Notes
Integumentary System (Advanced)
Sections
Integumentary System (Advanced)
The integumentary system serves to both protect the body and assist in the maintenance of homeostasis.
Comprises the skin, which divides into:
- The Epidermis
- The Dermis
- The Skin Accessory Organs (derivatives): hair, glands, and nails
Epidermis
Superfical to Deep:
Stratum corneum: Outermost layer; it comprises numerous rows (25-30) of flat, dead cells that contain keratin and is continually sloughed off.
Stratum lucidum: Comprises clear-appearing cells because they lack nuclei and organelles; they do contain keratin and eleidin.
Stratum granulosum: Comprises 3-5 rows of cells that contain keratohyaline granules; this layer helps form the keratin cells of the epidermis.
Stratum spinosum: Comprises several rows of keratinocytes. During slide preparation, the cells shrink so that the intracellular bridges, the desmosomes, are visible as tiny spikes. Thus, they are sometimes call "prickle cells."
Stratum basale: Forms the deepest layer of the epidermis. It comprises a single layer of cuboidal keratinocytes that are active in cellular reproduction (mitosis). Melanocytes, which produce pigment, are found in this layer – these cells determine our skin color. This layer is also responsible for hair growth
Hair growth occurs when stratum basale generates new hair cells that push the old, keratinized hair cells through the follicle to form hair fibers.
"Come Let's Get a Sun Burn"
Use the "Come Let's Get a Sun Burn" to remember the layers
Come - Corneum
Let's - Lucidum
Get a - Granulosum
Sun - Spinosum
Burn - Basale
Types of Skin
Thin skin covers most of our body. It is "thin" because it lacks a stratum lucidum and has a thinner layer of stratum corneum than thick skin does. It also has hair follicles and their associated glands. 75 to 150 μm thick.
Thick skin is restricted to discrete areas that are commonly traumatized, such as the palms of the hands and soles of the feet. It has the stratum lucidum and thicker layer of stratum corneum to provide protection on surfaces that are commonly coming into contact with other things (things we hold, climb, walk on, etc). 400 to 600 μm thick.
Dermis
Papillary layer is a thin layer of loose connective tissue with finger-like projections, called dermal ridges (aka dermal papillae), which interdigitate with the epidermal down-growths (epidermal papillae) to form fingerprints.
Reticular layer forms the bulk of the dermis; it comprises a dense layer of collagen bundles and elastic fibers.
Both layers are vascularized.
Hypodermis
A subcutaneous layer of fascia that comprises loose areolar connective tissue and adipose tissue. This richly vascularized layer stores fat and provides insulation and cushioning, and allows the skin to attach to underlying muscle without restricting movement.
Accessory organs
Derivatives/appendages of the skin.
Hair
Shaft, root, and dermal papilla.
Hair follicle invaginates the epidermis.
The outer root sheath of the hair follicle is continuous with the epidermis.
The Hair follicle comprises:
Hair shaft, which is the slender filament at the center of the follicle that extends above the epidermis.
Hair root, which is the expanded region of the hair follicle, deep within the dermis at the root of the hair follicle.
Dermal papilla, which contains the capillary network that nourishes the hair follicle; not to be confused with dermal papilla that interdigiate with epidermis.
Hair Growth Phases:
Anagen phase is a growing phase.
Catagen phase is growth respite phase.
Telogen phase is a terminal resting phase (when hair falls out).
Clinical Correlation: Albinism
Arrector pili
The arrector pili comprises smooth muscle and is attached to the dermal sheath surrounding the hair follicle.
When you "feel the hair on the back of your neck stand up," it is because arrector pili muscle have contracted.
This commonly occurs in cold temperature and in frightful emotional situations; the muscle fiber contracts, which causes the hair follicle to elevate, and forms a depression in the skin at the muscle attachment site to the dermis (forming goose bumps).
Glands
Sebaceous glands: Commonly associate with hair follicles; they are branched acinar, holocrine glands, which have a lobulated appearance.
They secrete sebum (an admixture of an oily/lipid substance and degenerating epithelial cells) into hair follicles.
Keeps hair supple, skin soft, protects against microorganisms, and maintains the hydration status of the epidermis.
Sweat Glands: Eccrine and Apocrine
Eccrine glands secrete sweat and are most prominent on the palms, soles of the feet, and forehead.
Sweat is formed through the filtration the blood into a hypotonic solution that is primarily water with small amounts of such products as salt, antibodies, metabolic waste, vitamin C, and dermcidin.
Apocrine glands are specialized, and (unlike the nearly ubiquitous eccrine glands) are associated with hair follicles, and confined to specific regions, namely: the axilla, areolar nipple, and perianal region. These sweat glands are activated at puberty, under the influence of sex hormones.
Other apocrine, non-sweat producing glands are ceruminous glands, which lie in ear canals and secrete cerumin, and mammary glands, which produce and secrete milk.
Nails
Comprise a nail bed, nail plate, cuticle, lunula, hyponychium, and nail root.
Sensory Nerve Receptors
Within papillary layer: Meissner copuscles (Mechanosensitive, light touch detection); Unmyelinated nerve fibers
(transmit pain and temperature sensation).
Within reticular layer: Pacinian corpuscles & Krause end-bulbs (Mucocutaneous (eg, oral cavity) receptors.
Clinical Correlations: Neuropathy Sensory Receptors
Clinical Correlations: Common Skin Lesions