Biology 211 Anatomy & Physiology I Integumentary System

The Integumentary System Skin = Integument Largest organ in body – 15% of body weight Skin + accessory organs (hair, nails, glands) = Integumentary system

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

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

- Keratinocytes in stratum basale (& stratum spinosum) (Epidermis) Keratinocytes move from stratum basale to stratum corneum, dying as they do so. Average = 4 - 6 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

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

Skin Color Most significant factor is melanin 2 forms: eumelanin (brownish black) pheomelanin (reddish yellow) Melanin: produced by melanocytes accumulates in keratinocytes Different pigmentation of skin: similar numbers of melanocytes, different amounts of melanin produced Also Carotene = yellow Hemoglobin in blood = red/pink

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 (strength) Elastic (stretchable)

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

Hair Distributed over all skin except: palms of hands soles of feet nipples glans of penis & clitoris minor labia Minimal trunk & limb hair Thicker on scalp to retain heat Eyebrows enhance facial features, shade eyes Nostril hair filters dust & other particulates Pubic hair, axillary hair, anal hair retain pheromones

Hair Formed in follicles in dermis Consists of layers of dead, highly keratinized keratinocytes “Vellus” hair is finer. Covers arms, legs, back, chest, etc. “Terminal hair” is longer and courser. Scalp, pubic hair, axillary hair, eyelashes, eyebrows, male facial hair

Shaft Root Bulb

Medulla: Loosely arranged keratinocytes Thickest in terminal hair; absent in vellus hair 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 pigments called pheomelanin Blonde color produced by intermediate levels of pheomelanin and low levels of eumelanin The same gene that produces pheomelanin also increases the number of freckles on the skin, so redheads often have more freckles.

Texture of hair is due to the shape of the hair shaft. 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 (smooth 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 Secrete watery sweat for cooling Apocrine: Located only in axillary, pubic, anal regions Larger than eccrine glands Duct opens into opening of hair follicle Thicker sweat, high content of protein and fats Contains scent molecules: sexual, fear, etc.

Sweat is usually 99% water with a pH between 4 and 6 Contains significant amounts of sodium, potassium, calcium, chloride, and trace amounts of other minerals ~ 500 ml/day at rest, more at warmer temperatures 2,000 ml/hour during moderate to intense exercise

Modified Sweat Glands Ceruminous glands in external ear canal. Secretion combines with sebum to form earwax Mammary glands in breast

Sebaceous (oil) glands: - Branched tubular glands - Duct opens into opening of hair follicle - Most common on face & scalp - Secretes sebum consisting of lipids, proteins, ions, carbohydrates to protect the skin and hair

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

Burns: Major cause of accidental death Classified by depth of tissue involvement Superficial: involves epidermis only Partial thickness: involves epidermis and some dermis Full thickness: epidermis, dermis, and deeper tissue destroyed

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 and invade dermis Highly malignant