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 with the deepest are: stratum basale, stratum spinosum, stratum granulosum, and stratum corneum.
14. An additional layer called the stratum lucidum is in thickened skin.
15. In healthy skin, production of epidermal cells is balanced with loss of dead skin cells from the stratum corneum.
16. The rate of cell division increases where the skin is frequently rubbed or pressed.
17. Calluses are thickening of the stratum corneum.
18. Corns are keratinised conical masses on the toes.
19. Specialised cells in the epidermis called melanocytes produce melanin.
20. Melanin provides skin colour and absorbs UV radiation.
21. Melanocytes lie in the stratum basale and the underlying connective tissue of the dermis.
22. The extensions of melanocytes transfer melanin to epidermal cells by a process called cytocrine secretion.
1. The boundary between the dermis and epidermis is uneven because the epidermis projects inward and the dermis has papillae between the ridges of the epidermis.
2. Fingerprints form from the undulations of the dermis and epidermis.
3. The dermis binds the epidermis to the subcutaneous layer.
4. The dermis is largely composed of irregular dense connective tissue that includes tough collagen fibres and elastic fibres in a gel-like ground substance.
5. The dermis also contains smooth muscle that can wrinkle the skin of the scrotum.
6. Some smooth muscle of the skin is associated with hair follicles.
7. In the face, skeletal muscles are anchored to the dermis.
8. Nerves cell processes are scattered throughout the dermis.
9. Pacinian corpuscles are stimulated by heavy pressure.
10. Meissner’s corpuscles are stimulated by light touch. D. Subcutaneous Layer
1. The subcutaneous layer consists of loose connective and adipose tissues. 2. No sharp boundary separates the dermis and subcutaneous layers because fibres of the dermis are continuous with fibres of the subcutaneous layer. 3. The...