INTEGUMENTARY SYSTEM

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

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

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

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

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

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

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

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

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

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

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

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)

Accessory Structures (blood, hair follicles, glands) 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)

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

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

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 Arrector pili muscles attaches to each hair follicle Contraction causes hair to stand up Causes goose bumps

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

Specialized 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