Skin and Glands Flashcards
Layers of the epidermis
Basale Spinosum Granulosum Lucidum Corneum
Epidermis is of ectodermal origin
Stratum Basale
Mitotically active cells that attach directly to the basement membrane by hemidesmosomes. Single layer of basophilic cuboidal or columnar cells.
Stratum Spinosum
Still mitotically active, but cells are starting to differentiate. Keratinocytes are connected to each other by desmosomes. Largest layer of epidermis.
Stratum Granulosum
Bundles of Keratin aggregates bound via accessory proteins like filagrin (keratohyalin granules)
Stratum Lucidum
Palms and soles of feet only. No nuclei or granules
Stratum Corneum
Non-nucleated dead cells filled with keratin.
As you go higher, fat and desmosome linkages disappear until “squames” start to sluff off
Psoriasis
T Lymphocytes are overactive causing an autoimmune reaction in the skin, leading to irritation and increased keratinocytes causing thickening and scaling of the skin
Thin vs. Thick skin
Size of Stratum Corneum
Thick skin DOES NOT have hair follicles (palms and soles)
What does Keratohyalin promote?
Within the SG layer, it promotes the dehydration of cells and cross-linking of keratin fibers
Layers of Dermis
Papillary Layer
Reticular Layer
Papillary Layer
Fine bundles of collagen. Loose connective tissue in this area that interdigitates with the epidermis for strong attachment. Mast cells, fibroblasts and leukocytes are present here
Reticular layer
Large bundles of collagen. Much thicker, dense irregular connective tissue with more fibers and fewer cells. Elastic fibers also present
Where are melanocytes?
Basal layer but they project to spinosum
Eumelanin
Brown and Black melanin
Pheomelanin
Melanin for redheads
Cytology of melanocytes
- Many small mitochondria
- Short cisternae of RER
- Well developed golgi
Steps of melanin synthesis
- Tyrosine synthesized in RER, processed in the golgi
- Tyrosine accumulates in the vesicles that also have a fine matrix of other proteins (Stage I melanosomes)
- Stage II melanosomes: Melanin synthesis begins
- Stage III - Deposited and accumulated melanin
- Stage IV - No tyrosinase left and melanosome is mature and full of melanin
Activity of Tyrosinase
Converts tyrosine to DOPA which is polymerized and transformed to melanin
Melanosomes after they bud off
Keratinocytes cleave melanosomes off of melanocytes, they go to nearby keratinocytes in the spiney layer and basal layer and go close to the nucleus to shield against UV radiation
Albinism
Dysfunction in the melanocyte pathway or tyrosinase pathway causing hypopigmentation. Related to vitiligo where you lose pigmentation due to melanocyte deterioration (depigmentation)
Moles
Melanocytes proliferate in small areas. Can be indicative of cancer
Merkel Cells
Slowly adapting somatosensory cells that are found in the SB.
Allow for light touch discrimination of objects/shapes
Unencapsulated sensory receptors
Merkel Cells
Free nerve endings
root hair plexus
Where are free nerve endings
In papillary dermis and low epidermis - Good for high/low temperature, pain, itching, and also tactile
Root Hair plexus
Web of sensory fibers surrounding the bases of hair follicles in reticular dermis to detect hair movement
Encapsulated Receptors
Meissner’s Corpuscles
Lamellar/Pacinian Corpuscles
Krause End Bulbs
Ruffini Corpuscles
Meissner’s Corpuscles
Also called Tactile corpuscle. Sensitive to light touch (concentrated on the fingers, foreskin, and lips)
Located just beneath the epidermis (in the dermal papillae)
Rapidly adapting Mechanoreceptor
Pacinian Corpuscles
Also called Lamellar Corpuscles. Detect deep pressure changes and vibrations.
Very large receptor field. Located deep in the dermis.
Rapidly Adapting Mechanoreceptor
Krause Ends Bulbs
Thermoreceptors for sensing cold temperatures.
Located in the penis and clittoris (genital corpuscles) and in the eye, lips, tongue, and trunk.
Ruffini Corpuscles
Slowly adapting Mechanoreceptor
Sensitive to the stretch and torque of skin
Types of receptors
Mechanoreceptors Thermoreceptors Nociceptors Electromagnetic Receptors Chemoreceptors
Temperature control in the skin
- Constrict arterioles = constrict blood = retain heat in cold situations
- Evaporative cooling using eccrine glands
- Dilate arterioles to give off heat
Cuticle
Outermost area of the shaft. Heavily keratinized squamous cells
Medulla
Most interior of the hair shaft. Moderately keratinized
Cortex
Between the root sheath and the medulla. Heavily keratinized and densely packed
Dermal papilla
Cells produce signals that drive the growth of hair follicles (projects into the cortex)
Stages of hair growth
Anagen - Long period of mitotic division
Catagen - Brief period of arrested growth and regression of the hair bulb
Telogen - Final long period of inactivity, hair shedding
Types of glands
Exocrine Glands
Endocrine Glands
Paracrine Glands
Exocrine Glands
Dump into ducts
Types of exocrine glands
Merocrine (Eccrine)
Apocrine
Holocrine
Merocrine
Sometimes called Eccrine glands (major sweat glands of the human body). Makes granules and release chemicals
Apocrine
Granules “buds off,” taking part of the cell’s cytoplasm
Holocrine
Whole cell breaks down
Endocrine Glands
Sit on the basement membrane and dumps into the blood
NOT EXOCRINE
Paracrine Glands
Secrete signals that act on nearby cells
NOT EXOCRINE
Duct cells
Reabsorb sodium from the sweat to reduce loss of sodium
What are melanocytes derived from?
From neural crest cells (and they are found in the SB)
In the skin, what is the most superficial layer in which nuclei are present?
Stratum Granulosum
Where does lamellar body secretion occur and for what purpose?
In the Stratum Granulosum
Forms a waterproofing boundary for the skin (secretes lipids)
What purpose to desmosomes serve?
Because the epidermis is avascular, desmosomes create channels that permit the flow of nutrients and the movement of cells
What type of proteins are prevalent in the SG?
Cysteine and histidine rich proteins that bind keratin filaments together
How do basal cells, as the become keratinocytes, change to toughen the epithelium?
Cross-linking of the cytoplasmic proteins
Langerhan’s cells
Dendritic cells (APCs that endocytose antigens and transport them to the lymph nodes, initiating the immune response)
What staining would reveal Langerhan’s cells?
Antibody staining (CD1)
In a normal H&E stain, it is too hard to differentiate b/w these cells and keratinocytes
Where is the highest concentration of melanosomes in the skin?
SS for darker skin
SB for lighter skin
Degradation of melanosomes occurs faster in dark-skin or light-skin people?
Light-skin
Function of melanocytes
Melanocytes make melanin that is packages into melanosomes
Myoepithelial cells
Squeeze and force sweat through ducts (ducts reabsorb various ionic components of sweat)
Sebaceous gland
Holocrine secretion of oily material to allow for waterproofing
What makes your hair turn white?
Loss of melanocytes
Goblet cell
Unicellular, merocrine gland that secretes mucus
What type of gland is the thyroid?
Endocrine (b/c it does not have any ducts)
Which organs have both exocrine and endocrine components
Liver and pancreas
What cell types are prevalent in keratinocytes
Keratinocytes consists mainly have keratinized stratified squamous epithelium
Is the number of melanocytes b/w sexes equal?
Yes, however, the distribution of melanin IS NOT
What stimulates melanin production?
- Sun exposure
- MSH
- ACTH
- Estrogen
- Progesterone
Arrector pili
Small muscles attached to hair follicles that cause hair to stand on end (goose bumps)
Sebum
The oily/waxy matter produced by sebaceous glands to lubricate and waterproof the skin
Arteriovenous anastomoses
Connection b/w and artery and a vein
