Week 3 Flashcards
What is the role of the AER (apical ectodermal ridge)?
It organizes the limb bud on the proximo-distal axis - limbs lengthen proximal to distal - cells further from the AER differentiate into cartilage & muscle
-It secretes FGF to stimulate the growth & development of mesenchyme
What do Homeobox genes control?
Positioning of limbs on ventrolateral body wall
What is the ZPA?
Zone of Polarizing Activity - specialized mesenchymal cells on caudal surface that respond to FGF’s and AER. ZPA expresses Shh and Shh deteremines anterior-posterior axis (thumb vs. little finger, great toe vs. baby toe)
Where does apoptosis occur in development and why?
It is programmed cell death and happens in certain areas of AER/determines locations of individual digits
What causes cutaneous fungal infections?
Malassezia (tinea versicolor), Dermatophytes = Microsporum, Epidermophyton, Trichophyton (3 major geniuses)
What is Wood’s Lamp?
UV-A light under which some fungi fluoresce
Where is tinea veriscolor usually found?
- It’s caused by Malassezia furfur which is a yeast that converts to mold during disease
- Requires lipids so it’s found predominantly in areas with lots of sebaceous glands
- Individuals 15-24 yrs old
- Tropical climates
- Hyperpigmentation common
What can cause seborrheic dermatitis, scaly (cradle cap)?
Malassezia - can be diagnosed with KOH, looks yellow-green in Wood’s lamp - looks like spaghetti & meatballs under the microscope
What is the treatment for seborrheic dermatitis (cradle cap)?
Topical: Selenium sulfide or Ketoconazole Shampoo
-Recurrence common!
How do dermatophytes invade?
They enter through breaks in the skin, secrete proteases & keratinases
- Fungal antigens cause inflammation (kerion)
- They grow best at 25deg C but are unable to survive at 37deg C so they can’t invade very deep into the tissue
How do you diagnose dermatophytes?
-KOH, grow on Sabouraud’s agar
How do you treat dermatophytes?
Topical griseofulvin, terbinafine or itraconazole - 1 month
- Oral for nail, hair infections but need to monitor for hepatotoxicity - Often reoccur
What does trichophyton rubrum cause?
It’s the most common cause of tinea pedis - looks like red circle with white in the middle
- Transfer at swimming pools
- Most common cause of tinea capitis in children
Microsporum
- Hair & skin
- Diagnosis with wood’s light - blue/green
- Spindle shape macroconida
Sporothrix schenckii
- Dimorphic & causes “rose gardener’s disease” more often due to puncture of the hand with an infected plant
- Spreads from lesion via lymphatic channels
- Usually only occurs in immunocompromised
