Skin Physiology Quiz

Integumentary System Overview

• The integumentary system is the body's largest organ system
• It is approximately 7% of the body's total weight
• The skin is roughly 1.5 to 4.4 mm thick
• It has two main layers: epidermis and dermis
• Subcutaneous tissue lies beneath the dermis
• The integumentary system includes skin, glands, hair, and nails,

Learning Objectives

• Identify the components and functions of the integumentary system
• Identify major skin structures and their functions
• Describe dermal circulation
• Explain how skin senses touch, pressure, and pain
• Describe the structure, growth process, and functions of hair and nails
• Explain why mammary glands are specialized integumentary glands.

Skin & Subcutaneous Tissue

• Skin is the body's largest organ

Skin

• The skin is approximately 7% of body weight
• It is typically 1.5 to 4.4 mm thick
• Has two layers: the epidermis and dermis
• The subcutaneous tissue lies beneath the dermis

Hypodermis

• The subcutaneous layer lies deep to the dermis.
• It is composed of areolar and adipose tissue.
• Functions of the hypodermis include insulation, shock absorption, energy storage, and anchoring.

Epidermis Layers

• Stratum corneum: outermost layer of dead keratinocytes
• Stratum lucidum: found in thick skin (palms/soles), comprised of flat, dead keratinocytes
• Stratum granulosum: few layers of keratinocytes; keratinohyaline granules form keratin; lamellar granules have waterproofing glycolipid; cells lack nutrient access.
• Stratum spinosum: spiny appearance; intermediate filaments for strength and flexibility; contains keratinocytes and dendritic cells (part of the immune system); provides mechanical stress resistance.
• Stratum basale (stratum germinativum): deepest layer; actively dividing cells; contains tactile epithelial cells (Merkel cells) and melanocytes.
• Mnemonic: "Come, Let's Get Sun Burned"

Main Cell Types of the Epidermis

• Keratinocytes: most abundant; produce keratin for strength and water resistance; produce antibiotics and enzymes; dead at the skin's surface
• Melanocytes: found in the stratum basale; protect from UV damage; determine skin, hair, and eye color
  • Eumelanin: dark pigment
  • Pheomelanin: lighter pigment
• Tactile epithelial cells (Merkel cells): mechanoreceptors for light touch and pressure; located in the basal layer
• Dendritic cells (Langerhans cells): part of the immune system; monitor and process pathogens; protect against infections and skin diseases

Functions of the Skin

• Protection: from abrasion and penetration
• Body temperature regulation: through sweat; vasodilation or vasoconstriction
• Excretion: of waste products in perspiration
• Production of vitamin D: using UV radiation
• Sensory reception: through nerve endings

Dermis

• A strong, flexible connective tissue,
• Rich with blood vessels and nerves; has two layers
• Papillary dermis: superficial layer; includes dermal papillae; increases surface area for gas, nutrient, and waste exchange; nourishes epidermis via capillaries; contains receptors for light touch and vibration; regulates body temperature;
• Reticular dermis: deeper layer; 80% of dermis tissue; dense irregular connective tissue; rich nerve supply for pressure and pain; vascular plexuses for nutrient delivery and temperature regulation; contains the dermal plexus, subpapillary plexus.

Cleavage Lines and Flexure Lines

• Cleavage lines: separations between collagen fibers that provide skin strength. Surgical incisions parallel to these lines heal better.
• Flexure lines: deep creases in areas where the dermis tightly attaches to underlying structures (e.g., palms, fingers, soles.)

Hypodermis

• Located beneath the skin
• Contains areolar and adipose tissues
• Anchors skin, insulates, stores energy, and provides cushioning and protection
• Distribution varies by sex

Skin Color

• Melanin: main pigment, made from tyrosine
• Carotene: yellow-orange pigment from foods
• Hemoglobin: oxygenated blood gives a rosy undertone in light-skinned individuals.

Appendages of the Skin

• Nails: scale-like epidermal modifications made of hard keratin; free edge extends past the fingertip; nail plate covers the nail bed; root is at the base of the nail; nail folds skin around the nail; eponymia (cuticle)

• Hair: flexible strand of dead keratinized cells; found everywhere except palms and soles; root is embedded in the skin; shaft projects above skin; made of tough keratin; 3 concentric layers - medulla, cortex, and cuticle

Hair Structure

• Three layers of keratinized cells: medulla (central core), cortex (surrounds medulla), and cuticle (outermost layer)

Additional Hair Structures

• Hair follicles: structure in skin where hair grows
• Hair bulb: base containing the hair matrix for hair and pigment production.
• Root plexus: Sensory nerve network around the hair bulb.

Arrector Pili Muscle

• Smooth muscle attached to hair follicles
• Causes hair to stand erect (goosebumps)
• Thermoregulation and Protection.

Types and Growth of Hair

• Vellus hairs: fine, short, lightly pigmented; cover body; light insulation; sensory perception; present in children and adults
• Terminal hairs: thick, coarse, pigmented; develop during puberty; found on scalp, eyebrows, eyelashes, armpits and groin; provides insulation, protection, and secondary sexual characteristics.
• Lanugo: fine, soft, unpigmented hair; covers the fetus in the womb; shed before or shortly after birth; provides warmth and protection.

Hair Thinning and Baldness

• Androgenetic Alopecia: hereditary, hormone-driven thinning at the crown and hairline (men) or overall thinning (women)
• Alopecia Areata: autoimmune disorder, patchy hair loss on the scalp and body
• Telogen Effluvium: temporary thinning due to stress, illness, or hormonal changes.
• Age-Related Thinning: gradual thinning with age, influenced by hormones and genetics.

Sebaceous Glands

• Found everywhere except palms and soles
• Secrete sebum via holocrine secretion
• Associated with hair follicles
• Functions of sebum include lubrication, barrier, antimicrobial properties, and hair conditioning.

Sudoriferous Glands (Sweat Glands)

• Widely distributed on the body
• Secrete sweat, mostly water; salts and metabolic wastes
• Two types of sweat glands:
  • Eccrine glands: most abundant; found on palms, soles, and forehead; produce odourless watery sweat; small coiled glands open onto skin surface; thermoregulation, skin hydration, microbial defence
  • Apocrine glands: found in axillary, anal, and genital areas; open into hair follicles; activated during puberty; secrete thick milky sweat with musky odour.

Modified Apocrine Glands

• Ceruminous glands: produce earwax, protect the ear
• Mammary glands: produce milk; activated by hormones
• Ciliary glands: lubricate eyelashes and prevent dry eyes.

Integumentary System Conditions

• Burns (first, second, third degree)
• Skin cancer (Basal cell carcinoma, Squamous cell carcinoma, Melanoma)
• Infections (acne vulgaris, warts, ringworm)

Aging Skin

• Skin thins and becomes less elastic
• Skin inflammations become more common
• Prone to rashes and infections

Summary

• The integumentary system protects the body from external harm and regulates temperature.
• It includes the skin, hair, nails, and glands.
• It serves as a barrier and sensory interface.
• Aging leads to changes in skin and decreased wound healing.

Test your knowledge on the functions and structures of the skin with this quiz. Covering topics from the epidermis to different types of glands, you'll explore key concepts related to human anatomy and physiology. Perfect for students studying skin biology or those interested in dermatology.