Exam 2 Review Ch 5, 6, 9, 10 - A&P 1

What are epidermis cells?

keratinized stratified squamous epithelium

Keratinocytes

• Most abundant cell type

• produce fibrous keratin protein for protection and water-

  resistance

Melanocytes

• Located in the deepest layer

• synthesize melanin pigment to shield keratinocyte nuclei

  from UV damage

Langerhans (dendritic)

• Macrophages that activate the immune system against pathogens

  entering the skin

Merkel (Tactile)

• Sensory receptors located at the epidermal-dermal junction

• Sense light touch

Epidermal Layers ( From Deep to Superficial ) ( include Thick Skin and Thin)

Stratum Basale, Stratum Spinosum, Stratum Granulosum, Stratum Lucidum (only in thick) , Stratum Corneum

Stratum Basale

• Single row of actively dividing stem cells attached to the dermis

• Contains melanocytes and Merkel cells

Stratum Spinosum

• Several layers of web-like keratinocytes bound by desmosomes

• Contains Langerhans cells

Stratum Granulosum

• Three to five layers of flattening cells undergoing keratinization

• Cytoplasm fills with keratohyalin granules and water-resistant lamellar granules

Stratum Lucidum

• Clear, flat, dead layer of keratinocytes

• Only present in thick skin ( palms of hands and soles of feet )

Stratum Corneum

• 20 to 30 layers of dead, flat, completely keratinized, enucleated cells

• Functions as a durable, waterproof protective barrier.

Skin Pigments and Clinical Conditions

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Melanin

• Yellow-to-black pigment produced by melanocytes

• Protects skin from UV radiation.

Carotene

• Yellow-to-orange pigment acquired from diet (e.g., carrots)

• Accumulates in stratum corneum and hypodermal fat.

Hemoglobin

• Oxygen-carrying pigment in red blood cells

• Gives fair skin a pinkish/rosy hue when blood flows through dermal capillaries.

Freckles

• Localized, concentrated accumulations of melanin resulting from sun exposure

Cyanosis

• Blueness of the skin, mucous membranes, or nail beds

• Indicates poorly oxygenated blood or respiratory distress

Jaundice

• Yellowing of the skin and whites of the eyes

• Indicates liver malfunction causing a buildup of bilirubin in body tissues

Skin Color as a Health Indicator

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Pallor (Paleness)

Caused by

• vasoconstriction

• anemia

• low blood pressure

• or extreme emotional stress

Erythema (Redness)

Caused by

• vasodilation due to inflammation

• fever

• allergies

• embarrassment

• or heat

Jaundice (Yellowing)

• Signifies liver disorders, bile duct blockages, or excessive destruction of red blood cells.

Cyanosis (Blueing)

• Signals hypoxemia, cardiovascular failure, or hypothermia.

Bruising (Hematomas) (Hint: points to . . .)

Points to mechanical trauma, blood clotting disorders, or vitamin deficiencies.

Structure of the Dermis & Cleavage Lines

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What is the dermis?

a flexible, vascular connective tissue layer beneath the epidermis, divided into two layers

Papillary Layer

• Superficial 20% of dermis

• Made of areolar connective tissue

• Features finger-like dermal papillae containing capillary loops, free nerve endings, and Meissner & corpuscles.

Reticular Layer

• Deep 80% of dermis

• Made of dense irregular connective tissue

• Filled with coarse collagen fibers that provide tensile strength and elastic fibers that give elasticity.

Cleavage (Lines of Cleavage)

• Topological patterns formed by the parallel bundles of collagen fibers in the reticular layer

• Clinical relevance: Incisions made parallel to cleavage lines heal faster and scar less than incisions made across them

Functions of the Skin

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Protection

• Chemical barrier - (acid mantle, melanin)

• physical barrier - (keratin, glycolipids)

• and biological barrier - (dendritic cells, macrophages).

Thermoregulation

• Sweat glands produce sweat to cool the body via evaporation

• dermal blood vessels dilate to release heat or constrict to conserve it

Cutaneous Sensation

• Sensory receptors detect touch, pressure, vibration, temperature, and pain

Metabolic Functions

• Synthesizes Vitamin D3 (cholecalciferol) when exposed to UV light, which is crucial for calcium absorption

Blood Reservoir

• Dermal vasculature holds up to 5% of the body & total blood volume, shifting it to muscles or organs when needed

Excretion

• Eliminates small amounts of nitrogenous wastes (ammonia, urea, uric acid), water, and salts through sweat

Structure and Function of Nails and Hair

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Nails

• Structure

  • Hard plates of dead, heavily keratinized epidermal cells.

  • Includes the

    • free edge

    • Nail

    • body (visible portion)

    • Nail root (embedded in skin)

    • and nail matrix (actively growing proximal region)

• Function

  • Protect the dorsal surfaces of fingers and toes

  • Assist in picking up small items

Hair (Pili)

• Structure

  • Strands of dead, hard-keratinized cells

  • Consists of

    • a shaft (projects above skin)

    • Root (embedded within dermis)

    • and bulb ( deep base containing the matrix and hair papilla for nourishment )

  • Surrounded by a hair follicle and anchored to an arrector pili muscle ( smooth muscle pulling hair upright, creating “goosebumps” ).

• Function

  • Senses light touch

  • Protects scalp from UV damage and heat loss

  • Prevents entry of foreign particles (eyebrows, eyelashes, nose hairs)

Exocrine Glands of the Skin

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Eccrine (Merocrine) Sweat Glands

• Abundant on palms, soles, and forehead

• Secretes true sweat (99% water, salts, metabolic wastes) via exocytosis

• Primary function is thermoregulation

Apocrine Sweat Glands

• Confined to axillary (armpit) and anogenital regions

• Secretes sweat plus lipids and proteins into hair follicles

• Odorless until broken down by skin bacteria (causes body odor)

• Activate at puberty

Unsure of extact function

Sebaceous (Oil) Glands

• Found all over the body except palms and soles

• Secretes sebum (an oily mixture of lipids and cell fragments) into hair follicles via holocrine secretion (entire cell ruptures)

• Lubricates hair/skin and exerts bactericidal properties

Ceruminous Glands

• Modified apocrine glands located in the external ear canal

• Secretion mixes with sebum to form cerumen (earwax), trapping foreign particles and insects.

Touch Receptors of the Skin

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Meissner’s (Tactile) Corpuscles

• Encapsulated receptors located in dermal papillae

• detect light touch, flutter, and low-frequency vibrations

Pacinian (Lamellar) Corpuscles

• Large, onion-like encapsulated receptors located deep in the dermis/hypodermis

• Detect deep pressure and high-frequency vibrations

Merkel Discs (Tactile Discs)

• Free nerve endings associated with Merkel cells in the stratum basale

• Detect continuous, steady light touch and pressure

Root Hair Plexus

• Network of sensory nerve endings wrapped around the base of hair follicles

• Detect hair movement

Free Nerve Endings

• Unencapsulated dendrites extending into the epidermis

• Primarily detect pain (nociceptors) and temperature (thermoreceptors).

Skin Cancer Types

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Basal Cell Carcinoma

• Most common and least malignant type

• Arises from cells in the stratum basale that proliferate and invade the dermis

• Appears as shiny, dome-shaped nodules

• Cured by surgical excision in 99% of cases.

Squamous Cell Carcinoma

• Second most common type

• Arises from keratinocytes of the stratum spinosum

• Appears as scaly, reddened papules on the scalp, ears, and lower lip

• Grows rapidly and can metastasize if not removed

Melanoma

• Most dangerous and malignant type. Arises from melanocytes

• Highly metastatic and resistant to chemotherapy.

• Identified using the ABCD(E) rule:

  • Asymmetry, Border irregularity, Color variation, Diameter >6mm, and Evolving shape/size.

Classification of Burns

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What are burns?

tissue damage inflicted by intense heat, electricity, radiation, or chemicals, denaturing cell proteins

First-Degree (Superficial)

• Only the epidermis is damaged

• Symptoms include redness, swelling, and pain (e.g., sunburn)

• Heals in days without scarring

Second-Degree (Partial-Thickness)

• Injures the epidermis and upper dermis

• Key symptom is

  • the presence of blisters, alongside redness and severe pain

• Heals with minimal scarring if infection is prevented.

Third-Degree (Full-Thickness)

• Consumes the entire thickness of skin (epidermis and entire dermis)

• Nerve endings are destroyed, leaving the burned area painless

• Appears gray-white, cherry-red, or blackened

• Requires skin grafting to heal

The Rule of Nines

• Clinical estimation tool that divides body surface area into sections of 9% (or multiples of 9) to quickly calculate fluid loss and replacement needs in burn patients