Biology 211 Anatomy & Physiology I Skin The Integumentary System

The Integumentary System Skin=Integument Skin + accessory organs (hair, nails, and cutaneous glands)= Integumentary system Dermatology=scientific study and medical treatment of the integumentary system Skin-the most vulnerable organ—exposed to radiation, trauma, infections, injurious chemicals Lgst. organ—15% body wt

Functions of Integumentary System (skin & its products) Barrier to keep water and solutes in Barrier to keep bacterial, dirt, etc. out Protection against abrasion Contains sensory receptors for touch, temperature, pressure, pain, etc. Temperature regulation via hair, sweat, & amount of blood flow Blood reservoir Synthesis of vitamin D Excretion

Three Layers of skin: Epidermis: Stratified squamous epithelium; outer layer is "keratinized" or "cornified" Dermis: Dense irregular connective tissue Hypodermis: Adipose connective tissue (technically not part of system

Epidermis: Avascular. Depends on blood vessels in underlying dermis for its nutrition Cells formed by mitosis in deepest, or basal, layer, then get pushed into more superficial layers or "stata"

(Epidermis) Stratum Basale = Single row of dividing cells Stratum Spinosum = Three or four layers of cells; Some cell division Stratum Granulosum = Three or four layers of cells; Actively synthesizing protein keratin Stratum Lucidum = One or two layers of dying cells Stratum Corneum = Many layers of flat, dead, scale-like cells full of keratin

Primary cell type in epidermis = keratinocytes which produce large amounts of protein keratin Other cell types: Melanocytes produce pigment melanin & transfer it to keratinocytes Langerhans cells (immune cells) protect against pathogens and toxins Merkel cells detect touch and pressure; transfer this information to sensory receptors in the dermis

Most significant factor is melanin Skin Color Most significant factor is melanin 2 forms (1) eumelanin (brownish black) and (2) pheomelanin (reddish yellow) Other factors include hemoglobin (red to pink) and carotene (yellow) Different races have same # of melanocytes, amount of melanin produced differs Melanin accumulates in keratinocytes

Abnormal Color Cyanosis—blue, lack of hemoglobin Erythema—abnormal redness, increased blood flow or blood pooling Pallor—pale, ashen, poor blood flow Albinism—lack of melanin Jaundice—yellowing, hi levels of bilirubin (hi rate of erythrocyte destruction Bronzing—deficiency of glucocorticoids Hematoma—bruise, blood clot

- Keratinocytes in stratum basale (& stratum spinosum) (Epidermis) Keratinocytes move from stratum basale to stratum corneum, dying as they do so. Average = 6 - 8 wks - Keratinocytes in stratum basale (& stratum spinosum) lie along basement membrane; divide by mitosis - Older ones pushed toward surface by newer cells - Melanocytes transfer melanin to keratinocytes - Keratinocytes synthesize large amounts of keratin and flatten out as they move toward surface - Older cells die but remain attached to each other - Cells eventually shed from stratum corneum

Dermis: Dense irregular connective tissue Separated from epidermis (stratified squamous epithelium) by basement membrane Highly vascular Highly innervated Two Layers: Papillary layer just below epidermis Reticular layer forms deep 80%

Dermis: Contains many types of sensory receptors for touch, pressure, vibration, pain, temperature, etc. Some = simple nerve endings Others = complex structures with multiple cell types

Dermis = Dense irregular connective tissue. Thus: Cells = Fibroblasts / Fibrocytes Macrophages Mast cells Lymphocytes etc. Fibers = Collagen (therefore strong, flexible) Elastic (therefore stretchable) Weight gain tears collagen fibers producing striae (stretch marks)

Appendages of the skin Hair follicles and hair Sweat glands Sebaceous (oil) glands Nails on fingers and toes All begin as epidermis of embryo; grow down into dermis

- Distribuled over all skin except: palms of hands Hair - Distribuled over all skin except: palms of hands soles of feet nipples glans of penis & clitoris minor labia - Formed in follicles located deep in dermis - Consists of layers of dead, highly keratinized keratinocytes

Function of Hair Trunk and limb hair considered vestigial Scalp only place where it is thick enough to retain heat Eyebrows enhance facial features Vibrassae (guard hair) are used to filter particulates from the ear and nose

Shaft Root Bulb

Medulla: Loosely arranged keratinocytes Cortex: Densely packed keratinocytes Cuticle: Keratinocytes loosely arranged like scales

Black or brown color due to eumelanin produced by melanocytes and transferred to keratinocytes in follicle. Red color produced by pigment called pheomelanin Blonde color produced by intermediate levels of pheomelanin and low levels of eumelanin Texture of hair due to The rounder the hair shaft, the straighter it will be The flatter the hair shaft, the more curled it will be

Each hair is associated with: One or more sebacious (oil) glands An arrector pili muscle A plexus of nerves around the root

Sweat Glands - 2 to 3 million - Two types: Merocrine: Distributed over all skin except nipples (Eccrine) Simple coiled glands in dermis Duct leads to sweat pore on surface Secreted watery sweat for cooling Apocrine: Located only in axillary, pubic, anal regions Larger than eccrine glands Duct opens into opening of hair follicle Secretes thicker sweat, high content of proteins and fats. Contains specific scent molecules: sexual, fear, etc.

Sweat is usually 99% water with a pH between 4 and 6 Sweat glands produce 500ml of insensible perspiration (no noticable wetness)daily Diaphoresis—sweating with wetness (up to 1 l per hr when exercising or in heat) Two specially modified sweat glands: Ceruminous—found in the external ear canal. Secretion combines with sebum and dead epidermal cells to form earwax (keeps eardrum pliable, canal waterproof and has a bactericidal effect) Mammary --milk producing glands found in the female breast (modified apocrine glands)

Sebaceous (oil) glands: - Branched tubular glands - Duct opens into opening of hair follicle - Secretes sebum, consisting of lipids, proteins, ions, carbohydrates,

Nails: - Tips of fingers and toes - Thick layer of densely packed keratinocytes - Produced by nail matrix at proximal end, hidden under eponychium or cuticle Deeper layers of epidermis = nail bed Average growth: 0.5 mm per week

Nails Flat nails allow for fleshy, sensitive fingertips Serve as tools for digging, grooming and manipulation Useful in medical diagnosis Iron deficiency—flat or concave Long term hypoxia (oxygen deficiency)—clubbed

Carcinomas (cancers) of the skin: Basal Cell Carcinoma: Keratinocytes of stratum basale proliferate, invade dermis Relatively low malignancy Squamous Cell Carcinoma: Keratinocytes of epidermis proliferate May or may not invade dermis Moderate malignancy Malignant Melanoma: Melanocytes of epidermis proliferate, invade dermis Highly malignant

Burns Leading cause of accidental death Classified by depth of tissue involvement 1st degree—involves epidermis only 2nd degree—involves epidermis and some dermis 3rd degree—involves epidermis, dermis and some deeper tissue are destroyed 1st and 2nd degree burns are considered partial thickness burns, and 3rd degree is a full thickness burn