1. Chapter 5 b Appendages of the Skin

2. Skin Appendages Includes several derivatives of the epidermis Sweat glands Sebaceous (oil) glands Nails Hair follicles Hair

3. Sweat Glands

4. Sweat glands Widely distributed in skin Also called sudoriferous glands –Sudor = Sweat More than 2.5 million per person

5. Sweat glands Different types –Prevent overheating of the body –Secrete cerumen (ear wax) –Secretion of milk

6. Sweat glands Two main types: –Eccrine –Apocrine

7. Eccrine Sweat Glands Eccrine glands Most numerous, widely distributed – especially abundant on the palms, soles of feet, and the forehead

8. Eccrine Sweat Glands Eccrine glands Simple, coiled tubular gland –Secretory part lies coiled in the dermis –Open to skin surface by ducts (pores)

9. Sweat Composition Mostly water (99%) Some salts (mostly NaCl) Vitamin C Antibodies Dermicidin (a microbe-killing protein) Lactic acid (attracts mosquitoes)

10. Sweat Composition Traces of metabolic waste Small amounts of some ingested drugs Normally sweat is acidic pH between 4-6

11. Sweat Function Sweating is regulated by the sympathetic division of the autonomic nervous system We have little control Major role is to prevent overheating of the body Excretes waste products Acidic nature inhibits bacteria growth

12. Sweat Function –Heat induced sweating helps dissipate excess heat Prevents overheating of the body Begins on the forehead –Emotionally induced sweating (Cold Sweats) Brought on by fright, embarrassment, nervousness Begins on palms, soles, armpits

13. Apocrine Sweat Glands Found in the axillary (arm pit) and anogenital areas Larger than eccrine glands Ducts empty into hair follicles

14. Apocrine Sweat Gland Secretion contains same component as sweat plus fatty substances and proteins Odorless when secreted, but when decomposed by bacteria on skin, turns musky – basis of body odor Sometimes has a milky or yellowish color

15. Apocrine Glands Begins functioning at puberty Becomes active during pain, stress, and sexual encounters May be analogous to the sexual scent glands of animals

16. Other Sweat Glands types Ceruminous glands –modified apocrine glands in external ear canal that secrete cerumen (earwax) –Deters insects and block entry of foreign material

17. Other Sweat Glands types –Mammary glands – specialized sweat glands that secrete milk –Considered part of the female reproductive system

18. Sebaceous (oil) glands  Simple alveolar glands  Found all over the body – except palms and soles of feet  Small on body trunk and limbs, but large on face, neck, and upper chest

19. Sebaceous (oil) glands Produce oil (sebum) Lubricants and softens skin and hair Kills bacteria Most with ducts that empty into hair follicles Glands are activated at puberty Stimulated by hormones

20. Homeostatic Imbalances When a sebaceous gland duct is blocked by accumulated sebum, it forms a whitehead If whitehead material oxidizes and dries, it darkens to form a blackhead

21. Homeostatic Imbalances Acne is an active inflammation of sebaceous glands – usually caused by a bacterial infection, often staphylococcus

22. Homeostatic Imbalances Seborrhea (cradle cap) in infants –Caused by overactive sebaceous glands –Begins on the scalp as pink raised lesions that gradually become yellow to brown Careful washing to remove excessive oil often helps

24. Nails Scale-like modification of the epidermis Clear protective covering on the dorsal surface of the distal part of a finger or toe (lacks pigment) Correspond to the hooves or claws of other animals Contains hard keratin (skin contains soft keratin)

25. Nails Each nail has –a free edge –A body (visible attached portion) –A root (embedded in the skin) Deeper layers of the epidermis extend beneath the nail as the nail bed Thickened proximal portion of the nail bed, called the nail matrix responsible for nail growth

26. Nails Nails appear pink because of capillaries in the underlying dermis Region that lies over the matrix appears as a white crescent call the lunula Proximal and lateral borders are overlapped by skin folds called nail folds

27. Nails Proximal nail fold projects onto the nail body called the cuticle Underneath the free edge is called the quick

28. Nail Structures Slide 4.22 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Free edge  Body  Root of nail  Cuticle Figure 4.9

30. Hair Distribution Millions of Hairs are distributed over the entire skin surface except –Palms, soles, lips, nipples and portions of the external genitalia

31. Hair Function Functions of hair include: –Helping to maintain warmth (more so in other mammals) –Alerting the body to presence of insects on the skin (main function) –Guarding the scalp against physical trauma, heat loss, and sunlight

32. Hair Function Functions of hair include: –Eyelashes shield the eyes –Nose hairs filter large particles like lint and insects from the air we breath

33. Structure of Hair Filamentous and flexible strands of dead keratinized cells produced by hair follicles Made up of the shaft projecting from the skin, and the root embedded in the skin Contains hard keratin –which is tougher and more durable than soft keratin of the skin and does not flake off

34. Structure of Hair If shaft is flat and ribbonlike in cross section, the hair is kinky or curly

35. Structure of Hair If shaft is oval, hair is wavy

36. Structure of Hair If shaft is round, hair is straight and tends to be course

37. Hair Slide 4.18 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Produced by hair bulb  Consists of hard keratinized epithelial cells  Melanocytes provide pigment for hair color Figure 4.7c

38. Structure of Hair – 3 layers 1. Medulla 2. Cortex 3. Cuticle Medulla –Central core –Consists of large cells and air spaces –Absent in fine hairs

39. Structure of Hair – 3 layers 1. Medulla 2. Cortex 3. Cuticle Cortex –Bulky layer surrounding the medulla –Several layers of flattened cells

40. Structure of Hair – 3 layers 1. Medulla 2. Cortex 3. Cuticle Cuticle –Outermost layer –Single layer of overlapping cells

41. Figure 5.6a The hair shaft consists of a core called the medulla, a cortex, and an outermost cuticle

42. Hair conditioners smooth out rough surface of cuticle to make hair look shiny Cuticle tends to wear away at the tip of the hair shaft, allowing the keratin fibrils in cortex and medulla to frizz out, creating ‘split ends’

43. Color Pigmented by melanocytes at the base of the hair Gray or white hair results from decreased melanin production and from the replacement of melanin by air bubbles in the hair shaft

44. Hair Follicle Root sheath extending from the epidermal surface into the dermis Deep end is expanded forming a hair bulb A knot of sensory nerve endings (a root hair plexus) wraps around each hair bulb Bending a hair stimulates these endings, hence our hairs act as sensitive touch receptors

45. Hair Follicle Figure 5.6c

46. Associated Hair Structures Slide 4.20 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Hair follicle  Dermal and epidermal sheath surround hair root  Arrector pilli  Smooth muscle  Sebaceous gland Figure 4.7a

47. Types of Hair Vellus – pale, fine body hair found in children and the adult female Terminal – coarse, long hair of scalp, eyebrows, axillary (armpit), and pubic regions

48. Hair Growth Rate of hair growth – 2.5 cm per week, but varies some with age and gender Each follicle goes through growth cycles Active stage – active growth, last from weeks to years Regressive stage – Hair matrix cells die, hair bulb shrivels somewhat Resting stage – lasts one to three months

49. Hair Growth After resting stage, the matrix proliferates again and forms a new hair to replace the old one that has fallen out or will be pushed out by the new hair. We lose about 90 scalp hairs daily Follicles of eyebrows only stay active 3 to 4 months, which is why eyebrows are not as long as the hair on our heads

50. Hair Thinning & Baldness Alopecia –hair thinning in both sexes (as we age) True, or frank, baldness –Genetically determined and sex-influenced condition –Male pattern baldness is most common

51. Other causes of hair loss or thinning –Fever, surgery, severe emotional trauma, drugs, protein-deficient diets Hirsutism = excessive hairiness –In women may be the result of an adrenal gland or ovarian tumor

52. Rosacea Usually on cheeks or nose Begins as a sudden flushing of the skin that goes away Then this flushing reoccurs, lasting longer each time Eventually it becomes a persistent condition Usually strikes between the ages of 30 to 50

53. Rosacea Sometimes associated with heavy drinking – but not true Alcohol does worsen the condition, but so does spicy foods, hot baths, and exposure to sun Comedian W.C. Fields had this condition on his nose

54. Port Wine Stains Blazing red birthmarks –Bright pink to purple blotches on the skin Some Central American countries thought these were the mark of the devil Gypsies believed they were signs of the mother’s guilt

55. Port Wine Stains No known cause Happens during fetal development Laser therapy can remove, but is very costly

56. Tattoos Using a needle to deposit pigment in the skin dermis Originated around 8000 BC Can be dangerous –Risk of allergic reaction and bloodborne infectious diseases such as hepatitis

57. Quiz Appendages of the Skin Next time! Complete study guide pages 106-108