The Integumentary System

Transcription

1 The Integumentary System Consists of the skin and its accessory organs; hair, nails, and cutaneous glands Inspection of the skin, hair, and nails is significant part of a physical exam Skin is the most vulnerable organ Exposed to radiation, trauma, infection, and injurious chemicals Receives more medical treatment than any other organ system Dermatology scientific study and medical treatment of the integumentary system

2 Functions of the Skin Resistance to trauma and infection, protection Other barrier functions Waterproofing, UV radiation Vitamin D synthesis Skin first step, liver and kidneys complete the process Sensation Thermoregulation Vasoconstriction/vasodilation Transdermal absorption Administration of certain drugs steadily through thin skin via adhesive patches

3 The Skin and Subcutaneous Tissue The body s largest and heaviest organ 15% of body weight Most skin is 1 to 2 mm thick Two layers Epidermis: stratified squamous epithelium Dermis: connective tissue layer Hypodermis another connective tissue layer below the dermis Thick skin on palms and sole, and corresponding surfaces on fingers and toes Has sweat glands, but no hair follicles or sebaceous (oil) glands Epidermis 0.5 mm thick Thin skin covers rest of the body Epidermis about 0.1 mm thick Possesses hair follicles, sebaceous glands, and sweat glands

4 The Integumentary System (Skin)

5 The Epidermis Dead cells at the surface packed with tough protein called keratin Lacks blood vessels, has some verve endings for touch and pain. Depends on the diffusion of nutrients from underlying connective tissue Composed of stratified squamous epithelium which can be cell layers thick depending on location the major cell type is the keratinocyte The cells of the epidermis are arranged into 5 structurally and functionally distinct layers called strata each strata is made of one or more types of cells each providing a specific function for the epidermis

6 Cells of the Epidermis 1. Stem cells Undifferentiated cells that give rise to keratinocytes In deepest layer of epidermis (stratum basale) 2. Keratinocytes: synthesize keratin 3. Melanocytes Occur only in stratum basale Synthesize pigment melanin that shields DNA from ultraviolet radiation 4. Tactile (Merkel) cells Touch receptor cells in basal layer associated with dermal nerve fibers 5. Dendritic (Langerhans) cells Macrophages found in stratum spinosum and granulosum Guard against toxins, microbes, pathogens that penetrate skin

7 Cells of the Epidermis Stratum corneum Stratum lucidum Stratum granulosum Sweat pore Exfoliating keratinocytes Dead keratinocytes Sweat duct Living keratinocytes Stratum spinosum Dendritic cell Tactile cell Melanocyte Stem cell Stratum basale Dermal papilla Tactile nerve fiber Dermis Dermal blood vessels

8 Layers of the Epidermis The most superficial layer of the epidermis are the cells that are subjected to the physical forces that come from the outside of the body friction, abrasion, puncture As a result, these cells continuously fall off from the surface of the skin exfoliation The exfoliated cells are constantly replaced by cells in the deepest strata of the epidermis which are constantly dividing (mitosis) maintaining a constant epidermal thickness the rate of mitosis equals the rate of exfoliation

9 Stratum Corneum Outermost strata made of keratinized cells Resistant to abrasion, penetration, and water loss Made of up to 30 layers of dead keratinocytes accounts for up to 75% of the epidermal thickness Most superficial layer of keratinocytes exfoliate from the surface of the body Stratum Lucidum Thin translucent zone seen only in thick skin found on the palms of the hand and souls of the feet (calluses) Cells have no nucleus or organelles

10 Stratum Granulosum Three to five cell layers deep made of keratinocytes Keratinocytes accumulate vesicles (granules) filled with the protein keratin and glycolipids which are exocytosed the exocytosed keratin wraps around the cell membrane of the keratinocyte creating a thick coat which provides protection from abrasion and puncture the exocytosed glycolipids fills the extracellular spaces between the keratinocytes and provides a waterproofing property to skin forms a barrier between surface cells and deeper layers of the epidermis cuts off nutrient supply to the cells of the lucidum and corneum to die

11 Stratum Spinosum Several cell layers deep made of: Keratinocytes become somewhat flattened and spiny-shaped Langerhans (dendritic) cells phagocytose foreign substances such as bacteria and viruses that attempt to enter the body through the skin alert the immune system to the presence of foreign substances

12 Stratum Basale (germinativum) Deepest of the epidermal strata made of a single layer of cells (consisting of 3 cell types) Keratinocytes undergo mitosis rapidly to replace the cells that are exfoliated from the surface as these keratinocytes move up through the more superficial strata Melanocytes produce the brown pigment melanin to protect against UV radiation (sunlight) damage to DNA of keratinocytes Merkel (tactile) cells touch receptors that provide sensory perception

13 Melanocytes Occur only in the stratum basale Melanin is shed from the melanocytes onto neighboring keratinocytes of the strata spinosum and basale. 2 Forms of Melanin Eumelanin: brownish-black pigment. Pheomelanin: reddish-yellow, sulfur-containing pigment. Dark skin: produces greater quantities of melanin, and breaks it down more slowly. Melanin will accumulate into several epidermal layers. Light skin: produces less melanin, and breaks it down quickly so that it doesn t spread beyond the stratum basale. UV exposure increases the productivity of melanocytes.

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15 The Dermis Dermis connective tissue layer beneath the epidermis Ranges from 0.2 mm (eyelids) to 4 mm (palms, soles) Composed mainly of collagen with elastic fibers, reticular fibers, and fibroblasts Well supplied with blood vessels, sweat glands, sebaceous glands, and nerve endings 2 Layers: Papillary layer Reticular layer

16 Dermis Papillary layer Reticular layer

17 The Dermis Papillary layer superficial zone of dermis Thin zone of areolar tissue in and near the dermal papilla Allows for mobility of leukocytes and other defense cells should epidermis become broken Rich in small blood vessels 20% of the thickness of the dermis Its superior surface contains fingerlike projections called dermal papillae which keep it firmly attached to the superficially located epidermis Dermal papillae contain sensory receptors such as tactile corpuscles (touch receptors) and free nerve endings (sense pain)

18 Reticular layer 80% of the thickness of the dermis Elastic fibers provide stretch-recoil properties Location of: hair and associated follicles pacinian corpuscles (pressure receptors) blood vessels glands

19 The Hypodermis Hypodermis Subcutaneous tissue Mostly adipose Pads body Binds skin to underlying tissues Drugs introduced by injection Highly vascular and absorbs them quickly Subcutaneous fat Energy reservoir Thermal insulation 8% thicker in women

20 Skin Colors of diagnostic value Cyanosis blueness of the skin from deficiency of oxygen in the circulating blood (airway obstruction, lung disease, cardiac arrest, cold weather) Erythema abnormal redness of the skin due to dilated cutaneous vessels (exercise, hot weather, sunburn, anger, or embarrassment) Pallor pale or ashen color when there is so little blood flow through the skin that the white color of dermal collagen is visible (emotional stress, low blood pressure, circulatory shock, cold, anemia) Albinism genetic lack of melanin that results in white hair, pale skin, and pink eyes Jaundice yellowing of skin and sclera due to excess of bilirubin in blood (cancer, hepatitis, cirrhosis) Hematoma (bruise) mass of clotted blood showing through skin

21 Hair Filamentous strands of dead keratinized cells produced by hair follicles Contains hard keratin which is tougher and more durable than the soft keratin of the epidermis The long thin hair shaft is visible above epidermis The hair root is in the dermis within a follicle Pigmented by melanocytes at the base of the follicle

22 Hair Function and Distribution Hair is distributed over the entire skin surface except palms, soles, and lips, nipples and portions of the external genitalia Functions of hair include: Retain body heat The follicle of the hair is connected to piloerector muscles that contract when cold raises hair on skin surface (goose bumps) increasing the thickness of the insulation barrier at the surface of the skin Provide sensory perception Limbs and trunk have 55 to 70 hairs per cm 2 Face about 10 times as many 30,000 hairs in a man s beard 100,000 hairs on an average person s scalp Number of hairs does not differ much from person to person or even between sexes

23 Structure of the Hair and Follicle Hair shaft Sebaceous gland Hair receptor Hair root Apocrine sweat gland Blood capillaries in dermal papilla Piloerector muscle Bulge Hair matrix Hair bulb Dermal papilla Hair is divisible into three zones along its length Bulb: a swelling at the base where hair originates in dermis or hypodermis Only living hair cells are in or near bulb Root: the remainder of the hair in the follicle Shaft: the portion above the skin surface (a)

24 Dermal papilla bud of vascular connective tissue encased by bulb Provides the hair with its sole source of nutrition Hair matrix region of mitotically active cells immediately above papilla Hair s growth center Three layers of the hair in cross section from inside out Medulla Core of loosely arranged cells and air spaces Cortex Constitutes bulk of the hair Cuticle Composed of multiple layers of very thin, scaly cells that overlap each other Hair matrix Hair bulb Dermal papilla (b) 0.5 mm Connective tissue root sheath Epithelial root sheath Hair medulla Hair cortex

25 Hair Texture and Color Texture related to differences in cross-sectional shape Straight hair is round Wavy hair is oval Curly hair is relatively flat Color due to pigment granules in the cells of the cortex Brown and black hair is rich in eumelanin Red hair has a slight amount of eumelanin but a high concentration of pheomelanin Blond hair has an intermediate amount of pheomelanin and very little eumelanin Gray and white hair results from scarcity or absence of melanin in the cortex and the presence of air in the medulla

26 Three layers of hair (c.s.) Medulla Core of cells and air spaces Cortex Constitutes bulk of the hair, several layers of keratinized cells Cuticle multiple layers of very thin, scaly cells that overlap each other Hair Texture and Color Cuticle Medulla Cortex (a) Blond, straight Eumelanin Pheomelanin (b) Black, straight Eumelanin Pheomelanin (c) Red, wavy Air space (d) Gray, wavy

27 The Hair Cycle: 3 Stages: Hair Growth Anagen: 90% of hair, hair cells multiply in the follicle and push the hair deeper into the dermis. Also forms the hair root sheath. Hair root sheath cells transform into hair cells which produce keratin and then die as they are pushed away from the papilla. Catagen: Mitosis in the sheath ceases. The base of the hair hardens and is no longer anchored in the papilla. Telogen: Rest period. *When anagen begins anew, the new hair will push out the old.

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29 Nails hard derivatives of the stratum corneum. composed of very thin, dead, densely packed cells, filled with parallel fibers of hard keratin. Nail plate: the hard part of the nail. Free edge: end which overhangs the tip of the finger or toe. Nail body: the visible attached portion of the nail. Nail root: extends proximally under the overlying skin. Nail bed: the skin underlying the nail plate. It s epidermis is called the hyponychium.

30 Nail matrix: A growth zone at the proximal end of the nail, composed of stratum basale. Mitosis (1mm/week). Lunule: white crescent at the proximal end of a nail. Cuticle (eponychium): a narrow zone of dead skin.

31 Exocrine glands of the skin Sweat glands merocrine sweat glands secrete water to cool of the body apocrine sweat glands scent glands that secrete a milky substance rich in fatty acids in response to stress or sexual stimulation Sebaceous glands secrete an oily substance (sebum) into a hair follicle softens the skin Ceruminous glands secrete a waxy substance (cerumen) in the ear canal keeps eardrum flexible kills bacteria

32 Skin Cancer Skin cancer induced by the UV rays of the sun Most often on the head and neck Most common in fair-skinned people and the elderly One of the most common cancer One of the easiest to treat Has one of the highest survival rates if detected and treated early Three types of skin cancer named for the epidermal cells in which they originate Basal cell carcinoma, squamous cell carcinoma, and malignant melanoma

33 Skin Cancer (a) Basal cell carcinoma Basal cell carcinoma - Most common type - Least dangerous because it seldom metastasizes - Forms from cells in stratum basale - Lesion is small, shiny bump with central depression and beaded edges

34 Skin Cancer (b) Squamous cell carcinoma Squamous cell carcinoma - Arise from keratinocytes from stratum spinosum - Lesions usually appear on scalp, ears, lower lip, or back of the hand - Have raised, reddened, scaly appearance later forming a concave ulcer - Chance of recovery good with early detection and surgical removal - Tends to metastasize to lymph nodes and may become lethal

35 Skin Cancer (c) Malignant melanoma Malignant melanoma - Skin cancer that arises from melanocytes; often in a preexisting mole - Less than 5% of skin cancers, but most deadly form - Treated surgically if caught early - Metastasizes rapidly; unresponsive to chemotherapy; usually fatal

36 Burns Classified according to the depth of tissue involvement First-degree burn: partial-thickness burn; involves only the epidermis Marked by redness, slight edema, and pain Heals in a few days Most sunburns are first-degree burns Second-degree burn: partial-thickness burn; involves the epidermis and part of the dermis Leaves part of the dermis intact Red, tan, or white Two weeks to several months to heal and may leave scars Blistered and very painful Third-degree burn: full-thickness burn; the epidermis and all of the dermis, and often some deeper tissues (muscles or bones) are destroyed Often requires skin grafts Needs fluid replacement and infection control

37 Degrees of Burn Injuries Partial-thickness burns Full-thickness burns (a) First degree (b) Second degree (c) Third degree

38 Tissue Repair Damaged tissues can be repaired in two ways: Regeneration: replacement of dead or damaged cells by the same type of cell as before Restores normal function Skin injuries and liver regenerate Fibrosis: replacement of damaged cells with scar tissue Holds organs together Does not restore normal function Severe cuts and burns, healing of muscle injuries, scarring of lungs in tuberculosis

39 Healing of a cut in the skin: Severed blood vessels bleed into cut Mast cells and damaged cells release histamine Dilates blood vessels Increases blood flow to area Makes capillaries more permeable 1 Bleeding into the wound Blood plasma seeps into the wound carrying: Antibodies Clotting proteins Blood cells

40 Blood clot forms in the tissue Loosely knitting edges of cut together Inhibits spread of pathogens from injury site to healthy tissue Forms scab that temporarily seals wound and blocks infection Scab Blood clot Macrophages Fibroblasts Leukocytes Macrophages phagocytize and digest tissue debris 2 Scab formation and macrophage activity

41 New capillaries sprout from nearby vessels and grow into wound Deeper portions become infiltrated by capillaries and fibroblasts Macrophages remove the blood clot Fibroblasts deposit new collagen Begins 3 4 days after injury and lasts up to 2 weeks Scab Blood capillary Granulation tissue 3 Formation of granulation tissue (fibroblastic phase of repair) Macrophages Fibroblasts

42 Tissue Repair Surface epithelial cells around wound multiply and migrate into wound area beneath scab Epithelium regenerates Connective tissue undergoes fibrosis Scar tissue may or may not show through epithelium Remodeling (maturation) phase begins several weeks after injury and may last up to 2 years Epidermal regrowth Scar tissue (fibrosis) 4 Epithelial regeneration and connective tissue fibrosis (remodeling phase of repair)