Biology 141

1. Biology 141 Integumentary System Chapter 5

2. The Integument • Integument: Skin – largest body organ • Integumentary System: • Skin • Hair • Nails • Function: • Protection • Maintain body temperature • Provide sensory input Dermatology: medical specialty dealing with the integumentary system

3. Structure of the Skin • Cutaneous membrane: skin • Epidermis – superficial layer • Dermis – deep layer • Subcutaneous membrane • Hypodermis – fat layer; not technically a part of the skin.

4. Structure of the Skin • The 2 layers of skin; • epidermis • Multilayered epithelial tissue • thinner • Dermis • Connective tissue • thicker

5. Epidermis • Cell types found in the epidermis: • Keratinocytes: • multilayered • Produce keratin protein (tough, water repellant) • Melanocytes • Produces pigment melanin to protect nuclear DNA in keratinocytes • Langerhans cell • Immune response • Merkel cells • Contact Merkle discs to detect sensations

6. Epidermis Tissue Layers • Composed of different strata (layers) • outermost - dead cells • Innermost - Cells divide • Cells die as they are pushed upward • Layers originate from the deepest cell layer of columnar cells called the stratum germinativum.

7. Sublayers of the Stratum germinativum • Stratum basale ("base layer") • Cells of stratum basale are closest to the blood supply in the dermis and are thus the healthiest  • Only these cells can reproduce • Stratum spinosum ("spiny layer") • Cells are pushed from below and become "squished" and look "spiny" on cross sectional view • Because the cells are farther away from the dermal blood supply, they are less healthy and thus don't reproduce

8. Basal Cell Carcinoma • Low magnification (left) of skin cross-section of shows different layers (epidermis, dermis and subcutaneous tissue), and • areas of tumor invasion.  • Higher magnification (right): tumor cells resemble those in the normal basal cell layer of the epidermis.  • Tumor cells appear to bud off from the epidermis and grow downward as islands and cords of basophilic cells with hyperchromatic nuclei. 

9. Epidermis Tissue Layers (deep to superficial) • Stratum germinativum ("growth layer") • stratum basal – germination basement layer • Stratum spinosum – “thorn-like” • Stratum granulosum "grainy layer" • Stratum lucidum "clear layer" • Stratum corneum “horny layer” (top layer)

10. Epidermis: Tissue Layers • stratum basal: • Single row of cuboidal or columnar keratinocytes. • Some are stem cells • Contains • Melanocytes • Langerhans cells • Merkle cells and discs

11. Epidermis: Tissue Layers • stratum basal – • Damage to this layer damages stem cells • Unable to regenerate skin • Require skin grafts • Grafts can be autologous (same individual) or transplanted from a donor. • Skin sheets can also be grown in the lab

12. Epidermis: Tissue Layers • stratum spinosum • multilayered keratinocytes • Few Langerhans cells and Melanocytes

13. Epidermis: Tissue Layers • stratum granulosum • Multilayered, flattened keratinocytes • Cells undergoing apoptosis • Secretes water repellant • cells loose nuclei, appear grainy • Keratohyalin (a precursor to keratin) forms in granules here

14. Epidermis: Tissue Layers • stratum lucidum: • Multilayered, dead keratinocytes • with large amount of keratin • Translucent and flattened • Found only in thick skin (hairless) • Fingertips • Palms • soles

15. Epidermis: Tissue Layers • stratum corneum: • Multilayered • Flat, dead keratinocytes • primarily keratin protein • "horny layer" - cells have processes • Flattened cells filled with keratin form "keratinized layer" and make this "keratinized stratified squamous epithelium" • Constant friction results in callus formation

17. Dermis • Dermis: • Connective tissue • Contains • Blood vessels • Nerves • Glands • Hair follicles

18. Dermis 2 main regions: • Papillary: upper layer • Reticular: deep layer

19. Dermis • Papillary: upper layer • lies next to the epidermis • contains the derma papillae (projections into the upper epidermis) • epidermal ridges creat fingerprints, palm prints and footprints. • Contain capillaries • Contain Meisssner corpuscles (tactile receptors) • Contain free nerve endings • Senses temperature, pain, itch, tickle

20. Dermis • Reticular: deep layer • Attaches to the subcutaneous layer • Dense irregular connective tissue • contains more collagen fibers • increasing the strength of the skin. • Contains: • Few adipose cells • Hair follicles • Nerves and Pacinian corpuscles (deep pressure) • Sebaceous glands (oil) • Sudoriforous glands (sweat)

21. Accessory Structures • Receptors: Meissner’s corpuscles and Pacinian corpuscles • Meissner’s: located in the papillary layer of dermis • project into the papillae. • touch receptors • Pacinian: spherical, onion-like • Lie deep in the reticular layer • pressure

22. Meissner’s Corpuscle detects light touch Papillary layer Pacinian Corpuscle detects deep touch (pressure) Reticular layer Sensory receptors in the Dermis

24. Dermis • Tears in the reticular region of the dermis result in stretch marks. • Incisions against the grain of the collagen fibers = wide scar • Incisions with the grain = thin scar

25. Structural Basis of Skin Color • Skin color pigments: • Melanin • Hemoglobin • Carotene • Melanin – number of melanocytes the same in all people • Amount of melanin produced varies • Accumulation results in • Age spots • Freckles • moles

26. Melanin • Function: • Absorbs UV radiation • Prevents damage to DNA in epidermal cells • Neutralizes free radicals

27. Found in RBCs Skin color depends on amount of oxygen in the blood Blue – cyanotic: low oxygen Yellow - jaundice: high bilirubin Liver damage Red – erythema: engorgement of capillaries Injury Heat Infection Inflammation Allergic reaction White – pallor: low number of RBC Shock anemia Hemoglobin

28. Carotene • Yellow-orange pigment found in egg yolks and orange vegetables • Precursor to vitamin A • Excessive dietary intake results in accumulation in the subcutaneous layer

29. Albinism / Vitiligo • Albinism: Inherited inability to synthesize melanin • Melanin is not produced in skin, hair, and eyes. • Vitiligo: partial or complete loss of melanocytes in patches of skin • Immune system attacks and destroys melanocytes.

30. Accessory Structures Hair: pili • Columns of dead, keratinized cells - compactly cemented together. • hair shaft – portion of the hair that projects above the surface. • root – portion below the surface extending into the dermis.

31. Hair • Hair shaft and root consist of 3 concentric layers of cells: • Medulla • Cortex • Cuticle

32. Cuticle showing scales No medulla, brown pigment granules in cortex Human Hair • Light medulla

33. Hair follicle: composed of the root sheath – encasement with 2 layers: Internal root sheath produced by matrix, surrounds root External root sheath extension of epidermis The Dermal root sheath is part of the dermis Hair

34. Hair • bulb - enlarged region of the root containing the follicular papilla (involution of loose connective tissue).

35. Hair • arrector pili muscle – smooth muscle that upon contraction forces the skin into goose bumps.

36. Accessory Structures Glands: sebaceous and sweat glands • Sebaceous glands: • Usually connected to hair follicles • secretes sebum (oil) • Moisturizes hair and skin • keeps hair pliable. • Keeps skin soft • Inhibits bacteria

37. Blocked sebaceous gland Acne: Inflammation of a sebaceous gland. • Normal sebaceous gland

38. Sudoriferous Glands (Sweat glands) 2 main types of glands: eccrine and apocrine • eccrine: • empty directly out through the skin surface • tubular with a coiled basal portion located deep in the dermis • Regulates body temperature • apocrine: • larger, empty directly into the hair follicle canal • secretory portion located in the subcutaneous layer • Excretory duct opens into hair follicle • stimuli: psychic factors; emotions, sexual excitement

39. Sudoriferous Glands

40. Accessory structures and location

42. Ceruminous Glands • Modified sweat glands in the external ear. • Produce ear wax (cerumen) • Provides a sticky barrier

43. Nails • Tightly packed, hard, keratinized epithelial cells. • Structure: • Nail body: visible portion • Pink due to capillary bed • Free edge: part that extends past the digit • White due to lack of capillaries • Nail root: portion buried in a fold of skin

44. Nails

45. Types of Skin • 2 types of skin based on structure: • Thin (hairy) skin • Thick (hairless skin)

46. Thermoregulation: by sweat and blood flow Blood reservoir 8-10% of blood flow Protection Against external assault Cutaneous sensations Tactile, pressure, pain, temperature, tickle Excretion and absorption Excrete salts, water, and small amounts of CO2 and urea Absorbs lipid molecules (vitamins A,D,E and K, drugs, lotions, poisons, heavy metals, steroids) Synthesis of vitamin D UV light activates precursor molecules that can be modified by the liver. Vit. D produces calcitrol which aids in the absorption of calcium in the GI tract. Functions of the Skin

47. Maintaining Homeostasis: Skin Wound Healing • Wound healing can occur via 2 routes: • Epidermal Wound Healing – affects only the epidermis. • Deep Wound Healing – wound extends to dermis and subcutaneous layers

48. Epidermal Wound Healing • Injury response: • Basal cells detach from the basement membrane. • Hormone (epidermal growth factor) stimulates basal stem cells to divide to replace migrating cells. • Migrating cells move across wound • Cells stop migrating upon touching other cells (contact inhibition)

49. Deep Wound Healing • 4 phases: • Inflammatory: • clot formation closes the wound, WBC kill invaders • Migratory: • scab formation, epithelial cells migrate, fibroblasts produce fibrin for scar tissue • Proliferative: • Extensive growth of epithelial cells, depositing collagen fibers • Maturation: • Scab sloughs off, collagen fibers organize

50. Development of the Integumentary System • Epidermis is derived from the ectoderm • Dermis is derived from the mesoderm