INTEGUMENTARY SYSTEM Bio 137 Anatomy & Physiology I
Organ System • Groups of closely related organs that work together to perform similar functions • For each organ system studied, know: • What are the organs that compose the system? • What are the functions of the system?
Structures of the Integumentary System • Organ: • Skin • Accessory Structures • Hair • Sweat Glands • Sebaceous Glands • Nails
Skin • Also called the Cutaneous Membrane • The largest human organ by weight & surface area • 22 ft2 • 4.5-5kg (16% of body weight) • Thickness varies by location: eyelids vs. heels of feet
Structure of the Skin • Composed of 2 layers • Epidermis – epithelial tissue • Dermis – connective tissue • Subcutaneous (SubQ) layer below dermis • Adipose and areolar connective tissue • We lose almost a kg of skin epithelium a year that becomes a major part of household “dust”.
Integumentary System Functions • Protection • Immunity • Regulation of body temperature • Excretion • Sensory reception • Synthesis of vitamin D • Blood reservoir
The Epidermis • Types of skin: • Thin (hairy) skin covers all body regions except the palms, palmar surfaces of digits, and soles. • Thick (hairless) skin covers the palms, palmar surfaces of digits, and soles.
Epidermis • Keratinized Stratified Squamous Epithelium • Avascular • Usually very thin, 0.07mm-0.12mm • Outermost cells are keratinized and dead • These cells are sloughed off as new cells below mature and move up
Cells of the Epidermis • The epidermis contains fourmajor types of cells: • Keratinocytes • Melanocytes • Langerhans cells • Merkel cells
Cells of The Epidermis • Keratinocytes(90% of the cells) • Produce keratin - a tough fibrous protein that provides protection. • Melanocytes • Produce the pigment melanin that protects against damage by ultraviolet radiation. • Langerhans cells • Macrophages that originated in the red bone marrow. • Involved in the immune responses. • Merkel cells (least numerous) • Function in the sensation of touch along with the other adjacent tactile discs (receptors).
Epidermis • Keratinized stratified squamous epithelium • 5 distinct layers of the epidermis in thick skin (4 in thin) • Stratum corneum • Stratum lucidum • Stratum granulosum • Stratum spinosum • Stratum basale Outermost Deepest
Epidermal Layers • Stratum corneum– Oldest, outermost layer • 25-50 layers of dead keratinocytes, filled with keratin • Continuously shed • Constant friction can stimulate the cell production in this layer and produces a callus • Stratum lucidum - Only in thick skin of soles and palms • 4-6 layers of dead keratinocytes • Stratum granulosum- non-dividing 3rd layer • 3-5 layers of keratinocytes undergoing apoptosis (cell death) • Barrier between metabolically active and dead cells
Epidermal Layers • Stratum spinosum • Multilayered keratinocytes • Stratum basale– deepest layer • Contains melanocytes and a single row of cuboidal keratinocytes undergoing mitosis • Skin stem cells (Youngest layer of cells) produces all other epidermal layers
Five Epidermal Layers epidermis dermis granulosum spinosum basale corneum lucidum 16
Growth of the Epidermis • Keratinization • Process where new cells in the stratum basalemove up in epidermal layers and accumulate more and more keratin protein • Takes about 4-6 weeks
Melanin Distribution • Melanin Pigment is produced by melanocytesin the stratum basale • Eumelanin (brown to black) • Pheomelanin (yellow to red) • Same # of melanocytes in individuals BUT different amounts of melanin produced by these cells • Melanin production affected by our DNA, sunlight, chemicals and drugs
The Epidermis • Skin Pigments • Freckles are clusters of concentrated melanin triggered by exposure to sunlight. • Molesare benign localized overgrowth of melanocytes • Malignant melanoma is a cancerof melanocytes.
Skin Conditions • Production of epidermal cells closely balances loss of dead cells • If skin is rubbed regularly rate of mitosis increases • Calluses and corns • Psoriasis - chronic skin disease • Cells divide seven times more frequently • Shed prematurely: 7-10 days • Make abnormal keratin: flaky, silvery scales at skin surface • Effective treatments: suppressing cell division
The Epidermis • Skin Pigment Disorders • Vitiligo– The partial or complete loss of melanocytes in the skin. • Irregular white spots in skin • Possible autoimmune disorder • Albinism is the inherited inability to produce melanin. • Characterized by the complete or partial absence of pigment in the skin, hair, and eyes due to a defect of an enzyme involved in the production of melanin.
Aging • With age, there is an increased susceptibility to pathological conditions • Decubitus ulcer
The Dermis • Connective tissue containing collagen and elastic fibers • 1mm - 2mm thick • Contains: • Blood vessels, nerves, Hair follicles and glands are embedded here • Functions: Binds epidermis to underlying tissues & nourishes epidermis, great tensile strength
2 Layers of Dermis 1. Papillary Layer – thin uppermost layer • Thin collagen fibers with elastic fibers • Dermal papillae - Responsible for a person’s fingerprint • Sensory receptors for touch (Meissner’scorpuscles) 2. Reticular Layer – attached to SubQ • Thick Collagen fibers with elastic fibers • Abundant capillary networks • Hair follicles, glands, vessels & nerves here • Tears or excessive stretching in this region cause stretch marks
Subcutaneous Layer • Also called the hypodermis • Contains adipose tissue, blood vessels, nerves & Pacinian Corpuscles • Attaches skin to underlying tissue subQ
Sensory Receptors for Touch • The skin contains different types of sensory receptors to differentiate between the different tactile (“touch”) sensations. • Light touch, pressure, vibration, itch and tickle • Meissner’s Corpuscles • Light touch receptors • Located in dermal papillae of papillary layer • Abundant in hairless portions of skin • Lips, fingertips, palms, soles, nipples, external genitalia • Pacinian Corpuscles • Deep pressure receptors • Located deep in dermis and/or subcutaneous layer • Found in deeper dermal tissues of hands, feet, penis, clitoris, urethra, breasts, tendons and ligaments
Hair • Hair is present on most skin surfaces except the palms, anterior surfaces of fingers, and the soles of the feet. • It is composed of dead, keratinized epidermal cells. • Genetics determines thickness and distribution. • Functions in touch sensations, protects the body against the harmful effects of the sun and against heat loss.
Hair • Hair develops from epithelial cells at the base of a hair follicle deep in the dermis • Hair shaft – superficial portion above skin surface • Hair follicle – below the level of the skin • Hair root – penetrates deep in dermis • Color is due to melanin production from stratum basale
Nails • Nails are composed of hard, keratinized epidermal cells located over the dorsal surfaces of the ends of fingers and toes. • Nail structures include: • Free edge • Transparent nail body (plate) with a whitish lunula at its base • Nail root embedded in a fold of skin • Functions: • Manipulation • Protection
Skin Glands • Recall from Chapter 4 that glands are epithelial cells that secrete a substance. • Sebaceous (oil) glands are connected to hair follicles. • They secrete an oily substance called sebum which does 2 important things: • Prevents dehydration of hair and skin • Inhibits growth of certain bacteria
Eccrine Sweat Glands • Most numerous • Secrete a water solution (600ml/day) that cools the body • Secretion is water, salts and wastes (urea/uric acid); no odor • Respond to elevated temperature & emotional stress • Function throughout life • Common and widely distributed throughout skin • Forehead • Neck • Back
Apocrine Sweat Glands • Secretion empties into a hair follicle • Located mainly in the SubQ layer • Not involved in thermoregulation • Function from puberty on • Secretion is water, salts, wastes and cellular debris that is metabolized by bacteria = ODOR • Most abundant Locations: • Axillary region (Armpit) • Groin
Skin Glands • Ceruminous glands are modified sweat glands located in the ear canal. • Along with nearby sebaceous glands, they are involved in producing a waxy secretion called cerumen (earwax) which provides a sticky barrier that prevents entry of foreign bodies into the ear canal.
Integumentary System Functions • Protection • Regulation of body temperature • Excretion • Sensory reception • Immunity • Synthesis of vitamin D • Blood reservoir
Integumentary System Functions • Protection • Moisture loss • Injury • Microorganisms • Chemicals • The skin is the 1st line of defense in the immune system!!!
Regulation of Body Temperature • Involves sweat glands • Shivering • This is the diagram we covered on the very first day of class!
Sensory Reception • Meissner’s Corpuscles • Light Touch receptors • Located in dermal papillae • Pacinian Corpuscles • Deep Pressure receptors • Located deep in dermis or subcutaneous layer
Integumentary System Functions • Immunity • Langerhan Cells • Specialized immune cells that reside in the epidermis • Interact with T cells in immune responses • Acidic pH of perspiration retards microbe growth
Integumentary System Functions • Synthesis of Vitamin D: • Requires sunlight • Needed for bone development, growth and remodeling • Promotes absorption of calcium and phosphorous from the small intenstine • Cholesterol →Provitamin D → Vitamin D Sunlight (In skin)
Integumentary System Functions • Blood reservoir: • 10% of our blood vessels are located in dermis
Wound Healing • Two kinds of wound-healing processes can occur, depending on the depth of the injury. • Epidermal wound healing occurs following superficial wounds that affect only the epidermis. • Deep wound healing occurs when an injury extends to the dermis and subcutaneous layer. • Loss of some function and development of scar tissue usually occurs.
Wound Healing • Inflammation is a normal response to injury, especially if deep • Blood vessels dilate and become leaky • Skin becomes reddened, swollen, warm • This provides tissues with more nutrients and oxygen which aids in healing • Also allows for WBC to enter tissue and prevent infection • Macrophages remove foreign material and begin tissue repair
Burns • A burn is tissue damage caused by excessive heat, electricity, radioactivity, or corrosive chemicals that denature (break down) the proteins in the skin cells. • Burns destroy some of the skin's important contributions to homeostasis—protection against microbial invasion and desiccation, and thermoregulation. • Burns are graded according to their severity.