Integumentary System: Skin, Hair, and Protection

Integumentary System Overview

• Chapter 5 of Seeley & Tate is a resource for this topic.
• The integumentary system includes the skin, hair, nails, and glands.
• The skin protects, provides sensation, regulates temperature, produces vitamin D, excretes waste, and provides immunity.
• The skin is the largest organ, making up 6-8% of body weight, and presents 1.5-2 m² of external surface.

Skin Functions: Protection

• The skin protects against external factors such as bacteria, chemicals, friction, and temperature.
• Melanin provides a chemical defense against ultraviolet light.
• The skin acts as a permeability barrier against excessive water loss or uptake, and allows for terrestrial life.
• Selective permeability allows lipophilic drugs like steroid hormones to be administered via skin patches.

Skin and Body Temperature Regulation: Feeling Too Cold

• Contraction of hair erector muscles traps a layer of warm air for extra insulation.
• The rate of sweating decreases to prevent energy loss.
• Vasoconstriction reduces blood flow near the skin surface to minimize heat loss.
• Nerve impulses from the hypothalamus cause shivering in skeletal muscles to generate heat.
• The liver increases the metabolic rate to produce extra heat.

Skin and Body Temperature Regulation: Feeling Too Hot

• The hypothalamus sends messages to sweat glands, increasing the rate of sweat production.
• Heat energy converts sweat into water vapor, which lowers the body temperature.
• Vasodilation of arterioles near the skin surface allows more blood to reach the surface for heat loss by radiation.
• Relaxation of hair erector muscles prevents heat from being trapped near the skin.

Skin's Sensory Role

• Sensory receptors in the skin constantly monitor the environment.
• Mechanoreceptors throughout the skin enable interactions with physical objects.
• Sensory functions include sensing pain, itch, tickle, temperature, touch, and pressure
• Also incorporates two-point discrimination.

Metabolic Functions of Skin

• Skin cells synthesize vitamin D3 through local action of UV light, needed for calcium metabolism and bone formation.
• Excess electrolytes can be removed through sweat.
• The subcutaneous stores a significant amount of energy in the form of fat.

Skin and Sexual signalling

• This incorporates pigmentation and hair as visual indicators of health for attraction between sexes across vertebrate species.
• Sex pheromones produced by apocrine sweat glands and other skin glands are also factors.

Skin Layers

• Epidermis: The most superficial layer of the skin, consisting of epithelial tissue and rests on the dermis; resists abrasion, reduces water loss.
• Dermis: A deep layer of connective tissue; responsible for structural strength and leather is comprised of this tissue in animal hides.
• Hypodermis: Beneath the skin, it is not a part of either the cutaneous membrane or the integumentary system; loose connective tissue that connects the skin to underlying structures

Epidermis Details

• A stratified squamous epithelium that is avascular and instead, is nourished by diffusion from capillaries in the papillary layer of the dermis.
• Composed of cells arranged into layers or strata and it is separated from dermis by a basement membrane.

Cell Types Within the Epidermis

• Keratinocytes are the most abundant epidermal cells, producing keratin for strength.
• Melanocytes produce melanin, which is transferred to keratinocytes and contributes to skin color, and all people have the same amount.
• Langerhans' cells are part of the immune system.
• Merkel's cells detect light, touch, and superficial pressure.

Eumelanin Specifics

• A brownish black pigment produced by specialized cells in the epidermis, called melanocytes, among cells of the basal layer and in the hair follicles.
• Production of pigmentation determined by genetics, hormones, and exposure to light
• Ultrastructurally, a melanocyte is a pale-staining cell with numerous small mitochondria, short cisternae of rough endoplasmic reticulum (RER), and a well-developed Golgi apparatus

Skin Colour Determinants

• Pigments like melanin are produced by melanocytes.
• It provides protection against UV light, can be black-brown, or yellowish or reddish.
• Blood circulating through the skin imparts a reddish hue that increases during blushing, anger, and inflammation.
• Thickness of stratum corneum: Thicker areas can appear yellowish.

Other Skin Tone Conditions

• Cyanosis: A bluing caused by decreased blood oxygen content.
• Addison's Disease and Pregnancy can also affect skin tone

Dendritic (Langerhans') Cells Detail

• Antigen-presenting dendritic cells which are seen usually in the spinous layer, and constitute 2-8% of the epidermal cells
• Their cytoplasmic processes reach between keratinocytes of all epidermal layers, thus forming a dense network
• These cells can bind, process, and present antigens to T lymphocytes, working in immunity alongside dermal lymphocytes and immune cells
• Microorganisms do not penetrate the epidermis without alerting these dendritic cells.

Tactile (Merkel) Cells

• Epithelial tactile cells are mechanoreceptors that contain keratin filaments but few melanosomes.
• They contain dense-core neurosecretory granules containing peptides, and Merkel cell carcinoma, very aggressive and difficult to treat.
• Clinical importance: Merkel cell carcinoma is 40 times less common than malignant melanoma, but has twice the mortality rate.

Epidermal Cell Dynamics

• Desquamate: Cells of the deeper layers undergo mitosis and move outwards, older cells slough off the surface.
• Keratinization: As cells move outward, they fill with keratin, die, and serve as a layer that resists abrasion.

The Five Epidermal Strata

• Stratum basale(germinativum): The deepest, mitotically active single layer where cells become keratinized, taking 45-56 days for the cells to reach the surface and desquamate.
• Stratum spinosum: Located superficially to basale; 8-10 layers of cells with desmosomes, limited cell division, lamellar bodies and additional keratin fibers
• Stratum granulosum: Contains keratohyalin protein, superficial layers degenerate where the nucleus and organelles die.
• Stratum lucidum: A thin, clear zone found only in palms and soles.
• Stratum corneum: The most superficial, consisting of 25 or more layers of dead squamous cells joined by desmosomes.

Desmosomes

• A cell structure specialized for cell-to-cell adhesion: spot-like adhesions randomly arranged on the lateral sides of plasma membranes.
• Help to resist shearing forces, found in simple and stratified squamous epithelium and assist in muscle tissue.
• The intercellular space is very wide (about 30 nm).

Thick and Thin Skin Characteristics

• Thick Skin: Has all 5 epithelial strata, including the S. Lucidum found on the palms of hands fingertips, and soles of feet where they undergo pressure or friction
• Thin Skin: More flexible, covers the body except for the areas of thick skin, has hair, and the S. lucidum is generally absent
• Callus: An increase in number of layers in stratum corneum. When this occurs over a bony prominence, a corn forms.

Additional Skin Factors to note

• Entire skin thickness depends on where, .5mm is typically the skin thickness of an eyelid.
• On the back and shoulders, the integument's skin thickness hovers closer to 5.0mm

Dermis Details

• Connective tissue with many fibers, fibroblasts, macrophages, adipocytes, and blood vessels; also contains nerves, hair follicles, smooth muscles, glands, and lymphatic vessels.
• Performs sensory functions, including pain, itch, tickle, temperature, touch, vibration, pressure, and two-point discrimination.
• Variable in thickness, composed of two layers which are Papillary and Reticular

The Two Dermis Layers

• Papillary: The outer 1/5, it is areolar with lots of elastic fibers, dermal papillae, capillary beds, forms fingerprints and creates whorls of ridges
• Also contains touch receptors (Meissner's) and free nerve endings sensing pain.
• Reticular: The inner 4/5, being a dense irregular connective tissue that utilizes collagen and elastic fibers, contains some adipose, hair follicles, nerves, oil glands, ducts of sweat glands Heat sensors are also a factor for hot regions of derma.

Cleavage (Tension) Lines and Striae specifics

• Cleavage lines: Are lines where elastin and collagen fibers are oriented; important in surgery because incisions parallel to these lines result faster healing
• Skin can be overstretched and that would result in striae (stretch marks)

Hypodermis specific

• Contains loose connective tissue, it's depth is deep to skin and is composed of collagen and elastic fibers.
• Hosts types of cells such as fibroblasts, adipocytes, and macrophages.
• Half of the fat of a body resides in the epidermis which is considered the body's energy reserve.
• It also holds a subcutaneous tissue.
• Can provide some support and structure to the skin.

Hair Shaft

• Protrudes above skin surface
• Consists of internal parts labeled as Medulla: Central axis, Cortex: Forms bulk of hair and Cuticle: Forms hair surface.

Hair Follicle

• A hair follicle is found everywhere on a human's body, with the exception of soles, lips, nipples, genitalia, and distal segments of fingers and toes
• Internal matrix is source of hair
• Dermis projects into the bulb which provides what is the blood supply.
• It Cycles the hair through growth and resting stages, growing the length at 0.3 mm / day.

Hair Color and Baldness Factors

• Caused by varying amounts and types of melanin, being melanin can be black-brown and red.
• Muscles: Arrector pili, type of smooth muscle.
• Skin pushed up by movement of hair follicle to conserve body heath by trapping air.
• Permanent hairloss is medically know as: pattern baldness

Gland Facts

• Sebaceous Glands: Holocrine, oily secretion which prevents drying & may inhibit bacteria which empties into hair follicle.
• Sweat (Sudoriferous) Glands: traditionally called apocrine and holocrine.

Sweat Glands : Merocrine/Eccrine Vs Apocrine

• Merocrine/eccrine sweat glands: Simple coiled tubular glands opening onto the skins surface while they produce isotonic fluid that contains ammonia, urea, uric acid and lactic acid; also involved in hyposmotic control
• Apocrine Sweat Glands, located in auxillae, and regions of genitalia, activate usually nearing the time puberty comes about.

Ceruminous and Mammary Glands

• Ceruminous glands are modified merocrine sweat glands, in the external auditory meatus.
• They produce earwax (cerumen) which, in combination with hairs, prevents entry of dirt and insects and keeps the eardrum supple.
• Mammary glands are modified apocrine sweat glands covered with reproductive chapter of female body

Nail structures

• Nail body is stratum corneum
• Eponychium or cuticle is corneum superficial to nail body, while hyponychium is that of corneum beneath the free edge.
• Grow continuously unlike hair, fingernails are faster at 0.5-1.2 mm/ day; faster than toenails

Summary of Integumentary System Functions: Protection

• Abrasion: Sloughing off of bacteria as desquamation occurs.
• Pathogen Block: Against microorganisms and other foreign substances; bacteriostatic glandular secretions in skin also utilize cells of the immune system.
• Block UV Radition and provide nails for self defense.
• Acts as barrier to diffusion of water to help keep the body hydrated

Integumentary Facts - Regulations and Vit D & Wastes

• Sensation of Pressure, temperature, pain,heat, cold, touch, and movement are handled within this system for haptic experience.
• Temperature regulation: sweating and radiation from this system keeps a body feeling heat and cold based on environmental status & more.
• A significant waste removal mechanism with significant excretion: Water, salt, urea, ammonia, uric acid

Integumentary Issues - Aging Factors and Frostbite

• Skin becomes dry and ages rapidly from sunlight
• Skin infections more likely due to thinning skins
• Decrease is blood supply limits the tempurature body regulation mechanism
• Frostbite, like burins, has three degrees with hyperemia and skin swelling being a indicator there are issues.

Explore the integumentary system, including skin, hair, nails, and glands. Learn about skin functions, protection against external factors like bacteria and UV light, and temperature regulation. Discover how skin maintains water balance and enables drug delivery.