Integumentary System PDF

SKIN largest organ of the human body also known as the cutaneous membrane (dry) Thinnest part is the eyelid Thickest part is heels STRUCTURE OF THE SKIN 1. Epidermis—layer of avascular epithelial tissue 2. Dermis—tough layer of vascularized fibrous connective tissue 3....

SKIN largest organ of the human body also known as the cutaneous membrane (dry) Thinnest part is the eyelid Thickest part is heels STRUCTURE OF THE SKIN 1. Epidermis—layer of avascular epithelial tissue 2. Dermis—tough layer of vascularized fibrous connective tissue 3. Hypodermis—subcutaneous tissue/layer of adipose tissue. Connective tissue found is areolar and adipose. “Within the dermis and the epidermis, you will find the skin’s accessory structure such as hair,nails, glands” Functions of the Skin 1. Protection- the skin protects the body from mechanical trauma, pathogens, and environmental damage. a. Physical & chemical barrier against invasion i. e.g. keratin:tightly packed cells, Langerhans:low pH, produces bactericidal chemicals b. Reduces water loss c. Prevents UV damage 2. Excretion/Absorption- the skin excretes waste and impurities via sweat a. Excretion removes wastes (salts, CO2, ammonia, urea) b. Limited absorption (transdermal drugs & toxic materials that are lipid soluble) 3. Vitamin D Synthesis- the skin synthesizes vitamin D when exposed to ultraviolet radiation (Cholesterol is the precursor form of Vitamin D, so vitamin d begins in the body as cholesterol found in the skin's epidermis. Whenever the sun hits the skin, cholesterol is converted to calciferol. After calciferol enters the bloodstream, it will get modified to calcitriol which is the active form of vitamin D< the liver and kidney do this modification) a. Aids in calcium absorption (cannot absorb calcium if no Vit D) b. Requires UV 4. Thermoregulation- the skin maintains a stable internal body temperature through negative feedback loops. a. Vasoconstriction (less heat loss) & vasodilation (more heat loss) b. Sweating c. Muscle contractions (exercise) & shivering 5. Blood reservoir- 8 to 10% of total blood flow (resting state) 6. Sensation-the skin has sensory receptors that detect internal and external environmental change such as heat, cold, and/or pain. a. Tactile:touch (Merkel & Meissner), pressure & vibrations (Pacinian corpuscles) b. Thermal:warm & cool c. Pain EPIDERMIS made up of keratinized stratified squamous epithelium. Made of 4 different cell types in 5 layers. -Keratinocytes, Melanocytes, Langerhans, Merkel cells Stratum Basale/Stratum Germinativum (deepest layer) the one attached to the dermis meaning basal layer. (has highly mitotic keratinocytes, stem cells, merkels, and melanocytes) Made up of a single row of cells, most of which are keratinocytes. consist of single layer of stem cells most metabolically active and most active in mitosis because it is close to the blood supply im the dermis Also contains melanocytes which contain melanin Melanin ○ a pigment molecule and is one of the components of the skin that determines its color and protects the skin from ultraviolet radiation. Also contains tactile cells which act as the sensory receptor for touch Keratinocytes ○ Rapidly dividing cell that push new cells up into the layers above, to help regenerate dead skin, and producing lots of keratin as they do so. ○ This is necessary because millions of dead keratinocytes rub off your skin every day, due to friction and even more from your hands and feet, so these constantly dividing cells in the stratum basale ensure that a new epidermis forms every few weeks, so that we always have our skin intact. ○ tight intercellular junction joined by desmosomes Stratum Spinosum looks spiky that’s why it’s sometimes called as prickly layer thickest layer of the epidermis containing 8-10 layers of cells (has living keratinocytes, langerhans, and melanocytes) Made up of several layers of cells with a weblike system of intermediate filaments attached to desmosomes. also contains dendritic cells that are able to ingest foreign substances and activate immune system near blood supply, it’s cells are metabolically active and can undergo mitosis helps to produce vitamin D Stratum Granulosum, or Granular Layer 4-6 layers thick and keratinization begins here 3-5 rows of cells (has dying keratinocytes has large granules inside of its cells and these cells release a lipid-based substance through exocytosis  When cells get far enough from the dermal capillaries below to receive sufficient nutrients, so the cell fill up with keratin as they die, and they flatten while the organelles disintegrate which makes the cell tougher and scalier, which allows for the outer layers to better protect the body Stratum Lucidum or Clear Layer This is 2-3 cell layers thick ONLY found in thick skin (fingertips, palms, soles) large amounts of dead keratin made of dead keratinocytes that have become flat and clear where they begin to aggregate into arrays called tonofilaments Stratum Corneum 20-30 cell layers thick most superficial layer of the epidermis all cells are anucleated (nucleus has disintegrated) dead cells, with thick plasma membrane surrounding lots of keratin KERATINOCYTES LIFE CYCLE Produced in the Stratum Spinosum Sheds in the Stratum Corneum Can shed from environmental and physical stress Shed cells are replaced by mitosis Cells primarily divide at night Other Cells in the Epidermis Dendritic (Langerhans Cells) made in bone marrow but migrates to epidermis Found in Stratum Spinosum Phagocytic immune cells that protect the skin and underlying tissue from pathogens (macrophages) Protects the skin and underlying tissues from pathogens Merkel cells Oval cells found in the Stratum Basale Sensory receptors that detect light touch, shapes, and textures Also found in the fingertips,lips,and base of hair Melanocytes Found in the Stratum Basale Produces melanin, a protein that gives pigment to skin THICK VS THIN SKIN Thick skin Consist of all five layers of the epidermis with a thick Stratum Corneum Equivalent to the size of a paper towel  Lacks hair follicles and arrector pili muscle Contains sweat glands Found in palms of hands and soles of feet Subject to lots of mechanical stress No sebaceous gland More numerous sudoriferous gland Thin skin Consist of only four layers of the epidermis, lacking the Stratum Lucidum Equivalent to the size of a sheet of printing paper Has hair follicles and arrector pili muscle has both sebaceous and sweat glands. (fewer sudoriferous glands than thick skin) Subject to less mechanical stress “When exposed to extra pressure, both thick and thin skin will develop extra layers of the Stratum Corneum which will result in a callus.” Dermis Houses blood supply Anchors epidermis in place made of connective tissue with collagen (gives strength) and elastic fibers (gives stretch and recoil), and is full of nerves and blood vessels. where hair follicles begin (hair follicles are only found in thin skin, not thick skin) has two sections: papillary and reticular layer Papillary layer most superficial layer of the dermis thinner layer consist of areolar or loose connective tissue Thin Collagen fibers and fine elastic fibers anchor dermis and epidermis together. Connect it through the epidermal ridges. consists of Phagocytes and fibroblasts Has blood capillary loops leaves room for defensive cells to patrol the area for bacteria that may have made it through the skin. The word papillary refers to the projections from the surface of this layer, which are called dermal papillae, that stick out into the epidermis above. Dermal Papillae - houses tiny blood vessels called capillaries that diffuse oxygen and nutrients - houses sensory receptors called Tactile (Meissner corpuscles) - in areas where there is a lot of friction, like the hands, these papillae sits on mounds called dermal ridges which cause ridges in the epidermis as well, which are meant to enhance the gripping ability of the fingers, and they are visible as the lines on our fingertips. “Continuous trauma to a certain area can disrupt the collagen fibers that anchor the dermis and the epidermis in place. The dermis and epidermis will separate which will result in a fluid filled pocket called a blister” Reticular layer Deepest and thickest layer of the dermis consist of dense irregular connective tissue more fibers in reticular than Papillary layer houses thick Collagen fibers that strengthen the dermis and protects deeper layers houses course Elastic fibers that allow skin to revert after stretching (If there is extreme stretch such as stretching from pregnancy or weight gain, these elastic fibers could permanently tear forming stretch marks) houses Proteoglycan cells that hydrate the skin (draw water into ground substance of dermis which helps moisturize skin and keep it firm) A network of blood vessels sits below this, just before the hypodermis You’ll find blood vessels, sweat glands, hairs, sebaceous glands, and sensory receptors One main type of receptor which is the Pacinian corpuscles or lamellated corpuscles that respond to change in pressure and vibration Skin Markings shows interaction between the dermis and epidermis which can be found on the palms of the hands and plantars of the feet Thick collagen fibers arrange the dermal papillae into dermal ridges The epidermis will blend in with dermal papillae that lies underneath, which creates epidermal ridges. These ridges function to increase the gripping ability of the hands and feet. Along the epidermal ridges, you will find tiny sweat pores that excrete sweat. It forms a thin film on the skin which is known as a fingerprint. In between bundles of collagen fibers, you’ll find gaps which indent and form cleavage lines or tension lines As the reticular layer tightly packs to underlying structures, it will create a deep crease named flexor lines SKIN APPENDAGES Hair or pili, are filamentous structures that project from the skin’s (thin skin) surface. a flexible strand made largely of dead keratinized cells (hard keratin which is a bit different from soft keratin found in cells of the epidermis which makes them more durable and not as flaky. produced by hair follicles which possess a root deep inside the follicle where the keratinization is happening, and a shaft, the part closer to the surface of the skin and then extending outside the body where keratinization is complete. consist of three layers of cells ○ inner medulla  containing large cells and soft keratin found in thick hairs only ○ middle cortex which is several layers of flattened cells contains hard keratin highly structured ○ outer cuticle most superficial layer a single layer of overlapping cells, the most keratinized cells in the hair When outer cuticle becomes worn out, a split end can occur STRUCTURES OF THE HAIR Shaft- projects from the surface of skin (all of the hair cells are dead, location is above skin ) Root- embedded in the dermis of skin (living hair cells) Hair Papilla- indentation at the base of the hair bulb that contains blood vessels that nourish hair follicle Hair bulb- structure at the deep end of the hair follicle (root + hair papilla) Hair Matrix- structure at the base of hair bulb that produces new hairs via mitosis (area of hair that undergoes mitosis to make new hair cells) Hair follicle- infolding surrounding the hair root, sac where hair grows, has nerve ‘hair root plexus’ & blood supply (root is embedded in the hair follicle) Epithelial Root Sheath- has two parts: Outer component: attaches hair follicle to the dermis Inner component: attaches tightly to the root Dermal Root Sheath- supports the hair follicle and separates it from the dermis Arrector Pili Muscles- attached to dermal root sheath are tiny bands of smooth muscle (involuntary) that cause hairs to stand up when they contract, this is known as piloerection. Piloerection occurs when we are cold or frightened, giving the skin what we know as “goosebumps” Disorders: Alopecia- baldness where hair follicles are gone and no hair can grow anymore Electrolysis & chemotherapy affect cells in the matrix which leads to hair loss Hypertrichosis- disorder where a person creates too much hair Hair Pigment & Texture  ○ Lanugo is a type of thin hair that has no pigment. It grows on the skin of a fetus, and usually falls out by the time the baby is born. This is replaced by either terminal or vellus hair. ○ Vellus hair is thinner than terminal hair, and is nonpigmented. ○ Terminal hair is thick, coarse, and pigmented. It is found on the scalp, eyelashes, and eyebrows. During puberty, some terminal replaces vellus such as armpits, pubic regions, limbs; face/chest in men) Men: 95% terminal, 5% vellus. Women: 35% terminal, 65% vellus ○ Hair color is determined by melanin (eumelanin:dark pigment & pheomelanin:light pigment such as blonde or red). ○ As we age, melanocytes produce less melanin, and the hairs that are growing begin to lose pigment, causing white or gray hair. (gray hair=no melanin being deposited, white hair=air bubbles deposited in hair shaft instead of melanin) Nail hard structures located at the end of our digits contain hard keratin. products of modification of the epidermis for gripping and manipulation STRUCTURES OF THE NAIL Nail plate- rests on top of epidermal nail bed and divides into the nail body and nail root Nail bed- deep to nail plate, nourishes and protects the nail Nail body- visible part of nail Nail root- lies under the skin Nail matrix- part of the nail root with living, dividing cells. Supplies oxygen to the nail, sight of nail growth. (cells actively undergoing cell division) Proximal nail fold- covers edge of root (surrounding the nail) Eponychium- known as cuticle, found at the base of the nail. Protects matrix from infection Nail folds- overlapping of the skin that borders the nail laterally and medially. Hyponychium- skin that lies under the free edge of the nail Lunula- half shaped moon area where keratin accumulates. Vascularity deeps (less pink) Glands EXOCRINE GLANDS 1. Sweat glands or sudoriferous glands found almost everywhere on the surface of the skin totalling to about 3 million 2 types of sweat glands eccrine or merocrine sweat glands ○ (most common, secretion occurs in the dermis)  ○ resulting fluid or sweat travels through the tube towards a funnel-shaped opening called a pore. (excrete sweat through a PORE) ○ Sweat is 99% water but contains some salts and metabolic wastes ○ Sweat secrete antimicrobial agents to fight against the growth of pathogens on skin ○ also function in thermoregulation ○ concentrated in forehead, palms, soles ○ functional at birth apocrine sweat gland ○ secrete fat and protein which cause body odor ○ found fewer in the body like armpits, anal area, and areola ○ excrete sweat into hair follicles ○ can cause cold sweats ○ Sweat these glands release is odorless but bacteria on skin will metabolize the sweat which causes odor. ○ concentrated in armpit, groin, around nipples ○ functional at puberty ceruminous gland ○ secretes a thick fluid called cerumen (earwax) into hair follicles. Cerumen lines the ears and functions to lubricate the eardrum. mammary gland ○ produce sweat called milk. Milk contains proteins, lipids, sugars, and immune cells to nourish a newborn 2. Sebaceous gland/oil gland secretes sebum which lubricates hair and skin usually connected to hair follicle to make it soft functional at puberty small ducts with secretory cells named acini cell surrounding them branched alveolar glands that secrete sebum which is made of oily lipids these ducts empty a waxy oily liquid called sebum (oil) into either a hair follicle or through a small pore. soften and lubricate hair and skin, slowing water loss and killing certain bacteria helps maintain acidic pH which create a hostile environment for pathogens preventing them from growing on the skin In sebaceous secretions, an acini cell will accumulate products such as dead cells and different types of lipids until it ruptures. However, some bacteria can thrive in sebum, causing something that we know as a pimple or a bump. SKIN PIGMENTATION Melanin ranges in colors of orange-red to black. produced by melanocytes in the stratum basale more melanin is synthesized when exposed to UV radiation (tanning).  Amount of melanin production in different individuals results in skin color variation NOT increase in number of melanocytes composed of two tyrosine amino acids that are joined by the enzyme tyrosinase functions: Protect keratinocytes from mutating due to UV exposure & Prevent skin from synthesizing too much Vitamin D in response to radiation (Too much vit D results in calcium imbalance and kidney failure) Melanin can be unevenly distributed throughout the skin: Moles are produced when a high amount of melanocytes are proliferated in one spot (benign concentration of melanocytes; also called as NEVUS) Freckles are produced when pigment is concentrated in one spot from a high amount of melanin production (accumulation of melanin in patches) Albinism is an inherited genetic disorder where melanocytes fail to produce the tyrosinase enzyme. This lack of skin pigmentation can increase the risk of DNA damage of keratinocytes. (Tyrosinase catalyzes the melanin protein, without it, no melanin can be produced) Vitiligo is the complete loss of melanocytes causing white blotches Certain conditions affect skin color Anemia or shock (pallor color) is decreased blood flow or vasoconstriction of blood vessels. Cyanosis (blue color) is decreased oxygen or respiration Erythema (redness) is increased blood flow or vasodilation Jaundice (bilirubin) is liver dysfunction Carotene Gives yellow-orange pigment Lipid-soluble molecule Usually ingested in diet from yellow and orange foods Accumulates in stratum corneum Hemoglobin Gives skin a pinkish hue An iron containing protein in our blood that binds and transports oxygen also contributes to skin pigment Turns a bright orange-red color when oxidized Tattooing ink is deposited in dermis some are more painful depending on the location because some parts have more tactile sensors They sometimes fade due to lymph flushing PATHOLOGY OF SKIN The most common type of skin pathology is a Wound. A wound is any disruption of the skin’s integrity. They may disrupt the epidermis, dermis, or deeper tissues There are different kinds of wounds: ○ Lacerations (cuts)  ○ Burns ○ Skin cancers Wound treatment can vary amongst severity. For instance, a laceration may be treated with sutures (stitches), whereas a burn may be treated with surgical repair. Athlete’s foot Cause is fungal infection (tinea pedis) Signs are itchiness, red peeling skin between the toes Boils (furnacles) and carbuncles Cause is inflammation of hair follicles Signs are Carbuncles are clusters of boils caused by bacteria Cold sores (fever blisters) Cause is Human Herpesvirus 1 Signs are blisters, itch, and sting Impetigo Cause is bacterial infection Signs are characterized by pink, fluid-filled raised lesions around mouth/nose Contact dermatitis Cause is exposure to chemicals Signs are allergic responses such as itching, redness and swelling of the skin Psoriasis Cause is triggered by trauma, infection, hormonal changes, or stress Signs are red, epidermal lesions covered with dry, silvery scales that itch, burn, crack, or sometimes bleed Burns A burn is a skin wound caused by heat, extreme cold, electricity, chemicals, and/or radiation. There are three classifications of burn woumds, all based on the extent of tissue damage. - Dangers are protein denaturation and cell death, dehydration, electrolyte imbalance, circulatory shock - Result is loss of body fluids and infection from the invasion of bacteria How is the extent of a burn estimated?- rule of nines (body is divided into 11 areas where each area represents 9% of total body surface area) Degree Burns 1. Superficial - only epidermis is damaged; skin is red and swollen 2. Partial-thickness: epidermis and superficial part damaged; skin is red, painful, and blistered, regrowth can occur 3. Full-thickness - destroys epidermis and dermis (burned area is painless), skin grafts -regeneration is not possible, burned area is gray-white/black 4. full -thickness - extends into deeper tissues (bone, muscle, tendon), appears dry and leathery, surgery, possible amputation Criteria for deeming burns Over 30% of body = 2nd deg burns Over 10% of body = 3rd/4th deg burns 3rd/4th deg of the feet, hands, feet, or genitals - Burns affect the airways - Circumferential burns have occurred First-degree burns: most minor and most superficial because only the epidermis is damaged. Symptoms are erythema (redness) and minor pain. Usually require no treatment, no blisters or permanent damage Second-degree burns: also called partial thickness burns. Damage is caused to the epidermis and either some or all of the dermis. Symptoms are pain, blistering, scarring. Usually require medical treatment. Third-degree burns: Most damaging, also known as full thickness burns. Damages to the epidermis, dermis, and hypodermis. Muscle and bone may also be damaged. Symptoms are severe scarring, lost of hair follicles, and dehydration due to fluid loss. Swelling and infection may also occur. Treatment may result in skin grafting. Skin Cancer Cancer is a very common skin disease. It is caused due to mutations in the DNA that cause cells to lose control over their cell cycle. This can lead to tumors, which is a cluster of undifferentiated cells. Tumor cells can metastasize, or travel to other parts of the body, alter the structure of a tissue and prevent the tissue from functioning properly. There are three common types of skin cancers: Basal Cell Carcinoma: The most common type of skin cancer, a cancer of keratinocytes in the stratum basale. Usually found in skin that is frequently exposed to UV radiation. Forms a nodule with a central crater that develops into an ulcer. Can be completely treated by surgical removal. Squamous Cell Carcinoma: Second most common. A cancer of keratinocytes in the stratum spinosum. Most commonly found on the head and neck. Forms a scaly patch that ulcerates or bleeds. Metastasized to lymph nodes if not removed. Can be surgically removed. Malignant Melanoma: Most severe, cancer of melanocytes. Deadly (5% of skin cancers). More likely to metastasize due to the arms of cancerous cells. Arms of melanocytes allow cancerous cells to extend down to the blood vessels of the dermis and access the cardiovascular & lymphatic system. Treatment can include surgical removal, chemotherapy, and radiation therapy. ○ Malignant Melanoma mole can be detected early on and is distinguishable from other skin cancers using the ABCDE rule:  Asymmetrical shape- both sides of the mole are uneven Border irregularity- Mole has jagged edges or blurriness Color- Mole is blue-black or different colors Diameter- Mole is larger than 6mm or the size of a pencil eraser Evolving- Mole is continually changing in shape and size Developmental aspects of skin 1. Lanugo - downy hair, covers the body by 5th/6th month of fetal development - disappears by birth 2. Vernix caseosa - oily covering, is apparent at birth 3. Milia - small white spots, common at birth and disappear by the 3rd week 4. Acne - may appear during adolescence WOUND HEALING Primary Intention - edge to edge healing - leave a minimal scar Secondary Intention - inside out healing - leave keloid or some striations Tertiary Intention - leave open intentionally Phases of Wound Healing 1. Hemostasis- immediate response. Blood leaking so constriction occurs. Platelets start to aggregate and clot forms. A plug forms to stop the bleeding.(Bleeding stopped + blood clot formed) 2. Inflammatory- a couple days after injury. Blood starts to dilate or vasodilation. Macrophage sees the debris on the injury site and takes out the trash. As it takes out the trash, it leaves growth factors which signal the fibroblasts to the area. a. Inflammation, Pain, Scab, Heat, Redness 3. Proliferation- weeks to months. Fibroblasts drop off collagen to generate tissue and help close the wound. Oxygen is important for cell growth. 4. Maturation- years. As collagen has been deposited, we will have a granular tissue formed and wound closed. Barriers to Wound Healing 1. Unrelieved pressure due to decreased oxygen to the localized area 2. Dehydration and Overhydration 3. Repeat trauma 4. Infection or Bacteria in the area 5. Necrosis in the area 6. Biofilm in the area 7. Systemic Factors: Age, Respiratory or cardiac disease, Nutrition, Medication, Immunocompromised Complication in Wound Healing 1. Infection 2. Hemorrhaging 3. Dehiscence (wound starts to open up) 4. Evisceration (organs come out)