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Chapter 5

Integumentary System

 

Skin (Integument)

•      Consists of three major regions

•    Epidermis  – outermost superficial region

•    Dermis – middle region

•    Hypodermis – deepest region

Epidermis

•      Composed of keratinized stratified squamous epithelium, consisting of four                            distinct cell types and four or five layers

•      Cell types include keratinocytes, melanocytes, Merkel cells, and Langerhans’ cells

•      Outer portion of the skin is exposed to the external environment and functions in protection

Cells of the Epidermis

•      Keratinocytes – produce the fibrous protein keratin

•      Melanocytes – produce the brown pigment melanin

•      Langerhans’ cells – epidermal macrophages that help activate the immune system

•      Merkel cells – function as touch receptors in association with sensory nerve endings

Layers of the Epidermis:

Stratum Basale (Basal Layer)

•      Deepest epidermal layer firmly attached to the dermis

•      Consists of a single row of the youngest keratinocytes

•      Cells undergo rapid division, hence its alternate name, stratum germinativum

Stratum Spinosum (Prickly Layer)

•      Cells contain a weblike system of intermediate filaments attached to desmosomes

•      Melanin granules and Langerhans’ cells are abundant in this layer

Stratum Granulosum (Granular Layer)

•      Thin; three to five cell layers in which drastic changes in keratinocyte appearance occurs                                         

•      Keratohyaline and lamellated granules accumulate in the cells of this layer

Stratum Lucidium (Clear Layer)

•      Thin, transparent band superficial to the stratum granulosum

•      Consists of a few rows of flat, dead keratinocytes

•      Present only in thick skin

Stratum Corneum (Horny Layer)

•      Outermost layer of keratinized cells

•      Accounts for three quarters of the epidermal thickness

•      Functions

•    Waterproofing

•    Protection from abrasion and penetration

•    Renders the body relatively insensitive to biological, chemical, and physical assaults

Dermis

•      Second major skin region containing strong, flexible connective tissue

•      Cell types include fibroblasts, macrophages, and occasionally mast cells and white blood cells

•      Composed of two layers – papillary and reticular

Dermis: Papillary Layer

•      Papillary layer

•    Areolar connective tissue with collagen and elastic fibers

•    Its superior surface contains peglike projections called dermal papillae

•    Dermal papillae contain capillary loops, Meissner’s corpuscles, and free nerve endings

Dermis: Reticular Layer

•      Reticular layer

•    Accounts for approximately 80% of the thickness of the skin

•    Collagen fibers in this layer add strength and resiliency to the skin

•    Elastin fibers provide stretch-recoil properties

Hypodermis

•      Subcutaneous layer deep to the skin

•      Composed of adipose and areolar connective tissue

Skin Color

•      Three pigments contribute to skin color

•    Melanin – yellow to reddish-brown to black pigment, responsible for dark skin colors

•   Freckles and pigmented moles – result from local accumulations of melanin

•    Carotene – yellow to orange pigment, most obvious in the palms and soles of the feet

•    Hemoglobin – reddish pigment responsible for the pinkish hue of the skin

Sweat Glands

•      Different types prevent overheating of the body; secret cerumen and milk

•    Eccrine sweat glands – found in palms, soles of the feet, and forehead

•    Apocrine sweat glands – found in axillary and anogenital areas

•    Ceruminous glands – modified apocrine glands in external ear canal and secrete cerumen

•    Mammary glands – specialized sweat glands that secret milk

Sebaceous Glands

•      Soften skin when stimulated by hormones

•      Simple alveolar glands found all over the body

•      Secrete an oily secretion called sebum

Hair

•      Helps maintain warmth, alerts the body to presence of insects on the skin, and guards the scalp against physical trauma, heat loss, and sunlight

•      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 skin

•      Made up of the shaft projecting from the skin and the root embedded in the skin

•      Consists of a core called the medulla, a cortex, and an outermost cuticle

Hair

•      Pigmented by melanocytes at the base of the hair

Hair Follicle

•      Root sheath extending from the epidermal surface into the dermis

•      Deep end is expanded forming a hair bulb

•      A knot of sensory nerve endings (a root hair plexus) wraps around each hair bulb

•      Bending a hair stimulates these endings, hence our hairs act as sensitive touch receptors

Hair Follicle

Types of Hair

•      Vellus – pale, fine body hair found in children and the adult female

•      Terminal – coarse, long hair of eyebrows, scalp, axillary, and pubic regions

Hair Thinning and Baldness

•      Alopecia – hair thinning in both sexes

•      True, or frank, baldness – genetically determined and sex influenced condition (i.e., male pattern baldness)

Structure of a Nail

•      Scalelike modification
of the epidermis
on the distal,
dorsal surface
of fingers
and toes

Functions of the Integumentary System

•      Protection – chemical, physical, and mechanical barrier

•      Body temperature

•      Regulated by dilation (cooling) and constriction (warming) of dermal vessels

•      Sweat glands increase secretions to cool the body

•      Cutaneous sensation – exoreceptors sense touch and pain

•      Metabolic functions – synthesis of vitamin D in dermal blood vessels

•      Blood reservoir – skin blood vessels store up to 5% of the body’s blood volume

•      Excretion – limited amounts of nitrogenous wastes are eliminated from the body in sweat

Skin Cancer

•      Basal cell carcinoma

•      Squamous cell carcinoma

•      Melanoma

Basal Cell Carcinoma

•      Least malignant and most common skin cancer

•      Stratum basale cells proliferate and invade the dermis and hypodermis

•      Slow growing and do not often metastasize

•      Can be cured by surgical excision in 99% of the cases

Squamous Cell Carcinoma

•      Arises from keratinocytes of stratum spinosum

•      Arise most often on scalp, ears, and lower lip

•      Grows rapidly and metastasizes if not removed

•      Prognosis is good if treated by radiation therapy or removed surgically

Melanoma

•      Cancer of melanocytes is the most dangerous type of skin cancer

•      Melanomas have the following characteristics (ABCD rule):

•    A:  Asymmetry; the two sides of the pigmented area do not match

•    B:  Border is irregular and exhibits indentations

•    C:  Color (pigmented area) is black, brown, tan, and sometimes red or blue

•    D:  Diameter is larger than 6 mm (size of a pencil eraser)

Melanoma

•      Treated by wide surgical excision accompanied by immunotherapy

•      Chance of survival is poor if the lesion is over 4 mm thick

Burns

•      First-degree – only the epidermis is damaged

•    Symptoms include localized redness, swelling, and pain

•      Second-degree – the epidermis and upper regions of dermis damaged

•    Symptoms mimic first degree burns, but blisters also appear

•      Third-degree – involve entire thickness of the skin

•    Burned area appears gray-white, cherry red, or black, and there is no initial edema nor pain (since nerve endings are destroyed)

Rule of Nines

•      Estimates the severity of burns

•      Burns considered critical if:

•    Over 25% of the body has second-degree burns

•    Over 10% of the body has third-degree burns

•    There are third-degree burns on face, hands, or feet

Developmental Aspects of the Integument: Fetal

•      Epidermis develops from ectoderm

•      Dermis and hypodermis develop from mesoderm

•      Lanugo – downy coat of delicate hairs covering the fetus

•      Vernix caseosa – substance produced by sebaceous glands that protects fetus’s skin in the amnion

Developmental Aspects of the Integument: Adolescent to Adult 

•      Skin and hair become oilier and acne may appear

•      After one reaches the 20s and 30s, skin shows the effects of cumulative environmental assaults

•      Scaling and dermatitis become more common

Developmental Aspects of the Integument:
Old Age

•      Epidermal replacement of cells slows and skin becomes thinner

•      Skin becomes dry and itchy

•      Subcutaneous fat layer diminishes, leading to intolerance of cold

•      Decreased elasticity and loss of subcutaneous tissue leads to wrinkles

•      Decreased numbers of melanocytes and Langerhans’cells increase the risk of skin cancer