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Glossary of Anatomy Chapter 5: Integument

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Epidermis
Avascular, keratinized stratified squamous epithelium consisting of four distinct cell types and 4-5 distinct layers.
Cells of the Epidermis (4 types)
Keratinocytes, melanocytes, Langerhans' cells, Merkel cells
Keratinocytes
Most abundant epidermal cells.

Function to produce keratin fibrils.

Tightly connected via desmosomes.

Visually notable as flattened cells in the epidermis.
Keratin
Fibrous protein that gives the epidermis its durability and protective capabilities.

Water-proofer.
Melanocytes
Spidery black cells in the epidermis that produce melanin.
Melanin
Brown-to-black pigment that provides a protective umbrella over the nuclei of the cells in the deeper epidermal layers, shielding their genetic material from the damaging effects of UV radiation.

Melanin granules are visually notable as dark-staining "spots" in the stratum basale (and the deeper cells of the stratum spinosum).
Langerhans' Cells
"Epidermal Dendritic Cells"

Phagocytic cells of the epidermis that play a role in immunity.

Visually notable as large, dark bodies in the stratum spinosum associated with long dendrites.
Merkel Cells
Occasional spiky hemispheres that, in conjunction with sensory nerve endings, form sensitive touch receptors called Merkel discs located at the epidermal-dermal junction.
Layers of the Epidermis (5)
Stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, stratum corneum
Stratum Basale
A single row of cells immediately adjacent to the dermis.

Cells are constantly mitotic.

10-25% melanocytes.

Visually notable for: dark spots in cells, straightness of cell boundaries, mitotic cells, dark melanocytes, and branching merkel cells.
Stratum Spinosum
Epidermal stratum consisting of several cell layers immediately superficial to the stratum basale.

Cells contain thick weblike bundles of intermediate filaments made of pre-keratin protein.

Cells divide fairly rapidly, but less so than in the stratum basale.

Last layer of epidermis to receive sufficient nourishment via diffusion from the dermis.

Visually notable for cells which still have some straightness to their boundaries and dark/dense Langerhans' cells with long projections. Cells become less straight-edged and more oblong toward the superficial surface and desmosomes are visible between cells.
Stratum Granulosum
A very thin epidermal layer named for the abundant granules its cells contain.

Contains lamellated and keratohyaline granules.

Cells are beginning to die at the upper border of this layer.

Notable for its profusion of dark-staining granules and flattened cells.
Lamellated Granules
Granules which contain a waterproofing glycolipid that is secreted into the extracellular space.
Keratohyaline Granules
Granules which combine with the intermediate filaments in the more superficial layers of the epidermis to form the keratin fibrils.
Stratum Lucidum
Epidermal layer that consists of a very thin translucent band of flattened, dead keratinocytes with indistinct boundaries.

Present only in "thick" skin.
Stratum Corneum
Outermost epidermal layer.

20-30 cell layers thick. Cells are dead and their flattened, scalelike remnants are fully keratinized.

Cells are constantly rubbing off and being replaced by division of deeper cells.

Visually notable for many layers of very flat, plain cells.
Hypodermis
Layer just deep to the dermis, not actually considered a part of the skin.

It is primarily composed of adipose tissue.
Dermis
Dense irregular connective tissue layer that varies in thickness.

Located just deep to the epidermis and superficial to the hypodermis.

Contains two layers.
Papillary Layer
Superficial dermal region.

Composed of areolar connective tissue. Very uneven with dermal papillae on surface, attaching the dermis to the epidermis above.

Abundant capillary networks in the layer furnish nutrients for the epidermal layers and allow heat to radiate to the skin suface.

Also contains Meissner's corpuscles.
Dermal Papillae
Fingerlike projections from the superficial surface of the papillary layer which attach the dermis to the epidermis above.
Meissner's Corpuscles
Pain and touch receptors located in the papillary layer of the dermis.

Ovoid structure with "squiggles" inside in cross section (looks sort of like a cartoon depiction of a mitochondrion in cross section) which occur at the termination point of some sensory nerve fibres.
Reticular Layer
Deepest skin layer.

Composed of irregular connective tissue.

Contains many arteries and veins, sweat and sebaceous glands, and Pacinian corpuscles.
Pacinian Corpuscles
Pressure receptors located in the reticular layer of the dermis.

Ovoid structure that is inscribed with concentric ovals in cross section. Associated with nerve branches.
"Thick" Skin
Skin of the palm of the hand/fingertips and sole of the foot.

Has the stratum lucidum.
"Thin" Skin
All skin other than that of the palm of the hand/fingertips and sole of the foot.

Does not contain the stratum lucidum.
Hair Root
Pinhead shaped structure that is the subcutaneous extension of the hair shaft.
Hair Follicle
Sheath surrounding the hair root.
Eccrine Sweat Gland
Merocrine sweat glands. Coiled, tubular gland whose duct extends to open in a funnel-shaped pore at the skin surface. Secretes sweat.
Hair Follicle Receptor
Nerve branchings that surround the hair follicle in the dermis to receive sensory input.
Adipose Tissue
Globular fat cells that make up the majority of the hypodermis.
Sensory Nerve Fibre
Nerve branchings which extend upward through the dermis. Terminate in free nerve endings or corpuscles.
Arrector Pili Muscle
Small bands of smooth muscle cells that connect each hair follicle to the papillary layer of the dermis.

When these muscles contract, the slanted hair follicle is pulled upright, dimpling the skin surface with goose bumps.

Also exerts pressure on the sebaceous glands surrounding the follicle, causing a small amount of sebum to be released.
Sebaceous Gland
Globular structure associated with the superficial portion of the hair follicle that secretes oil (sebum) onto the epidermal surface.

Holocrine glands. Sebum softens and lubricates hair and skin, slows water loss, and is bactericidal.
Free Nerve Ending
Termination of sensory nerve fibres in the dermis which is not associated with a corpuscle.
Pore
Opening in the epidermis which connects to an eccrine sweat gland.
Hair Shaft
Portion of a hair which protrudes from the epidermis.
Free Edge of Nail
Part of fingernail used in scratching.
Body of Nail
Region of fingernail to which polish is applied.
Lateral Nail Fold
Folds of skin flanking the nail.
Lunula
Lighter coloured crescent at the base of the nail.
Eponychium
Cuticle at the base of the nail.
Nail Matrix
The thickened proximal part of the nail bed containing germinal cells responsible for nail growth.

As the matrix produces the nail cells, they become heavily keratinized and die.
Root of Nail
The part of the nail that is embedded in the skin and adheres to an epithelial nail bed.
Proximal Nail Fold
Fold of skin at the base of the nail, proximal to the eponychium.
Nail Bed
Extension of the stratum basale beneath the nail.
Hair Bulb
A collection of well-nourished germinal epithelial cells at the basal end of the hair follicle.

As the daughter cells are pushed farther away from the growing region, they die and become keratinized.
Sebum
Product of the sebaceous glands.

Mixture of oily substances and fragmented cells that acts as a lubricant to keep the skin soft and moist and prevents the hair from becoming brittle.
Epithelial Membrane
A simple organ consisting of an epithelial sheet bound to an underlying layer of connective tissue proper.
Cutaneous Membrane
The skin.

A dry membrane with a keratinizing epithelium.
Mucous Membrane
Membranes composed of epithelial cells resting on a layer of loose connective tissue called the lamina propia.

Line all of the body cavities that open to the body exterior (respiratory, digestive, and urogenital tracts).

All are "wet" membranes, but not all secrete mucus.
Serous Membrane
Epithelial membranes composed of a layer of simple squamous epithelium on a scant amount of areolar connective tissue.

Exists as linings and coverings in closed body cavities.

Secrete serous fluid which lubricates the organs and body walls, reducing friction.

Parietal--lines a cavity
Visceral--covers an organ
Pleura--in pleural cavity
Peritoneum--in abdominopelvic cavity
Pericardium--in pericardial cavity
Synovial Membrane
Membrane composed entirely of connective tissue.

Lines the cavities surrounding joints, providing a smooth surface and secreting a lubricating fluid.
Types of Epithelial Membranes (3)
Cutaneous, mucous, serous
Cleavage/Tension Lines
Separations between the bundles of interlacing collagen fibres that run parallel to the skin surface in the reticular layer of the dermis.
Flexure Lines
Dermal folds that occur at or near joints, where the dermis is tightly secured to deeper structures.
Striae
Dermal tearing indicated by silvery white scars/"stretch marks"
Blister
The separation of the epidermal and dermal layers by a fluid-filled pocket.
Factors in Skin Colour
(1)Melanin
(2)Carotene
(3)Blood oxygenation and volume
Sudoriferous Glands
Sweat-secreting glands distributed over the entire skin surface, except the nipples and parts of the external genitalia.
Sweat
Hypotonic filtrate of the blood. 99% water, lactic acid, metabolic wastes, salts, vitamin C, antibodies, dermicidin (antimicrobial), pH 4-6. Prevents body overheating.
Apocrine Sweat Gland
Sweat glands confined to axillary and anogenital areas. Ducts empty into hair follicles. Sweat plus fatty substances and proteins upon which bacteria feed.

Little role in thermoregulation.
Ceruminous Gland
Modified apocrine gland that secretes earwax (cerumen).
Mammary Gland
Modified apocrine sweat gland that secretes milk.
Hyponychium
Underside of the free edge of the nail.
Vellus Hair
Fine hair
Terminal Hair
Coarse scalp, eyebrow hair
Hair Growth Cycles
Anagen (active growth phase)
Catagen (regressive growth phase--hair matrix cells die)
Telogen (resting phase of 1-3 months)
Matrix proliferates again.

Nutrition & hormones = most important factors. Hair growth under control of many proteins.
Alopecia
Hair thinning/baldness
Male Pattern Baldness
Genetically determined, sex-influenced condition. Witched-on response to DHT causes follicular growth cycles to become so short that the hair may never become visible.
Functions of the Integumentary System (6)
(1) Protection: chemical (low pH & bactericidal agents), physical/mechanical (barrier & waterproofing), biological (Langerhans' cells)

(2) Body temperature regulation (sweat, blood shunting)

(3) Cutaneous sensation (bare nerve endings, hair follicle receptors, Meissner's corpuscles, Pacinian corpuscles, Merkel dics)

(4) Metabolic (vitamin D)

(5) Blood reservoir (~5%)

(6) Excretion (nitrogenous wastes, salt, water)
Basal Cell Carcinoma
Least malignant, most common cancer.

Shiny, dome-shaped nodules.

Slow growing, low risk of metastasis.
Squamous Cell Carcinoma
Rapid-growing, high risk of metastasis if not removed.

Arises from keratinocytes of stratum spinosum.

Small, rounded, scaly elevation.
Melanoma
Cancer originating at melanocytes.

Most dangerous, highly metastatic.

Spreading brown to black patch.
Burn
Tissue damage inflicted by heat, electricity, radiation, or chemicals--all of which denature cell proteins and cause cell death in the affected areas.

Immediate threat: loss of fluids containing proteins and electrolytes

Later threat: infection after the 24 hour sterile period is over, immune system becomes deficient within 1-2 days after severe burn injury
First-degree Burn
Damages only the epidermis.

Symptoms: redness, swelling, pain

Heal in: 2-3 days
Second-degree Burn
Injures epidermis and upper region of the dermis.

Symptoms: redness, swelling, intense pain, blistering

Healing: Regenerates within 3-4 weeks if not infected
Third-degree / Full-thickness Burn
Burns the entire thickness of the skin, down to the hypodermis.

Symptoms: Redness, white-greyness, blackness, lack of pain

Healing: skin graft usually necessary
Burns are critical when.... (3)
(1) Over 25% of the body has 2nd degree burns

(2) Over 10% of the body has 3rd degree burns

(3) There are 3rd-degree burns to the face (danger to respiratory system), hands, or feet.
Developmental Aspects of the Integumentary System
Ectoderm --> epidermis

Mesoderm --> dermis & hypodermis

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