Integumentary System

1. Integumentary System Chapter 5

2. Overview • Composed of skin and it’s derivatives (sweat & oil glands, hairs and nails) • Primary function is protection

3. The Skin I Two distinct regions • Epidermis - outermost protective shield - composed of epithelial cells - avascularized, obtains nutrients by diffusing through tissue fluid from blood vessels in the dermis • Dermis - makes up bulk of skin - tough, leathery layer; fibrous connective tissue - vascularized

4. The Skin II • The dermis and epidermis rest on subcutaneous hypodermis, (superficial fascia) • Not technically part of skin, but shares many of its functions • Mostly adipose tissue w/ some areolar connective • Stores fat • Anchors skin to underlying structures (usually muscle), but allows free sliding • Shock absorber and insulator

6. Epidermis • Avascular, keratinized stratified squamous epithelium • Cells: • Keratinocytes (majority) • Melanocytes • Langerhan’s cells (a.k.a. epidermal dendritic cells) • Merkel cells • Layers/strata (from deep to superficial): • Stratum basale (basal layer) • Stratum spinosum (prickly layer) • Stratum granulosum (granular layer) • Stratum lucidum (clear layer) *not found in “thin” skin • Stratum corneum (horny layer)

7. Dermis - Overview • Dense, irregular connective tissue; Well-supplied with blood vessels, lymphatic vessels & nerves • Cells typical of connective tissue proper: fibroblasts, macrophages, occasional mast cells & WBCs • Semi-fluid matrix heavily embedded with collagen, elastin and reticular fibers • Contains cutaneous receptors, glands & hair follicles

8. Layers of the Dermis • Papillary – superficial & relatively thin • Areolar connective tissue • Dermal papillae that protrude into epidermis • Epidermal ridges that produce fingerprints • Reticular – deep, 80% of dermal thickness • Connective fibers more densely interwoven • Less dense regions between collagen bundles produce cleavage (tension) lines in skin • Points of tight dermal attachment to hypodermis produce dermal folds or flexure lines

9. Skin Color • Skin color reflects the amount of pigments (melanin & carotene) & oxygenation level of hemoglobin in the blood • Melanin production is stimulated by exposure to UV light • Melanin is produced by melanocytes & transferred to keratinocytes where it protects keratinocyte nuclei from damaging effects of UV radiation • Skin color can be affected by emotional state • Alterations in skin color may indicate certain diseases

10. Appendages of the Skin: Sweat Glands • a.k.a “suduriferous” glands • 2 sub-categories • Eccrine (merocrine) sweat glands • Distributed over entire body surface, primary function is thermoregulation • Simple, coiled tubular glands that secrete a salt solution with a few other solutes • Ducts usually empty to skin surface via pores • Apocrine sweat glands • May function as scent glands • Primarily in axillary and anogenital areas • Secretion similar to that of eccrine secretion, but also contains proteins & fatty substances on which bacteria thrive

11. Appendages of the Skin: Sebaceous (oil) Glands • All over body surface, except hands and soles • Simple, aveolar glands, ducts usually empty into hair follicles • Oily secretion, called sebum, lubricates the skin and hair, and acts as a bactericidal agent. • Activated (at puberty) and controlled by androgens

12. Hair • Hair consists of dead, heavily keratinized cells • Hair color reflects amount and kind of melanin present • 2 regions: • Root (embedded in skin) • Shaft (projects from the skin) • Hair structure: • Central medulla (core) • Cortex • Outer cuticle

13. Hair Follicles • Extend from epidermal surface into the dermis, deep end expands forming a bulb • Richly vascularized • Sensory nerve endings, root hair plexus, wraps around each hair bulb. Bending hair stimulates these endings, hair act as sensitive touch receptors • Arrector pili muscles pull follicles into an upright position, producing goose bumps • Components: • inner epidermal root sheath, enclosing the matrix (region of hair bulb that produces hair) • Outer connective tissue sheath derived from dermis

14. Types & Growth of Hair • Two classifications: • Vellus: body hair of children and adult females • Terminal: coarser, longer hair of eyebrows & scalp • Usually darker • Appear in axillary and pubic regions during puberty • Influences on hair growth and density: • Poor nutrition = poor hair growth • Conditions that increase blood (chronic physical irritation or inflammation) flow generally enhance local hair growth

15. Hair Thinning and Baldness • Hair grows fastest from teen years to 40s, then slows • Hair thinning or alopecia results from hairs are not replaced as fast as they are shed • True baldness (male-pattern baldness) is an x-linked genetic condition

16. Nails • Scale-like modification of the epidermis • Correspond to hooves or claws or other animals • Composed of keratin, like hair • Normally appear pink because of bed of capillaries under nail bed, region over thick nail matix appears as a white crescent, “lunula”

17. Functions of the Integumentary System • Protection: chemical barrier (antibacterial sebum), physical barrier (hardened keratinized surface), and biological barrier (phagocytes) • Temperature regulation: Skin vasculature & sweat glands, regulated by nervous system • Cutaneous sensation: sensory receptors respond to temperature, touch, pressure and pain • Metabolic functions: Vitamin D synthesized from cholesterol in skin cells • Blood reservoir: extensive vascular supply of dermis • Excretion: sweat contains small amounts of nitrogen wastes

18. Homeostatic Imbalances – Skin Cancer • Most common cause is UV exposure • Basal cell carcinoma and squamous cell carcinoma are cured if removed before metastasis • Melanoma (cancer of melanocytes), is less common but more deadly Basal Cell CarcinomaSquamous Cell CarcinomaMelanoma

19. Homeostatic Imbalances – Burns • Initial threat is loss of protein and electrolyte rich body fluids, which may lead to circulation collapse • Bacterial infection is also a significant threat • Rule of Nines to evaluate extent of burn • Classified, in increasing severity, as first-degree, second-degree and third-degree. Third degree requires grafting for recovery

20. Evaluating Burns

21. Developmental Aspects • Epidermis develops from embryonic ectoderm, dermis (and hypodermis) develop from mesoderm. • Fetus exhibits a downy lanugo coat. Fetal sebaceous glands produce vernice caseosa, which helps protects fetal skin from watery environment. • Newborn’s skin is thin. During childhood, skin thickens and more subcutaneous fat is deposited. During puberty, sebaceous glands are activated and terminal hairs appear in greater numbers. • In old age, rate of epidermal declines and skin and hair thin. Skin glands become less active. Loss of collagen, elastin fibers and subcutaneous fat lead to wrinkling. Delayed action genes cause graying and balding. Photodamage is a major cause of skin aging.