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Integumentary System

Skin

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Integumentary System

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    1. Integumentary System

    2. Skin – the body’s largest organ Accounts for 15% of the body weight Consists of two layers – epidermis and dermis Mostly 1 – 2 mm thick but ranges with location Difference mainly related to the thickness of the dermis Classified as thick or thin based on the relative thickness of the epidermis alone

    3. Thick skin – covers palms, soles, and corresponding surfaces of the fingers and toes Epidermis – about 0.5 mm thick because of a very thick surface of dead cells called the stratum corneum Has sweat glands but no hair follicles or sebaceous glands Thin skin – covers the rest of the body Epidermis – about 0.1 mm thick with a thin stratum corneum Has hair follicles, sebaceous glands, and sweat glands

    5. Functions of the skin Resistance to trauma and infection Other barrier functions Vitamin D synthesis Sensation Thermoregulation Social functions

    6. Epidermis Keratinized stratified squamous epithelium Surface with dead cells packed with protein called keratin Lacks blood vessels and depends on diffusion of nutrients from underlying dermis Sparse nerve endings Most sensations in the skin due to nerve endings in the dermis

    7. Cells of the Epidermis – five types Stem cells – undifferentiated cells that undergo mitosis – give rise to keratinocytes – found in the deepest layer of epidermis which is the stratum basale Keratinocytes – great majority of epidermal cells – almost all cells seen on a slide are keratinocytes Melanocytes – Occur in the stratum basale – synthesize black or brown melanin – branching processes that shed melanin fragments from their tips

    8. Tactile (Merkel) cells – found in the basal layer of the epidermis – few in number – receptors for the sense of touch – associated with an underlying dermal nerve – the cell and the nerve called a tactile (Merkel) disc Dendritic (Langerhans) cells – found in the stratum spinosum and the stratum granulosum – macrophages that originate in the bone marrow – migrate to the epidermis, oral cavity, vagina and esophagus – protect against toxins and microbes

    9. Layers of the epidermis – from youngest to oldest Stratum basale – mainly a single layer of cuboidal or low columnar stem cells and keratinocytes resting on the basement membrane – melanocytes and tactile cells scattered among these – stem cells give rise to keratinocytes that migrate toward the surface and replace lost surface cells

    10. Stratum spinosum – several layers of keratinocytes – thickest layer in thin skin but stratum corneum thickest layer in thick skin - deepest layer still capable of mitosis – lose this ability as they move further upward – become flatter the higher up they go - keratinocytes with desmosomes and tight junctions Stratum granulosum – three to four layers of flat keratinocytes – more in thick skin than in thin skin – cells contain keratohyalin

    11. Stratum lucidum – thin translucent zone superficial to the stratum granulosum – seen only in thick skin – keratinocytes densely packed with eleidin, which is important in the synthesis of keratin – cells have no nuclei or other organelles – indistinct cell borders Stratum corneum – up to thirty layers of dead keratinized cells – resistant to abrasion, penetration, and water loss

    14. Life history of a keratinocyte Keratinocytes are shoved upward by the dividing cells below. Cells grow flatter and they produce lipid filled membrane coating vesicles. In the stratum granulosum the keratinocytes undergo apoptosis. The keratohyalin granules release a substance that binds to the cytoskeleton and converts them to keratin. The membrane coating vesicles release a lipid mixture that spreads out over the cell surface and waterproofs it.

    15. An epidermal water barrier forms between the stratum granulosum and the stratum spinosum. It consists of lipids secreted by the keratinocytes and tight junctions between the keratinocytes. The epidermal water barrier is crucial to retaining water and preventing dehydration. Cells above the barrier die Therefore the stratum cornea consists of compact layers of dead keratinocytes.

    16. Dermis – ranges from 0.2 mm thick in the eyelids to 4 mm thick in the palms and soles – composed of collagen, elastic and reticular fibers – contains fibroblasts and all the cells usually found in fibrous connective tissue – contains blood vessels, sweat glands, sebaceous glands, nerve endings, hair follicles, and nail roots Smooth muscle (piloerector muscles) – associated with hair follicles – contract in response to cold, fear, and touch Skeletal muscle – attached to the dermis in the face and produces facial expressions

    17. Dermal papillae Epidermal ridges Friction ridges Dermis in sensitive areas

    18. Dermis –two layers Papillary layer – thin zone of areolar tissue in the dermal papillae – loosely organized tissue allows for mobility of leucocytes and other defenses Reticular layer – deeper and much thicker – dense irregular connective tissue – thick bundles of collagen with less room for ground substance – striae or stretch marks caused by stretching of the skin tearing the collagen

    19. Hypodermis - also called subcutaneous tissue or superficial fascia Has areolar and fat tissue Binds the skin to the underlying tissue Medications are frequently injected into this area because of vascularity Subcutaneous fat – hypodermis composed mostly of adipose tissue – not uniformly distributed – absent in scalp but copious in breast, abdomen, hips and thighs – 8% thicker in women than in men – infants and the elderly have less fat and therefore cold intolerance

    20. Skin Color Melanin – most significant factor in skin color – produced by melanocytes – accumulates in the keratinocytes of the stratum basale and stratum spinosum Two forms of melanin – a brownish black eumelanin – a reddish yellow sulfur containing pigment known as pheomelanin Hemoglobin – skin redder in places where blood capillaries come close to surface such as the lips Carotene – yellow pigment acquired from egg yolks and yellow and orange vegetables – concentrated in stratum corneum, subcutaneous fat, and skin of the heel

    21. Abnormal skin colors Cyanosis – blueness in the skin from a deficiency of oxygen in the circulating blood Erythema – abnormal redness of the skin –occurs with exercise, hot weather, sunburn, anger and embarrassment – caused by increased blood flow in dilated cutaneous blood vessels or from pooling of red cells that have escaped from the capillaries

    22. Pallor – a pale color that occurs when there is so little blood flowing through the skin that white collagen shows through – seen in emotional stress, low blood pressure, circulatory shock, cold temperatures, severe anemia Albinism – a genetic lack of melanin that results in white hair, pale skin and pink eyes – lack of tyrosinase which is needed to make melanin from tyrosine – autosomal recessive transmission

    23. Jaundice – Yellowing of the skin and whites of the eyes secondary to high levels of bilirubin in the skin Bronzing – a golden brown skin color – seen in Addison disease which is adrenal insufficiency Hematoma – a mass of clotted blood seen through the skin – bruise – usually due to trauma – can be seen in clotting disorders

    24. Skin markings Friction ridges – from dermal papillae in the fingertips – fingerprints – formed during fetal life and remained unchanged for life – unique pattern for everyone – not even identical twins have the same fingerprints Flexion lines – lines on the flexor surfaces of the digits, palms, wrists, and elbows – mark sites where the skin folds during flexion of the joints Freckles – flat melanized patches that vary with heredity and sun exposure Moles – elevated patch of melanized skin - harmless

    25. Hemangiomas – birthmarks – patches of discolored skin caused by benign tumors of the dermal capillaries – Capillary hemangiomas are bright red to purple, slightly swollen and usually disappear in childhood – Cavernous hemangiomas (port wine stain) are flat and last for life

    26. Hair and nails – accessory organs – composed of hard keratin – more compact than the soft keratin seen in the stratum corneum of the skin Pilus – hair is known as a pilus or plural pili – slender filament of keratinized cells that grows from an oblique tube in the skin called a hair follicle Three types of hair Lanugo hair – fine unpigmented hair that appears on the fetus in the last 3 months – most of it replaced by vellus hair by the time of birth

    27. Vellus hair – fine unpigmented hair – constitutes two – thirds of the hair of women and one – tenth of the hair of men – constitutes all of the hair of children except the eyebrows, eyelashes, and hair of the scalp Terminal hair – longer, coarser, and pigmented – forms the eyebrows, eyelashes, and the scalp – after puberty it forms the axillary hair, pubic hair, male facial hair, and hair on the trunk and limbs

    28. Structure of the Hair and Follicles Three zones along its length Bulb – a swelling at the base where the hair originates in the dermis Root – the remainder of hair within the follicle Shaft – portion above the skin surface Dermal papilla – provides the hair with its sole source of nutrition Hair matrix – above the papilla – region of mitotically active cells – hair’s growth center – all cells higher up are dead

    29. Cross section of the hair Medulla – loosely arranged cells and air spaces found in thick hairs but absent in thin hairs Cortex – a layer of keratinized cuboidal cells Cuticle – a surface layer of scaley cells

    30. Hair follicle – a diagonal tube that dips deep into the dermis Epithelial root sheath – extension of the epidermis Connective tissue root sheath – derived from the dermis Hair receptors – nerve fibers associated with the follicle Pilorector muscle – bundle of smooth muscle fibers that extend from dermal collagen fibers to the connective tissue root sheath – responds to cold, fear and other stimuli – controlled by sympathetic nervous system – make hair stand on end

    33. Hair texture and growth Texture related to differences in cross–sectional shape – straight hair is round – wavy hair is oval – curly hair is flat Hair color – due to pigment granules in the cells of the cortex – brown and black hair have eumelanin – red hair has some eumelanin but a high concentration of pheomelanin – blond hair has a moderate amount of pheomelanin and only a small amount of eumelanin – gray and white hair have no melanin in the cortex and air in the medulla

    39. Hair Growth and Loss Hair cycle – three phases Anagen Catagen Telogen Alopecia Pattern baldness Hirsutism

    40. Functions of Hair Mostly vestigial Scalp hair – helps to retain heat – protects from sunburn Guard hairs or vibrissae hairs - prevent foreign particles from entering the nose or ears Eyelashes – shield the eyes from windblown debris Eyebrows – keep sweat from getting into the eyes

    41. Nails – clear hard derivatives of the stratum corneum – composed of very thin, dead, scaley cells densely packed together and filled with parallel fibers and hard keratin – distinguishing characteristic of primates – Growth – fingernails 1 mm per week and toenails slower – new cells added to nail plate by mitosis in the nail matrix at its proximal end

    43. Cutaneous Glands Sweat glands or sudoiferous glands – two kinds Merocrine or eccrine – most numerous - myoepithelial cells – insensible perspiration – diaphoresis Apocrine – occur in the groin, anal region, areola, and the beard area Sebaceous glands – produce sebum – holocrine glands with ducts that open into the hair follicle

    46. Ceruminous glands – found only in the external ear – forms earwax or cerumen – simple coiled tubular glands – ducts lead to skin surface – waterproofs auditory canal and has a bactericidal function Mammary glands – milk producing glands that develop within the female breast – prominent in pregnancy and lactation – modified apocrine sweat glands – produce a richer secretion and channel it through ducts to a nipple

    48. Skin Cancer – induced by ultra violet rays of the sun – most often on the head and neck – most common in fair-skinned people and the elderly – very common cancer but easy to treat Basal cell carcinoma – most common type of skin cancer – least dangerous because it seldom metastasizes – arises from cells in the stratum basale and eventually invades the dermis Squamous cell carcinoma – arises from keratinocytes in the stratum spinosum – usually found on the scalp, ears, lower lip, or dorsum of the hand – chance of recovery is good with early detection and surgical removal – if neglected it can metastasize to lymph nodes and can be lethal

    49. Malignant melanoma – most deadly skin cancer – accounts for 5% of skin cancers – often arises from the melanocytes of a preexisting mole – metastasizes quickly and can be lethal – risk is greatest for people who experienced sunburn as children especially redheads – men have higher incidence of malignant melanoma than women – 70% of cases on malignant melanoma are associated with an oncogene BRAF - uncertain if the BRAF oncogene alone can cause malignant melanoma

    50. ABCD rule for recognizing malignant melanoma A for symmetry (one side of the lesion looks different than the other) B for border irregularity – scalloped C for color (often a mixture of brown and black sometimes red or blue) D for diameter (greater than 6mm) Treated by wide surgical excision

    51. UVA, UVB, Sunscreens Both can initiate skin cancer No such thing as a healthy suntan As the use of sunscreen has increased so has the incidence of skin cancer People who use sunscreen have a higher incidence of basal cell carcinoma than people who do not Some chemicals in sunscreen damage DNA Still not known if sunscreens are helpful or harmful

    52. Burns – a leading cause of accidental deaths – fluid loss, infection and the toxic effects of eschar First degree burns – involve only the dermis – redness, slight edema and pain – heal in a few days – rarely leave a scar – sunburn Second degree burns – involve the epidermis and part of the dermis – may be red or blistered and painful – may take several weeks to heal and may leave a scar – epidermis regenerates by division of epithelial cells in the hair follicles and sweat glands and around the edges of the burn – bad sunburns and scalds Third degree burns – epidermis and dermis completely destroyed – epidermis can only regenerate from edges of the wound – often requires skin grafts

    60. Management of burns Fluid replacement Antibiotics Nutrition Debridement Skin grafts

    61. Skin grafts Autograft Split thickness graft Isograft Allograft Heterograft Artificial skin Immunosuppressants

    62. Interactions Between the Integumentary System and Other Organ Systems Skeletal system – skin in vitamin D synthesis promotes calcium absorption needed for bone growth and health – bone supports skin at scalp and other places Muscular system – vitamin D synthesis promotes calcium absorption needed for muscle contraction – skin dissipates heat generated by muscle – active muscles generate heat and warm skin – muscles contract and produce facial expression

    63. Nervous system – sensory impulses from skin transmitted to nervous system – nervous system regulates diameter of cutaneous vessels – stimulates perspiration – stimulates piloerector muscle Endocrine – Sex hormones cause changes in skin at puberty and menopause Circulatory system – dermal vasoconstriction diverts blood to other organs – skin prevents loss of fluid form cardiovascular system – vasoconstriction can increase blood flow – circulatory system delivers oxygen, nutrients and hormones to skin a carries away wastes

    64. Lymphatic system – skin detects foreign substances – lymphatic system controls fluid balance and prevents edema – immune cells protect skin from infection and promotes tissue repair Respiratory system – nasal hairs filter particles – respiratory system provides oxygen and removes carbon dioxide Urinary system – skin complements urinary system by excreting salts and some nitrogen wastes in sweat – urinary system maintains electrolyte and ph balance

    65. Digestive system – vitamin D synthesis promotes intestinal absorption of calcium – digestive system provides nutrients for skin development and function Reproductive system – cutaneous receptors respond to erotic stimuli – mammary glands produce milk – gonadal sex hormones promote growth and maturation of skin

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