Chapter 5: Integumentary System

(5) Components of the Integumentary System
-Sweat Glands
-Sebaceous glands
(5) Functions of the Integumentary System
-Protection and immunity
-Temperature regulation
-Vitamin D production
Two Major Tissue Layers of the Skin
1. Epidermis: Most superficial layer of the epithelial tissue; resists abrasion and reduces water loss through the skin
2. Dermis: epidermis rests son this deeper layer of connective tissue; provides structural support
-Skin rests on it
-not part of the skin but shares some functions
-loose connective tissue (areolar and adipose)
-Absorbs shock, insulates, connects skin to underlying structures (ie. muscles)
-contains 1/2 of the body's adipose tissue
-Avascular; nourished by diffusion from capillaries of papillary layer of the dermis
-cells arranged into layers or strata (4 or 5 layers)
-Separated from dermis by basement membrane
Cells of the deeper layers undergo mitosis; as they move towards the surface, older cells slough off
How many keratinocytes are lost every minute via desquamation?
As cells move outward through the layers they fill with keratin, die, and serve as a layer that resists abrasion and forms permeability layer
(4) Types of Epidermal cells
-Dendritic (Langerhans) cells
-Tactile (Merkel) cells
-90% of epidermal cells
-tightly connected by desmosomes
-arranged in 4-5 layers
-produce keratin for strength and prevention of water loss
-Contribute to skin color; produce pigment called melanin which is transferred to keratinocytes to color skin and absorb damaging UV light
Dendritic (Langerhans) cells
-part of the immune system
-phagocytic cells and can phagocytose foreign material to eliminate it
Tactile (Merkel) Cells
-sensory receptors to sense touch
(5) Epidermal Strata (deep to superficial)
1. Stratum basale
2. Stratum spinosum
3. Stratum granulosum
4. Stratum lucidum (only in thick skin)
5. Stratum corneum

Mnemonic: Boys Say Girls Look Cute (BSGLC)
Stratum Basale
-deepest portion of the epidermis
-single layer of stem cells with high mitotic activity
-10-25% of layer is composed of melanocytes
-firmly attached to dermis
Stratum Spinosum
-several layers thick
-limited cell division
-desmosomes provide structural strength to skin; cells appear spiky because of the desmosomes
-scattered among keratinocytes are abundant melanin granules and dendritic cells
Stratum Granulosum
-4-6 layers of flattened keratinocytes undergoing apoptosis (too far from nutrients of lower layers)
-Keratinization begins as cells accumulate granules of keratohyalin
-Lamellar granules accumulate and eventually move to plasma membrane and release lipid contents into intercellular space; results in a water-repellant sealant preventing loss of water and entry of foreign materials
Stratum Lucidum
-Thin, clear zone (2-3 rows of flat, dead keratinocytes)
-found only in thick skin of palms and soles
Stratum corneum
-most superficial
-20-30 layers of dead squamous cells joined by desmosomes
-protect deeper layers from injury or microbial infection
-cells are cornified (dead with hard protein envelope, filled with keratin)
-cells are surrounded with lipids released from lamellar bodies --> water repellant barrier
-As desmosomes break apart, cells are desquamated from surface and replaced by cells from deeper strata
-Forms in skin that is subjected to friction/pressure
-increase in number of layers in the stratum corneum
-When a callus forms over a bone prominence
-excessive desquamation of cells on the scalp
How long does it take cells to move from basale to corneum?
25-45 days
-Chronic skin disorder
-keratinocytes divide and move more quickly than normal to the surface
-results in premature shedding (as little as 7-10 days)
-immature keratinocytes make abnormal keratin
-forms flaky, silvery scales at the skin surface
Functions of the Dermis
-Gives flexible, structural strength
-sensory functions: pain, itch, tickle, temperature, touch, pressure, two-point discrimination
Composition of the Dermis
-C.T. with fibers, fibroblasts, macrophages, some adipocytes, some mast cells
-contains nerves, blood vessels, lymphatic vessels
-contains hair follicles, smooth muscles, oil glands
Two Layers: Papillary and Reticular
Papillary Layer
-Superficial 1/5 of dermis
-Loose C.T. with lots of thin elastic fibers
-capillary beds service overlying epidermis
-fine touch receptors (Meissner's)
-Free nerve endings sensing pain
-Dermal papillae --> fingerprints
Reticular Layer
-Deep 4/5 of dermis
-Dense irregular C.T. with collagen (strength) and elastic fibers
-Some adipose, hair follicles, nerves, oil glands, ducts of sweat glands, heat sensors
-In thick skin, dermal papillae lie on top of the dermal ridges, which give rise to epidermal ridges (called friction ridges)
-Enhance gripping ability
-Contribute to sense of touch
-Sweat pores in ridges leave identifying films of sweat called fingerprints
Cleavage Lines in Reticular Layer
-Caused by many collagen fibers running parallel to skin surface
-externally visible
-important in surgery (if incision is parallel to lines, there is less gapping, faster healing, and less scar tissue
Flexure Lines
-Dermis tightly secured to deeper structures
-Skin cannot slide easily during joint movement causing deep creases
-Visible on hands, wrists, fingers, soles, toes
Dermal Tears
Extreme stretching of skin can cause tears in the dermal layer, leaving silvery white scars called striae (stretch marks)
Acute, short-term traumas can cause them to form
-fluid-filled pockets that separate dermal and epidermal layers
-layers separate due to trauma, and the fluid fills the space between them
Skin Color
-Determined by pigments, blood circulation, and thickness of stratum corneum
-blood circulation imparts reddish hue and can increase during blushing, anger, inflammation
-Areas with thicker stratum corneum can be yellowish in color
Blue color in skin caused by decrease in blood oxygen content
Melanin Pigment
-protects against UV damage
-reddish-yellow to brownish-black in color
-produced by melanocytes and packaged into melanosomes; taken up by keratinocytes to shield DNA from sunlight damage
-production is dependent on genetics, hormones, and exposure to light
-light exposure --> keratinocytes secrete chemicals --> stimulates melanin production --> deposits in skin --> visible as a "sun tan"
Carotene Pigment
-yellow to orange pigment found in vegetables
-accumulates in stratum corneum and hypodermis
-can be converted to vitamin A
-Vitamin A is required to maintain good vision and epidermal health
-Deficiency or absence of pigment
(4) Accessory Skin Structures
-Hair and hair follicles
-Sweat Glands
-Sebaceous glands
-found almost everywhere on human body
-composed of shaft (protrudes above skin surface) and root (located below surface; base of root is the hair bulb
-column of dead, keratinized epithelial cells arranged in 3 layers: Medulla (central axis), Cortex (forms bulk of hair), and Cuticle (forms hair surface)
Hair follicles
-surrounds root of hair
-extend from dermis to epidermal surface
-hair bulb (associated with sensory nerve endings (touch receptors))
-arrector pili muscles (smooth muscle attached to follicle; responsible for "goose bumps")
-Sebaceous glands attached (supply oil to hair shaft)
(2) Stages of Hair Growth
Growth: cells added at base and hair elongates
Rest: follicle shortens and holds hair in place - after rest, hair falls out and new hair replaces the old hair
Hair color
Caused by varying amounts and types of melanin produced by melanocytes in the hair bulb matrix and deposited in cortical cells
-Melanin can be yellow, rust, black, brown
-Pheomelanin is red
-Gray/White hair is a result of decreased melanin production and increased air bubbles in hair shaft
Average rate of hair growth and loss
-0.3 mm/day
-Lose about 90-100/day
Thinning or balding of hair
Male Pattern Baldness
Follicles respond to testosterone by shortening the growth cycle so hairs may never emerge from the follicle before shedding occurs
-With age, the amount of melanin in the hair decreases and tiny air bubbles may accumulate (leads to hair color fading and texture changing)
Parts of the Nail
-Body of nail (thin plate): layers of stratum corneum cells containing very hard keratin
-Proximal nail root (under skin)
-Eponychium (cuticle): corneum superficial to nail body
-Hyponychium: corneum beneath the free edge
Nail Matrix: cells that give rise to the nail
Nail Growth
Grows continuously unlike hair
-0.5 to 1.2 mm/day
Eccrine (Merocrine) Sweat Glands
-most common type of sweat gland
-simple, coiled, tubular glands (coiled part in dermis, duct exiting through epidermis)
-Has it's own pores on surface of skin
-Main function is to regulate body temperature through evaporation
-nervous system stimulation causes contraction --> pushes sweat out
-500mL of sweat excreted on an inactive day
-released in sweat
-toxic to some bacteria (protective function)
Apocrine Sweat Gland
-begin functioning at puberty
-simple, coiled, tubular
-ducts usually open to hair follicles
-secrete basic components of regular sweat plus organic compounds
-compounds are odorless but when acted upon by bacteria, may become odiferous
-found mainly in axillae (armpit), genitalia, around anus
-are actually merocrine glands
Ceruminous Glands
modified apocrine sweat glands located in the ear canal
Earwax (cerumen)
-composed of a combination of sebum from sebaceous glands and secretion from ceruminous glands
Function of Cerumen
In combination with hairs inn ear canal, prevents dirt and insects from entry; also keeps eardrum supple
Mammary Glands
Modified apocrine sweat glands located in breasts
Sebaceous Glands
-Produce sebum (oily, white secretion rich in lipid)
-Holocrine (death of secretory cells)
-most empty into hair follicle
-Softens hair and skin and inhibits bacterial growth
-Not on palms or soles
-relatively inactive until puberty
-When blocked, turn into whiteheads
Usually an infectious inflammation of sebaceous glands, resulting in pimples
"Cradle Cap"
Type of seborrhea on infant's scalp
-caused by overactive sebaceous glands
Vitamin D Production
-requires activation of a precursor molecule in the skin by UV rays in sunlight
-enzymes in kidneys then modify the activated molecule --> calcitriol (most active form)
Hormone that aids in absorption of calcium in foods from GI tract into the blood
Function of Ca2+
-Bone formation, growth, repair
-Nerve and muscle function
Multiple Sclerosis (MS)
Autoimmune disease characterized by demyelination of nerve fibers in both the brain and spinal cord
-interferes with nerve conduction
-more common in areas with less sunlight (further from equator)
-result of decreased calcium uptake, because less calcitriol
Cutaneous Sensation
Pressure, temperature, pain, heat, cold, touch, movement of hairs
Insensible Perspiration
Continuous unnoticeable sweating (500mL per day)
Sensible Perspiration
Visible output of sweat (usually in response to nervous system stimulation)
Skin Cancer
-Most skin tumors are benign and do not spread
-Risk Factors: UV radiation, irritation of skin
Basal Cell Carcinoma
-Least malignant
-Most common type (80%)
-Usually detected before metastasis occurs
Squamous Cell Carcinoma
-Second most common
-Can metastasize if not removed
-Cancer of melanocytes
-2-3% of skin cancer
-highly metastatic
-resists chemotherapy
-key to survival is early detection and wide surgical excision
ABCDE Rule of Skin Cancer Detection
A. Asymmetry
B. Border irregularities (indentations)
C. Color (contains several colors)
D. Diameter larger than 6mm
E. Evolving
First degree burn
-Epidermal damage only
-Redness, edema (swelling), pain
Second degree burn
-Epidermal and upper dermal damage
-Blisters appear
Third degree burn
-Entire thickness of skin involved
-Skin is grey, white, red, or blackened
-Not immediately painful (nerve endings destroyed)
-Skin grafts are often necessary
Treatment of Burns
-temporary covering
-skin graft
Extend of Severity Regions (Rule of Nines)
-Anterior and posterior head and neck: 9%
-Anterior and posterior upper limbs: 18%
-Anterior and posterior trunk: 36%
-Perineum: 1%
-Anterior and posterior lower limbs: 36%
Burns considered critical if...
- >25% of body has second degree burns
- >10% of body has third degree burns
-face, hands, or feet bear third degree burns