Mix5

Question 1

Characterize the relative rates of cardiac action potential in the heart from fastest to slowest:

Answer 1

Purkinje system&raquo_space; Atrial muscle&raquo_space; Ventricular muscle&raquo_space; AV node.

“Park AT Venture Avenue”
* AV nodal conduction speed is slowest (rate of .05m/sec)

Question 2

Stimulant drugs like methylphenidate and amphetamines are first line drugs in the treatment of kids with ADHD. What is their MOA?

Answer 2

They work by increasing release of NE and dopamine from their vesicular storage sites, and also function to block NE and dopamine reuptake at synapses in the prefrontal cortex.

Question 3

How would you calculate Positive likelihood ratio?

Answer 3

• likelihood of having a disease given a positive result.

PLR (+) = Sensitivity / (1-specificity)

Question 4

How would you calculate the Negative likelihood ratio?

Answer 4

• likelihood of having a disease given a negative result.

NLR (-) = (1-sensitivity)/specificity

Question 5

If there is reassortment of genomic segments when 2 or more diff versions of the virus infect the same host cell, then this would be an example of (antigenic drift/antigenic shift):

Answer 5

antigenic shift.

• This is how influenza viruses are able to undergo such rapid rates of genetic shift (due to their segmented genome).

Question 6

What role do neurophysins play in the release of oxytocin and vasopressin?

Answer 6

Neurophysins are carrier proteins for oxytocin and vasopressin, and are produced in the paraventricular and supraoptic nuclei. They bind the oxytocin and vasopressin and act as chaperone molecules as the complex is shuttled toward the nerve terminals in the posterior pituitary.

• Mutations in these proteins may be a cause of diabetes insipidus.

Question 7

Why are granulomas formed in TB infection?

Answer 7

TB causes a TH1 response involving the activation of CD4 T cells followed by an IL2 and IFN-g mediated activation of Macs and cytotoxic T cells. This immune reaction causes a “walling off” of the tuberculous foci&raquo_space; caseating granuloma made of epitheloid cells, Langhans multinucleated giant cells, fibroblasts, and collagen.

The granuloma provides the Macs with an opportunity to isolate and kill the remaining bacteria.

Question 8

What are the 4 types of common antibiotics that are implicated in causing C diff colitis?

Answer 8

Clindamycin, fluoroquinolones, penicillins, and broad spectrum cephalosporins

Question 9

What is the MOA of toxin A and B in the context of the pathogenesis of C diff infection?

Answer 9

C diff produces 2 toxins: Toxin A (enterotoxin) and Toxin B (cytotoxin). Both act synergistically. They both need to bind specific R on intestinal mucosal cells and are then internalized. Both inactivate Rho-regulatory proteins involved in actin cytoskeleton maintenance.

This causes disruption of intracellular tight junctions&raquo_space; cell rounding/retraction as well as ^ paracellular intestinal fluid secretion&raquo_space; diarrhea. Both toxins also have inflammatory effects (including neutrophil recruitment) and can induce apoptosis, furthering their effects.

Question 10

What medication would you administer in a case of hypertensive emergency in order to prevent/minimize end organ damage?

Answer 10

Fenoldopam - short acting, selective, peripheral dopamine-1 R agonist with little to no effect on alpha or beta adrenergic R.

** Dopamine-1 R stimulation&raquo_space; activation of adenylyl cyclase and raises intracellular cAMP&raquo_space; vasodilation of most arterial beds&raquo_space; drop in BP.

Question 11

What serious side effect do you need to be concerned about when you treat hyperthyroidism with thionamides instead of radioactive iodine?

Answer 11

Thionamides like methimazole and propylthiouracil can be used to treat mild hyperparathyroidism because they function by inhibiting thyroid peroxidase (causing impaired iodine organification). BUT they can cause agranulocytosis.

• Also be aware that while methimazole is used more often, it is teratogenic so moms should use PTU.

Question 12

What’s the rate limiting step in bile acid synth?

Answer 12

cholesterol 7a-hydroxylase

Question 13

How could you differentiate an aspergilloma from a cancerous growth on CXR?

Answer 13

Aspergilloma will shift when the patient changes position.

Question 14

What type of Rx would you offer as first line therapy for OCD?

Answer 14

SSRI

Question 15

What structures do you need to pass through when you perform a cricothyrotomy?

Answer 15

1. Skin
2. Superficial cervical fascia (including SubQ fat and platysma muscle).
3. Investing and pretracheal layers of the deep cervical fascia
4. Cricothyroid membrane.

Question 16

What two muscles are the primary muscles responsible for wrist extension?

Answer 16

extensor carpi radialis brevis (ECRB) and extensor digitorum.

Both connect to the lateral epicondyle as their primary attachment site. ** Overuse of these muscles can cause tennis elbow from a backhand stroke.

Question 17

What kinds of microscopic/histopathologic changes characterize the tendonitis seen in golfer’s/tennis elbow?

Answer 17

Overuse of the muscles of wrist flexion and extension can cause repetitive microtrauma of the tendons of those muscles at their attachment site and lead to angiofibroblastic tendinosis (excess fibroblasts and neovascularization). * No true inflammatory infiltrate.

Question 18

What 3 muscles are responsible for flexion of the forearm?

Answer 18

biceps brachii, brachialis, and brachioradialis

Question 19

Why does Klebsiella preferentially involve the upper lobes of the lung?

Answer 19

Klebsiella colonizes the oropharynx and gets microaspirated into the upper lobes during sleep. Since the Pt is lying down the bacteria end up in the upper lobes.

Question 20

If a patient is exposed to radioactive iodine, why would you give them potassium iodide as an antidote?

Answer 20

Energy dependent transport of organic iodide into the thyroid follicular cell (iodide trapping) is accomplished by sodium iodide symporter on the basolateral membrane of the thyroid follicular cell. Because this transporter takes up all isotopes of iodide (and other ions like perchlorate and pertechnetate), high serum levels of nonradioactive iodide can competitively inhibit the radioactive iodide from entering the thyroid follicular cell.

Large ^ in serum iodide levels also inhibit iodine organification (Wolff Chaikoff effect) and cause reduced thyroid hormone levels.

Question 21

By what mechanism does propylthiouracil contribute to the treatment of hyperthyroidism.

Answer 21

Inhibits thyroid peroxidase

• Thyroid peroxidase oxidizes iodide ions to form iodine atoms for addition on tyrosine residues on thyroglobulin in the colloid.

Question 22

What’s the MOA of rifampin in treating TB?

Answer 22

Inhibits bacterial DNA dependent RNA Pol.

Question 23

Chloramphenicol, clindamycin, linezolid, and macrolides are all protein synthesis inhibitors that act on the ___ ribosome

Answer 23

50s

Question 24

Tetracyclines, doxycycline, and aminoglycosides are all protein synthesis inhibitors that act on the ___ ribosome

Answer 24

30s

Question 25

Why would long term use of PPI (i.e. omeprazole) be assoc with ^ risk of osteoporosis?

Answer 25

PPI use can decrease Ca2+ absorption. Insoluble Ca2+ (i.e. calcium carbonate) requires an acidic environment for proper absorption and acid suppressing meds can interfere with this absorption.

Question 26

Why would anticonvulsants like phenytoin, carbamazepine, and phenobarb ^ the risk of osteoporosis?

Answer 26

They are inducers of CYP450&raquo_space; ^ Vit D catabolism and ^ PTH levels&raquo_space; elevated bone turnover and higher risk of osteoporosis.

Question 27

What’s the MOA of caspofungin in treating candida and aspergillus infections?

Answer 27

Blocks synth of the glucan component of the cell wall (caspofungin does not bind ergosterol). Caspofungin is as member of the class of echinocandin drug type.

Question 28

How does cyclosporine work in preventing transplant rejection?

Answer 28

Decreases synth of IL-2 (inhibiting T cell proliferation)

Question 29

What molecule is secreted by panc acinar cells that prevents premature trypsin activation in the pancreas?

Answer 29

SPINK-1 (serine peptidase inhibitor kazal type 1). Mutations in this can cause hereditary pancreatitis where trypsin is not susceptible to inactivating cleavage by itself (trypsin)

Question 30

What cardiac abnormality is a late sequelae of acute rheumatic fever?

Answer 30

Mitral regurg/stenosis