SM: Week 2 Flashcards
What are some characteristics of fungi?
- eukaryotic organisms
- have cell wall for protection
- ergosterol is dominant membrane sterol
- require preformed organic compounds for growth (heterotrophic)
- comes in three different forms: yeast, mold, dimorphic
- forms spores which can be used to identify the source of fungi
What are some features of yeast?
- single celled fungi
- reproduce through budding (blastoconidia) – if the bud remains it forms pseudohyphae
What are some features of mold?
- multicellular
- grows in forms called hyphae
- many produce cross walls of hyphae called septae
- nonseptate hyphae do not exist
- masses called mycelia
What are some features of dimorphic fungi?
- exist as yeast in the body, mold in the environment
What are some different fungal spores?
- conidia (asexual spores of mold)
- arthroconidia (formed from joints in hyphae then fragmentation)
- blastoconidia (yeast cell buds)
- haustoria (hyphae on parasitic fungi)
o Spores are used to identify the source of the infectious fungi
Polyenes: Amphortericin B and Nystatin
- mechanism, spectrum, distribution, toxicity
Fungicidal
o Mechanism: binds ergosterol, creates holes in membrane which allows leakage of electrolytes
o Spectrum: broad, used for invasive systemic fungal infections (meningitis) in immunocompromised patients, active against yeast and mold
o Distribution: long tissue half-life, liposomal form can cross BBB, small fraction is excreted
o Toxicity: 80% nephrotoxicity!!!! toxic because binds cholesterol, nystatin is toxic systemically – topical use only
Azoles: Fluconazole, Itraconazole, Ketoconazole
- mechanism, spectrum, distribution, toxicity, resistance
Fungistatic
o Mechanism: binds fungal P-450 enzyme (Erg11) – blocks production of ergosterol
o Spectrum: widely used, spectrum varies
o Distribution: orally available, efflux pump in brain
o Toxicity: drug-drug interactions, hepatotoxicity, nephrotoxicity, alters hormone synthesis (AVOID DURING PREGNANCY!)
o Resistance: altered cytochrome P-450
Allylamines: Terbinafine (Lamisil)
- mechanism, spectrum, toxicity, resistance
Fungicidal
o Mechanism: inhibits squalene epoxidase –> toxic accumulation of squalene
o Spectrum: dermatophytes
o Toxicity: topical drug interactions with CYP2D6 substrates
o Resistance: rare human pathogens, mutant binding site, efflux transporters
Flucytosine (5-FU)
- mechanism, spectrum, distribution, toxicity, resistance
Fungistatic
o Mechanism: antimetabolite, selectively taken up, converts to 5-FU in fungi; interferes with DNA/RNA synthesis
o Spectrum: narrow – yeast forms of candida albicans and cryptococcus
o Distribution: oral, penetrates CNS
o Toxicity: only partially selective for yeast, leads to bone marrow suppression
o Resistance: cotreat with amphotericin B to increase uptake and minimize resistance
Griseofulvin
- mechanism, spectrum, distribution, toxicity, resistance
Fungistatic
o Mechanism: binds to microtubules and inhibits spindle formation –> multinucleate cells
o Spectrum: dermatophytes (greater uptake)
o Distribution: lipids increase oral absorption, concentrates in dead keratinized layer of skin
o Toxicity: teratogenic
o Resistance: change to beta-tubulin
Echinocandins: caspofungin
- mechanism, spectrum, distribution, toxicity, resistance
Fungicidal (candida), Fungistatic (aspergillus)
o Mechanism: cell wall inhibitor – block synthesis of beta (1,3)-d-glucan (polysaccharide)
o Spectrum: candida albicans, systemic
o Distribution: IV, large molecular wt prohibits CNS penetration
o Toxicity: limited, fever, rash at site of injection
o Resistance: unknown (new drug)
There are two types of cutaneous fungal infections. What are these?
- tinea versicolor (pityrosporium versicolor)
- dermatophytes
What are the diagnostics used in fungal skin infections?
- collect skin, nail, or hair
- 10% KOH, can add stain
- view under microscope
- Wood’s lamp (UV-A light), cause some fungi to fluoresce
- PCR
- culture (some use Sabouraud’s agar)
What is the causative agent of tinea versicolor and what are some characteristics of this fungus?
Malassezia furfur
- is a yeast that is part of the normal flora
- converts to mold in disease (dimorphic)
- requires lipids, primarily found in sebaceous glands in young individuals (15-24 yo)
- associated with seborrheic dermatitis, cradle cap
What are some diagnostic findings for tinea versicolor and what is the effective treatment of this fungus?
- Diagnosis:
o KOH
o Wood’s lamp – yellow-green
o culture requires olive oil
o skin scrapping – “spaghetti and meatballs” - Treatment:
o topical therapy = selenium sulfide or ketoconazole shampoo; reoccurrence is common
What is the pathogenesis, diagnosis, and treatment of dermatophytes?
- Pathogenesis: monomorphic molds enter through breaks in the skin and secrete proteases and keratinases; grow best at 25C, unable to survive at 37C – remain in the skin
- Diagnosis: KOH test, grow on Sabouraud’s agar
- Treatment: topical griseofulvin, terbinafine, itraconazole
Note: dermatophytes require keratin to grow so restricted to hair, nails, and superficial skin
What are the three different causative agents of dermatophytes?
- trichophyton rubrum (tinea pedis)
- microsporum canis/fulvum (hair and skin)
- epidermophyton floccosum
What fungus causes subcutaneous infections?
sporothrix schenckii (dimorphic) – “rose gardener’s disease”
What is the pathogenesis, diagnosis, and treatment of sporothrix schenckii?
- Pathogenesis: fungi spread from initial lesion through lymphatics and form nodular lesions; can spread to bone and joints
- Diagnosis: biopsy of lymph node, culture in Sabouraud agar containing antibiotics, grow at different temps to confirm dimorphism
- Treatment: oral itraconazole for 3-6 months
What fungus causes an opportunistic infection?
candida albicans
What is the pathogenesis, diagnosis, and treatment of candida albicans?
- Pathogenesis: seed in areas with less normal flora, chronic mucocutaneous candidiasis may suggest individual has T-cell dysfunction, may be a sign of diabetes (poor circulation)
- Diagnosis: based on clinical appearance, can do skin scrapping
- Treatment: keep skin dry, clotrimazole or other azole cream
Where are common sites to see candida albicans infections?
- superficial infections – diaper dermatitis (skin folds and around anus)
- corners of mouth (anagular cheilitis)
- toenail or edge of nails (paronychia)
- oropharyngeal (thrush)
- vaginal and systemic infections (binds to mucosa)
Within the visceral nervous system, where are the cell bodies of afferent sensory neurons located?
- cell bodies are located in the DRG (pseudounipolar)
Within the ANS, where are the cell bodies of the efferent motor neurons located?
Two neuron system:
- preganglion - located within gray matter in brainstem or spinal cord (CNS)
- postganglion - located in peripheral motor (autonomic) ganglia (PNS)
o can be either parasympathetic or sympathetic
Recount the steps from the sympathetic preganglionic neuron from its cell body to the sympathetic chain.
- Preganglionic cell body found in the intermediolateral cell column (lateral horn) within the spinal cord (multipolar neurons)
- axons go out the ventral root to the spinal nerve and continue to the ventral ramus and pass through the white communicating ramus to either synapse on:
o paravertebral ganglia (sympathetic chain ganglia)
o prevertebral ganglia, by passing through the sympathetic chain ganglia
What are the four options for a sympathetic preganglionic neuron to travel once its entered the sympathetic chain?
- ascend within the chain
- descend within the chain
- synapse once enter chain (at same level as entered)
- pass through chain to form the splanchnic nerves, then synapse on the prevertebral ganglia
What spinal cord segments give rise to sympathetic preganglionic neurons and where are the cell bodies of the neurons located?
- T1- L2 (location of intermediolateral cell column, aka lateral horn)
- this is the location of the preganglionic cell bodies
Where will the preganglionic sympathetic neurons terminate?
- paravertebral ganglia (sympathetic chain)
2. prevertebral ganglia (celiac, superior/inferior mesenteric ganglia)
How do the postganglionic sympathetic neurons reach their destinations: spinal nerves, heart/lungs, head, other thoracic structures?
- Spinal nerves/other visceral organs: gray communicating rami
- Heart/lungs: cardiopulmonary nerves (cell bodies within the middle/inferior cervical paravertebral ganglia/upper 5 thoracic paravertebral ganglia)
- Head: cephalic arterial rami, aka periarterial sympathetic plexus
How is the adrenal medulla innervated with sympathetic innervation?
- preganglionic nerve via splanchnic nerves
- the cells of the adrenal medulla act as cell bodies of the postganglionic neurons
o release norepinephrine into the vascular system
o causes system-wide sympathetic response as opposed to sympathetic innervation of specific cells
What cranial and spinal nerves are involved in the parasympathetic nervous system?
Cranial: CN III, VII, IX, and X
Sacral: S2,3,4
What are the preganglionic and postganglionic neurotransmitters/receptors and cell body locations for the sympathetic division of the ANS?
-Pre: cell body found in intermediolateral cell column (lateral horn)
o Neuro/receptor: ACh (nicotinic receptors)
- Post: cell body found in paravertebral or prevertebral ganglia
o Neuro/receptor: NE, E, sometimes ACh
• NE (a1, a2, B1, receptors)
• E (B2 receptors)
What are the excitatory and inhibitory receptors between a1, a2, B1, and B2 receptors?
- excitatory = a1, B1
* inihibitory = a2, B2
What are the preganglionic and postganglionic neurotransmitters/receptors and cell body locations for the parasympathetic division of the ANS?
- Pre: cell bodies found in the brainstem or sacral spinal cord
o Cranial: CN III, VII, IX, and X
o Sacral: S2,3,4
• Neuro/receptor: ACh (nicotinic) - Post: cell bodies found in CN III, VII, IX
o Neuro/receptor: ACh (muscarinic)
Compare and contrast the visceral and somatic sensory fibers in regards to cell body location and function of the fibers.
Cell bodies located in DRG (pseuodunipolar)
- Visceral: peripheral process located by organ it is sensing (GI tract, smooth muscle, gland)
- Somatic: peripheral process located in skeletal muscle, skin
What are some different types of skin ulcers?
- pressure
- venous
- arterial
- neurotrophic
- special: pyoderma gangrenosum, cancer
What are the different stages of pressure ulcers?
- Stage I: non-blanchable erythema.
- Stage II: like an unroofed blister, dermis exposed.
- Stage III: exposed subdermal tissues, note undermined edges.
- Stage IV: exposed tendon or bone.
- Unstageable: any wound with unobservable base due to eschar, exudate
How are pressure ulcers treated?
- manage tissue loads (zero tolerance for pressure on wound)
- manage bacterial colonization/infection (cleanse and debride wound, antibiotic?)
- nutritional support (increase protein intake)
- local wound care (cleanse, debride, avoid antiseptics – kill fibroblasts)
Wound care corresponds to the stage of the ulcer. What is the appropriate care for stage I ulcers?
o I: cleanse with non-drying soap and water, don’t apply dressings
Wound care corresponds to the stage of the ulcer. What is the appropriate care for stage II ulcers?
o II: cleanse with saline, dress with polyurethane film, hydrocolloid wafer
- Goal = provide environment conducive to granulation of tissue; keep surrounding skin dry
Wound care corresponds to the stage of the ulcer. What is the appropriate care for stage III ulcers?
o III: debridement if eschar or slough present; cleanse with saline; dress with hydrocolloid, alginate, or hydrogel
- Goal = debride necrotic tissue and protect granulation tissue
Wound care corresponds to the stage of the ulcer. What is the appropriate care for stage IV ulcers?
o IV: same as stage III
- Odor can be a problem: apply metronidazole gel, activated charcoal
- Osteomyelitis is main issue for non-healing
- Operative repair could be considered; skin grafts used sometimes
What are some causes of pressure ulcers?
- Occult fracture (hip, vertebral)
- Stroke
- Metabolic problem: hyponatremia, hyperosmolar, uremia
- Medications: sedative, anticholinergic, steroid
Where are venous ulcers commonly found and why? What do venous ulcers look like?
They are typically seen in the medial malleolus due to the distribution of the saphenous vein.
The skin appears dark brown due to hemosiderin deposits, is edematous (tender to palpation), and will not diurese (drain).
What are the two venous systems in the leg?
- Deep system (high pressure) – clots arising here are known as deep venous thrombosis (DVT), pose a risk for pulmonary embolism (PE)
- Superficial system (low pressure) – protected from high pressure system due to valves in deep veins and perforators
• Connected by perforator veins
What are some risk factors for venous ulcers?
- Overload: CHF, obesity
- Obstruction: clot, tumor
- Pump malfunction: inactivity, neurological disease/injury
How are venous ulcers treated?
- same debridement and cleansing regimens as pressure ulcers
- control of edema is essential:
o restore venous return by external pressure (30-40 mmHg in the ankle)
• “TED” socks (provide ~18 mmHg)
• Unna boot
• commpression hose/pumps
What is the appearance and location of arterial ulcers?
- Appearance: circumscribed, “punched out” ulcers, often multiple
- Location: in well perfused areas: lateral malleolus, tibial, feet/toes
What are some features of arterial ulcers?
- Claudication is a major sign – reduced blood flow to leg, results as cramping pain; decreased pain upon sitting/rest
o may precede leg ulcer by months/years - Ulcerations at end-branch arteries most likely due to arterial ischema
o Look for these signs: hair loss, absent pulses, Hx of hypertension, cigarette smoking, diabetes, or vascular disease (MI, abdominal aortic aneurysm)
What test is used to determine if the wound is an arterial ulcer? Describe what the findings out be.
Ankle-brachial Index (ABI):
- normal = 1.0 or above
- ABI below 0.8 causes claudication
- ABI below 0.4 causes rest pain
o How to measure: the dorsalis pedis systolic BP divided by systolic pressure at brachial artery
o Note: ABI can also predict arteriosclerosis in pts and causes an increased risk of arteriosclerosis in coronary and cerebral arteries, thus pts often succumb to MI or strokes rather than complications of leg ischemia
What is the causation, location, and treatment of Buerger’s disease (thrombangiitis obliterans)?
- often seen in young smokers
- found in the hands and feet; associated with thrombophlebitis
- Tx: STOP SMOKING!!!!!
o fail to stop –> 43% result in amputation
o stop smoking –> 6% result in amputation
What are some differentiating features of Buerger’s disease compared to atherosclerotic arterial ulcers?
In Buerger’s disease:
- both have venous and arterial involvement
- more diffuse involvement of upper and lower extremities