Integumentary System The skin and related structures

Functions of Your Skin Barrier against microorganisms Prevents water loss Thermoregulation - helps control body temperature (click for link) Thermoregulation Cutaneous sensation (for sensing your environment) Excretion of wastes (sweating) Aids in vitamin D production (helps body absorb calcium and protects against some cancers) Stores 5% of body’s blood

Layers of the skin Epidermis (outer most layer) Dermis (below epidermis) Hypodermis (consists of adipose tissue (fat) - separates skin from muscles (technically not part of skin)) See Figure 5.1 on pg 153

Epidermis (see figure 5.2 on pg 154) Top portion of the skin Avascular (has no blood vessels - nutrients diffuse from the blood vessels in dermis) Contains four types of cells: Melanocytes (produce melanin (pigment) - blocks UV radiation) Keratinocytes (produce keratin - helps prevent water loss and acts as “tough” covering) Langerhans’ (dendritic) cells (part of immune system - prevents infection in the skin) Merkel cells (sensory receptors for touch)

Epidermal layers (see figure 5.2 on pg 154) Outer (superficial) to inner (deep) Stratum corneum (dead cells filled with keratin - makes resistant to penetration and abrasions) Stratum corneum Stratum lucidium (only in thick skin) Stratum granulosum Stratum spinosum Stratum basale (bottom layer) - new cells arise from this layer through mitosis (cell division). Melanocytes found here

Epidermal Layers

Dermis Contains blood vessels supplying cells of epidermis Contains nerve endings, sweat glands, hair follicles, sebaceous (oil) glands Composed of the proteins collagen (strength) and elastin (stretch & recoil)

Dermal Layers Papillary layer - top portion - forms ridges called dermal papillae (forms fingerprints) - Rich in blood vessels Reticular layer - mostly collagen and elastin fibers - Hair rooted here - Contains coiled portion of sweat glands

Appendages of the skin Sudoriferous (sweat glands) Sebaceous (oil) glands Hair Nails

Sudoriferous Glands (main types) Eccrine (merocrine) glands Most abundant type Most numerous on forehead, palms and soles of feet Empty secretion on skin surface Secretion is 99% water, some salts, and small amounts of urea, ammonia, lactic acid Apocrine glands Found in axillary (armpit) and anogenital region Empty secretions onto hair follicles Secretions also have fatty acids and proteins (broken down by bacteria - causes body odor)

Other Sudoriferous Glands Ceruminous glands Make cerumen (earwax) Mammary glands Produce milk in females

Sebaceous (oil) glands Attached to hair follicle: release sebum (oil) onto hair Found throughout skin, but most numerous on face, neck, upper chest Help to moisturize and waterproof hair and skin A pimple results when a sebaceous gland is infected

Hair - Shaft - part of hair extending out of the skin - hair follicle (pinching in of the epidermis - surrounds hair) - Hair matrix (area of dividing new cells) - Papilla - dermal tissue at the hair root which supplies nutrients to the matrix - Hair follicle receptor - nerve ending surrounding base of follicle

Hair Growth Growth phase: - last from weeks to years (scalp) - Gets shorter (especially for men) after 40s* - Regulated by hormones and nutrition Regressive phase: - follicle shrinks, matrix cells die, hair falls out *Hair loss occurs when growth phase becomes too short for new hair to emerge from scalp

Homeostatic Imbalances of the Skin Skin cancers (3 main types) Burns (1st, 2nd, and 3rd)

Genes that Control Cell Division Proto-Oncogenes Initiate mitosis (accelerator) Tumor suppressor genes Inhibit mitosis (brake) *mutations must occur to both types of genes for cancer to develop

Skin Cancers Basal Cell carcinoma most common (30% of fair skinned people will get it 99% cure rate (surgically removed) involves stratum basale cells slow to metastasize

Skin Cancers Squamous Cell carcinoma common on head and hands (but can happen on any exposed area) Can appear as red scaly elevated bump Can spread rapidly if not detected early arises from cells in stratum spinosum (keratinocytes)

Skin Cancers Melanoma metastasizes (spreads) quickly/ highest mortality rate Appears as spreading brown/black patch one-third of cases arise from pre-existing moles

Self-examination for melanoma ABCD(E) rule Asymmetry (sides are not the same) Border (has indentations/bumpy texture) Color (variation in the same patch) Diameter (larger than a pencil eraser) Evolution (the patch changes)

Second Degree Burns Epidermis and papillary layer of dermis (or deeper into dermis) Blistering occurs due to damaged blood vessels Skin heals in 3-4 weeks on average

Third Degree Burns Involves full thickness of skin (dermis, epidermis, hypodermis) Dehydration most immediate threat Low blood pressure due to fluid loss Threat of infection Skin grafts often necessary