Understanding the Integumentary System: Functionality and Structure of Skin

1. INTEGUMENTARY SYSTEM

2. Introduction to the SKIN! • Integumentary System • Skin (aka- cutaneous membrane) • Nails • Hair Follicles • Skin Glands • The skin is the largest organ by weight • Functions: • Protective covering • Slows water loss • Regulates body temperature • Houses sensory receptors • Excretes small amounts of waste • Helps in vitamin D formation

3. Tissues of the Skin- Into to Layers • 2 distinct layers • Epidermis • Outer layer • Stratified squamous epithelium • Dermis • Inner layer • Connective tissue • Smooth muscle tissue • Nervous tissue • Blood • Layers are separated by a basement membrane

4. Tissues of the Skin- Hypodermis • Subcutaneous layer • Aka- hypodermis • Not part of the skin • Areolar and adipose tissues • Binds skin to underlying organs • Helps insulate • Contains blood vessels that supply the skin • The dermis and hypodermis lack a sharp boundary

6. Tissues of the Skin- Injections • Intradermal injections • Injected into the skin • Subcutaneous injections • Injected into the hypodermis • Administered through a hollow needle • Also called hypodermic injections • Transdermal patches • Drug passes into the epidermis through a permeable membrane • Motion sickness, chest pain, blood pressure, smoking cessation

7. The Epidermis- Characteristics and Functions • Lacks blood vessels • Thickest on palms and soles (0.0-1.4 mm) • Other body regions average 0.07-0.12 mm • Production of new epidermal cells balances loss of dead cells in healthy skin • Skin does not completely wear away • Cell division increases where skin is rubbed/pressed regularly • Leads to calluses and corns • Protective Functions • Shields against water loss • Prevents injury • Protects against harmful chemicals • Keeps out pathogens

8. The Epidermis-Layers • 4 main layers: • Stratum corneum • Outermost layer • Keratinized, dead epithelial cells • Keratinization- hardening of cells, waterproof keratin proteins made and stored in the cells • Stratum granulosum • Strantumspinosum • Stratum basale • Deepest layer • Able to divide and grown • Receive nutrients from dermis • Contains melanocytes

9. The Epidermis- Pigmentation • The epidermis contains melanocytes • Produce the pigment melanin • Found in the stratum basale • Melanin • Provides skin color • Absorbs UV radiation

10. Effect of Environmental Factors • Sunlight, UV light, X rays • Rapidly darken melanin • Stimulate melanocytes to produce more pigment • Pigment is transferred to nearby cells • Effect of Blood • Well oxygenated blood is bright red • Light-complexioned people may appear pink • Dilated vessels redden the skin • Overheated, embarrassed, under the influence of alcohol • Constriction of vesssel cause loss of color • Low body temperature, frightened/anxious person

11. Human Skin Color • Determined by heredity and environmental & physiological factors • All people have ~same number of melanocytes • Differences in skin color result from different amounts of melanin produced • Controlled by several genes • More melanin = darker skin

12. The Dermis- General Characteristics • The boundary between the epidermis and dermis is uneven • Dermal papillae extend from dermis into ridges of the epidermis • Increases surface area • Most abundant in hands and feet • Form fingerprints • Genes determine general patterns • Fetal movement forms distinct characteristics • The dermis binds epidermis to underlying tissues • Thickness ranges from 0.5 mm to 3.0 mm

13. The Dermis- Layers • Papillary Layer • Upper layer • Areolar connective tissue • Reticular Layer • Lower layer • Dense irregular connective tissue • Give skin toughness and elasticity

14. The Dermis- Additional Components • Smooth muscle fibers • Can wrinkle the skin (testes) • Associated with hair follicles and glands • Skeletal muscle fibers • Voluntary movements (facial expressions)

15. Nerve cells • Carry impulses to dermal muscles and glands • Carry sensory impulses away from sensory receptors • Lamellated corpuscles • In deep dermis • Respond to heavy pressure • Tactile corpuscles • In upper dermis • Sense light touch and texture • Accessory Structures (blood, hair follicles, glands)

16. Accessory Structures of the Skin-Nails • Protective coverings • Components: • Nail plate • Nail bed • Skin surface • Lunula • Most actively growing region • Produces keratinized, dead cells • Wears away with normal use • Analogous to hoofs and claws of other animals

17. Accessory Structures of the Skin- Hair Follicles • Hair is present on all surfaces except: palms, soles, lips, nipples and parts of external reproductive organs • Not well developed on other surfaces (forehead) • Originates in epidermis • Nourished by dermis • Grow, divide and push older cells toward surface • Cells become keratinized and die • Create the hair shaft

18. Average hair loss is 20-100 hairs a day • A single hair grows 2-6 years and is then replaced by a completely new hair • Genes determine hair color • direct the type and amount of pigment produced by melanocytes • Arrectorpili muscles attaches to each hair follicle • Contraction causes hair to stand up • Causes goose bumps

19. Accessory Structures of the Skin- Glands • Sebaceous glands • Associated with hair follicles • Oil glands • Produce sebum (oil and cell fragments) • Ducts usually empty into hair follicles • Activated by hormones • Keep hairs and skin soft, pliable and waterproof • Not on palms or soles

20. Sweat glands • ~2 million per person • Widespread • Originates in deep dermis • Eccrine glands • Most numerous • Abundant on forehead, neck, back • Palms and soles • Respond to elevated body temperature • Also respond to emotional stress • Apocrine glands • Develop a scent as they mix with skin bacteria • Activated at puberty • React to emotional upset, fright, pain, sexual arousal • Most unmberous in axillary regions and groin • Specialized sweat glands • Ceruminous glands- ear wax • Female mammary glands- milk