Human Anatomy & Physiology, Sixth Edition

5Integumentary System

Functions of the Integumentary System

Chemical & physical barrier Body temperature regulation Cutaneous sensation Synthesis of vitamin D

Skin (Integument)

Figure 5.1

Layers & Cells of the Epidermis:

stratum spinosum

stratum granulosum

stratum corneum

cell membranes filled with cross-linked keratin

dying cells filled with keratin & lipid granules

keratinocytes actively producing keratin filaments

stratum basale

mitotically dividing cells

Dermis

Fibrous connective tissue, blood vessels, nerves & small muscles Papillary layer - areolar Reticular layer - reticular

Hypodermis

Subcutaneous layer not technically integument Composed of adipose and areolar connective tissue Thermal insulation & shock absorption

Skin Color

Pigments Melanin – reddish-brown Carotene – yellowish-orange

Hemoglobin

Sweat Glands & Modified Sweat Glands

Eccrine – all over body, empty to pore Apocrine –axillary & anogenital areas, empty to hair

follicle Ceruminous glands – secrete cerumen (ear wax) Mammary glands – secrete milk

Sebaceous Glands

Simple alveolar glands distributed all over body Oily secretion called sebum Secreted to pore or hair follicle Prevents desiccation & waterproofs skin

Keratinized Processes

Stratum corneum Nail Hair Keratinization

soft & hard keratin degree of crosslinking of keratin proteins

Keratin is a long filamentous protein Transglutaminase joins glutamic acid residues on

neighboring keratin proteins creating a keratin aggregate ~ 15 distinct keratin proteins

Keratin Diseases

Epidermolysis bullosa Mutations in keratin proteins such that they can not

be properly crosslinked

Structure of a Nail

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

Figure 5.4

Hair

Bundles of keratinized cells produced in follicles Follicles are epithelial cells deeply invaginated into

the dermal layer Pigmented by melanocytes Sensory nerve endings wraps each follicle Connected to papilary dermis by tiny arrector

muscle

Hair Follicle – Sagittal & Cross Sections

Types of Hair

Vellus – lightly pigmented, finer body hair Terminal – coarser, long hair

eyebrows, scalp, beard, axilla, and pubic Coarseness determined by depth of follicle Curliness determined by shape of follicle

Basal Cell Carcinoma

Most common skin cancer Stratum basale cells proliferate and invade the

dermis and hypodermis Slow growing and non-metastatic Surgical excision effective in

99% of cases

Squamous Cell Carcinoma

Keratinocytes of stratum spinosum Most frequent on scalp, ears, and lower lip Rapid growing and metastatic Early surgical removal followed by irradiation Poor prognosis if metastasized

Melanoma

Cancer of melanocytes Most dangerous type of skin cancer

Highly metastatic Resistant to chemotherapy

Treated by wide surgical excision & immunotherapy Chance of survival is poor if the lesion is over 4 mm

thick

Melanoma

Melanomas are characterized by the ABCD rule A: Asymmetric: halves of the pigmented unequal B: Border: irregular with indentations C: Color: black, brown, tan, sometimes red or blue D: Diameter: larger than 6 mm

Burns

1st -degree – only the epidermis

localized redness, swelling, and pain

2nd -degree – epidermis and upper regions of dermis

Like first degree burns with blistering

3rd -degree – entire thickness of the skin is damaged

Burned area appears gray-white, cherry red, or black; no initial edema or pain

Rule of Nines

Estimates the severity of burns

Burns considered critical if: 2nd degree > 25% of body 3rd degree >10% of body 3rd degree on face, hands, 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 the skin of the fetus in the amnion

Developmental Aspects of the Integument: Adolescent to Adult

Skin and hair become oilier and acne may appear Skin shows the effects of cumulative environmental

assaults around age 30 Scaling and dermatitis become more common

Epidermal replacement of cells slows and skin becomes thinner

Skin becomes dry and itchy Subcutaneous fat layer diminishes Decreased elasticity and loss of subcutaneous tissue

leads to wrinkles Decreased numbers of melanocytes and Langerhans’

cells increase skin cancer risk

Developmental Aspects of the Integument: Old Age