Lecture 3: Skin and Appendages Flashcards
What is the Integument made up of ?
Stratified Squamous Epithelium (epidermis), which is keratinized and dermis, which is made up of connective tissue in 2 layers.
Hypodermis
is a layer of the skin and others consider it a superficial fascia overlying muscles that is mainly adipose tissue and connective tissue
What are the functions of the skin?
Barrier, Homeostasis, Immunologic, Sensory, Endocrine, and Excretion
What are the differences between the thin and thick skin?
Thick skin is mainly palms and sole of the feet. No hair follicles. While the thin skin is the rest of the body.
What layer does the thick skin have that the thin does not ?
Stratum Lucidum
What is apart of the thin skin that is not apart of the thick skin ?
Sebaceous Gland
What are the two layers ?
Epidermis and Dermis
Epidermis
is stratified squamous, keratinized epithelium and has 5 identifiable layers in thick skin
Dermis
connective tissue and has two identifiable layers
What are the 5 layers of the epidermis ?
- Stratum Germinativum
- Stratum Spinosum
- Stratum Granulosum
- Stratum Lucidum (only thick skin)
- Stratum Corneum
Stratum Germinativum
This is a mitotically active area.
- cubodial or columnar cells that rest on the basal lamina.
What are the stratum germinativum attached to ?
They are attached to the basal lamina by the hemidesmosomes
What are the adjacent cells of the stratum germinativum attached by ?
Desmosomes
Stratum Spinosum
Made up of polygonal cells that have spiny projections that form “intercellular bridges”
- Mitoses seen in this layer also
What are the intercellular bridges are now known to be locations of ?
Desmosomes
What are the contributions of the intercellular bridges ?
Cohesiveness of the epidermis .
What type of desmosomes are present in stratum spinosum?
Cytokeratin Type III
Malphigian Layer
- is the stratum germinativum and stratum spinosum
- region of keratinocyte proliferation
Stratum Granulosum
characterized by basophilic granules, keratohyaline granules, and membrane coating granules
Keratohyaline granules
which are not membrane bound
Membrane Coating Granules
Membrane Bound Granules
What do these granules contain?
glycosaminoglycans and phospholipids that are extruded out into the extracellular space
What does is the role of having these granules ?
- form a barrier to micro-organisms, foreign substances and most importantly water
What is the water barrier in the epidermis is partially formed by ?
lamellar bodies, secretion is high in lipids
What happens when the keratinocytes mature and differentiate ?
they produce keratin hyaline granules and lamellar bodies
What is the function of the keratin hyaline ?
- increase in number and release their contents into the cytoplasm as the cell dies
Stratum Lucidum
most prominent in thick skin
- it is a translucent layer that is very acidophilic cells that do not have nuclei and organelles
Stratum Corneum
- Flattened Keratin- filled cells
- Devoid of any organelles and nucleus
What is another name for stratum Corneum ?
horny cells or squams
1st Degree Burns
Damage to superficial epidermis
2nd Degree Burns
Epidermis completely destroyed
3rd Degree Burn
Full-thickness burn
- Destroys epidermis and dermis
- Skin grafts are necessary
What are the cells found in the Epidermis ?
- Keratinocytes
- Melanocytes
- Langerhans Cells
- Merkel Cells
Keratinocytes
- predominant cell type in the epidermis
- go through a very specialized differentiation to give rise to the protective dead cell layer ( stratum corneum)
What is the origin of the Keratinocytes ?
Ectodermal Origin
What is the origin of the Melanocytes ?
Neural Crest Origin
Why are the Langerhans cells not attached ?
because they need to be able to wonder in and out
What are the Langerhans Cells responsible for ?
- engulfing invading microorganisms in the epidermis and presenting antigens to lymphoid cells in the dermis
In AIDS and HIV positive patients, the Langerhans cell cytoplasm contain what ?
- HIV-1 in their cytoplasm, and may serve as reservoir for the virus
What technique must be used for the Langerhans cells ?
- cells cannot be distinguished easily in H and E stained tissue
Melanocytes are located ?
Stratum Germinativum
How do the melanocytes maintain their epidermal-melanin units ?
- can replicate slowly throughout life
What are the melanocytes attached to ?
- Hemidesmosomes
What are the melanocytes not connected to ?
- Keratinocytes by Desmosomes
What is Cytocrine secretion ?
- melanin granules are injected into keratinocytes
Where is melanin predominantly in the skin?
Keratinocytes
What is the position that melanin granules take ?
- above the nuclei of keratinocytes in the strata germinativum and spinosum
Where are merkel cells predominantly found ?
thick skin where touch is acute
What are the two distinct layers of the Dermis ?
- Papillary and Reticular
What does the papillary contain ?
- loose connective tissue containing fibroblasts, mast cells, and macrophages
What does the reticular layer of the dermis include ?
- Dense irregular CT composed of collagen fibers, type 1
What are the appendages of the skin ?
- Hair Follicles
- Sweat Glands
- Sebaceous Glands
- Mammary Glands
- Nails
What are the two sweat glands ?
- Eccrine Sweat-Glands
- Apocrine Sweat Glands
How are the sweat glands developed ?
- as invaginations of epidermis into the underlying connective tissue
Eccrine Sweat Glands
- simple, coiled tubular glands , secrete a non-viscous fluid.
- Evaporation of the fluids cools skin
What do sweat glands contain ?
Catabolites
What are myoepithelial cells ?
- are specialized cells that squeeze the secretions from the sweat acini
Why are the eccrine sweat glands considered acidophilic ?
- because they contain actin filaments
What are apocrine sweat glands ?
- specialized glands located in the axillary areolar and anal region
What do the ducts in the apocrine sweat glands secrete ?
- secrete viscous, odorless fluid
- the secretion attains a distinctive odor by the action of bacteria that reside on the skin
The Sebaceous Glands are found where ?
- skin of the lips, the glans penis and the clitoris where they are not associated with hair follicles
What do the sebaceous glands secrete ?
- secrete sebum by the holocrine secretion
When do the sebaceous glands become more active ?
- puberty
What does the sebaceous glands respond to ?
- hormones
Sebaceous glands are an ideal spot for ?
Bacterial growth when they are clogged
What type of cells are at the base of the gland ?
germinal cells
What happens when the sebaceous glands fill with sebum ?
- their nuclei become pyknotic and are eventually lost
Nails
are plates of keratinized epithelial cells
- they are able to assess the oxygenation of blood
nail root
germinal root
nail bed
- consists of stratum germinativum and stratum spinosum only ( the malpighain layer)
Where does the epithelium of the nail bed arises from ?
- nail matrix
Nail matrix extends ?
deep to the root
How does the nail grow ?
- proximal end and slides over the nail bed, nail bed does not contribute to the nail plate
Free Nerve Endings
unmyelinated axons that penetrate the basal lamina of the epidermis to enter the stratum germinativum and spinosum
Meissner Corpuscles are abundant
in thick skin as well as in the skin of the lips and nipples
Pacinian Corpuscle
found in the dermis and often, hypodermis, of both thick and thin skin
