Topic 27: Skin and Appendages

What are the cellular layers of the epidermis?

Stratum basale, Stratum spinosum, stratum granulosum, stratum lucidum(only in thick skin), and stratum corneum.

What is anagen, catagen and telogen?

Terms of the hair growth cycle anagen: period of growth, new hair develops catagen: period in which hair growth stops Telogen: period in which follicle atrophies and the hair is eventually lost.

What is the location, function and structure of the basal lamina?

The basal lamina is a structural attachment site for the basal epithelial to the underlying connective tissue. It is composed of laminins(type IV collagen), and various proteoglycans(perlecan) and glycoproteins(enactin/nidogen).

What does the epidermal water barrier consist of?

The cell envelope: a layer of insoluble proteins on the inner service of the cell membrane Lipid envelope: A layer of lipids attached to the cell service body by ester bonds.

What is the role of the follicular bulge and hair matrix?

The follicular bulge contains epidermal stem cells that migrate down to the hair matrix in the bulb. They account for the growth of the hair.

What constitutes the hypodermis?

The layer of loose connective tissue just below the reticular layer of the dermis which penniculous adiposus, arrector pili muscles.

What is the change of pH that occurs in the epithelium and what does it accomplish?

The pH decreases from 7.17 in the stratum granulosum to around 4.5-6 in the stratum corneum. This facilitates the break down of the nucleus and other organelles in the keratinocytes.

What is a tonofilament?

Intermediate filament of the keratinocyte. Made of keratin filaments.

What is the distinctive feature of the keratinocytes in the stratum granulosum?

Keratohyalin granules; they contain filaggrin and trichohyalin, both of which function as a promoter in the aggregation of keratin filaments into tonofibrils.

What is cellular organelle releases the molecules of the epidermal water barrier?

Lamellar bodies

Describe apocrine sweat glands.

Large-lumen coiled tubular glands associated with hair follicles; limited distribution(axillae, aereolae, genitalia,), secrete pheromones. Merocrine secretion.

What is the location structure and function of Ruffinis corpuscles?

Ruffinis corpuscles are mechanoreceptors that are sensitive to skin stretch and torque. They are located in the dermis.

Describe sebaceous glands.

Secretory gland that develops as an outgrowth of the external root sheath of the hair follicle; secretes sebum via holocrine secretion.

Describe eccrine sweat glands.

Simple, coiled tubular structure, located over the entire body, play a role in temperature regulation, composed of secretory and duct segments.

What is the process of re-epithelization in wound healing?

Cells of the Stratum basal surrounding the wound site proliferate and spread across the wound underneath the scab. As they begin to grow, the layered structure of the epithelium is remade and the keratinized cells push the scab off.

What proteins are found in the lipid envelope of keratibocytes?

Ceramides and acylglucosylceramides

What cells are found in the secretory segment of eccrine sweat glands?

Clear cells(watery secretion), dark cells(protienaceous secretion), and myoepithelial cells.

What does the reticular layer of the dermis consist of?

DICT; characterized by thick irregular type I collagen bundles and elastic fibers.

What is the location, stucture and function of desmosomes?

Desmosomes offer cell to cell adhesion between the keratinocytes in the stratum spinosum. They contain desmoplakins and plakoglobins, desmogleins, and desmocollin molecules.

Describe the mechanism and molecules behind desquamation of keratinocytes.

Desquamation occurs via pH dependent process that occurs by the proteolysis of desmosomes by KLK serine peptidases.

What type of nerve transmitters stimulate the sweat glands?

Eccrine: cholinergic-in response to physical stress Apocrine: adrenergic-in response to emotional stress

How does reepithelization occur following full thickness injury to the epithelial layer?

Epithelial stem cells from neighboring follicular bulges migrate to the wound site and initiate reepithelization.

What is the location structure and function of free nerve endings of the skin?

Free nerve endings lack a connective tissue or schwann cell sheath. They terminate in the stratum granulosum and wrap around hair follicles. They transmit fine touch, heat, cold, pain, and in the case of the nerve endings associated with hair follicles movement.

What are hairs composed of?

Heavily cross linked hard keratin with three layers: Medulla, Cortex(KAPs), and cuticle of the hair shaft.

What is the location and function of hemidesmosome?

Hemidesmosomes connect the epithelium to the underlying connective tissue of the dermis. It consists of an intercellular attachment plaque(plectin, BP 230, Erbin), transmembrane proteins(Collagen XVII, @6B4 integrins), anchoring fibrils(type VII collagen).

What cells are found in the internal root sheath?

Henle's layer, Huxley's layer, internal root sheet cuticle.

What does the papillary layer of the dermis consist of?

Loss connective tissue with type I and Type III(reticular fibers) collagen. Houses nerves and blood vessels.

What is the location structure and function of Meissner's corpuscles?

Meissner's corpuscles are located in the dermal papillae. They are touch receptors responsible for sensing light touch and sensitivty especially in the lips, fingers and toes.

What is the location structure and function of pacinian corpuscles?

Pacinian corpuscles are located reticular layer and hypodermis and are abundant around the finger tips. They are deep pressure receptors for mechanical touch and vibration. The nerve fiber runs in the center of lamellar circles made up of fibroblast like cells.

What are the two layers of the dermis?

Papillary layer and the reticular layer.

What is primary union(first intention) wound healing?

The type of healing that occurs after surgical incision in which wounds theater usually clean and uninfected have their edges approximated by surgical sutures.

What is the histological difference between thick and thin skin?

Thick skin has the stratum lucidum layer in the epidermis in between the stratum granulosum and the stratum cornuem. Thick skin has epidermal ridges(finger prints), more sweat glands, an absence of hair follicles/sebaceous glands, and more sensory receptors.

Where is thick skin and thin skin found?

Thick skin is the hairless skin on the palms and soles of the feet. Elsewhere the skin possess much thinner epidermis and is called thin skin.

What role does the follicular bulge play following epidermal injury?

When the epidermis is injured the epidermal stem cells of the follicular bulge migrate to the site of injury and participate in resurfacing the wound site.

How are wounds by 3rd degree burn of exstensive full thickness abrasion healed?

grafting epidermis to cover the wound.

What is secondary union(secondary intention)?

healing that occurs in traumatic wounds with separated edges, which are characterized by more extensive loss of cells and tissues. Involves the generation of granulation tissue.

What are the structural components of the growing hair follicle?

infundibulum, isthmus, Follicular bulge, bulb, and dermal papilla.

What type of cells are present in the epidermis?

kertinocytes, melanocytes, Merkel's cells, Langerhans cells.