Dermis and adnexal structures Flashcards
What is the dermis?
What kind of strenght does it provides?
• Structural & physiologic support network • Contains:
– blood vessels
– nerves
– appendageal structures (hair, glands, etc.)
- Provides major *tensile strength* of the skin
- Thickness varies with location
– on average 1 - 4 mm in depth
What are the two layers of the dermis?
1) Papillary dermis – upperlayer
– *thin collagen bundles
– interlockswith epidermal rete
Functions:
- increases strength
- increases surface area
2) Reticular dermis
– deepe rlayer
– thick collagen bundles
– visible elastic fibers
What are the three building block of the dermis?
Which one forms the tensile strenght?
Which one facilitates diffusion of substances?
Three “Building Blocks” of the Dermis
- Collagen – forms the tensile strength
- Elastic fibers–allow for resilience
3. Ground substance–facilitates diffusion
Basic of collagen in the skin:
What pattern with what AA does it usually have?
Which collagen is the most common?
Which collagen forms a large part of the fetal epidermis?
Which one is part of the basement membrane?
Anchorin fibrils is the role of collagen ___.
α-helical structure,
-Gly-X-Y pattern • X = proline, Y = hydroxyproline
• >25 types synthesized by the body
• A few are of particular relevance:
– Collagen I = >85 wt.% of adult dermis
– Collagen III = large part of fetal dermis
– Collagen IV = “basement membrane zone” –
Collagen VII = **anchoring fibrils*
Collagen production:
Procollagen is synthesized where?
Cross-linking of procollagen depends upon_______.
- PROcollagen is synthesized within fibroblasts
- Excreted extracellularly
- Cleaved enzymatically into TROPOcollagen
- Tropocollagen aggregates, becomes cross-linked
- Cross-linking dependent upon vitamin C (co-factor).
What is scurvy?
Due to deficiency in________.
How long does it take to show up after deficiency?
Scurvy is an acquired disease, not congenital.
–> Vitamin C is a required co-factor in collagen synthesis.
-Deficiency results in decreased mature collagen
Signs and symptoms 1-3 mos. after deprivation
Key Findings:
– keratotic plugging of hairs
– perifollicular hemorrhage
– “corkscrew” hairs
– hemorrhagic gingivitis
Also weakness, delayed healing.
Ehler-Danlos Syndrome
Congenital
What are 4 findings characteristics of this syndrome?
A family of disorders based upon erroneous collagen synthesis
• Mutations at various stages of collagen production yield findings such as
– hyperextensible skin
– hyperextensible joints
– fragile blood vessels
– poor wound healing
Ehler-Danlos Syndrome
Which one is caused by a defect in collagen V and is characterized by hypermobility, joint laxity, absent frenula, molluscoid tumors, hernias?
Which one is caused by defective collagen III and is characterized by arterial, uterine, intestinal rupture, atrophic scars, limited lifespan?
Which one is due to a defect in collagen I and is characterized by congenital hip dislocation severe hypermobility, skin fragility, atrophic scarring?
Classification schema
Classical
Vascular
Arthrochalasia
Ehler-Danlos Syndrome
Absence of what also characterizes EDS?
Absence of the **inferior labial and lingual frenula in Ehlers-Danlos syndrome.
Elastic fibers
**Minor constituent of dermis, provides resiliency
- Thin fibers (1-3 um)
- Intertwined among collagen bundles
• Special stains are required to visualize (VVG=Verhoff Van giesof)
Solar Elastosis –
An Acquired Disorder of Elastic Fibers
Sun-damaged elastic fibers
Basophilic (blue) material within superficial dermis
**HISTOLOGICCLUE UNDER MICROSCOPE**
Indicates tissue is from older person in a sun-exposed site
Pseudoxanthoma Elasticum
Results in _______.
Arterial rupture seen particularly in the ____.
Caused by a mutation in MDR gene
• Net result - calcified, brittle elastic fibers •
Disease is associated with:
– “plucked chicken” skin
– systemic hypertenision
– angioid streaks in the retina
– arterial rupture (particularly in the eye)
Ground Substance
What are the two main glycosaminoglycans?
“Pie filing” of the dermis
• Protein-sugar moieties
– absorb 10,000x their weight in water:
– hyaluronic acid
– dermatan sulphate
• “Glued” together with fibronectins
• Gelatinous mass that functions as a sponge
Blood Vessels of the Dermis
Do the epidermis contains vasculature?
Epidermis contains NO vasculature!
- Depends entirely on the dermis for nutritional support via diffusion.
- Skin vessels considered as two plexi
– superficial plexus
– deep plexus
What are some disorders of capillary loops?
–>Dilated, tortuous capillaries are noted in diseases with increased epidermal turnover.
Inflammation of Capillaries and Venules Causes Vasculitis:
Immune complexes from:
– drug hypersensitivity
– infection
– neoplastic disorders
– collagen vascular disease
***Deposit in small blood vessel walls
Type III Gel & Coombs reaction
“Palpable purpura” - combination of inflammation and hemorrhage
Nervous tissue
What are the two important types of nerve fibers to be aware of?
Which ones are heavily myelinated and conduct rapidly?
Which of the Type A fibers is the largest and is used for propioception and large motor units?
Which type A fiber carries touch?
Which type A fiber forms the spindle organs in the muscle stretch receptors?
Which type is unmyelinated and slow-conducting?
Which fiber conveys sensation of diffuse, dull, and is non-localizing and also used fot temperature and itching sensation??
Type A- heavily myelinated,–> conduct rapidly
– Type A fibers subdivided into four groups by fiber size
• Type A-α (largest) - proprioception and large motor units
- Type A-β - carries touch
- Type A-γ - **spindle organs in the muscle stretch receptors
- Type A-δ (smallest) - fast-localizing initial component of pain.
• Type C fibers -unmyelinated,slow-conducting
– convey sensation of diffuse, dull, non-localizing
– **temperature and itching sensations
What is ITCH?
Where in the skin are Meissner’s corpuscles found?
What do Meissner’s corpuscles do?
Which corpuscles have “onion-like” structures located in the dermis and are involved in pressure and vibration?
Where are pacinian corpuscles highest in density?
Meissner’s Corpuscles – “pine- cone” like structures located near DEJ, involved in fine touch, highest density on pulps of digits.
Pacinian Corpuscles – “onion” like structures located in the dermis, involved in pressure and vibration, highest density on genitals
Adnexal structures of the classical dermis:
Basics of hair
Which type of hair is fine, thin, apigmented?
Wich type of hair is dark, thick, coarse?
Hair follicle is divided into infundibulum, isthmus, and ______.
Types of hair
– Terminal hair
- dark
- thick
- coarse
– Vellus hair
- fine
- thin
- apigmented
- Hair follicle anatomy – Divided into thirds
– Infundibulum (upper third), isthmus (middle third), matrical region (lower third)
Embryonic origin of hair
upper bulge–> _____
Middle bulge–> _____
Lowe bulge–> ______
Follicular unit is derived from the PEG (“primitive ectodermal germ”)
Classic example of embryologic “induction”
–>Mesenchyme “induces” the overlying neuroectoderm
Downward bud with 3 “bulges”
– upper = apocrine gland (+/-)
– middle = *sebaceous gland
– lower = attachment arector pilori
What are the cycles of the normal scalp?
Anagen—>_________
Telogen–>_________
Catagen—>_______
Contains > 100,000 hairs
• Hairs randomly engaged in 1 of 3 cycles
– anagen (growth) – 85%
– telogen (rest) – 10-15%
– catagen (involution: transition phase between anagen and telogen) – 1-5%
• Cycles follow a “basic rule of threes”
– anagen – 3 years
– telogen – 3 months
– catagen – 3 weeks (or less)
Androgenic alopecia
Treatment of hair loss
Finasteride makes hair follicles become deeper in dermis/fat.
Sebaceous glands
Are an example of holocrine glands in that the method of secretion involved entire sebocytes (sebaceous gland cells) being secreted and in the process breaking-down to extrude the contents.
What causes acne?
Disease of pilosebaceous unit
– abnormal follicular maturation
– comedone formation (black/white heads)
– plugged follicular environment allows overgrowth of P. acnes
– P. acnes liberates FFAs and/or ruptures follicle
– later events yield dermal inflammation
