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Questions and Answers
The skin is the largest organ of the body by surface area and ______.
The skin is the largest organ of the body by surface area and ______.
weight
The outer, thinner layer of the skin is called the ______.
The outer, thinner layer of the skin is called the ______.
epidermis
The inner, thicker layer of the skin is known as the ______.
The inner, thicker layer of the skin is known as the ______.
dermis
The epidermis consists of keratinized stratified squamous ______.
The epidermis consists of keratinized stratified squamous ______.
The skin's subcutaneous layer is also called the ______.
The skin's subcutaneous layer is also called the ______.
The average thickness of the skin is between ______ and 2 mm.
The average thickness of the skin is between ______ and 2 mm.
Keratinocytes make up about ______% of the cells in the epidermis.
Keratinocytes make up about ______% of the cells in the epidermis.
Lamellar granules produce a water repellent ______ for the skin.
Lamellar granules produce a water repellent ______ for the skin.
The subcutaneous layer is also called the ______.
The subcutaneous layer is also called the ______.
The subcutaneous layer helps attach the skin to underlying ______.
The subcutaneous layer helps attach the skin to underlying ______.
The accessory structures of the skin include hair, skin glands, and ______.
The accessory structures of the skin include hair, skin glands, and ______.
Hair is primarily composed of dead, ______ epidermal cells.
Hair is primarily composed of dead, ______ epidermal cells.
Sebaceous glands secrete an oily substance called ______.
Sebaceous glands secrete an oily substance called ______.
Eccrine sweat glands help to cool the body by ______ cooling.
Eccrine sweat glands help to cool the body by ______ cooling.
There are different types of hairs, including lanugo, vellus hairs, and ______ hairs.
There are different types of hairs, including lanugo, vellus hairs, and ______ hairs.
Hair color is determined by the amount and type of ______.
Hair color is determined by the amount and type of ______.
The cells that produce the pigment ______ protect against damage by ultraviolet radiation.
The cells that produce the pigment ______ protect against damage by ultraviolet radiation.
The deepest layer of the epidermis is called the ______ or stratum germinativum.
The deepest layer of the epidermis is called the ______ or stratum germinativum.
Stratum lucidum is present only in ______ skin, such as the skin of the fingertips and palms.
Stratum lucidum is present only in ______ skin, such as the skin of the fingertips and palms.
The outer papillary region of the dermis consists of areolar connective tissue containing thin ______ and elastic fibers.
The outer papillary region of the dermis consists of areolar connective tissue containing thin ______ and elastic fibers.
Keratinization occurs as cells move from the deepest layer to the surface, resulting in the accumulation of protective ______.
Keratinization occurs as cells move from the deepest layer to the surface, resulting in the accumulation of protective ______.
The epidermis typically contains four major layers in ______ skin and five major layers in thick skin.
The epidermis typically contains four major layers in ______ skin and five major layers in thick skin.
The stratum spinosum consists of 8-10 layers of ______.
The stratum spinosum consists of 8-10 layers of ______.
Dandruff is an excess of keratinized cells shed from the ______.
Dandruff is an excess of keratinized cells shed from the ______.
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Study Notes
Structure of the Skin
- Skin is the largest organ by surface area and weight, covering about 2 square meters (22 square feet) and weighing 4.5-5 kg (10-11 lbs), approximately 16% of body weight.
- Average skin thickness ranges from 0.5 to 4 mm, thinnest on eyelids and thickest on heels.
- Comprised of two main layers: epidermis (outer, thinner layer of epithelial tissue) and dermis (inner, thicker connective tissue layer).
- Beneath the dermis lies the subcutaneous (hypodermis) layer, connecting skin to underlying tissues.
Cells of the Epidermis
- Consists of four major types of cells:
- Keratinocytes: Comprise about 90% of cells; produce keratin for protection and lamellar granules for water resistance.
- Melanocytes: Produce melanin, providing protection from UV damage.
- Langerhans cells: Immune cells originating from red bone marrow.
- Merkel cells: Sensory cells involved in touch sensation.
Layers of the Epidermis
- Thin skin has four major layers, while thick skin has five.
- Stratum Basale (Stratum Germinativum): Deepest layer where continuous cell division occurs.
- Stratum Spinosum: Composed of 8-10 layers of keratinocytes.
- Stratum Granulosum: Contains keratohyalin and lamellar granules.
- Stratum Lucidum: Present only in thick skin (e.g., fingertips, palms, soles).
- Stratum Corneum: Comprises multiple layers of dead keratinocytes that are continuously shed and replaced; friction can lead to callus formation.
Dermis Structure
- Composed of connective tissue with collagen and elastic fibers, providing strength and elasticity.
- Divided into two layers:
- Papillary Region: Areolar connective tissue with dermal papillae, capillary loops, corpuscles of touch, and free nerve endings.
- Reticular Region: Denser layer with more collagen fibers for strength.
Functions of the Skin
- Regulates body temperature.
- Acts as a barrier against external elements.
- Detects sensations like touch, pain, and temperature.
- Stores blood and synthesizes vitamin D.
- Facilitates excretion and absorption.
Accessory Structures of the Skin
- Includes hair, nails, and skin glands.
- Hairs serve multiple roles: protection, reducing heat loss, and sensing light touch.
Hair Characteristics
- Composed of dead, keratinized epidermal cells; includes a shaft (above skin) and root (below skin).
- Hair follicles contain epithelial and dermal root sheaths.
- Types of hair: lanugo (fine hair), vellus (short, fine hair), and terminal (thick, pigmented hair).
- Hair color is determined by the type and amount of melanin.
- Sebaceous glands associated with hair follicles secrete sebum to prevent dehydration and inhibit bacteria.
Skin Glands
- Sebaceous Glands: Secrete sebum, keeping skin and hair moisturized.
- Sudoriferous (Sweat) Glands: Two types exist:
- Eccrine Sweat Glands: Major component of thermoregulation through evaporation and waste elimination.
- Apocrine Sweat Glands: Located in axillae, groin, and areolae; produce a thicker secretion, often associated with emotional stress.
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