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Usmle > Block 26 > Flashcards

Block 26 Flashcards

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USMLE® Step 1 flashcards
1
Q

Stop codons

A

-they function only to stop translation, they dont add amino acid to polypeptide chain.

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2
Q

Bacillus anthracis

A
  • woolsorters disease: spores of b.antracis are very small once they are inhaled they enter the alveoli and are ingested by macrophages. From the lung the organism rapidly move to mediastinal lymph nodes and cause hemorrhagic mediastinitis.
  • once the spores germinate into vegetative cells they will begin to produce the three part anthrax toxin and clinical symptoms will rapidly follow.
  • B.anthrax virulant factor is poly D antiphagocytic capsule.
  • they form long chain that are described as medusa heads.
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3
Q

Telomerase function

A

Is to prevent chromosomal shortening,

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4
Q

S-100 immunoreactivity in brain tumors is found in

A
  • schwanoma ( tumors of the peripheral nervous system that arise from schwan cells, microscopically they appear biphasic with highly cellular areas.
  • microscopically they appear biphasic with highly cellular areas (antonini A pattern), with myxoid regions of low cellularity (antoni B pattern), that forms palisading atterns with interspersing nuclear free zones called verocay bodies.
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5
Q

MCCune albright syndrome

A

Pathogenesis:

  • mosaic somatic mutation in the GNAS gene encoding the stimulatory a subunit of the G protein
  • constitutive activation of adenylate cyclase leads to overproduction of several hormones

Clinical features:

  1. Cafe au lait(hyperpegmented macules)
  2. Endocrine abnormalities(precocious puberty, hyperthyrodism)
  3. Fibrous dysplasia( multiple osteolytic appearing lesion of the hip and pelvis)(increased risk for pathological fractures)(increased secretion of IL-6 and activation of osteoclasts).
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6
Q

Legg clave perthes disease

A

Young children that results in isolated idiopathic osteonecrosis of the hip

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7
Q

Essential tremor

A
  • the most commonly diagnosed movement disorder
  • also referred as familial tremor as its often follows autosomal dominant inheritance
  • positive family history is essential for diagnosis sometimes
  • patients symptoms improve with alcohol classicaly
  • treatment is propronalol as first line
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8
Q

Hb C disease

A

Missense mutation

- glutamate residues (negatively charged) is replaced with (lysine) positively charged.

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9
Q

Glucokinase (gestational diabetes)

A
  • glucokinase has a lower glucose affinity than other hexokinases, this allows it to function as a glucose sensor in beta cells by varying the rate of glucose entry into the glycolytic pathway based on blood glucose levels.
  • heterozygous mutations of the glucokinase gene cause a decrease in beta cell metabolism of glucose, less ATP formation and diminished insulin secretion.
  • this produces a type of maturity onset diabetes of the young, which is charactrized by mild, nonprogressive hyperglycemia that often worsens with pregnancy induced insulin resistance.
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10
Q

Mutation in factor V gene

A
  • normal PTT even in the presence of activated protein C
  • factor Va resistance to inactivation by activated protein C —> hyper-coagulability.
  • factor V leiden mutation and mutation in the prothrombin gene are the most common inherited causes of hyper coagulability.
  • usually present with multiple DVT, PE , with a normal PTT
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11
Q

EBV

A
  • kissing disease
  • fever, profound fatigue
  • lymphadenopathy and lymphocytosis with atypical lymphocytes
  • slpenomegaly
  • myalgia may be presenmt
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12
Q

The vascular endothelium vasodilation mediation

A
  • its mediated by actylcholine, bradykinin, serotonin, substance P and shear force.
  • these stimuli active specific membrane receptors present on endothelial cells, leading to increase in cytosolic calcium levels.
  • this cause activation of endothelial nitric oxide synthase which synthesizes NO from arginine, NADPH and O2
  • NO then diffuse into adjacent smooth muscle cells—> activates cGMP —> relaxation of smooth muscles.
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13
Q

Amino acid derivatives

A
  1. Phenylanine —> tyrosine

2. Tryptophan —

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14
Q

Cavernous sinus thrombosis

A
  • commonly due to contigous spread of an infection from the medial third of the face, sinuses or teeth.
  • the infection can communicate in a retrograde fashion into the cavernous sinus through the valveless facial venous system.
  • common pathogens include S.aureus, streptococci and rarely fungal.
  • clinically , diplopia, fever, headache, ocular muscle paralysis due to injury of cranial nerve III, IV, and VI.
  • loss of afferent corneal reflex, chemosis and proptosis may also be evident due to impaired venous drainage through ophthalmic veins.
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15
Q

EBV increase risk of malignancy for

A
  • burkitt lymphoma
  • nasopharyngeal carcinoma
  • CNSL in HIV
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16
Q

Neurophysins

A

Carrier protein for oxytocin and vasopressin hormones produced within paraventricular and supraoptic nuclei, respictevely and released from the posterior pituitary.
- neurophysins are produced within the neuronal cell bodies of hypothalamic nuclei. They bind oxytocin and vasopressin and acts as chaperone molecules as they are shuttled towards the nerve terminals in the posterior pituitary.

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17
Q

Ankylosing spondylitis clinical

A
  • low back pain ( onset <40 y.o, insidious onset, improves with exercise but not with rest and pain at night)
  • hip and buttock pain
  • limited chest expansion and spinal mobility
  • enthesitis (inflammation at the site of insertion of a tendon to the bone)
  • systemic symptoms (fever, chills, fatigue ,weight loss)
  • acute anterior uveitis.( unilateral pain, photophobia and blurry vision)
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18
Q

Half life in first order kinetics

A

-in first order kinetics drugs, the steady state concentration os reached in 4 to 5 half lives, thus it would take apprximately 40 hours or four times of half life of 10 hours for the drug that have a half life of 10 hours to reach approximately 95% steady state concentration.

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19
Q

In case of hypoparathyroidism what is the treatment

A

Calcitriol (not calcidiol because conversion of calcidiol to calciterol depends on PTH )

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20
Q

Cinacalcet

A

Is calcimimetic that allosterically activates calcium sensing receptor in PT gland, decreasing PTH release.
-its used in secondary hypoerparathyrodism in dialysis patients

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21
Q

What is the diagnostic test for N.gonnorrhea

A

Nucleic acid amplification testing (NAAT ) is the diagnostic test of choice for gonnorrhea.

  • urethral gram stain and culture can also be obtained for diagnosis and determination of antibiotic sensitivities.
  • Tx of choice is ceftriaxone and azithromycin(because of high chances of chlamydia coinfection)
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22
Q

BestThrombin inhibitor

A

-unfractioned heparin due to the fact that it inhibits both thrombin and factor Xa

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23
Q

Aspiration syndromes

A

1.Pneumonia : lung parynchema infection, aspiration of upperairway or stomach microbes
Clinically present days after aspiration with cough, increased sputum, CXR infiltrates in depndent lung segment and can progress to abscess.
2. Pneumonitis : lung parynchema inflammation, due to aspiration of gastric acid with direct tissue injury.
-it presents hours after aspiration event, ranges from no symptoms to nonproductive cough, decreased O2 and respiratory distress.
-CXR infiltrates resolves without antibiotics.

24
Q

What is the cause of insulin resistance in DM 2

A

-chronic elevation in free fatty acid is a result of increased lipolysis contribute to insulin resistance by impairing insulin dependent glucose uptake and increasing hepatic gluconeogenesis.

25
Q

Idiopathic intracranial hypertension (pseudotumor cereberi)effect on retina

A
  • the condition usually occur in obese women with daily headache, bilaterally symmetric papilledema and transient visual disturbances related to impaired cerberal venous outglow and elevated intracranial pressure.
  • symptoms characterstically worsens during valsalva as intracranial pressure increases.
  • increased intracranial pressure is transmitted through the cereberospinal fluid in the subarachinoid space, which is contineous with optic nerve sheath,
  • the buildup of pressure compresses the optic nerves externally which in turn impairs axoplasmic flow within the optic nerves causing bilateral papilledema.
26
Q

Greater saphenous vein extraction for CABG

A

-its done inferolaterally to the pubic tubercle .

27
Q

Lightening related complication

A
  1. Cardiac : cardiac arrest, arrythmias
  2. Neurologic: seziures, confusion, respiratory arrest
  3. Dermatologic: lichtenberg figures, burns
  4. Msucolskeletal : rhabdomylesis, bone fractures, compartment syndrome
  5. Tympanic membrane rupture, curling ulcers and cataracts
28
Q

Cocaine intoxication signs and symptoms

A
  1. Euphoria
  2. Agitation and psychosis
  3. Chest pain
  4. Seziures
  5. Tachycardia
    6, hypertenstion
  6. Mydriasis
29
Q

Cocaine mechanism of action

A
  1. Cocaine inhibits presynaptic reuptake of monamines resulting in symphatetic stimulation and CNS activation .
  2. Its also potent vasocnostrictor that can promote myocardial ischemia by causing coronary artery vasospasm and increased platelet aggregation.
  3. When its used intranasally it can cause nasal mucosal atrophy and nasal septal perforation
30
Q

Tomaxifen side effects

A
  1. Hot flushes
  2. Venous thromboembolism
  3. Endometrial hyperplasia and carcinoma.
31
Q

Chrons disease predisposition for gallstones

A

Increases bile acid wasting

32
Q

Major risk factors for sephageal cancer

A 
Esophagela SCC:
1. Alcohol use
2. Tobacco smoking
3. Consumption of N-nitroso containing food 
Esophageal adenocarcinoma: 
1. Barrets 
2. GERD
3. Obesity
4. Tobacco use.
33
Q

Bisphosphonate mechanism of action

A
  • inhibits mature osteoclast mediated bone resorption.
  • bisphosphonate have a chemical structure similar to pyrophosphate and attach to hydoxyapatite binding sites on bony surfaces.
  • osteoclast that resorb the bone take up the bisphosphonate and are unable to adhere to more bony surface to continue resorption.
  • bisphosphonates decrease osteoclast activity, induce osteoclast apoptosis and decrease development and recruitment of osteoclast precursor cells, the net results os to slow the rate of bone loss and some patients may experience a small increase in bone mineral density.
34
Q

Ulnar nerve injury

A

-the nerve enters the wrist between the hook of the hamate and pisiform bone in a fibroosseous tunnel known as guyons canal, here it divides into a superfacial branch that provides sensation over the medial 1/ 1/2 digits and hypothenear eminence

Injury leads to :

  1. Hypothenear atrophy
  2. Fifth digit sensation loss
  3. Ulnar claw during extension
  4. Weakness of the lumbricals
35
Q

Failure of obliteration of omphalomesenteric duct is seen in

A

Meckels diverticulum

36
Q

Fusion of the ventral and dorsal pancreatic buds defect leads to

A
  • pancreatic divisum
37
Q

Midgut rotation around the SMA

A

Can result in midgut malrotation.
Cecum rests in the right upper quadrant instead of the right lower quadrant, additionally ladds fibrous bands connect the retroperotonium in the RLQ to the right colon/cecun by passing over the second part of the duodenum, causing intestinal obstruction in the process.
-because the mesenteric base is narrowed the messentery is vaulnrable to twist around SMA

38
Q

Cell junctions

A

Type of junction Proteins used. Function
1. Gap junction Connexin. Intracellular communication.
2. Tight junction. Claudins, occludinn (paracellular barrier
3. Adherens junction. Cahedrins
4. Desmosomes. “. “. “. “”
5. Hemidesmosomes. Integrins
3,4, and 5 all used un cellular anchoring

39
Q

Diffuse esophageal spasm

A
  • stimulated by esophageal distension from a fodd bolus, the contraction originate above the site of distension and propel the bolus downward in a coordinated fashion . In DES several segments of the esophagus contract inappropriately at the same time which apperas disorganized non perstaltic contractions on esophageal manometry and corckscrew esophagus.
  • patients frequently have intermittent sold liquid dysphagia, chest pain heart burn and food regurgitation.
  • DES involves impaired inhibitory neurotransmission within esophageal myenteric plexus.
40
Q

Tertiary syphilis

A

-it begins with vasa vasorum endarteritis and obliteration, resulting in inflammation, ischemia, and weakening of the adventitia. Aneurysmal dilation of the thoracic aorta results and can extend to involve the aortic valve ring.

41
Q

Minimal change disease is

A

The most common cause of nephrotic syndrome in young children

  • and often occurs after an inciting event such as upepr respiratory tract infection, bee sting or immunization.
  • systemic T cell dysfunction leads to the production of glomerular permeability factor, a cytokine that damages podocytes and decrease the anionic properties of the GBM.
  • loss of negative charge results in selective loss of albumin in the urine which causes hypoalbuminemia and edema.
  • EM shows effacement of foot processes and fusioin.
42
Q

What is found primarily in the sciatic foramen

A

Its a major pathway for pelvic neurovascular structure to the lower limbs.

  • its divided into greater sciatic foramen and lesser sciatic foramen divided by sacrospinous ligament.
  • the periformis occupies most of the space of greater sciatic foramen, running above it include the superior gluteal vessels and superior gluteal nerve.
  • below the piriformis include the inferior gluteal vessels, internal pudendal vessels, and multiple nerves. (Piriformis syndrome).
43
Q

What is the difference between conjugate vaccine and polysacharide vaccine

A
  • conjugate pneumococcal vaccine induce more robust immune response through B and T cell activation .
  • on the other hand polysaccharide vaccine protects against wider range of serotypes.
  • the 13- valent pneumococcal conjugate vaccine contains nontoxic diphtheria protein conjugated to the polysaccharides that boosts the immune response through T cell recruitment.
44
Q

PRPP synthetase gene mutation leads to

A

Gout.

Increased levels of PRPP is charactrized by accumulation of uric acid leading to hyperurecmia and hyperuricosuria.

45
Q

Gout- cells responsible for intense inflammatory response

A

Neutrophils. —> phagocytosis of urate crystals by neutrophils —> release of various cytokines and inflammatory mediators that lead to further neutrophils activation and chemotaxis, resulting in a positive feedback loop that amplifies the inflammatory response .

46
Q

Colchecine effect on neutrophils

A

Impairs neutrophils migration and phagocytosis by interfering with microtubule formation. Colchecine also decreases tyrosine phosphorylation in response to monosodium urate crystals, resulting in decreased neutrophil activation.

47
Q

Skin rash the worsen with sun exposure

A

Pellagra

  1. Dermatitis : bilateral, symmetric on sun exposed areas of the body and is charactrized by rough thick scaly skin
  2. Diarrhea is due to atrophy of coulmnar epithelium of the GI tract
  3. Demantia is due to neuronal degeneration in the brain and spinal cord, with lesions similar to thoses associated with pernicious anemia.
    - pellagra can be seen in nutritional intake impairment
    - it can be also seen in carcinoid syndrome, prolonged isoniazid therapy or hartnup disease.
48
Q

Niacin source and essential component of the coenzyme

A

Niacin can be obtained through dietary intake or synthesized endogenously from tryptophan.
- niacin is essential component for NAD.

49
Q

HCM murmur causes

A

-its charactrized by assymetric ventricular septal hypertrophy and variable dynamic left ventricular outflow tract obstruction. Systolic anterior motion of the mitral valve toward the IV septum can cause eccentric mitral regurgitation and exacerbate LVOT obstruction.

50
Q 
Caspofunugin 
Nystatin
Triazoles
And flucocytosine 
Terbinafine
A
  1. Caspofunigin : inhibit synthesis of glucan, component of fungal cell wall.
  2. Nystatin and amphotericin B, binds to ergosterol molecules in the fungal cell membrane creating pores and causing cell lysis
  3. Triazoles: inhibit the synthesis of ergosterol
  4. Flucocytosine: it interferes with fungal cell RNA and protein synthesis .
  5. Terbinafine: inhibit squalene epoxide
51
Q

Insulin and proinsulin formation

A
  • insulin MRNA codes for preproinsulin —> translation in RER to proinsulin.
  • proinsulin —> changes —> golgi —> secretory granules.
  • endopeptidases in the secretory granules cleaves proinsulin into insulin an C peptide, which are then stored within granules until they are secreted from the cell via exocytosis
52
Q

Clostridium perfringens

A
  • gram positive bacillus responsible for 95%. Of cases of gas gangrene(clostridial myonecrosis), are abundant in soil n can inoculate penetrating injury sites.
  • on entering the host, the spores germinate in the anaerobic envirnoment into vegetative cells which produce a phospholipase toxin that attacks cell membranes.
  • it can also cause late onset food poisoning that is charactrized by transient watery diarrhea, spores germinate in digestive tract then begins to elaborate toxin
53
Q

Glossopharyngeal injury will result in

A
  1. Loss of gag reflex
  2. Loss of general sensation in the upper pharynx, posterior tongue, tonsils and middle ear cavity and loss of taste sensation of the posterior third of the tongue.
54
Q

Niacin side effects

A
  • niacin improves hyperlipidemia by decreasing hepatic synthesis of triglycerides and VLDL and reducing clearance of HDL. Its the most effective agent for raising HDL levels.
  • side effects includes flushing
  • hyperglycemia and hepatotoxicity
  • decrease renal excertion of uric acid leading to elevated blood levels and increased risk for acute gouty arthritis
55
Q

5a-reductase deficiency

A
  • 5a-rductase converts Testosterone to DHT.
  • there are 2 types of 5a reductase type 1 is present in postpubescent skin and type 2 found predominantley in genetalia
  • internal genatalia develops normally due to presence of testosterone while external genetalia needs DHT thus it doesnt develop proporely resulting in male pseudohermaphroditism.
  • this untill they reach puberty, when they reach puberty, high levels of testosterone and the action of 5a -reductase type 1 result in masculinization with male pattern muscle mass, voice deepening, penile and scrotal growth, and testicular descent.
56
Q

Gram positive cocci in clusters/ or in chain

A

In cluster = staphylococcus

In chain= streptococci`

57
Q

Sever combined immune deficiency

A

A life threatining immune deficiency syndrome that presents in infancy. Its caused by a variety of mutation in different genes that results in impaired T and B cell development and function.

  • this leads to comprimised cell mediated and humoral immunirty with eventual development of severe viral and bacterial infection as maternal immunity wanes (after 6 months).
  • common features include candidiasis , failure to thrive, and persistant diarrhea.
  • lab studies show very low or absent CD3+ T cells and hypogamma globulinemia.
  • thymic aplasia or hypoplasia is common.

Usmle (45 decks)

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