Integumentary System Anatomy and Physiology

Integumentary System Overview

• The integumentary system is the body's largest organ, accounting for approximately 7% of body weight.
• It's roughly 1.5 to 4.4 millimeters thick.
• It has two main layers: the epidermis and the dermis.
• The subcutaneous tissue (hypodermis) lies below the dermis.
• The integumentary system includes skin, hair, nails, and glands.
• Its functions include protection, temperature regulation, excretion, vitamin D production, and sensory reception.
• The skin's structure and conditions change throughout life.

Learning Objectives

• Students will identify major components of the integumentary system and their functions.
• Students will identify major structures of the skin, glands, and their functions.
• Students will describe the role of dermal circulation in sensing touch, pressure, and pain.
• Students will explain hair and nail structure, functions, and growth processes.
• Students will discuss the specialization of mammary glands as integumentary glands.

Skin and Subcutaneous Tissue

• The skin is the body's largest organ.
• The subcutaneous layer (hypodermis) lies below the dermis.
• The hypodermis comprises areolar and adipose tissues.
• Functions of the hypodermis include insulation, shock absorption, energy storage, and anchoring the skin.

Skin

• The epidermis is the outermost layer of the skin.
• The dermis is the layer beneath the epidermis.
• The subcutaneous tissue (hypodermis) lies below the dermis.

Epidermis

• It's the outermost layer of the skin.
• It's a protective barrier between the body and the external environment.
• The epidermal layers include stratum corneum, stratum lucidum (in thick skin only), stratum granulosum, stratum spinosum, and stratum basale (stratum germinativum).

Epidermal Layers

• Stratum corneum: outermost, horny layer of dead keratinocytes.
• Stratum lucidum: clear layer, in thick skin only, comprised of flat, dead keratinocytes.
• Stratum granulosum: few layers of keratinocytes; keratinocytes above lack nutrient access.
• Stratum spinosum: spiny appearance; contains intermediate filaments for strength and flexibility.
• Stratum basale: deepest layer, actively dividing cells attach to dermis, contains tactile epithelial cells and melanocytes; actively dividing cells.

Main Cell Types of the Epidermis

• Keratinocytes: most abundant epidermal cells, create keratin for strength and water resistance; produce antibiotics and enzymes.
• Melanocytes: produce melanin, protect from UV damage, determine skin, hair, and eye color; found in the stratum basale.
• 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; found in stratum spinosum

Keratinocytes

• Compose the majority of the epidermis.
• Produce keratin, a fibrous protein important for skin strength and water resistance.

Melanocytes

• Found in the stratum basale
• Produce melanin, which protects against UV damage and determines skin, hair, and eye color.

Tactile Epithelial Cells

• Mechanoreceptors for light touch and pressure.
• Located in the epidermis (basal layer)

Dendritic Cells

• Part of the immune system, crucial for monitoring and processing pathogens.
• Found in the stratum spinosum, protecting against infections and skin diseases.

Melanocyte Disorders

• Hyperpigmentation is a result of overactive melanocytes (e.g., sunspots, melasma).
• Hypopigmentation occurs due to underactive melanocytes (e.g., vitiligo).

Dermis

• The dermis is a strong, flexible connective tissue layer beneath the epidermis, rich in blood vessels and nerves.
• It comprises the papillary and reticular dermis.
• Papillary dermis: superficial layer.
• Reticular dermis: deeper layer.

Papillary Dermis

• Includes dermal papillae, increasing surface area for gas, nutrient, and waste exchange.
• Nourishes epidermis via capillaries.
• Contains receptors for light touch and vibration.
• Regulates body temperature.

Reticular Dermis

• Dense irregular connective tissue.
• Provides most of the skin's strength.
• Contains collagen and elastic fibers, responsible for the skin's flexibility.
• Contains vascular plexuses for nutrient delivery and temperature regulation (dermal plexus, subpapillary plexus).
• Contains nerve receptors for pressure and pain.
• Composed of cleavage lines.

Cleavage Lines

• Cleavage lines represent separation between underlying collagen fibers in the reticular dermis.
• Surgical incisions parallel to cleavage lines heal better than those made across them.

Flexure Lines

• Flexure lines are deep creases, crucial for flexibility. They occur in areas with significant dermal attachments to underlying structures like palms, wrists, soles, fingers, and toes.

Hypodermis/Subcutaneous Tissue

• Located beneath the skin.
• Made of areolar and adipose tissues.
• Anchors skin, providing insulation, storing energy, and offering cushioning and protection.
• Distribution varies between sexes.

Skin Color

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

Appendages of the Skin

• Nails
• Hair

Nails

• Scale-like epidermal modifications made of hard keratin.
• Free edge extends past fingertips.
• Nail plate covering the nail bed.
• Root at the base of the nail.
• Surrounded by nail folds (skin).
• Eponychium (cuticle): skin around the nail.

Hair

• Flexible strand of dead, keratinized cells.
• Found everywhere except palms and soles.
• Embedded within follicles.
• Shaft projects above the skin's surface.
• Made of tough, durable hard keratin.

Hair Structure

• Medulla (central core)
• Cortex (surrounds medulla)
• Cuticle (outermost layer)

Additional Hair Structures

• Hair follicles: structures in the skin where hair grows.
• Hair bulb: base of hair, contains the matrix (involved in hair growth)
• Root plexus: sensory nerve network around hair bulb.

Arrector Pili Muscle

• Tiny smooth muscle attached to hair follicles.
• Causes hair to stand erect when contracting (goosebumps).
• Plays a role in thermoregulation and protection.

Hair Types and Growth

• Vellus hair: fine, short, lightly pigmented hair found on most parts of the body; present in children and adults.
• Terminal hair: coarse, thick, pigmented hair; develops during puberty, notable on the scalp, eyebrows, eyelashes, armpits, and groin.
• Lanugo: fine, soft, unpigmented hair covering the fetus in the womb; typically sheds before or shortly after birth.

Hair Thinning and Baldness

• Androgenetic alopecia: (hormone-driven) thinning at the crown and hairline (men) or overall thinning (women).
• Alopecia areata: autoimmune disorder with patchy hair loss.
• 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

• Secrete sebum (an oily substance).
• Found everywhere except palms and soles.
• Primarily associated with hair follicles.

Sebum Function

• Lubrication.
• Barrier function.
• Antimicrobial protection.
• Hair conditioning.

Sudoriferous (Sweat) Glands

• Widely distributed on the body.
• Sweat is a blood filtrate (mostly water with salts and metabolic wastes).
• Two types: eccrine glands, and apocrine glands.

Eccrine Glands

• Most abundant type.
• Located in palms, soles, and forehead
• Produce odourless, watery sweat.
• Open directly onto skin surface, contributing significantly to thermoregulation and skin hydration.

Apocrine Glands

• Located in axillary, anal, and genital regions.
• Open into hair follicles.
• Activated during puberty.
• Produce thicker, milky sweat with a musky odor.

Modified Apocrine Glands

• Ceruminous glands: produce earwax.
• Mammary glands: produce milk, hormonally activated.
• Ciliary glands: lubricate eyelashes.

Integumentary System Conditions

• Burns (first, second, third degree)
  • First-degree: affects the epidermis.
  • Second-degree: damages the epidermis and upper dermis; often results in blisters.
  • Third-degree: destroys all skin layers; can appear white, red, or blackened.
• Skin Cancer:
  • Basal cell carcinoma least malignant and most common.
  • Squamous cell carcinoma is from keratinocytes of stratum spinosum.
  • Melanoma is caused by melanocytes and is the most dangerous type.

Infections

• Acne vulgaris: inflammation of sebaceous glands caused by bacteria and clogged follicles.
• Warts: caused by human papillomavirus (HPV) direct contact or contaminated surfaces.
• Ringworm: is a fungal infection producing a ring-shaped rash through direct skin-to-skin contact.

Aging Skin

• Skin thins and loses elasticity.
• Skin inflammations and rashes become more common.
• The skin becomes more susceptible to infections.

Summary

• The integumentary system acts as a protective barrier against external harm and regulates body temperature.
• It includes skin, hair, nails, and glands.
• The skin is a vital barrier and sensory interface. Aging leads to skin changes and less efficient wound healing.

Test your knowledge of the integumentary system with this quiz. Questions cover skin layers, hair structure, and the functions of different components like the epidermis, dermis, and hypodermis. The quiz also assesses understanding of cell types and tissue composition.