Integumentary System

integumentary system

consists of skin and accessory organs (hair, nails, glands), highly vulnerable to outside forces

skin

body’s largest and heaviest organ, receives more medical treatment than any other organ, exposed to UV radiation, trauma, infection, and chemicals

epidermis

keratinized stratified squamous epithelium layer of the skin, avascular

dermis

deeper connective tissue layer of the skin, vascular

hypodermis

CT (adipose) layer below dermis

kertain

tough protein found in the skin

dermcidin and defensins

natural antimicrobial proteins released by sweat glands

dendritic cells

immune cells in epidermis

functions of skin

resistance to trauma and infection, protects against water, UV radiation, and harmful chemicals, vitamin D synthesis, sensory functions, thermoregulation, and non-verbal communication

5, 4

there are _____ layers of the epidermis in thick skin, such as palms and soles, and _____ layers in thin skin on the rest of your body

sebaceous glands and hair follicles

thick skin does not have what two integumentary accessory features?

stratum basale

deepest layer of epidermis, connects to dermis, creates new keratinocytes, high rate of mitosis, tactile (Merkel) cells (connection to sensory neuron), melanocytes

stem cells

only found in stratum basale, highly mitotic and give rise to keratinocytes

keratinocytes

in all layers of the epidermis, most common, produce keratin, have a 30-40 day life cycle

melanocytes

found in stratum basale, produce melanin, which is exported from these cells through melanosomes which are taken in by keratinocytes, clustered on the superficial side of cell and act as “sun hat” for nucleus to protect DNA, activity can be genetically and hormonally determined, number of these cells similar among different skin colors, amount and distribution of melanin differs

dark skin

more melanin and more spread out across keratinocytes, and longer persistence

light skin

less melanin and less widely distributed (concentrated around nucleus of keratinocytes)

tactile (Merkel) cells

found in stratum basale, perceive touch, abundant on hands and feet

dendritic (Langerhans) cells

found in stratum spinosum and granulosum, macrophages (WBC) engulf bacteria, foreign particles, and damaged cells

stratum spinosum

second deepest layer of epidermis, desmosomes between keratinocytes give “spiny” appearance under microscope, keratinocytes pushed upward by newly dividing cells in s. basale, dendritic cells “wander” through here

desmosomes

these structures help provide structure and allow space for movement in the epidermis, found in s. spinosum

stratum granulosum

middle layer of epidermis, keratohyalin granules in cells (bind keratin proteins together and created very tough layer just inside membranes of cells), lamellar bodies release lipid mixture into extracellular spaces and act as water barrier, cells begin to die

stratum lucidum

second most superficial layer of epidermis, only in thick skin, transparent, flat cells (dead), clear protein eleidin

stratum corneum

most superficial layer of epidermis, up to 30 layers of dead keratinocytes (flattened and enucleated), still contain the keratin bundles and lipid coating from lamellar bodies, desmosomes keep them together when dead, eventually flake off as dander in process called “desquamation”

dermis

CT layer beneath epidermis, vascular, innervated, sweat and sebaceous glands, houses hair and nail roots, tattoo ink must reach this layer, contains fibroblasts that allow for repair when injured and produce ECM

papillary layer

upper layer of dermis, areolar CT, extends via dermal papillae into s. basale of epidermis which created fingerprints, nerve fibers and touch receptors, epidermis has epidermal ridges that reach downward

reticular layer

lower layer of dermis, dense irregular CT (thicker layer of dermis), itch, stretch, and pressure receptors (innervated), collagen and elastin fibers provide strength and elasticity (and growth), collagen binds to water to keep skin hydrated

hypodermis

subcutaneous tissue (mostly adipose CT), common site of drug injection (highly vascularized), energy reservoir and thermal insulation

glands

accessory of integumentary system, release something, endocrine and exocrine

endocrine glands

release chemicals into bloodstream (e.g., hormones)

exocrine glands

release chemicals via ducts to surface of epithelial tissue, sweat and sebaceous, all glands of integument are this type

aprocine and eccrine

two kinds of sweat (sudoriferous) glands

sweat

contains mostly water for thermoregulation, NaCl, fatty acids that create acid mantle (slightly acidic environment on skin), and pH 4-6 that prevents bacterial overgrowth

apocrine sweat glands

less abundant, located in genital region and axilla (armpit), inactive until puberty (sex pheromones), “scent glands”, ducts lead to nearby hair follicles, release fatty acids + water, goal is to attract mate for reproduction, not for thermoregulation, anchored in hypodermis

eccrine (merocrine) sweat glands

most numerous sweat glands, abundant on palms, soles, forehead, release water + salts + (few fatty acids) onto skin’s surface, release dermcidin, thermoregulation

sebaceous glands

short ducts opening into hair follicles, holocrine secretion (apoptosis; plasma membrane ruptures and cell dies to release oil), sebum secreted, which keeps skin and hair from becoming dry, brittle, and cracked and “waterproofs” the skin (keeps water in)