Integumentary System: Skin Structure & Function

Integumentary System

• This system forms the body's outer covering.
• It protects the body from external threats.

Integumentary System Structures

• Major organ: Skin
• Accessory organs include hair, nails, and glands.

Integumentary System Functions

• Protection and covering
• Sensation
• Thermoregulation
• Vitamin D synthesis
• Excretion & Osmoregulation

The Skin

• The largest organ in the body
• It forms 10-15% of the body weight
• Has three main layers: epidermis, dermis, and hypodermis
• Relevant fields of study are dermatology and cosmetology,

Skin: Epidermis

• This is the outermost layer of the skin.
• Has five main layers
• Blood vessels are absent.
• Functions include external surface protection and waterproofing
• It forms hair and nails
• Responsible for skin color.

Epidermis - Layers

• Stratum Corneum: The uppermost layer, with 15-30 layers of dead, keratinized, cornified squamous cells that continuously shed off.
• Stratum Lucidum: Only found in thick skin, such as palms and soles, providing extra thickness in areas prone to shock and pressure. It contains eleiden, a clear protein rich in lipids.
• Stratum Granulosum: Characterized by a grainy appearance. Here, active keratinocytes produce keratin. It consists of 3-5 layers. These cells generate large amounts of keratin and keratohyalin
• Stratum Spinosum: Known as the prickle cell layer. Contains irregular, polyhedral cells with cytoplasmic processes called "spines". Made of 8-10 layers of keratinocytes. Langerhans cells are present, which are dendritic cells that function as macrophages.
• Stratum Basale: The lowermost, single layer of columnar cells, serving as the mitosis layer that forms hair and nails. Contains melanocytes, which produce melanin. Also contains Merkel cells

Melanin

• Eumelanin and Pheomelanin dictate how dark, or light the skin pigment will be

Vitamin D

• Calcitriol is the active chemical form of Vitamin D, which is used by the body for absorption of calcium and phosphorus. This is needed for bone nourishment & repair.

Basement Membrane

• Occurs between the epidermis and dermis.
• It is a dense layer of extracellular matrix.
• It acts as skin glue, allowing cells to attach to underlying connective tissue and offers structural support.

Skin: Dermis

• The second layer of skin.
• Structures found in the dermis include areolar connective tissue, blood vessels, sensory receptors, and follicles & glands.

Areolar Connective Tissue

• Has elastin fibers that provide elasticity to the skin.
• Found in the papillary layer, a thin layer that provides nutrients to the skin's surface.

Blood vessels

• Veins, arteries and capillaries
• Provide nourishment to the skin cells
• Allow thermoregulatory functions, High body temperature causes dilation, low body temperature causes constriction

Sensory receptors

• Includes mechanoreceptors for pressure, touch, stretch & motion.
• Thermoreceptors for heat and cold
• Pain receptors or nociceptors for noxious/harmful conditions

Skin: Dermis Functions

• Functions include: contributes to elasticity
• Nourishes the epidermis
• Receives sensory stimulation
• Creates unchanging fingerprints and footprints for unique identity and grasping without slippage.

Skin: Hypodermis

• This is the lowermost layer, made of fat and adipose tissue.
• Located between the dermis and muscles.
• Thinnest in the eyelids, thickest in the buttocks (females), and tummy (males).
• It serves as a high-energy reserve, provides insulation and cushioning, and contributes to body contour.

Hair

• Produced by basale cells of the skin and made of keratin and cuticle.
• Found all over the body except on palms and soles.
• There are approximately 100,000 hairs throughout the body.
• Main parts are the hair root and shaft.

Hair Functions

• Thermoregulation
• Protection
• Sensation
• Non-verbal communication

Hair - Evolutionary Importance

• Human body hair facilitates darker skin.
• Glabrousness allows animals to use a small amount of hair for mechanosensation.

Nails

• Thin, hard coverings at the tips of fingers and toes that are made of cuticle and keratin.
• The main parts of a nail are the nail body/plate and the nail root.
• Nails give protection, enable grasping, and are modified to form defensive structures like claws.

Glands

• Structures embedded in the dermis that secrete various substances to aid skin functions Include sebaceous (oil) and sweat glands.

Sebaceous Glands

• Sac-like exocrine gland that opens to hair and out to the surface of the skin
• Secretes oil & sebum, which lubricates skin & hair and prevents dryness.
• Modified sebaceous glands in the eyelids are called Meibomian glands, which secrete oil and lubricate eyelashes.

Sweat Glands

• Coiled tubule-like exocrine gland opening to the surface of the skin
• Secrete sweat, mix of water, ions, nitrogenous waste and sometimes proteins.
• There are two types: eccrine and apocrine sweat glands.

Eccrine Sweat Glands

• Almost found everywhere
• Secretion composed of water, some NaCl, very small amounts of urea, uric acid, & potassium
• Functions in thermoregulation & minor excretion

Apocrine Sweat Glands

• Found only in some areas, armpit & anogenital area
• Active during puberty, emotional stress, & sexual stimulation
• Secretion is composed of water, proteins & amino acids,
• Contribute to body odor

Modified Sweat Glands

• Ceruminous glands secrete earwax to trap foreign molecules that enter the ear canal.
• Ciliary glands: are glands of Moll, are at the eyelid's margin. They produce tear-like substances for lubrication and protection of the eyes.
• Mammary glands: in mammals will secrete milk for early childhood

Effects of Aging on the Skin

• Aging depends on lifestyle, diet, genes, and personal habits.
• Exposure to the sun, pollution, stress, and obesity hastens aging.
• The skin becomes rougher and drier because of loss of the cuticle and decreased sebum production.
• Loss of elastin fibers in the connective tissues of the dermis leads to a loss of elasticity.
• More transparent due to thinning of the epidermis and dermis
• More fragile due to tissue death, and therefore is more prone to tearing
• More easily bruised occurs due to thinning on the walls of skin blood vessels
• Can develop discoloration due to decline in activity melanocytes.
• Losses fat- from the hypodermal region, specifically in the cheeks, temples, chin, nose, and eye
• More prone to developing benign tumors & lesions.
• Hair turns grey and thins due to hair follicles becoming less active (Telogen).

Common Integumentary System Problems

• Whiteheads
• Blackheads
• Papules
• Pustules
• Dandruff
• Athlete's Foot
• Psoriasis
• Eczema
• Warts
• Moles vs Melanoma

Skin Care

• Regularly cleanse your skin using suitable products.
• Always wash your skin with soaps that do not contain harsh substances.
• Always use sunscreens and avoid sun exposure during 10 AM-2 PM.
• Control hypertension & diabetes.
• Avoid smoking.
• Regularly exercise, including face exercise & body massage.
• Always have adequate sleep.
• Take supplements, minerals, and vitamins for healthier skin.