Unit II: Organization Integumentary System Part I Chapter 5

Integumentary System Body’s largest organ (15% of body wt, 2m2 surface area) Made of two layers: Epidermis Dermis Accessory Organs Hair Nails Cutaneous Glands Hypodermis Below the dermis Not part of the skin – 15% of body weight (keratonized stratified squamous cells) dermis - (fibrous connective tissue) 4. (adipose connective tissue)

Integumentary System Thick skin – covers the palms, soles, fingers and toes ~0.5mm stratum corneum is very thick (5 layers) no sebaceous glands or hair follicles Thin skin – covers the rest of the body ~0.1mm thin stratum corneum (4 layers) hair follicles and glands Epidermis Epidermal ridge Dermis Dermal papilla Thick skin LM x 225 Thin skin 1. thickness of epidermis ~0.5mm thick Stratum corneum – layer of dead cells 2. thickness of epidermis ~0.1mm

Functions of your Skin Protection of underlying tissues - bears most physical injuries. Barrier against pathogens - Few microbes can penetrate intact skin. Acid Mantle - slight acidity of pH 4-6 on the surface Water proofing Barrier to ultraviolet light (UV radiation) Vitamin D synthesis  Calcitriol – needed for bone health Cutaneous absorption & excretion – O2, CO2, fat soluble vitamins Sensory - touch, texture, pressure, vibration, and tissue injury Thermoregulation - thermoreceptors Communication Resists and recovers better than any other organ Packed with keratin – tough protein and desmosomes for durability. Bacteria and fungi colonize on the skin surface but numbers are kept in check by #3 which is unfavorable to the growth of microbes Keeps the body from absorbing excess water. Prevents body from losing excess water. Keeps this cancer-causing radiation from reaching deeper tissue layers. Skin carries out the first step in the synthesis needed for bone development and maintenance. The liver and kidneys complete the process. 1-2% of all blood oxygen, some CO2, many drugs and poisons, fat soluble vitamins all pass through the skin. Contains nerve endings that react to heat, cold, touch, texture, pressure, vibration, and tissue injury. Some areas have more than others – abundant on face not so much on back. Keeps us cool as well as retain heat. Nerve endings called thermoreceptors that transmit signals to the brain to increase or decrease blood flow close to the skin surface. Skeletal muscles insert on dermal collagen fibers and pull the skin to make expressions. Appearance of skin, hair, and nails important to social acceptance.

Structure of the Skin Epidermis Composed of five types of cells: Stem cells – undifferentiated cells Keratinocytes – majority of epidermis cells, durability and flexibility Melanocytes – synthesize pigment (melanin) shields from UV Tactile (Merkel) – receptors for touch Dendritic (Langerhans) – stand guard against foreign invaders, phagocytic Keratinized stratified squamous 2. come from stem cells, synthesize keratin fibrils: fibrous protein that gives epidermis its durability and flexibility 5. Dendritic name – general all over body; Langerhans – specific to skin; and “present” them to the immune system (phagocytic)

Layers of the Epidermis Cells: won’t see stem cells in lab because of when the timing of tissue samples. 5 cells 5 layers of epidermis Above the dermis (b) To see this in lab – need to be at 100-400x

Layers of the Epidermis Stratum basale Simple cuboidal epithelial cells 4 types of cells: keratinocytes, Melanocytes, Merkel cells, stem cells Stem cells constantly undergoing mitotic cell division simple cuboidal to low columnar cells resting on the basement membrane 10-25% of cells melanocytes

Layers of the Epidermis Stratum spinosum 8-10 layers of Keratinocytes Deepest cells undergo mitosis. Keratin filaments cause the cells to flatten near the surface. Desmosomes – attach the cells, give spiny appearance Langerhans cells – arise in bone marrow consists of several layers of keratinocytes. Stem cells divide less rapidly. Keratin filaments/fibers are produced by the keratinocytes. Desmosomes attach neighboring cells to each other and give cells their spiny appearance – giving it its name spinosum. Langerhans arise in bone marrow, protect against pathogens. Keratin protein is incorporated into longer keratin/intermediate filaments

Layers of the Epidermis Stratum granulosum 3-5 layers of keratinocytes Lamellated granules secrete glycolipids waterproof barrier forms a barrier between surface cells and deeper layers of the epidermis cuts off surface strata from nutrient supply Keratohyalin granules – cross links keratin filaments Granular layer consists of 3-5 layers of flat keratinocytes Contain … Glycolipids released by lamellated granules in this layer make a waterproof barrier Keratohyalin granules – used in keratinization = cross linking keratin fibers/filaments  nucleus and organelles disintigrate, cell dies  keratin fibers surrounded by keratohyalin (protein) keratohyalin  eleidin  keratin

Layers of the Epidermis Stratum lucidum Translucent zone found only in thick skin Keratinocytes filled with keratohyalin and eleidin Cells have no nuclei or other organelles Undergoing dehydration 2. Keratinocytes packed with eleidin - a precursor to keratin No nutrients to support organelles  dead cells! 4. This layer is pale and featureless because there are no organelles and eleidin doesn’t hold stain well.

Layers of the Epidermis Stratum corneum Consists of up to 30 layers of dead, dead, keratinized cells outermost layer where surface cells flake off.

Life History of Keratinocytes Produced by stem cells in stratum basale New cells push others toward surface - keratin filaments Cells grow flat and fill with keratohyalin Organelles disintegrate as they pass the water barrier Cells die and fill with keratin fibers Exfoliate New cells are typically formed at night, so you won’t see mitosis in any prepared slide. It takes about 30-40 days for a keratinocyte to be pushed up to the surface and flake off. Faster (in an injury or stressed skin - calluses) or slower (in old age). Water barrier is formed between the granulosum and stratum spinosum.

Layers of the Dermis

Layers of the Dermis 0.2mm – 4mm thick Fibrous Connective tissue composed of: fibroblasts collagen, elastic fibers: strength and flexibilty Accessory structures embedded here Layers papillary layer – surface layer, thin zone of areolar Dermal papillae - extensions of the dermis into the epidermis increase surface area for attachment, create finger prints reticular layer – thick layer of dense irregular 1. Thickness = 0.2mm to 4mm 2. Fibrous Connective tissue layer made of … Accessory structures: Cutaneous glands found here as well as hair follicles and nail roots embedded here. Vascularized with Smooth muscle (arrector pili) associated with the hair follicles which make them stand on end (goosebumps and natural wrinkles) and facial expressions. 3.papillary layer - thin zone of areolar tissue … forming the ridges of the fingerprints Reticular layer - thick layer of dense irregular tissue Boundary is vague. The reticular layer has more collagen fibers which when torn from being stretched too much is what forms stretch marks. Both layers have collagen and elastic fibers  strength and flexibility

Hypodermis Other names: Subcutaneous tissue/ superficial fascia Mostly adipose Functions: Hypodermic injections (subQ) highly vascular Limits tissue damage 1. Other names… Binds the skin to underlying tissues. Considered apart of muscular system. 2. Not uniformly distributed. Absent from scalp. 3. energy reservoir thermal insulation 4. Absorbs drugs quickly.

Skin Organs Hair Composed of hard keratin Hair found almost everywhere 2.5 million/75% on general body not head Not found on thick skin, nipples, lips differences between sexes or individuals Texture and color 3 different body hair types: lanugo -- fine, unpigmented fetal hair vellus -- fine, unpigmented hair of children and women terminal hair -- coarse, long, pigmented hair 1. (epidermal cells) but embedded in dermis 2. Differences in sexes is not the number of hairs in a given area but is difference in texture and color of hair 3. Terminal hair – of scalp - eyebrows, eyelashes, pubic hair, male facial hair, and some of the trunk and limb hair.

Structure of Hair and Follicle Cuticle Cortex Medulla Hair matrix Hair papilla Hair – keratinized cells Follicle – oblique tube Three zones: bulb = hair originates vascular tissue (papilla) in bulb provides nutrients root = within follicle shaft = above skin Three layers in cross section: Medulla (core): soft keratin Cortex: thick, hard keratin cuticle (surface): thin, hard keratin Arrector pili muscle Hair is filament of keratinized cells (dead!) made of epidermal cells is oblique tube within the skin (includes everything within skin) Bulb – hair originates, well nourished  pushed away  dies root – within follicle shaft – above skin 4. … abrasion to cuticle = split ends hair dye changes the color of the cuticle (normally translucent) Piloerector/arrector pili muscle – smooth muscle; connect follicle to papillar layer; stand hair upright to create a bubble around base to “insulate” – goosebump; sebaceous gland releases sebum at same time Nerve – wraps around just above bulb

Texture and Color of Hair Straight hair = round Wavy = oval Tight curls = flat Hair color = ratio of two types of melanin found in the cortex Difference in cross-sectional shape 4. Ratio of pigment in cells of cortex two types of melanin for hair pigment gray & white: absence of melanins in cortex and air in medulla

Hair Growth Cycle 90% of scalp follicles Detached from Hair falls out Epidermis Dermis Hair matrix Sebaceous gland Old club hair Piloerector New hair Bulge Club hair (detached from matrix) Club Dermal papilla Degeneration of lower follicle Hair bulb 2 3 Anagen (early) (Growing phase, 6–8 years) Stem cells multiply and follicle grows deeper into dermis; hair matrix cells multiply and keratinize, causing hair to grow upward; old club hair may persist temporarily alongside newly growing hair. Anagen (mature) Catagen (Degenerative phase, 2–3 weeks) Hair growth ceases; hair bulb keratinizes and forms club hair; lower follicle degenerates. Telogen (Resting phase, 1–3 months) Dermal papilla has ascended to level of bulge; club hair falls out, usually in telogen or next anagen. 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1. 3 repeating cycles 2. (90% of scalp follicles) grows down into dermis from epidermis lasts 6-8 years in young adult 3. (lasts 2-3 weeks); club hair being formed (detached from nutrients) 4. (lasts 1-3 months) hair falls out Hair falls out during catagen or telogen phase. You have anywhere from 50-100 scalp hairs that fall out daily. Development of hair follicle: Starts in epidermis during development After further growth becomes embedded in dermis produced by mesoderm. 90% of scalp follicles Detached from Hair falls out Grows down from epidermis nutrients

Hair Loss and Growth Alopecia - General term for all hair loss Pattern baldness sex-influenced trait males: XdefectY (can’t cover up) females: XdefectX (no baldness) expressed only with high testosterone levels follicles are sensitive to androgens  causes them to shrink when exposed  shorten their lifespan and prevents them from producing hair normally Hirsutism - excessive hair growth hormone imbalance (ovary or adrenal cortex tumor) (loss of hair from head/body sometimes to baldness) = Alopecia mainly results from aging but can be worsened by a number of factors – disease, poor nutrition (iron deficiency), emotional trauma (pulling out hair), hairstyling routines 2. genetic and hormonal (androgens) 3. a. Especially in women and children. Usually associated with menopause. excess hair where terminal hair not normally present (ex. Beard, chest hair) Risk factors: ↑ androgens, oversensitivity of follicles to androgen; ↑ insulin in females  stimulates ovaries to produce ↑ androgens  stimulate hair production Treatment: ↓ insulin levels Hair implants: take hair from back and put on scalp; living, active follicle that grows

Functions of Hair Body hair - (too thin to provide warmth) - alert us to parasites crawling on skin Scalp hair - heat retention and sunburn cover Beard, pubic and axillary hair - sexual maturity and help distribute sexual scents similar to pheromones Guard hairs - prevent foreign objects from getting in nostrils, ear canals or eyes Expression of emotions with eyebrows

Skin Organs Fingernail Structure Body – visible portion Free edge – grows away from body Root – embedded in skin; adheres to nail bed Nail bed – skin under nail Nail matrix – proximal part of nail bed, growth zone Nails: non-living material like hair; nearly translucent – pink = dermal blood supply turn blue = lack of oxygen in the blood

Nails Derivative of stratum corneum that grows downward densely packed cells filled with hard keratin New cells added by mitosis in the nail matrix Flat nails allow for fleshy, sensitive fingertips protect fingertip and surrounding soft tissue from injury enhances precise delicate movements; enhances sensitivity (counterforce) tool Medical diagnosis Ex.) iron deficiency = concave nails Length and growth rate related to the length of the terminal phalanges 3. Most mammals have claws – flat nails are a distinguishing characteristic of primates. 4. Concave - spoonlike others: dehydration; nutrient deficiency; problems elsewhere in the body shock – if nailbed doesn’t return to pink within seconds disease – horizontal ridges 5. … Grow ~3mm a month 3-6 months – regrow completely (fingers) 12-18 months – regrow completely (toes)