Integumentary System Flashcards
Functions of the skin
Protection, sensation, thermoregulation, metabolism, sexual signaling
General structure
Epidermis
Dermis
Subcutaneous layer
Epidermis
An epithelial layer of ectodermal origin. Includes hairs, nails, sebaceous glands, and sweat glands
Epidermis structure
Thin and Thick Skin (Epidermis)
Like all epithelia, the epidermis lacks capillaries, and the cells receive
nutrients and O2 by diffusion from the dermis.
Four (or five) layers of epidermis:
Stratum basale
Stratum spinosum
Stratum granulosum
Stratum lucidum (thick skin only)
Stratum corneum
Stratum corneum
First layer, most superficial
Epidermal layer that is the most superficial; 20-30 layers of dead, flattened, anucleate, keratin-filled keratinocytes; protects against friction and water loss.
Consists of 15-20 layers of squamous, keratinized cells
filled with filamentous keratins. These fully keratinized or cornified cells called squames are continuously shed at the epidermal surface
Stratum lucidum
Second layer
2-3 layers of anucleate, dead cells; seen only in thick skin
Found only in thick skin, consists of a thin, translucent layer of flattened keratinocytes. Nuclei and organelles have been lost, and the cytoplasm consists almost exclusively of packed keratin filaments.
Stratum granulosum
Third layer
3-5 layers of keratinocytes with distinct kerato-hyaline granules
Consists of three to five layers of flattened cells undergoing keratinization, a “terminal” process.
Stratum spinosum
Fourth layer
Several layers of keratinocytes all joined by desmosomes; Langerhans cells present
Normally the thickest layer; the cytoplasm actively synthesizes keratins, like the basal layer.
Stratum basale
Fifth layer, most deep layer
Deepest, single layer of cuboidal to low columnar cells in contact with basement membrane; mitosis occurs here; melanocytes and Merkel cells also
Epidermis cell types
Keratinocytes
Melanocytes
Merkel cells
Langerhans cells
Keratinocytes
The most common–90% of
epidermal cells. These cells produce keratin,
and form a stratified squamous keratinized
epithelium.
Melanocytes
Pigment-producing cells.
Located in the
epidermal basal layer (stratum basale) and synthesize melanin
granules and transfer them into neighboring keratinocytes. Transfer
occurs through many long,
branching melanocyte processes.
Langerhans cells
Antigen-presenting cells (APCs)
Form an important defense against pathogens and environmental damage
Develop in the bone marrow from monocytes, move into the blood, and migrate into epidermis
Merkel cells
Tactile epithelial cells.
Sensitive mechanoreceptors essential for light touch sensation. Abundant in highly sensitive skin like the fingertips.
The basolateral surfaces of
the cells contact expanded
terminal discs of unmyelinated sensory fibers
penetrating the basement
membrane. The complex of
nerve and cells is called a
Merkel disk.
Dermal papillae
Projections between the dermis and epidermis that interdigitate with epidermal ridges to strengthen adhesion
Subcutaneous layer or Hypodermis
A loose connective tissue layer with pads of adipocytes. It binds the skin loosely to the underlying tissues
What determines most of the physical properties of the epidermis?
lipid envelope and keratin-filled cells
Friction blisters
Lymph-filled spaces created between the epidermis and dermis of thick skin by excessive rubbing. This activity may produce thickening and hardening of the outer epidermal layers, seen as corns and calluses.
Psoriasis
Keratinocytes differentiate rapidly, causing thickening of the epidermis and increased keratinization and desquamation. Caused by an autoimmune reaction in the skin, which can also lead
to inflammation with redness, irritation, itching, etc.
Skin Cancer
One-third of all adult cancers originate in the skin. Most are from cells of the basal or spinous layers, producing, respectively, basal cell carcinomas and squamous cell carcinomas. Both types of tumors can be diagnosed and cut out early and are rarely lethal.
Burns
Tissue injuries caused by thermal, electrical, radioactive, or chemical agents
First-degree burn
A burn in which the damage is limited to the superficial
part of the epidermis.
Second-degree burn
A burn in which the damage extends through the
epidermis into the superficial part of the dermis. However, except
for their most superficial parts, the sweat glands and hair follicles are not damaged and can provide the source of replacement
cells for the basal layer of the epidermis.
Third-degree burn
The entire epidermis, dermis, and perhaps
underlying muscle are damaged. A minor degree of healing may occur at the edges, but the damaged portions require skin
grafting. The extent of the burn (percent of total body surface affected) is generally more significant than the degree (severity of
depth) in estimating its effect on the well-being of the victim.