SE Ch.3 – Physiology & Histology of the Skin

1. Some interesting facts about healthy skin

  • Skin is a strong barrier protecting us from the outside elements.
  • Skin layers, nerves, cellular functions, hair follicles, and glands work together harmoniously to regulate and protect the body.
  • The skin has miles of blood vessels, millions of sweat glands, and an array of nerves within a network of fibers.
  • Hormones, growth factors, and other biochemicals control the skin’s functions.
  • Healthy skin is slightly moist, soft, smooth, and somewhat acidic.

2. What are the six main functions of the skin?

Sensation, protection, heat regulation, excretion, secretion, and absorption

3. What is the barrier function?

The mechanism that protects the skin from irritation and intercellular transepidermal water loss

4. How does sebum protect the skin?

Sebum is an oily substance that coats the surface of the skin to slow water evaporation, maintain water levels in skin cells, and keep the skin soft and protected from outside elements.

5. What is the function of the sudoriferous glands?

Prevent the body from overheating

6. What routes does the skin have for absorption?

The routes of skin penetration are through follicle walls, sebaceous glands, intercellular, and transcellular.

7. Name the two components of the dermis.

The dermis contains two layers, the reticular layer below and the papillary layer above.

8. Name the five layers of the epidermis.

  1. Basal or stratum germinativum, the growth layer where continuous cell mitosis occurs
  2. Stratum spinosum, where the spiny cells desmosomes originate, Langerhans cells involved in the immune system, Merkel cells for touch receptors, and melanosomes for pigment distribution
  3. Stratum granulosum, the grainy cells produce keratin granules and additional lipids for protection
  4. Stratum lucidum, the clear cells providing protection; thickest on the palms and soles
  5. Stratum corneum, the horny cells, barrier layer with the acid mantle providing protection

9. What are keratinocytes?

Keratinocytes comprise 95 percent of the epidermis and contain both proteins and lipids. They are found in all layers of the epidermis, moving up from the basal layer to the stratum corneum, protecting the epidermis. They undergo many changes and can be either hard, A-keratin or soft, B-keratin. Hard keratinocytes are found in hair and nails.

10. Clarify the process of skin melanization.

Tyrosinase, an enzyme, stimulates melanocytes to produce melanosomes, pigment-carrying granules, via dendrite projections up through the layers of the skin, toward the surface. Melanin protects the skin from UV radiation and other injuries, as well as hormonal influences.

11. How does skin repair itself?

Blood and lymph are the fluids that nourish the skin. Networks of arteries and lymphatics send essential materials for growth and repair throughout the body. Water, vitamins, minerals, and other nutrients are all important for skin health. The blood supplies nutrients and oxygen to the skin. Nutrients are molecules from food such as protein, carbohydrates, and fats. Topical products with small molecules can nourish the epidermis.

12. What influences hair growth?

Hormonal influences and genetics determine the distribution of each person’s hair, along with its thickness, quality, color, rate of growth, and whether the hair is curly or straight.

13. What kind of keratin does hair contain?

Hair contains 90 percent hard B-keratin.

14. What kind of keratin do nails contain?

Nails are composed of hard B-keratin.

15. Name the two main types of nerves and describe what they do.

  • Motor, or efferent, nerve fibers convey impulses from the brain or spinal cord to the muscles or glands. Secretory nerve fibers are motor nerves attached to sweat and oil glands.
  • Sensory, or afferent, nerve fibers send messages to the central nervous system and brain to react to heat, cold, pain, pressure, and touch

16. What glands help regulate the body’s temperature?

Sudoriferous glands help to regulate body temperature.

17. What are the two main glands associated with the skin?

Sudoriferous and sebaceous glands

18. What are the two types of sweat glands?

Apocrine glands are found under the arms and in the genital area. Eccrine glands are found all over the body, but are primarily on the foreheads, palms of the hands, and soles of the feet.

19. How do the Langerhans cells, leukocytes, and T cells work to protect the body?

  • Langerhans cells work to absorb, process, and carry antigens to the nearest lymph node for further immune system action.
  • Leukocytes are white blood cells that have enzymes to digest and kill bacteria and parasites. These white blood cells also respond to allergens.
  • T cells play an important role in the immune system by attacking virus-infected cells, foreign cells, and cancer cells.

20. Describe the differences between UVA wavelengths, UVB wavelengths, UVC wavelengths, and HEV light and their effect on the skin.

  • UVA radiation, also known as aging rays, contributes up to 95 percent of the sun’s ultraviolet radiation that reaches the Earth’s surface. The longer wavelengths of UVA (320 to 400 nanometers) penetrate deeper into the skin and cause genetic damage and cell death. UVA weakens the skin’s collagen and elastin fibers, causing wrinkling and sagging in the tissues.
  • UVB radiation, also known as burning rays, causes burning of the skin as well as tanning, aging, and cancer. UVB wavelengths range between 290 and 320 nanometers. Although UVB penetration is shorter than and not as deep as UVA, these wavelengths are stronger and more damaging to the skin and can damage the eyes as well. On a positive note, UVB radiation contributes to the body’s synthesis of vitamin D and other important minerals.
  • UVC radiation has more energy than UVA or UVB. It reacts with the ozone high in our atmosphere and from humanmade sources, such as welding torches, and UV sanitizing bulbs that kill bacteria and other germs.
  • HEV, or high-energy visible light, is the blue light from your TV, computer, and smartphone, which is said to penetrate the skin more deeply than UV rays and damage collagen, hyaluronic acid, and elastin. There is some evidence that the light may also worsen pigmentation problems, such as melasma. Evidence tying it to skin cancers and deep wrinkles is scant, however, in part because the subject is too new for long-term study results to be available.

21. How do antioxidants stop free radical damage?

Antioxidants are components that have an extra electron, vital to neutralize the chain reaction that occurs when a molecule loses an electron and becomes unstable by donating its electrons to stabilize the free radical’s electrons.

22. What environmental influences affect skin health?

Pollutants in the air from factories, automobile exhaust, climate, humidity, and even secondhand smoke can all influence the appearance and overall health of our skin.

23. What happens to the skin during the aging process?

Estrogen levels fluctuate throughout a woman’s life and affect the skin’s protective barrier, epithelial (external covering) tissue, and dermis. As skin ages, capillary and other vascular walls begin to weaken, lipids are reduced, the lymphatic system is less efficient, glands slow down, and there are fewer fibroblasts. The skin thins and collagen has less ability to respond to physical changes from aging and sun damage. As estrogen is depleted, skin begins to lose its tone. Reduced glycosaminoglycans mean less moisture in the tissues; keratinocytes are reduced (slower cell mitosis); melanocytes are reduced (less protective pigment); and cellular exchanges are reduced. Testosterone levels become dominant as estrogen decreases, which can increase sebum production, pore size, and hair growth on the face.