Official Step 1 High Yield Concepts Thread

[Transposony]

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Let's discuss our doubts/offer clarifications about mechanisms/concepts for Step 1

ASK ANY QUESTIONS here.

To kick start the thread here is something I didn't know:

1. Penicillin-binding proteins (PBPs) are actually enzymes (transpeptidases & carboxypeptidases) which cross-link peptidoglycan. Penicillins binds to these enzymes and inactivating them thereby preventing cross-linkiing of peptidoglycan.

2. Periplasmic space (Gram -ve) contain proteins which functions in cellular processes (transport, degradation, and motility). One of the enzyme is β-lactamase which degrades penicillins before they get into the cell cytoplasm.
It is also the place where toxins harmful to bacteria e.g. antibiotics are processed, before being pumped out of cells by efflux transporters (mechanism of resistance).

There are three excellent threads which you may find useful:

List of Stereotypes

Complicated Concepts Thread

USMLE images

 

[dfib slim]

Besides RBCs, which cells do not express MHC class I?

 

[aspiringmd1015]

platelets? or were the platelets the blood cells that do express mhc 1 despite being non nucleated

 

[dfib slim]

platelets? or were the platelets the blood cells that do express mhc 1 despite being non nucleated

Nope, platelets express MHC I despite being non-nucleated.

 

[seminoma]

platelets? or were the platelets the blood cells that do express mhc 1 despite being non nucleated

Just remember that platelets are blebs of megakaryocyte cytoplasm and plasma membrane. Thus anything on the megakaryocyte membrane is likely on the platelet membrane too.

I think the other cell without MHC-1 is the cytotrophoblasts?

 

[dfib slim]

Just remember that platelets are blebs of megakaryocyte cytoplasm and plasma membrane. Thus anything on the megakaryocyte membrane is likely on the platelet membrane too.

I think the other cell without MHC-1 is the cytotrophoblasts?

syncytiotrophoblast

 

[dfib slim]

Why does the tau protein become hyperphosphorylated in alzheimers leading to Neurofibrallry tangle formation

From the inflammatory response generated by the A-beta amyloid aggregation.

 

[dfib slim]

I guess I meant to say before the baby is born, give the steroids to help mature the lungs, especially for premies
http://americanpregnancy.org/labor-and-birth/premature-birth-complications/
http://www.nichd.nih.gov/health/topics/preterm/conditioninfo/Pages/reduce.aspx

Yes, but the original question was what would give a premature neonate after delivery.

 

[dfib slim]

Haha well I've never even heard of this I don't think... this is high yield? Is this in first aid ?

It's mentioned in Pathoma

 

[pathologyDO]

It's mentioned in Pathoma

OK thanks

 

[faisal 2000]

what should i know about tall like receptor ?

 

[dfib slim]

Enzyme deficiency leading to dicarboxylic aciduria?

 

[Transposony]

Neonate presents with seizures found to have low blood levels of uric acid, and high levels of sulphite, xanthine, and uric acid in urine.
Which co-factor deficiency?

 

[Transposony]

Enzyme deficiency leading to dicarboxylic aciduria?

MCAD.

 

[shibby1111]

why is lactic acidosis seen in von gierke disease, a glucose-6-phosphatase deficiency?

 

[Mr. Mojo Risin]

why is lactic acidosis seen in von gierke disease, a glucose-6-phosphatase deficiency?

Increased G6P --> pyruvate --> lactate via LDH and ALT.

 

[pathologyDO]

Phenotypic female with a genotype of 46 XY has external female genitalia but internally has undescended testes. At the age of 12 the patient begins to develop clitoromegaly. What is the enzyme deficiency?

(Hint: In the Dominican they call them "guevedoces")

 

[dfib slim]

Phenotypic female with a genotype of 46 XY has external female genitalia but internally has undescended testes. At the age of 12 the patient begins to develop clitoromegaly. What is the enzyme deficiency?

5-alpha-reductase. Now what if that patient never developed clitoromegaly but developed female secondary sexual characteristics and amenorrhea?

 

[CodeRedDew]

5-alpha-reductase. Now what if that patient never developed clitoromegaly but developed female secondary sexual characteristics and amenorrhea?

Androgen insensitivity syndrome

 

[pathologyDO]

Patient from another country comes into your hospital. Patient appears jaundiced, with increased transaminases, and a decreased PTT. The patients history is pertinent for surgery a week prior. When asked if the patient has had any recent infections, he reports that he has been healthy and has not been ill. Checking your charts you note that he is currently febrile, however.

What is the cause of this patients symptoms?

What would you expect the patients albumin levels to be?

 

[aspiringmd1015]

Breasts bc of the estrogen normally secreted by the sertoli cells and peripheral conversion, but why is there amenorrhea?

 

[aspiringmd1015]

Most common tumor in postmenopausal women is fibroids or fibroadenoma?

 

[dfib slim]

Breasts bc of the estrogen normally secreted by the sertoli cells and peripheral conversion, but why is there amenorrhea?

No uterus. The sertoli cells still make mullerian inhibiting factor.

 

[aspiringmd1015]

whats the initial cause of increased LH in PCOS?

 

[pathologyDO]

whats the initial cause of increased LH in PCOS?

Due to hyperinsulinemia or insulin insensitivity which decreases hypothalamic feedback

 

[pathologyDO]

Most common bug causing otitis media?

 

[Transposony]

Most common bug causing otitis media?

Pneumococcus.

 

[pathologyDO]

Pneumococcus.

Right, now what is the most important virulence factor for this organism?

 

[Transposony]

Right, now what is the most important virulence factor for this organism?

Capsule.

IgA protease is also an important virulence factor which is also produced by H Influenzae and Neisseria (M&G).

 

[pathologyDO]

A female patient comes in with a classic presentation of chlamydia. What is the MOA for the antibiotic you would choose to use? Major side effect?

 

[dfib slim]

Right, now what is the most important virulence factor for this organism?

What makes it bile soluble?

 

[mcloaf]

Patient from another country comes into your hospital. Patient appears jaundiced, with increased transaminases, and a decreased PTT. The patients history is pertinent for surgery a week prior. When asked if the patient has had any recent infections, he reports that he has been healthy and has not been ill. Checking your charts you note that he is currently febrile, however.

What is the cause of this patients symptoms?

What would you expect the patients albumin levels to be?

Halothane hepatitis. Not positive about albumin though, low?

 

[pathologyDO]

Halothane hepatitis. Not positive about albumin though, low?

Boom, great job.

Since this is an acute process, the albumin will actually be NORMAL -> this is because albumin has a relaively long t(1/2) of about 20 days. Only chronic hepatitis causes decreased albumin levels!

 

[pathologyDO]

What makes it bile soluble?

intracellular autolytic enzyme activated by bile?

 

[aspiringmd1015]

h

Due to hyperinsulinemia or insulin insensitivity which decreases hypothalamic feedback

hyperinsulinemia decreases hypothalmic feedback?

 

[aspiringmd1015]

Why do thecal cysts develop in hydatiform moles

 

[aspiringmd1015]

How does preeclampsia cause ARDS?

 

[dfib slim]

h

hyperinsulinemia decreases hypothalmic feedback?

Peripheral conversion of androstenedione to estrone --> positive feedback for LH secretion. Hyperinsulinemia --> decreased liver production of SHBG --> more free androgens to undergo conversion to estrogens --> increased LH.

 

[pathologyDO]

How does preeclampsia cause ARDS?

Increased BP of pulmonary vessels (HTN) + vasoactive materials increase vessel permeability -> Pulmonary edema -> ARDS

 

[aspiringmd1015]

what about the proteinuria-decreased oncotic pressure? and also normally the protein within the interstitum, dont they normally suck out water from the alveoli keeping them dry? so if you lose protein you lose those protein, and thus more liquid can get in the alveoli?

 

[aspiringmd1015]

Peripheral conversion of androstenedione to estrone --> positive feedback for LH secretion. Hyperinsulinemia --> decreased liver production of SHBG --> more free androgens to undergo conversion to estrogens --> increased LH.

also this hyperinsulinemia theory, i think its still a theory at this point. think i read that in FA

 

[aspiringmd1015]

hyperinsulinemia causes just decreases protein syntheiss of SHBG or of all proteins made by the liver?

 

[aspiringmd1015]

How does adrenal insufficiency and cushing's both cause anovulation? i figured with loss of neg feedback, but what does increased acth have an effect on Lh, fsh, or gnrh

 

[syoung]

A female patient comes in with a classic presentation of chlamydia. What is the MOA for the antibiotic you would choose to use? Major side effect?

maxrolide or tetracyclines
Tetra- photosensitivity, teratogenic, GI distress, teeth discoloration in kids
macrolide- GI motility issues, arrhythmias from QT prolongation, cholestatic hepatitis, rash, eosinophilia, inhibition of cyp450. most of these are due to erythromycin, so azithro/clarithro are better

 

[dfib slim]

First reflex to return following spinal shock?

 

[aspiringmd1015]

bladder?

 

[pathologyDO]

First reflex to return following spinal shock?

Bulbocavernosus, aka bulbospongiosus reflex

 

[aspiringmd1015]

How does progesterone inhibit endometrial hyperplasia?

 

[pathologyDO]

How does progesterone inhibit endometrial hyperplasia?

Progesterones will cause decidualization of the endometrium and have anti-estrogenic effects. Progesterone has been shown to decrease estrogen receptors on the uterus and leads to vessel constriction, causing thinning of the endometrium. (When administered as progestins for endometrial hyperplasia)

 

[pathologyDO]

Patient with no other important history other than recurrent otitis media has been recently hospitalized due to injuries sustained in a motor vehicle accident. The patient had massive hemorrhaging and blood transfusions were given. Shortly after administration of the blood product, the patient begins to develop a rash and wheezing. What is the pathophysiology causing the patients symptoms?

 

[syoung]

type ii!