mitotically active basal cells, epithelial cells called the hair matrix that divide and differentiate in order to produce the epithelial cells that make large amounts of keratin, fill with keratin, and die, and produce the structure of the hair. The hair bulb surrounds a papula, the hair papula which is made of connective tissue, continuous with the dermis, and contains blood vessels, very small blood vessels called capillaries, and there are also nerves inside of the hair papula. The blood vessels provide nutrients to the growing epithelial cells in the bulb, just as the basal layer of the epidermis, stratum basale, divides and as cells differentiate, they migrate out towards the surface. In the hair follicle, basal cells divide and differentiate, and as they mature, they migrate out into the hair root, and as the hair root grows, the hair shaft pushes out past the skin and grows. The functions of the hair include protection, sensory input, thermoregulation, and communication. For example, the hair on the head can protect the skull, protect the top of the head from exposure to the sun. Hair in the nose and ears and around the eyes helps to protect the body by keeping small particles from getting into these openings. Hair of the eyebrows helps to prevent sweat from getting into the eyes. The sensory function of the hair, we'll see there's a hair follicle receptor that can detect movement of the hair and help contribute to our sense of touch. And for communication, hair grows in different parts of the body and thicker in the face on men to help communicate the maturity of a man after puberty. Then their hair becomes thicker, forming a beard, and this is a signal that the man is mature, and so is an important function for communication. Notice here there's a smooth muscle called erector pilae attached to the hair follicle. The erector pilae can pull on the hair follicle, and the hair stand up straight causing goose bumps. And in our ancestors that had more hair on the surface, more hair covering their body, the erector pilae causing the hair to stand up straight would have made them look more intimidating and also could have helped increase insulation. Hair can help to hold heat into our body and having our hair stand up on end would create a thicker layer of warm air surrounding the body to help insulate our body. Here's a light micrograph of a hair follicle. You can see the layers of epithelial cells within the hair follicle here that divide and differentiate and accumulate keratin as they differentiate dye forming the root of the hair that pushes up past the surface to form the shaft of the hair. We can also see adjacent to the hair follicle are a stratified cuboidal epithelium of the sebaceous gland. The sebaceous gland produces an oily secretion that will help to condition and lubricate the hair and protect against infection. The nervous tissue that's surrounding the hair follicle is called the hair follicle receptor. There are sensory nerve fibers that carry information from a variety of specialized amount of sensory receptors in the skin. The fibers carrying information from the hair follicle receptor detect movement of the hair which contributes to our sense of touch. There are also a variety of free nerve endings that we can see here in the illustration branching all through the dermis and epidermis. These free nerve endings contribute to our sense of pain as well as sense of temperature and itching sensations. The Bacinian corpuscle is a specialized touch receptor found deep in the reticular layer of the dermis that contributes to the sense of deep pressure and detecting vibration. Meisner's corpuscle is a touch receptor or somatosensory receptor that's found in the papillary layer of the dermis. These are especially common in the skin on the tips of our fingers that are very sensitive in order to detect light touch. The merkle cell is a specialized sensory receptor found in stratum basale of the epidermis which is sensitive to changes in the shape of the epidermis that stretch and pull on the merkle cell and then merkle cells communicate with sensory neurons that relay that information into the central nervous system to contribute to the somatosensation, the sense of touch the sense of our body position and the sense of touch in our skin. Here we see an illustration of a sebaceous gland and a light micrograph showing an image of a sebaceous gland attached to a hair follicle. Sebaceous glands have a stratified cuboidal epithelium and have the structure of a simple branched alveolar multicellular exocrine gland. The product that's secreted by sebaceous gland is an oil and this oil is known as sebum. Sebum helps to lubricate the hair and skin, condition the hair and skin to keep it from becoming brittle and dried out and also has an antibacterial property in order to help prevent infection. Here we can see an illustration showing an eccrine sweat gland and eccrine sweat gland is the most common type of sweat gland that produces a watery sweat in order to cool the body. They have a coiled tubular structure with a stratified cuboidal epithelium and the duct opens at the surface of the skin through the epidermis with a pore that opens to the skin surface and releases this watery secretion in order to help cool the body down. It's important to call this an eccrine sweat gland in order to distinguish it from another type of sweat gland called an apocrine sweat gland. Apocrine sweat glands are located in the axillary region, the armpit as well as the groin, face and nipples and they're stimulated by hormones during puberty and produce an oily sweat containing lipids and proteins that function as nutrients in order to support the growth of bacteria and this is what contributes to the characteristic odor associated with the body following puberty. Nails are another accessory structure produced from modified epidermal tissue. There are stem cells inside of the nail matrix that divide and differentiate and produce the hard keratin of the nails. The nail like the hair is essentially dead cells that filled with keratin and all that is left is the keratin that creates the exposed nail. This matrix surrounds the root of the nail which is covered by a proximal fold of skin where the proximal skin fold meets the exposed nail is the cuticle or eponychium and the exposed region of the nail is called the body of the nail Blood vessels under the body of the nail give the appearance of a pink color to the nail because we can view the dermis through the body of the nail where the blood vessels are traveling through the dermis and in some cases the nail body becomes discolored as a result of metabolites in the blood. For example this can be used in the diagnosis of respiratory diseases. The functions of the nail include protection. Nails provide a little bit of extra strength to the tips of the digits to the tips of our fingers and the tips of our toes. So the tips of the fingers and toes are the most vulnerable exposed to great forces. The nails can also help with defense they can function for scratching and tearing, clawing. Nails can also be useful tools for helping us to grasp small objects to increase our grip on an object.