Anatomy Lessons Anatomy of the skin The skin is the body's largest organ, covering the entire outside of the body and weighing approximately six pounds. In addition to serving as a protective shield against heat, light, injury, and infection, the skin also: - regulates body temperature. - stores water, fat, and vitamin D. - can sense painful and pleasant stimulation. Throughout the body, the skin's characteristics vary (i.e., thickness, color, texture). For instance, the head contains more hair follicles than anywhere else, while the soles of the feet contain none. In addition, the soles of the feet and the palms of the hands have much thicker layers. The skin is made up of the following layers, with each layer performing specific functions: - epidermis - dermis - fat layer epidermis The epidermis is the thin outer layer of the skin. The epidermis itself is made up of three sub-layers: stratuscorneum (horny layer) This layer contains continually shedding, dead keratinocytes (the primary cell type of the epidermis). The keratin, a protein formed from the dead cells, protects the skin from harmful substances. keratinocytes (squamous cells) This layer contains living keratinocytes (squamous cells), which help provide the skin with what it needs to protect the rest of the body. basal layer The basal layer is the inner layer of the epidermis, containing basal cells. Basal cells continually divide, forming new keratinocytes and replacing the old ones that are shed from the skin's surface. The epidermis also contains melanocytes, which are cells that produce melanin (skin pigment). dermis The dermis is the middle layer of the skin. The dermis is made up of the following: - blood vessels - lymph vessels - hair follicles - sweat glands The dermis is held together by a protein called collagen, made by fibroblasts (skin cells that give the skin its strength and resilience). This layer also contains pain and touch receptors. subcutis The subcutis is the deepest layer of skin and is also known as the subcutaneous layer. The subcutis, consisting of a network of collagen and fat cells, helps conserve the body's heat while protecting other organs from injury by acting as a "shock absorber."

Anatomy of a hair follicle The visible part of hair is dead. Yes, it's true. That beautiful bouncy hair that you have been admiring is just long shafts of dead cells. Now you are probably thinking -- well if it is dead, then how come it hurts if someone or something pulls on my hair? That is because each hair is rooted in a dynamic, living structure called a hair follicle, which is very much alive. Follicles (Latin for "little bag") are basically minute indentations of the outer layer of skin, also known as the epidermis. Straight follicles produce straight hair, while the bow-shaped ones produce curly hair. The outermost layer of the hair follicle is part of the dermal layer of the skin, which is the layer of skin under the epidermis. The follicle is connected to several other structures at this level. First, there is a "collar" of nerve endings around the follicle that send signals to your brain if your hair moves. This process is quite developed in mammals that feel their way through the world, such as dogs and cats. The tiny arrectorpili muscle is also connected to the outermost layer of the hair follicle. This muscle contracts due to cold or fright and causes the hair follicle to stand upright, creating a series of bumps on the skin known as "goosebumps." Two types of glands are located in the dermal layer of the skin: the sweat gland, which releases perspiration to keep us cool on hot days, and the sebaceous gland, which produces an oily substance called sebum that acts as a waterproof shield for the skin and hair and helps them to retain moisture. A small amount of sebum keeps hair shiny and lustrous; however, if it starts to build up, then your hair feels dirty. The lower part of the hair follicle or "bulb" is in the subcutaneous tissue, which is basically a layer of fat, cushioning muscles and bones. Matrix cells within the follicle bulb manufacture the hair shafts. The bulb encloses a dense network of capillaries (known as the papilla), which transport nutrients and oxygen to the busy matrix cells.

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