okay in this section we're going to talk about the structures and functions of hair so hair itself is actually made of dead keratinized cells and you don't find hair on the palm souls lips nipples or portions of the external genitalia but everywhere else you do find here and some of the functions of hair include you know sort of sensation of objects on your skin like insects hair on the head guards against physical trauma hair also protects from heat loss and shield the skin from sunlight exposure so you'd find that those areas of your body that are hairy are less likely to get burned by you know some burn now in terms of the structure of a hair we call these pill eye and there are basically flexible strands of dead keratinized cells in fact the hair itself is on a structured very similarly to the stratum corneum of your skin in the sense that it's a thick layer of dead keratinized cells however in this example hair is actually more of a tubular shape rather than being flat and superficial now it's produced by hair follicles which are essentially you know keratinocytes in the structure of stratified squamous epithelium and this contains hard keratin it's not like soft keratin they find in skin hard keratin is tougher and more durable and these cells don't flake away so that hairs typically stay as one solid band now in terms of regions of a hair we have the shaft versus the root the shaft is the area that extends above the scalp or just extends above skin this is where characterization is complete the root is the area within the skin or scalp here and it says where keratinization is still occurring now the three parts of a hair shaft include the medulla cortex and cuticle medulla means Marron so this is the central core of large cells and air spaces the cortex is several layers of flattened cells that surround the medulla in the cuticle is the outer layer that consists of overlapping layers of single cells now hair pigments are made by melanocytes within the hair follicle itself now turns out different combination of melons like there's yellow Rost brown or black melons these are what create the different hair colors turns out that red hair has an additional type of pigments called pheomelanin and gray or white hair results from melanin production that decreases instead you get air bubbles that fill melanin within the shaft instead of melanin itself now just looking at a cross-section of hair at the level of the root what we find is that this is the follicle itself so the follicle has peripheral connective tissue sheath and that's what attaches the actual epithelial layer here which is you know this epithelial root sheath now it turns out that these cells divide and push inward just like epithelium does in your skin in fact as these cells of divide and push inward they start to approach the hair itself and what we find is that by the time those cells make it to the hair they're essentially dead cells that are full of keratin in the hair shaft itself ours are the roof it's actually made of cuticle cortex and medulla the cuticle is sort of the outermost layer cortex is the you know this out layer here and the module is the the deeper central layer that can contain some air bubbles and this is of what makes up your hair itself now these hair follicles extend from epidermal surface to the dermis and essentially we got the bulb which is an expanded area deep in the follicle the hair follicle receptors is also called a root hair plexus have sensory nerve endings that wrap around the bulb and this is actually considered a sensory touch receptors because if your if your hair bends it's going to activate this hair follicle receptor now the wall of the follicle itself is made of a peripheral connected to sheath which is what we saw it's made from dermis I'll so call the fibre sheath and there's a glassy membrane which is basically a basal lamina and then we have the epithelial root sheath which is derived from epidermis because it's made of stratified squamous epithelium now the hair matrix is the actively dividing area of the bulb that produces new hair cells and as these cells divide they start to push upward and incorporate into the growing hair now as the matrix makes new cells it pushes older one upward in it turns out that our hair follicle also has an erector pili muscle attached which is basically a smooth muscle that's involved with goosebumps now the hair papilla is an extension of dermal tissue into the bulb of the hair itself and this actually supplies nutrients to the growing hair and specifically supplies nutrients to the hair matrix so just looking at this structure here this is actually a longitudinal section of the hair itself you can see you remember our connective tissue sheath on the outside we have our epithelial root sheath here and we have our hair itself with our medulla and the cortex now this expanded tip here is called the bulb and this protrusion of dermis into the bulb is called the papilla which contains lots of blood vessels and nerve endings and this is ultimately what supplies nutrients to the matrix which is here and this is ultimately the place where cells divide to grow into the extending hair itself and it makes sense that your that your nutrient supply would be close to the cells that divide a lot you can find some melanocytes nearby because these are the ones that basically incorporate melanin into the growing hair and that's ultimately what gives hair different color and in the absence of melanin hair is gonna be kind of grayish or white because of air bubbles rather than melanin itself now there's different types of hair vellus hair is pale find body hair you find in children and adult females thinking this is like peach fuzz terminal hair is the coarse long hair you find us on sky the scalloped eyebrows and it grows at puberty so you find this in the axillary and pubic regions and both sexes also the face and neck of males now nutrition hormones do affect hair growth so if senda individuals are having abnormalities in hair growth this could reflect you know hormonal or nutrient disturbances and follicle cycles between active and regressive phases and you lose about 90 scalp hairs a day and hair grows about 2.25 millimeters per week now alopecia is a term we used to describe for hair thing in both sexes after age 40 so alopecia is just an age related loss of hair but this difference from true or frank baldness because this is genetically determined and sex linked now this is what's associated with male pattern baldness because this is actually caused by a follicular response to a hormone called dihydrotestosterone or DHT dihydrotestosterone is a more potent form of testosterone but this actually causes hair to not grow as quickly which can lead to male pattern baldness now hair thinning can be induced by several factors for one if you have really high fever that can lead to the thinning of hair surgery emotional trauma can also leave us thinning of hair certain drugs like antidepressants and blood thinners or steroids chemo therapeutic drugs all these can lead to hair thinning protein deficient diets and there's other diseases like alopecia areata which is actually an autoimmune disease where immune system attacks the follicles some hair loss is reversible but others like from burns or radiation because it leaves a scar tissue and permanent injury of the cells these are permanent and so the hair unfortunately can't be recovered