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.
What factors contribute to skin color?
Melanin content in keratinocyte
Carotene
Number of blood vessels in the dermis
Pigments produced by the melanocyte
Eumelanin and Pheomelanin
Eumelanin
Brown or black pigments produced by the melanocyte, a specialized cell of the epidermis found
among the cells of the basal layer and in hair follicles.
Pheomelanin
A second, similar, pigment in humans found in red hair.
Melanin Synthesis
- Tyrosinase converts the amino acid tyrosine into different forms of melanin. Melanin pigment is linked to proteins, forming granules called melanosomes.
- Melanosomes are transported to the tips of the cytoplasmic extensions of the melanocytes. The neighboring keratinocytes absorb and transport the melanosomes toward their nuclei, where they form
a supranuclear cap that absorbs and scatters sunlight, protecting DNA of the living cells from the mutagenic effects of UV radiation.
Epidermal-melanin unit
On melanocyte plus its nearby keratinocytes.
What cells contain more pigment from melanosomes, keratinocytes or melanocytes?
Keratinocytes
Melanosome Formation
- Melanin formation
- Granules containing melanin mature. Mature granules are ellipsoid.
- Melanin granules are
transported to the tips of
the processes of the
melanocyte. Then taken to the neighboring keratinocytes of the basal and spinous layers. - In keratinocytes the melanin granules accumulate near the nucleus as a supranuclear cap shading the DNA against UV radiation.
Albinism
A congenital disorder producing skin hypopigmentation due to a defect in tyrosinase or
some other component of the melanin-producing
pathway.
Moles (benign melanocytic nevi; singular is nevus)
Melanocytes can normally proliferate in skin to produce moles (benign melanocytic nevi; singular is nevus) of various types.
Malignant melanocytes
Changes in the size or appearance of moles are
sometimes indicative of dysplasia that can progress
further to malignant melanoma. Malignant
melanocytes often penetrate the basal lamina, enter the dermis, and metastasize into blood and lymphatic vessels.
Dermis
Made of papillary layer and reticular layer.
Vascular
A layer of mesodermal connective tissue
Papillary layer
More superficial layer of dermis; composed of areolar connective tissue; forms dermal papillae; contains subpapillary vascular plexus.
Reticular layer
Thicker layer; Deeper layer of dermis; dense irregular connective tissue surrounding hair follicles, sebaceous glands, sweat glands, nerves, and deep plexus of blood vessels extending into subcutaneous layer.
Subcutaneous layer
Not considered part of the integument; deep to dermis; composed of areolar and adipose connective tissue.
Fibers of Dermis
Although most of the
protein fibers in dermis
are collagen, there are
also elastic fibers.
Subpapillary plexus
Between the papillary and reticular dermal layers
Capillary branches extend
into the dermal papillae and
form a nutritive capillary
network below the epidermis. A deep plexus
with larger blood and
lymphatic vessels lies near
the interface of the dermis
and the subcutaneous
layer
Dermis Misc.
Nutrients for epidermal keratinocytes diffuse into the avascular epidermis from the dermal vasculature through the basement
membrane
Both dermal regions contain a rich network of blood and lymphatic vessels. Nutritive vessels form two major plexuses, microvascular subpapillary plexus and deeper plexus
Dermal vasculature also has a thermoregulatory function.
The dermis is also highly innervated.
Subcutaneous Tissue
The subcutaneous layer
consists of loose connective tissue that binds the skin loosely to the subjacent organs, making it possible for
the skin to slide over them.
This layer, also called the
hypodermis or superficial
fascia, contains adipocytes
that vary in number and size.
Its vascular supply promotes rapid uptake of drugs injected here.
Tactile Sensory Receptors
Unencapsulated receptors:
Merkel cells, free nerve endings, and root hair plexuses
Encapsulated receptors: Meissner corpuscles, lamellated (Pacinian) corpuscles, and Ruffini corpuscles (bulbous corpuscles)
