Physiology Skin & The Integumentary System

PHYSIOLOGY CHAPTER 5: SKIN & THE INTEGUMENTARY SYSTEM

4 TYPES OF MEMBRANES 1) serous membranes: • line body cavities that don’t open to the outside • location: thorax, abdomen & the organs within • made of: simple squamous epithelium + loose CT

4 TYPES OF MEMBRANES 1) serous membranes: • Pleura = serosa lining the thoracic wall & lungs • Pericardium = serosa enclosing the heart • Peritoneum = serosa lining abdominopelvic cavity + viscera

4 TYPES OF MEMBRANES 2) mucous membranes: • line cavities & tubes that open to the outside • location: oral & nasal cavities, tubes of the digestive, respiratory, urinary, & reproductive systems • made of: epithelium w/ goblet cells + loose CT • secrete: mucus

4 TYPES OF MEMBRANES 3)

synovial membranes • location: the inner linings of synovial joint cavities • made of: dense CT + loose CT + adipose tissue • secrete: synovial fluid to lubricate joints

4 TYPES OF MEMBRANES 4)

cutaneous membranes: • Skin • Dry because it is exposed to air

INTRODUCTION • integumentary system = skin + accessory organs (hair, nails, sweat & oil glands) • hyperhidrosis = a condition of profuse, uncontrollable, unpredictable sweating

SKIN & ITS TISSUES • skin is a large organ vital to maintaining homeostasis • Skin stats: – Surface area = 1.2 to 2.2 square meters – Weight = 9 to 11 pounds – Accounts for 7% of an adult’s total body weight – 1.5 to 4 mm thick in various parts of the body – Integument = “covering”

functions of skin: – Protection: chemical, physical, biological – regulates body temperature – Insulation + fat storage – prevents water loss from deeper tissues

functions of skin: – houses sensory receptors sensitive to pain, temperature, touch, pressure – makes biochemicals such as vitamin D – excretes some waste – Blood reservoir – has an extensive vascular supply

2 layers of skin: • epidermis = outer layer made of stratified squamous epithelium

2 layers of skin: • dermis = thicker inner layer made of connective & epithelial tissue, smooth muscle, nervous tissue, blood

2 layers of skin: • the 2 layers are separated by the basement membrane

• a subcutaneous layer (hypodermis) made of loose CT & adipose tissue binds the skin to the organs under it

Epidermal cells • Keratinocytes – make keratin • Melanocytes – make melanin • Merkel cells – touch receptors • Langerhan’s cells – macrophages

EPIDERMIS: • 4 layers on most of the body: – stratum basale = base layer – stratum spinosum = prickly layer, keratinocytes are flatter and appear spiny – stratum granulosum = granular layer, granules form keratin in the upper layers and provide waterproofing

EPIDERMIS: • 4 layers on most of the body: – stratum corneum = horny layer

• A 5th layer on only thick skin: - stratum lucidum = clear layer, can only be found on palms & soles (thick skin), a row of thin, flat, dead keratinocytes

EPIDERMIS: • the deepest layer of the epidermis, the stratum basale (basal layer), contains cells that divide, mainly young keratinocytes

EPIDERMIS: • epidermal cells undergo keratinization as they mature & are pushed toward the surface • the outermost layer, the stratum corneum (horny layer), is made of dead epidermal cells which are eventually shed – 40 pounds in an average lifetime! – Cornu = horn – Totally new epidermis in 25-45 days!

EPIDERMIS: • the rate of cell division increases where skin is rubbed off regularly forming calluses & corns • the epidermis protects underlying tissues against water loss, injury, & the effects of harmful chemicals

EPIDERMIS: • melanin protects cells from the effects of UV light • melanocytes (cells that make melanin) transfer melanin to epidermal cells which determines skin color

SKIN COLOR: – genetically determined – varies based on the kind & amount of melanin produced, since all people have about the same number of melanocytes

SKIN COLOR: – influenced by environment (exposure to sun), chemically induced photosensitivity (some meds, perfumes, detergents, limes, celery) – influenced by physiological factors (blood color, diet, chemicals such as bilirubin) – 3 pigments affecting skin color = melanin, carotene, hemoglobin

DERMIS: • Composed of strong, flexible c.t. • Corresponds to animal hides used to make leather • dermis binds the epidermis to underlying tissues • has 2 layers: – Papillary – reticular

DERMIS: • fingerprints result from epidermal ridges projecting inward & dermal papillae projecting upward – genetically determined – increase friction & enhance gripping ability

DERMIS: • dermal blood vessels supply nutrients to all skin cells & help regulate body temperature (vasoconstriction, vasodilation) • the dermis also contains hair follicles, sweat glands, & sebaceous (oil) glands

DERMIS: • nerve fibers are scattered throughout the dermis – some carry impulses to muscles & glands – some are associated with sensory receptors in the skin, & they carry impulses to the brain & spinal cord

DERMIS:

SUBCUTANEOUS LAYER: • made of loose CT + adipose tissues • it helps supply the skin with blood • the adipose tissue helps conserve body heat

ACCESSORY ORGANS OF THE SKIN • hair – hairs develop in the follicles – new cells push older cells closer to the surface where they become keratinized & die – hair color is genetically determined – an arrector pili muscle attaches to each hair follicle & this pulls the hair erect when stimulated = goose bumps

Functions of hair • To sense insects on skin • Guards against physical trauma, heat loss, sunlight • Eyelashes shield eyes • nose hairs filter large particles from air

ACCESSORY ORGANS OF THE SKIN • sebaceous glands – holocrine glands that secrete sebum = a mix of oil & cellular debris – sebum keeps skin & hair soft, pliable, & waterproof – acts as a bactericide - function begins at puberty

ACCESSORY ORGANS OF THE SKIN • sweat glands = sudoriferous glands – exocrine glands which consist of a coiled tube – eccrine / merocrine sweat glands respond to elevated body temp. – apocrine sweat glands respond to pain or emotional stress, function begins at puberty – modified sweat glands include mammary glands & ceruminous glands in the outer ear canal – 2.5 million, most in palms, soles, forehead

ACCESSORY ORGANS OF THE SKIN • nails – protective coverings for fingers & toes – each nail consists of a nail bed + nail plate – the white moon-shaped lunula at the base of the nail plate is the area where cells are most actively dividing – again, cells become keratinized & die as they age

Apocrine sweat gland

eccrine sweat gland

REGULATION OF BODY TEMPERATURE • vital because heat affects the rate of metabolic reactions • heat is a product of metabolism • skin constantly loses heat to the air

REGULATION OF BODY TEMPERATURE • If temp is too high: – dermal blood vessels dilate – sweat glands secrete sweat

• if temp is too low: – dermal blood vessels constrict – sweat glands deactivate – skeletal muscles contract involuntarily = shivering

HEALING OF WOUNDS • skin injuries trigger inflammation (red, warm, swollen, tender) • dividing epithelial cells fill in shallow cuts • clots close deeper cuts

HEALING OF WOUNDS • scabs = clots + dried tissue • scars result from connective tissue replacing skin • granulations form in large open wounds

Wound healing

HEALING OF WOUNDS • Wound healing can be differentiated into three major phases – Inflammatory phase (1) The wound is rinsed by blood and filled with bloodcollagen and fibrin constituents. – Proliferative phase (2) Resorption of blood-collagen and reepithelialization. The reepithelialization is a movement of the surrounding epithelial cells to close the wound. – Maturation and remodeling phase (3) Growth of new epithelial cells.

Homeostatic imbalances of skin: • Skin cancer – Basal cell carcinoma = least malignant & most common – 30% of all white people get it – Squamous cell carcinoma - often on scalp & hands, grows rapidly and metastasizes – Melanoma = cancer of melanocytes, most dangerous type – ABCD rule: • Asymmetry, border irregularity, color, diameter

• Burns – 1st degree = epidermis is damaged • ex. sunburn

– 2nd degree = epidermis + part of the dermis are damaged, blisters occur – 3rd degree = epidermis + dermis + hypodermis are all damaged, nerve endings are destroyed – Evaluated by the “rule of nines”

Effects of aging: 1) Skin thins 2) Lubricating substances become deficient, so skin gets dry & itchy 3) Elastic fibers clump, skin loses elasticity 4) Sub Q fat layer diminishes, often cold • 3 & 4 cause wrinkles 5) Less melanocytes & Langerhan’s cells enhance the risk of skin cancer 6) Hair thins due to fewer active hair follicles