Anatomy and Physiology: Integumentary System

• The integumentary system includes the skin, subcutaneous tissue, nails, hair and glands

Overview

• Major topics include skin, subcutaneous tissue, nails, hair, glands, integumentary system conditions, and skin throughout life

Learning Objectives

• To identify the major components of the integumentary system and their functions
• To identify the major structures of the skin and glands, along with their functions
• To describe the role of dermal circulation
• To describe how the skin perceives touch, pressure, and pain
• To explain the structure, functions, and growth processes of hair and nails
• To explain why mammary glands are specialized integumentary glands

Skin

• The body's largest organ
• It makes up approximately 7% of body weight
• It is approximately 1.5 to 4.4 mm thick
• The two main layers are the epidermis and the dermis

Hypodermis

• Known as the subcutaneous layer, lies deep to thee dermis
• Composed of areolar and adipose tissues
• Functions include: Insulation, shock absorption, energy storage, and anchoring

Functions of the Skin

• Protection
• Body temperature regulation
• Excretion
• Production of vitamin D
• Sensory reception

Epidermis

• The outermost skin layer
• Functions as a protective barrier between the body and the environment
• Primarily made up of keratinized stratified squamous epithelium
• It is avascular
• Regenerates approximately every 28-30 days in adults

Main Cell Types of the Epidermis

• Keratinocytes: Most abundant epidermal cells, produced in the deepest layer
• Keratinocytes creates keratin for strength and water resistance
• Keratinocytes produce antibiotics and enzymes, are dead at the skin's surface
• Melanocytes: Found in the stratum basale, hair follicles, inner ear, and eye
• Melanocytes protect from UV damage, and determines skin, air, and eue color
• Two types of Melanocytes: eumelanin and pheomelanin
• Tactile epithelial cells: mechanoreceptors for for light touch and pressure
• Tactile epithelial cells transmit tactile signals to sensory nerve endings and alert harmful stimuli and are located in basal layer (fingertips/palms)
• Dendritic cells: Known as Langerhans cells found in the stratum spinosum
• Dendritic cells are part of the immune system, and Montior and process pathogens
• Dendritic cells protect against infections and skin diseases

Melanocyte Disorders

• Hyperpigmentation is a common condition characterized by overactive melanocytes, leading to an excess production of melanin, resulting in dark patches or spots on the skin (sunspots or melasma)
• Hypopigmentation occurs when melanocytes are underactive, it results in a decrease or absence of melanin production, leading to patches of abnormally light or white skin (vitiligo)

Layers of the Epidermis

• Mnemonic to remember order: "Come, Let's Get Sun Burned"
• Superficial to deep order
• Stratum corneum
• Stratum lucidum (only in thick skin)
• Stratum granulosum
• Stratum sonosum
• Stratum basale (stratum geminativum)

Stratum Corneum

• The horny layer
• Thick layer of dead keratinocytes, protects against abrasion and penetration

Stratum Lucidum

• Clear layer
• Found only in thick skin (palms, soles)
• Consists of few rows of flat, dead keratinocytes

Stratum Granulosum

• Contains few layers of keratinocytes
• Keratohyaline granules form keratin
• Lamellar granules contain waterproofing glycolipid
• Cells above this layer lack nutrient access

Stratum Spinosum

• Has a "Spiny" appearance
• Contains intermediate filaments for strength and flexibility
• Houses keratinocytes and dendritic cells, providing mechanical stress resistance

Stratum Basale

• Deepest epidermal layer, attached to dermis
• Cells actively divide and it contains tactile epithelial cells and melanocytes

Dermis

• Strong, flexible connective tissue
• Rich with blood vessels and nerves
• Two layers include papillary dermis (superficial layer), and reticular dermis (deeper layer)

Papillary Dermis

• Includes dermal papillae to increase surface area for gas, nutrient adn waste exchange
• Nourishes epidermis via capillaries
• Receptors for light touch and vibration, and regulate body temperature

Epidermal Ridges

• Fingertips are known as Friction ridges
• Dermal elevations that increase grip
• Fingerprints are unique pattern for identification

Reticular Dermis

• Makes up 80% of dermis
• Dense irregular connective tissue
• Rich nerve supply for pressure and pain sensation
• Vascular plexuses for nutrient delivery and temperature regulation
• Contains Dermal plexus and Subpapillary plexus

Cleavage Lines & Flexure Lines

• Cleavage lines: Separation between collagen fibers
• Provides skin strength in surgery, incisions along the length of these lines heal better
• Flexure lines: Deep creases in palms, wrists, soles, fingers, and toes

Hypodermis

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

Skin Colour

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

Nails

• Scalelike epidermal modification made of hard keratin
• Free edge extends past fingertip
• Nail plate covers nail bed
• Root is the based of the nail
• Nail folds are skin around the nail
• The eponychium is the cuticle

Hair

• Found everywhere except palms and soles
• Flexible strand of dead, keratinized cells
• Root os embedded skin, shaft projects above skin's surface
• Is made of tough, durable hard keratin

Hair Structure

• Consists of 3 concentric layers of keratinized cells
• Medulla: central core
• Cortex: surrounds medulla
• Cuticle: outermost layer

Additional Hair Structures

• Hair follicles: structure in skin where hair grows
• Hair bulb: base, contain matrix for hair and pigement production
• Root plexus: sensory nerve network around hair bulb

Arrector Pili Muscle

• Smooth muscle attached to hair follicle
• Hair stands erect when arrector pili contracts (goosebumps)
• Involved in thermoregulation and protection

Types and Growth of Hair

• Vellus hairs
• Terminal hairs
• Lanugo

Vellus Hair

• Fine, short, lightly pigmented that covers body, especailly face, neck and arms
• Provides Light insulation and sensory perception (airflow, touch)
• Present in children and adults

Terminal Hair

• Thick, coarse, pigmented found on scalp, eyebrows, eyeashes, armpits and groin
• Develops during puberty, and provides insulation, protection and secondary sexual characteristics

Lanugo

• Fine, soft unpigmented hair that covers fetus in the womb
• Shed before or shortly after birth, and provides warmth and protection

Hair Thinning and Baldness

• Androgenetic Alopecia: hereditary, hormone-driven thinning at the crown and hotline (men) or overall thinning (women)
• Alopecia Areata: autoimmune disorder, patchy hair loss on 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
• Most are associated with hair follicles

Function of Sebum

• Lubrication
• Barrier
• Antimicrobial
• Hair conditioning

Sudoriferous Glands

• Are widely distributed on the body
• Sweat is a blood filtrate that consist of 99% water with salts and metabolic wastes

Types of Sweat Glands

• Eccrine gland
• Apocrine gland

Eccrine Glands

• Are the most abundant
• Such as: palms, soles and forehead
• They Produce odourless, watery sweat
• Opens onto the skin surface, and aids thermoregulation, skin hydration and microbial defence

Apocrine Glands

• Found in axillary, anal, and genital areas
• Open into hair follicles, activated during puberty
• Produces with thick, milky sweat with musky odour

Modified Apocrine Glands

• Ceruminous glands: produce ear wax, protect the ear
• Mammary glands: produce milk, activated by hormones
• Ciliary glands: lubricates eyelashes, prevents dry eyes

Burns

• First-degree: affects only the upper epidermis
• Second-degree: damages epidermis and upper dermis; blisters form
• Third-degree: destroys skin thickness; area appears white, red, or blackened

Skin Cancer

• Basal cell carcinoma: Least malignant, most common
• Squamous cell carcinoma: Arises from keratinocytes of stratum spinosum
• Melanoma: Melanocyte cancer, most dangerous type

Infections

• Acne vulgaris: inflammation of sebaceous glands, caused by blocked hair follicles, bacteris, and excess oil
• Warts: growths caused by human papillomavirus (HPV), contagious through direct contact or contaminated surfaces
• Ringworm: fungal infection, ring-shaped rash contagious through contact

Aging Skin

• Skin thins and becomes less elastic
• Skin infammations become more common with age.
• Are prone to rashes and infection

Summary

• The integumentary system protects your body from external harm and also regulated temperature
• It includes skin, hair, nails, and glands
• Acts as both a barrier and sensory interface
• Aging leads to skin changes and decreased wound healing