11.28.11+-+Integumentary+System

Integumentary System


 * 1. Identify and describe the two layers of skin. Define the term hypodermis (subdermis). **

The two layers of the skin are the epidermis and the dermis; the epidermis is superficial to the dermis. The epidermis is a keratinized stratified squamous epithelium, primarily composed of keratinocytes, melanocytes, and Langerhans cells. It is subdivided into 5 strata (layers): germinativum, spinosum, granulosum, lucidum (only in thick skin), and corneum. The dermis is 2 layers of connective tissue. The more superficial is the papillary layer (loose connective tissue) and the deeper is the reticular layer (dense irregular connective tissue).

The hypodermis is the loose (fascial) connective tissue layer between the dermis and the rest of the body. It is not part of the skin, but directly deep to it.


 * 2. Describe the cellular and structural characteristics of the following layers of the epidermis: stratum germinativum, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum. Compare and contrast these layers in thin and thick skin. **

Stratum germinativum: Stratum spinosum: Stratum granulosum: Stratum lucidum: Stratum corneum:
 * Also called stratum basale. It is a single cell layer. Simple cuboidal epithelial cells. Composed of keratinocytes and melanocytes. Bound to each other via desmosomes and to the basal lamina via hemidesmosomes.
 * In this layer the the cells are synthesizing the keratin filaments. Visible interdigitation at the cell membrane boundaries provides cohesion. Still cuboidal. The thickest layer: stratified. Thicker in thick skin than in thin skin. Cytoplasm full of tonofibrils. Composed of keratinocytes, langerhans cells, and melanocytes.
 * In this layer the cells are beginning to flatten into squamous. Also stratified. Visible granules as the keratohyalin granules are being synthesized; at this stage the keratohyalin granules are strongly basophilic. They are still living functional cells. Composed of keratinocytes
 * Only present in thick skin. Cells have lost their nucleus/organelles: dead. Sratified squamous cells, but boxy like bricks. Composed of keratinocytes.
 * Another difference between thick and thin skin (thicker in thick skin). stratified squamous cells. Cells are no longer living. Connected via tight junctions. Composed of keratinocytes


 * 3. Describe the process of keratinization.**

Stratum basale cell undergoes mitosis, spits off a cell into the stratum spinosum. While in the stratum spinosum, many intermediate filaments called tonofilaments are synthesized and bundled into tonofibrils. The cell then moves into the stratum granulosum where basophilic keratohyalin granules are synthesized. Tonofibrils are bound with accessory proteins and as the cell moves into the stratum lucidum is converted into keratin. At this point synthesis stops and the nucleus and organelles disintegrate. The cell is desiccated and all that remains is keratin. The cells are still bound together by desmosomes, but other junctions have disappeared.


 * 4. Describe melanocytes, melanin granules, and melanosomes and their functions.**

Melanocytes insert granules of melanin into specialized cellular vesicles called melanosomes.

Melanocyte: Melanin granules: Melanosomes:
 * Cells that synthesize melanosomes and melanin granules, but stain lightly. They put out dendrites that press into the 6-8 keratinocytes that endocytose the tips that contain the melanosomes.
 * The functional unit of pigment. Synthesized by melanocytes, stored by keratinocytes within melanosomes.
 * The vesicle of melanin granules that is endocytosed by keratinocytes.


 * 5. Describe structure and function of Merkle's cells and Langerhans cells.**

Merkle's cells are round cells present in the stratum basale. They are sensory cells associated with sensory nerve fibers. They sense light touch.

Langerhans cells are differentiated monocytes within epithelium. They are part of the innate and adaptive immune system. They are primary antigen presenting cells. They have lots of dendrites. Once they phagocytose an antigen they migrate into lymph tissue and activate immune response.


 * 6. Compare and contrast papillary and reticular layers of the dermis.**

The papillary layer is thinner and more superficial (in contact with the epidermis). It is composed of loose connective tissue. It is composed of Type 1 collagen, elastic fibers and reticular fibers. A larger variety of cells are in this tissue: fibroblasts with mast cells and macrophages

The reticular layer of the dermis is thicker and slightly denser, but still classified loose CT. Formed by type 1 collagen and elastic fibers, but no reticular fibers. Mostly fibroblasts.


 * 7a. Describe the epidermal-dermal interface.**

The papillary layer of the dermis interdigitates with the epidermis with extensions called dermal papillae. The epidermal extensions are called epidermal pegs.


 * 7b. Describe the structure of the basal lamina and basement membrane.**

The basal lamina and the reticular lamina together form the basement membrane. The basal lamina is further subdivided into the lamina densa and the lamina lucida. The lamina lucida is most superficial and composed of anchoring fibrils. The lamina densa is composed of collagen IV. The reticular lamina is a mixture of collagen VII, III (reticular fibers) and proteoglycans.


 * 7c. Identify and describe the two types of anchoring complexes.**


 * Hemidesmosomes are one type of anchoring complex. They are associated with intermediate filaments in the cytosol. They are between epithelial cells and the subjacent basal lamina. Their trans-membrane proteins are called integrins. Outside the cell they are anchored via lectin to Collagen VII.


 * The other junctions are defined as non-hemidesmosomes. They can be called focal adhesions. They are like hemidesmosomes because they use integrins as their transmembrane protein, but affiliated with actin within the cell and laminins outside the cell. The laminins then associate with Collagen IV via nidogen.


 * || Hemidesmosomes || Focal Adhesions ||
 * Components || Cell-ECM || Cell-ECM ||
 * Cell Membrane Protein || Integrins || Integrins ||
 * Intracellular Anchor || Intermediate Filaments (keratin) || Actin ||
 * Type of Attraction || Heterophilic || Heterophilic ||
 * Function || Adhesion || Adhesion ||


 * 8. Define and describe the hypodermis.**

Loose connective tissue binding the dermal layer to the organ/tissue underneath. The superficial fascial layer grossly.


 * 9. Describe the structure of hair follicles, erector pili muscles, nails, sebaceous glands, eccrine sweat glands and apocrine sweat glands.**

Hair follicles: Erector pili muscles: Nails: Sebaceous glands: Eccrine sweat glands: Apocrine sweat glands:
 * These sheaths of tissue containing the hair are invaginations of the epidermal epithelium. The follicle is slightly different depending on which phase of growth the hair is currently in. During the growth phase (anagen), the follicle terminates in an enlargement called the hair bulb. The keratinocytes differentiate into the multiple layers of the hair. The outermost layer of keratinocytes of the follicle, called the external root sheath is continuous with the basal and spinous layers of the epidermis.
 * Muscles with origin from the deep side of the stratum basale. When flexed the hair shaft moves into an erect position.
 * The nail replaces the stratum corneum, stratum lucidum, and stratum granulosum. ONly basal and spinous layers lie beneath the nail plate. The plate extends from its base, the nail matrix and root.
 * Sebum (fatty wax) secreting branched acinar holocrine gland associated with ducts that mostly open into hair follicles. In the dermal layer.
 * Common sweat glands. Open onto the skin almost everywhere. Serous secreting. Irregular stratified cuboidal; 2 cell types: sweat producing "clear cells" and unknown function of "dark cells". Innervated by cholinergic fibers.
 * Puberty sweat glands (axilla and perineum). More protein rich mucosal secretion. Innervated by adrenergic nerve endings.


 * 9b. Describe the characteristics of the hair cycle and different hair types.**

There are 3 phases of the hair follicle:
 * Anagen (hair growth)
 * Catagen (hair regression and loss)
 * Telogen (follicle rest).

There are 3 phases of development associated with 3 hair types:
 * Fetus: fine, downy Lanugo hair.
 * Late Fetus: peach fuzz: Velus hair
 * Puberty: Andronergic/terminal hair (pubes?): replaces velus hair in all the places you would expect.

There are 3 hair types:
 * Asiatic: Broad width and Round shape
 * Caucasion: Variable width and Variable shape
 * African: Narrow width and Oval shape


 * 10. Describe the blood supply to skin. Include arterial and venous plexuses.**

The dermal layer contains two rich plexuses. The sub papillary plexus lies between the papillary and reticular dermal layers. The second layer lies between the hypodermis and the dermis. Dermal vasculature has many anastomoses that can be shut down to preserve heat or opened up to facilitate heat loss. The epidermis is non-vascularized.


 * 11. Identify the functions of skin.**

Protective Sensory Thermoregulatory Metabolic (Vitamin D3) Sexual Signaling (pheromones)


 * 12. Know the location of stem cells.**

Stem cells are found in two different places:

Future keratinocytes and melanocyte stem cells lie in stratum basale, particularly in epidermal pegs and papillae. Specifically they can also be found in hair papilla