Lecture 6: Integumentary System Exam 2 Review

Integumentary system organs

Hair, skin, and nails

What layers make up the integument (skin)?

Epidermis + dermis. The hypodermis (subcutaneous layer) sits deep to the dermis and is NOT considered part of the integument (textbook table), even though slide 1 lists it with the skin layers

Epidermis tissue type

Keratinized stratified squamous epithelial tissue (ET)

Dermis tissue types

Areolar CT (papillary layer) + dense irregular CT (reticular layer)

Hypodermis tissue type

Mainly adipose CT (plus some areolar CT)

Hypodermis functions

Body insulation and cushion; highly vascularized. AKA subcutaneous layer

Skin Function 1: Protection

Protects against physical injury, chemicals, microbes, UV radiation; selectively permeable to some chemicals

Skin Function 2: Prevent water loss

Water resistant but NOT completely waterproof; water is lost through perspiration

Skin Function 3: Temperature regulation

Insulation (fat in hypodermis), capillary networks (widen to release heat, narrow to keep heat), sweat glands (evaporative cooling)

Skin Function 4: Metabolic regulation

Skin produces vitamin D, which allows calcium and phosphate absorption

Skin Function 5: Immune defense

Epidermal leukocytes (dendritic cells); salt and sebum on the skin surface fight microbes

Skin Function 6: Sensory reception

Awareness of and response to external conditions; tactile (Merkel) cells detect touch

Is the epidermis vascular?

No, it is avascular. It gets nutrients by diffusion from blood vessels in the dermis (papillary layer)

5 strata of the epidermis, deep to superficial

Basale, Spinosum, Granulosum, Lucidum, Corneum. Mnemonic: "Before Signing, Get Legal Counsel"

Stratum basale (description)

Deepest stratum; single row of cuboidal to low columnar cells; quickly dividing (mitosis happens here); tightly attached to the basement membrane

Cell types in the stratum basale

Keratinocytes, melanocytes, tactile (Merkel) cells

Keratinocytes

Most common epidermal cell; makes keratin (tough protective protein)

Melanocytes

Secrete melanin pigment; located in stratum basale; pass melanin to keratinocytes in vesicles

Tactile (Merkel) cells

Touch receptors in the stratum basale; connect to a sensory nerve ending

Stratum spinosum (description)

Several layers of keratinocytes attached by desmosomes; contains epidermal dendritic cells

Epidermal dendritic cells

Leukocytes (immune cells) in the stratum spinosum that perform phagocytosis

Desmosomes

Cell junctions that hold keratinocytes together in the stratum spinosum

Stratum granulosum (description)

3-5 layers of flattened keratinocytes filled with keratin granules; keratinization begins here

Stratum lucidum (description)

THICK SKIN ONLY; 2-3 layers of flat, dead (anucleate) keratinocytes; extra protection from abrasion on palms and soles

Stratum corneum (description)

Most superficial; 20-30 layers of dead, flat, keratin-filled keratinocytes; protects against abrasion, penetration, dehydration, infection

Which strata are living vs dead?

Living: basale and spinosum. Granulosum: keratinization begins and cells start dying. Dead: lucidum and corneum

Thick skin

Palms and soles; 5 strata (has stratum lucidum); NO hair follicles

Thin skin

Most of the body; 4 strata (no stratum lucidum); HAS hair follicles

4 factors that determine skin pigmentation

Melanin, hemoglobin, carotene, skin thickness

Melanin

Dark pigment made by melanocytes; production activated by UV light

Hemoglobin (skin color)

Oxygen-binding protein in blood; bright red when bound to oxygen, giving skin a pink tone. Low oxygen gives a bluish tone

Carotene

Yellow pigment stored in adipose tissue

Papillary layer of dermis

Superficial dermis; areolar CT just deep to the epidermis; forms dermal papillae that interlock with epidermal ridges; its blood vessels nourish the epidermis

Dermal papillae vs epidermal ridges

Dermal papillae are bumps of dermis pushing up; epidermal ridges are folds of epidermis pushing down. They interlock to lock the two layers together

Reticular layer of dermis

Deeper dermis; dense irregular CT; resists tearing from stretching forces in different directions; surrounds blood vessels, hair follicles, nerves, sweat and sebaceous glands

Why is the reticular layer dense IRREGULAR CT?

Its collagen fibers run in many directions, so it resists stretching from many directions

Hair

Keratinized (dead) cells growing from hair follicles

Hair follicle origin

Made from specialized regions of the epidermis and dermis: epithelial tissue root sheath (from epidermis) + connective tissue root sheath (from dermis)

Hair matrix

Where new hair is produced; surrounds the hair papilla

Hair papilla

Region at the base of the hair where blood vessels enter; surrounded by the matrix

Hair bulb

Swelling at the base of the hair; LIVING cells near blood vessels

Hair root

Part of the hair embedded in the skin; DEAD cells

Hair shaft

Part of the hair projecting above the skin surface; DEAD cells

Layers of a hair, inner to outer

Medulla (core), cortex (middle), cuticle (outer)

Arrector pili muscle

Bundle of smooth muscle attached to the hair follicle; contraction makes hair stand erect (goosebumps)

Sebaceous gland

Secretes sebum into the hair follicle

Functions of sebum

Oily substance that lubricates/softens skin and hair, makes skin waterproof, collects dirt, protects from pathogens

Merocrine sweat gland

Watery sweat released onto the skin surface through pores; found on most of the body; key for cooling

Apocrine sweat gland

Protein-rich sweat released into hair follicles; found in axillary, nipple, anal, and genital areas

Exocrine glands of the skin

Sebaceous glands, merocrine sweat glands, apocrine sweat glands

1st degree burn

Epidermis only; heals in 3-5 days (example: sunburn)

2nd degree burn

Epidermis AND dermis; blisters; skin heals

3rd degree burn

Entire thickness of the skin; area is white, red, or black; scarring

Rule of 9s (purpose)

Estimates % of body surface area burned by dividing the body into regions worth 9% or multiples of 9%

Rule of 9s: adult values

Head/neck 9%; each upper limb 9%; anterior trunk 18%; posterior trunk 18%; each lower limb 18%; perineum 1% (total 100%)

Rule of 9s: infant values

Head/neck 18%; each upper limb 9%; anterior trunk 18%; posterior trunk 18%; each lower limb 14%; perineum 1%. Infant head is bigger and legs are smaller than an adult's

Basal cell carcinoma

Most common and least dangerous skin cancer; keratinocytes of stratum basale; surgically removed

Squamous cell carcinoma

Cancer of keratinocytes in the stratum spinosum; early treatment is important

Melanoma

Cancer of melanocytes; most fatal type; highest rate of metastasis

ABCDE of melanoma

Asymmetry; Border irregular; Color uneven/multiple colors; Diameter larger than 6 mm (pencil eraser); Evolving (changing size, shape, or color)

Decubitus ulcer

Damaged skin caused by sustained pressure restricting blood flow to the skin; AKA pressure ulcer or bedsore

Decubitus ulcer stages

Stage 1: skin unbroken but inflamed. Stage 2: broken to epidermis or dermis. Stage 3: extends to subcutaneous fat. Stage 4: extends to muscle or bone (undermining likely)

Skin aging (wrinkles)

Caused mainly by natural breakdown of collagen and elastin fibers, so firmness and elasticity are lost; worsened by UV exposure, facial expressions, and tobacco

Psoriasis

Autoimmune disease attacking keratinocytes, causing inflammation and rapid skin cell turnover; thick, raised, itchy, scaly patches; treated with immunosuppressant drugs