I. Skin and Its Tissues
1. The skin is composed of several kinds of tissues.
2. Skin is a protective covering that prevents many harmful substances from entering the body.
3. Skin also retards water loss and helps regulate body temperature.
4. Skin houses sensory receptors and contains immune system cells.
5. Skin synthesises vitamin D and excretes a small amount of waste products.
6. The two distinct layers of skin are epidermis and dermis.
7. The outer layer is called the epidermis and is composed of stratified squamous epithelium.
8. The inner layer is called the dermis and is made up of connective, epithelial, muscle, nervous, and blood tissue.
9. A basement membrane separates the two skin layers.
10. The subcutaneous layer is beneath the dermis.
11. The subcutaneous layer is composed of loose connective tissues and adipose tissue.
1. The epidermis lacks blood vessels.
2. The deepest layer of the epidermis is called the stratum basale.
3. The stratum basale is nourished by blood vessels in the dermis.
4. Cells of the stratum basale can divide and grow because they are nourished so well.
5. When new cells enlarge, they push old epidermal cells away from the dermis toward the surface of the skin.
6. The farther the cells travel, the poorer their nutrient supply becomes and eventually they die.
7. Older skin cells are called keratinocytes and are held together with desmosomes.
8. Keratinisation is the accumulation of keratin in epidermal cells which hardens the epidermis. 9. As a result of keratinisation, many layers of tough, tightly packed cells accumulate in the epidermis.
10. The outermost layer of the epidermis is called the stratum corneum.
11. The epidermis is thickest on the palms and the soles of feet.
12. Most areas of the epidermis have four layers.
13. The four layers starting...