1. Chapter 4: Skin & Body Membranes

7. Functions of the Skin  Thermoregulation  Protects body from mechanical damage (bumps/cuts), chemical damage, UV radiation, bacteria  Mini-excretory system to urea, salt and water  Sensory receptors  Manufactures protein and vitamin D

8. Structure of the Skin  1. Epidermis: stratified squamous epithelium that can keratinize. Cells are called keratinocytes. –Outermost layer: avascular –Keratin: fibrous protein component of nails, hair, calluses, and skin surface

9. 5 layers of epidermis  1. Stratum Basale or germinativum –Deepest layer –Gets nutrients –Cells divide here –New melanocytes and keratinocytes push up to become part of S.spinosum and S.granulosum

10.  2. Stratum spinosum –Keratinocytes provide a waterproof layer  3. Stratum granulosum –3-5 rows of flat cells –Cells fill with keratin granules –(cells die as they leave this row)

11. 5 layers (cont)  4. Stratum lucidum –Only found in palms and soles of feet –Clear flat, dead cells

12. 5 layers (cont)  5. Stratum corneum –Outermost layer 20-30cell layers thick. –Full of keratin –Shed and replaced every 25-45 days.

13. Skin color  Melanin: produced as body’s natural sunscreen –Protects against UV rays by shielding the DNA in the pigment –Colors range from yellow to black and are formed in the S. basale. (Freckles and moles)

14. Skin color  Carotene- orange yellow pigment deposited in the S. corneum.  Other colors –Cyanosis: poorly oxygenated blood causes blue skin

15. –Erythema: redness if embarrassed, fever, hypertension, allergy –Pallor or blanching: from fear, anger, anemia or low blood pressure

16. Skin color (cont)  Other colors –Jaundice: yellow from liver disorder, excess bilirubin in the blood. –Bruises- site where blood has escaped

17. Dermis (your “hide”) Dense connective tissue. Dense connective tissue.  Collagen: toughness & skin hydration  elastic fibers: elasticity/ stretching  Your leather shoes!

18. Regions of the Dermis  1. Papillary layer: fingerlike projections called dermal papillae.

19. –Form fingerprints, genetically determined –Contain capillary loops which provide nutrients to epidermis above.

20. Papillary layer  Contains pain receptors (free nerve endings) and touch receptors (Meissner’s corpuscles)

21. Regions of dermis (cont)  2. Reticular layer –Deepest skin layer –Contains blood vessels and capillaries (Maintains body temperature) –Sweat and oil glands –Deep pressure receptors called Pacinian corpuscles

22. Subcutaneous Layer  Aka: Hypodermis (below dermis)  Absorbs shock and insulates deeper tissue  Mostly adipose

23. Did you get it?  Create a simple diagram showing all the 3 major layers of the skin. Within each layer, label the sublayers as well.

25. Accessory Organs 1. Sebaceous Glands  Exocrine gland  Sebum (oil) lubricates skin and kills bacteria  arrector pili squeezes gland and forces oil out

26. Acne  Sensitive to male hormones –Acne at puberty  Ducts become blocked and secretions accumulate  Inflammation (pimple)  bacterial infection

27. 2. Sweat Glands  sudoriferous –2.5 million/person A. Eccrine Glands  Discharge onto skin through tube  All over body  Water, salt, urea, uric acid, vitamin C, lactic acid (mosquitoes), ammonia are produced  Heat regulation

28. B. Apocrine  Secretes into hair follicle –Axilllary and genital areas  Fun Fact: Odor caused by bacteria!

29. Accessory Structures  Hair –Produced in hair follicles –Hair papilla –Formed by stratum basale cells –Root/shaft

30.  Hair Shaft –Dead, keratinized cells –3 layers  Cuticle- surface  Cortex- provides stiffness  Medulla- core, soft

31.  Hair (cont) –Hormones account for hair development in scalp, pubic regions –arrector pilli muscles (smooth muscle): connect each side of hair to dermal tissue

32.  Hair color –Produced by melanocytes  Type of hair depends on shaft  flat: curly/kinky  Round: straight

33. Nails  Protect tips of fingers/ grasp objects  Structure –Scale-like modification of the epidermis –Dead cells filled with keratin –Colorless (except for lunula) pink from blood vessels underneath

35. Homeostasis  Injury/repair –Scab: blood clot (temporary fix) –Keloid: thickened area of scar tissue, covered by a shiny smooth epidermal surface (harmless)

36. Development of skin  Lanugo: hairy covering of fetus, shed by birth  Vernix caseosa: white, cheesy covering of fetus produced by oil glands to protect skin  Optimal appearance of skin- 20-30

38. Old Age  Amount of subcutaneous fat decreases (cold intolerance)  Less oil production and fewer collagen fibers (dryness/bruises)  By 50, # hair follicles dropped by 30%.  Melanin decreases/absent (gray or white)

39. Skin Cancer  1. Basal cell carcinoma: from S. basale –Least malignant, most common –Slow growing, 99% curable if surgically removed

40. Skin Cancer  2. Squamous cell carcinoma: from S. spinosum. Forms an ulcer often on the head –Will spread to lymph nodes –Prognosis is good if radiation or surgery

41. Skin cancer (cont)  3. Melanoma: cancer of the melanocytes –Often deadly –Forms where pigment is present (moles) –Spreads to surrouding lymph and blood vessels –Wide surgical excision and chemotherapy