RA3 Skin Flashcards
What are the 3 layers of skin?
- Epidermis
- Dermis
- Hypodermis (superficial fascia)
Which germ layers are the epidermis and dermis derived from?
Epidermis: ectoderm
Dermis: mesoderm
What kind of cells make up the epidermis?
Keratinised stratified squamous cells
Label the three skin layers in the diagram
Thick skin vs thin skin
1. Amount of hair?
2. Location?
3. Is the epidermis thick or thin?
Thick skin:
1. Hairless
2. Found on soles of feet, palms of hands, and the surface lining the fingers and toes
3. Epidermis is thick
Think skin:
1. Hairy
2. Found on all other parts of the body
3. Epidermis is thin. Thickness of dermis is variable.
What are the cells of the epidermis called?
Keratinocytes
Characteristics of keratinocytes:
1. What do they contain?
2. What structures do they form?
- They contain keratin, a type of intermediate filament.
- They form desomosomes (between cells) and hemidesmosome junctions (with the basal lamina).
What are the 4 layers of the epidermis?
*What is the additional layer found in thick skin?
- Stratum corneum
- Stratum granulosum
- Stratum spinsoum
- Stratum basale
*Stratum lucidum (present in thick skin) is found in between the stratum corneum and stratum granulosum
Characteristics of the 4 layers of epidermis:
1. Cell name (if have)
2. No. of layers of cells
3. Cell shape
4. Is it keratinised?
5. Unique feature
Stratum corneum:
1. Corneocytes/squames
2. Many layers (stratified)
3. Squamous
4. Keratinised (filaggrin-crosslinked keratin)
5. Corneocytes gradually make their way to the uppermost layer of the stratum corneum where they are eventually desquamated (detached from the skin)
Stratum granulosum:
1. NA
2. 1-3 layers
3. Squamous
4. Non-keratinised
5. Cells contain keratohyalin granules, which contain precursors of filaggrin proteins, which are involved in aggregating keratin filaments
Stratum spinosum:
1. NA
2. Several layers
3. Squamous in uppermost layer
4. Non-keratinised
5. Forms the bulk of the “alive” portion of the epidermis
Stratum basale:
1. Basal cells
2. Single layer
3. Cuboidal
4. Non-keratinised
5. Cells serve as stem cells for the epithelium and divide to produce keratinocytes
Label the 4 (or 5) layers of the epidermis in the diagram
Where are melanocytes found and what is their function?
Location: Stratum basale of epidermis
Function: Contains melanosomes (vesicles) filled with melanin, which protect keratinocytes by absorbing ultraviolet light
Where are Merkel cells found and what is their function?
Location: Stratum basale of epidermis
Function: They are the cell portion of Merkel nerve endings, which are mechanoreceptors that sense texture and light pressure
Where are Langerhans’ cells found and what is their function?
Location: Stratum spinosum of epidermis
Function: They are antigen presenting cells that take antigens to lymph nodes for presentation to other immune cells
What kind of connective tissue does the dermis contain?
Dense irregular connective tissue
What are the 2 layers of the dermis?
- Papillary layer: contains dermal papillae, some blood vessels and nerve endings, and thin collagen fibers
- Reticular layer: thicker layer below the papillary layer, contains thick collagen fibers
How are the dermis and epidermis connected?
The dermis has fingerlike projections called dermal papillae that are covered by projections of the epidermis called epidermal ridges
What are dermal papillae? What is their function?
Fingerlike projections of the dermis, which are covered by the epidermal ridges of the epidermis. They contian nerve endings (for body temperature regulation) and capillaires (to provide nutrients to the avascular epidermis).
What are papillary ridges?
Raised portions of the epidermis in the thick skin of the hands and feet. Constitute fingerprints and footprints.
What are the 4 types of encapsulated nerve endings?
- Merkel nerve endings
- Ruffini’s corpuscles
- Pacinian corpuscles
- Meissner’s corpuscles
Compare the 4 types of encapsulated nerve endings:
1. What do they sense?
2. Where are they found?
Merkel nerve endings:
1. Sense texture and light pressure
2. Found in the stratum basale of the epidermis
Ruffini’s corpuscles:
1. Sense stretch
2. Found in the dermis
Pacinian corpuscles:
1. Sense vibrations
2. Found in the hypodermis
Meissner’s corpuscles:
1. Sense movement against the skin
2. Found at the top of the dermal papillae
Compare the Pacinian and Meissner’s corpuscles:
1. Where are they found?
2. What do they sense?
3. Are their axons myelinated?
4. Are they surrounded by Schwann cells lamellae?
5. Do they contain fluid and connective tissue between the Schwaan cell lamellae?
6. What kind of path do their axon brances follow through the corpuscles? (spiral or straight)
Pacinian corpuscles:
1. Found in the hypodermis
2. Sense vibrations
3. Myelinated axon becomes unmyelinated once in the corpuscle
4. Surrounded by layers of Schwaan cell lamellae
5. Contain fluid and connective tissue between the Schwaan cell lamellae
6. Axon branches follow a straight path
Meissner’s corpuscles:
1. Found at the top of dermal papillae
2. Sense movement against the skin
3. Myelinated axon becomes unmyelinated once in the corpuscle
4. Surrounded by layers of Schwaan cell lamellae
5. Contain little fluid or connective tissue between the Schwaan cell lamellae
6. Axon branches follow a spiral path
What is the function of hair follicles?
- It is attached to the arrector pili muscle. Upon contraction, the hair stands erect and goosebumps are formed.
- The bulge towards the top of the hair moluecule serves as a reservoir for some of the stem cells of the epidermis. During wound healing, they replenish all cells of the epidermis, including the sebaceous gland and hair follicle.
What is the function of sebaceous glands?
Secrete sebum, which moisturises hair and skin, and prevents water from entering or leaving the skin
Characteristics and function of apocrine vs eccrine sweat glands:
1. Location
2. Type of secretion
3. Content of secretion
4. Secrete in response to?
5. Location of secretory portion
6. Epithelium type of secretory portion
7. Epithelium type of ducts
Apocrine sweat glands:
1. Found in the underarms, anus, genitalia, areola, nipples, ears, eyelashes
2. Merocrine secretion (vesicles fuse with plasma membrane to release contents)
3. Milky secretion containing proteins, carbohydrates, lipids, ammonia, and possibly pheromones
4. Secrete in response to emotional and sensory stimuli
5. Secretory portion is found in the hypodermis
6. Secretory portion has cuboidal to low columnar epithelium
7. Duct has stratified cuboidal epithelium
Eccrine sweat glands:
1. Found everywhere on the body except parts of the genitalia and lips
2. Merocrine secretion
3. Secrete water, salt, urea, ammonia, and uric acid - excretory and cooling function
4. Secrete in response to heat or stress
5. Secretory portion is found in the hypodermis
6. Secretory portion has simple cuboidal or columnar epithelium
7. Duct has stratified cuboidal epithelium
