The Skin

Skin Color Three factors for skin color: Amount and kind of melanin Amount of carotene (orange-yellow pigment) Amount of oxygen bound to hemoglobin More melanin production, darker skin color People with less melanin have a rosy color b/c oxygen rich blood flushes through membranes Skin turns yellow-orange when large amount of carotene is ingested

Influence of emotional stimulus. Possible diseases: Erythema: Jaundice, or Bruises or black-and-blue marks Blood has escaped circulation and clotted in tissue space = hematomas Unusual tendency to bruising CAN be caused by vitamin C deficiency or hemophilia (bleeder’s disease)

Erythema reddened skin (blushing) From embarrassment OR fever, hypertension, inflammation, allergy

Jaundice yellow cast abnormal yellow skin tone Liver disorder: excess bile absorbed into blood, circulated throughout, and deposited in body tissues

Pallor aka blanching pale skin tone Emotional stress OR anemia, low bp, or impaired blood flow

Cyanosis Hemoglobin is poorly oxygenated Blood and skin appear blue Common during heart failure Better apparent in mucous membranes and nail beds

Appendages of the skin Cutaneous glands Hairs Hair follicles Nails Each come out of the epidermis Each play a role in maintaining homeostasis

Cutaneous Glands All the exocrine glands Sebaceous glands Sweat glands Formed by cells of stratum basale Push into deeper skin Reside in dermis

Sebaceous (oil) glands Found all over skin, except palm and soles Ducts empty into hair follicles Product of the gland is called sebum Mix of oil and fragmented cells Keeps skin soft and moist Prevents hair from being brittle Contains bacteria killing chemicals Become active during adolescence

Blocking of sebaceous glands Whitehead appears Material accumulates, oxidizes, dries and darkens blackhead Acne Active infection of sebaceous gland Sebborhea Overactivity of sebaceous glands Begins on scalp as pink, raised lesions Gradually forms yellow/brown crust that flakes off as dandruff Can also occur in face and trunk

Sweat Glands More than 2.5 million per person Two types Eccrine apocrine

Eccrine Sweat Glands Produce sweat Acidic Reaches skin via pore Primarily water plus salts, vitamin C, metabolic wastes, lactic acid Acidic Inhibits bacterial growth Reaches skin via pore “pores” on face do not serve same purpose These are outlets for hair follicles Important in heat-regulation Come with nerve endings that cause sweat secretion if body temp is too high

Apocrine Sweat Glands Found in axillary and genital areas Secretions contain fatty acids, proteins, as well as things in eccrine secretions May have milky or yellowish color Odorless Bacteria can use proteins and fats as source of nutrients Leads to musky, unpleasant odor Begin function during puberty due to androgens Minimal role in thermoregulation Activated by nerve fibers during pain and stress

Hair and Hair Follicles Once upon a time… Served as insulator Today… Guards head Shields eyes Keeps foreign particles out of respiratory tract

Hair and Hair Follicle Hair is produced by a hair follicle Hair is formed by division of stratum basale epithelial cells in hair bulb matrix at the inferior end of the hair Bulk of hair shaft is dead material Each hair has central core (medulla) enclosed by cortex, which in turn is enclosed by cuticle Cuticle formed by overlapping layers Prevents matting and keeps hairs apart Heavily kreatinized for strength

Hair and Hair Follicles Pigment from melanocytes (prod melanin) Come in variety of size and shapes Determines type of hair i.e. oval shaft -> smooth & silky hair i.e. flat, ribbonlike shaft -> curly or kinky hair Arrector pili Small bands of smooth muscles Connect hair follicle to dermal tissue Muscle contraction leads to “goose bumps”

Nails Scalelike modificaiton of epidermis Three parts: free edge, body, root Borders overlapped by skin folds, called nail folds Thick proximal nail = cuticle Nail matrix responsible for growth Cells produce and become keratinized Mostly nonliving material Transparent and colorless Red color due to blood supply in dermis Lunula is white because thickened matrix