619 9/29 GLA Integument

Components of Integument

skin (epidermis and dermis)

hypodermis

hair

nairs

sweat glands

sebaceous glands

Epidermal Appendages

outgrowths of the epidermis into other areas

includes hair, nails, sweat glands, sebaceous glands

Integument Importance

largest organ in the body (15-20% of total body weight)

the interface between our bodies and the external environment

4 Integument Functions

protection

homeostasis

sensory

metabolic

Protection Function of Integument

barrier: physical, chemical, and biological barrier against external environment

immunologic: provides info through antigen processing to effector cells

Homeostasis Function of Integument

waterproof to prevent loss of bodily fluids

temperature regulation: provides insulation and mechanisms for heat diffusion (sweating)

Sensory Function of Integument

monitors external environment via receptors

Metabolic Function of Integument

endocrine: secretes hormones, cytokines, and growth factors/converts precursor molecules into active molecules (vitamin d)

excretion: exocrine secretion of sweat, sebaceous glands, and apocrine glands

Integument Layers Diagram

Integument Layers (Superficial to Deep)

epidermis (epithelium)

dermis (layer of loose ct and dense irregular ct)

hypodermis (superficial fascia)

deep fascia

skeletal muscle

Epidermis

epithelium composed of keratinocytes (epithelial cells)

Epidermal Layers Diagram

Epidermal Layers (Superficial to Deep)

stratum corneum

stratum lucidium

stratum granulosum

stratum spinosum

stratum basale

(come let’s get some beer)

Stratus Basale Histology

single layer of cuboidal/columnar cells, appears basophilic (purple)

Stratum Basale

contains stem cells that create new keratinocytes (the main epithelial cells located in the epidermis)

keratinocytes replicate and migrate upwards

Stratum Spinosum Histology

have desmosomes (“prickly” keratinocytes)

keratins are actively being synthesized by free ribosomes

slowly changing to eosinophilic cytoplasm in the upper layers of the stratum spinosum as intermediate fillaments assemble and fill more of the cytoplasm

Stratum Spinosum

upper layer of keratinocytes being to synthesize keratohyalin granules (aid in keratinization)

Stratum Granulosum Histology

1-3 layers of flat keratinocytes, granular appearance caused by cytoplasm filled with dark keratohyaline granules

Stratum Granulosum

keratinization beings, granules begin to promote formation of keratin filaments that are not fully keratinized yet

cells close to the stratum corneum start undergoing apoptosis and a decrease in pH from neutral to between 4.5-6

Keratohyaline Granules

contain filaggrin and trichohyalin, in stratum granulosum

Lamellar Bodies

in keratinocytes and stratum granulosum to form epidermal water barrier, secreted by exocytosis between the stratum granulosum and stratum corneum

2 Components of Water Barrier Whose Formation is Initiated by Lamellar Bodies

cell envelope

lipid envelope

Cell Envelope

component of water barrier whose formation is initiated by lamellar bodies

insoluble protein deposited on the inside of the plasma membrane of the bottom row of stratum corneum cells, creates the strong components of the mechanical barrier

Lipid Envelope

component of water barrier whose formation is initiated by lamellar bodies

layer of lipids attached to the cell surface producing “teflon-like” coating

Burn Victims Loss of Epidermal Water Barrier

puts them at risk for dehydration

Stratum Lucidium Histology

translucent layer of dead, flattened keratinocytes

Stratum Lucidium

only present in thick skin, fully keratinized because nuclei and organelles are lost and replaced by densely packed keratin filaments

Stratum Corneum Histology

16-20 layers of dead keratinized cells

Stratum Corneum

provides protection against abrasion, superficial layers continuously shed at the same rate new cells are being produced in deeper layers

Formation of Integument

occurs from deep to superficial layers

Thick vs Thin Skin

determined by the thickness of the epidermis

Thick Skin

on palms of hands and soles of feet, no hair follicles

5 well-defined layers

Thin Skin

everwhere else on the body, has hair follicles, lacks stratum lucidium

4 well-defined layers

4 Epidermal Cells

keratinocytes

langerhans cells

melanocytes

merkel cells

Keratinocytes

epidermal cell, epithelial cells, most abundant cells found in the epidermis

produce keratins and form epidermal water barrier

Langerhans Cells

epidermal cell, dendritic cells that migrate into the epidermis and become resident cells, originate from bone marrow and travel to epidermis via bloodstream

Langerhans Cells Function

phagocytize foreign structures in the epidermis and present the antigents to T lymphocytes in regional lymph nodes (adaptive immunity)

Langerhans Cells Appearance

hard to see with H&E because cells are clear, dendritic processes that extend into stratum corneum and “sense” the microenvironment

Melanocytes

epidermal cell, neural crest cells that produce pigment, in stratum basale

produce and then distribute melanin granules (via melanosomes) to neighboring keratinocytes

Merkel Cells

epidermal cell, mechanoreceptor cells (touch cells), in the stratum basale in regions with high tactile sensitivity

slowly adapting mechanoreceptors that function in cutaneous sensation

Merkel Cells Location

next to nerve endings

Keratinocyte Formation

stem cells are found in the deepest layer residing on the basement membrane

they differentiate as they migrate from the stratum basale to the corneal surface

the cells change both biochemically and morphologically as they ascend thorugh the layers of the epidermis

Melanocytes Appearance

dark, dense nucleus with clear cytoplasm

Melanin

a dark pigment that protects the skin from non-ionizing uv radiation

keratinocytes absorb melanin, which surrounds the nucleus and protects it

Skin Color Variation

everyone has approximately the same number of melanocytes, what varies is the production of melanin

What affects the melanin production rate?

both intrinsic and extrinsic factors including age, ethnicity, gender, variable hormone levels and well as UV radiation, climate and season changes, and chemical exposures

Tanning

UV light darkens existing melanin and increases the rate of melanin synthesis

Melanin and Skin Tone

most melanin stays in the basal portion of all skin types, however some can be found in upper layers of dark skin

in lighter skin, the melanin that is produced tends to be less concentrated and is more uniformly distributed within the lower layers of the epidermis, as a result these cell have little to no melanin remaining when they reach the stratum corneum

Dermis

layer of ct that mechanically stabilizes and metabolically sustains the overlying epidermis, also assists in themoregulation and sensation

2 Dermal Layers

papillary layer of type iii and iv collagen

reticular layer of type i collagen

Epidermal Ridges ad Dermal Papillae

projections off of the layers of the dermis that interlock with one another to stabilize the layers and prevent separation during abrasion

Why is it important that the papillary layer is loose CT?

all epithelium is avsacular, so there must be a layer of loose ct beneath with lots of space between the cells and blood vessels to allow diffusion of substances to and from the epithelium

Dermis Diagram

Dermal-Epidermal Junction

enhanced adhesion between the dermis and epidermis, involves dermal papillae and epidermal ridges

more prominent and abundant in skin commonly exposed to high friction, causes fingertips

3 Dermal Cells

fibrocytes/fibroblasts

macrophages

immunologic cells

Fibrocytes/Fibroblasts

dermal cell, most common cell in ct, create and repair extracellular matrix

Macrophages

dermal cell, phagocytic cells that digest pathogens, dead cells, and debris

Immunologic Cells

dermal cell, mast cells and b lymphocytes, contribute to skin homeostasis and immunosurveillance

Meissner’s Corpuscles

in dermal papillae, detect light touch (low frequency stimuli)

Meissner’s Corpuscles Appearance

look like swirled cotton candy

Pacinian Corpuscles

in reticular layers of dermis and hypodermis (deeper than meissner’s corpuscles), transmit vibration and pressure

Pacinian Corpuscles Appearance

lamellar organization, “onion-shaped”

Hypodermis (aka Superficial Fascia)

subcutaneous layer, technically not part of the skin

Hypodermis Appearance and Function

loose ct that reduces friction between the dermis and deep structures, various amounts of adipose tissue for thermoregulation

sometimes contains pacinian corpuscles, highly vascularized

Products of Epidermal Appendages

hair follicles → hair

sebaceous glands → sebum

eccrine sweat glands → sweat

apocrine sweat glands → mixed sweat and carbs, lipids, proteins

Eccrine/Merocrine Sweat Glands

duct of gland extends to skin surface, distributed throughout the body

secrete watery substance for thermoregulation

Eccrine/Merocrine Sweat Glands Appearance

sqiggly pasta

Apocrine Sweat Gland

actually merocrine secretion via exocytosis, ducts empty into hair follicles

secrete pheromones (stimulated by sex hormones), secretion is initially odorless but broken down by bacteria (smelly)

Apocrine Sweat Gland Location

mostly in As (axilla, areola of nipple, anal regions) and genitals

Apocrine Sweat Gland Appearance

lumens much larger than eccrine sweat glands

Eccrine vs Apocrine Gland

Components of Pilosebaceous Unit

hair shaft, hair follicle, arrector pili muscle, sebaceous gland

Pilosebaceous Unit Diagram

Pilosebaceous Unit Hair

hair is modified, keratinized epithelium

the hair follicle surrounds the root of the hair

Arrector Pili Muscle

smooth muscle of pilosebaceous unit, when contracted the hair stands up on end and “goose bumps” are visible

Secaceous Gland in Pilosebaceous Unit

produce and excrete sebum

Sebum

an oily/lipid substance released via holocrine secretion that lubricates the hair and surrounding skin

Pilosebaceous Unit Histology

Skin Vasculature

capillaries extend into the papilla to interact with the epidermis

Skin Innervation Review