UWorld Exam 1 Section 2

Question 1

What vitamin B deficiency will cause neuro symptoms?

Answer 1

B12 - due to abnormal myelin

Question 2

What is the difference between folate and B12 deficiency in clinical presentation

Answer 2

Both will have hematologic abnormalities (macrocytic megaloblastic anemia with hypersegmented PMNs)

Only B12 deficiency will have neuro sx

Question 3

What is the defect in Myasthenia gravis?

Presentation?

Answer 3

Autoantibodies against post-synaptic ACh receptors

Presents with ptosis, diplopia, and weakness that worsen with muscle use

Question 4

What is the defect in Lambert-Eaton myasthenic syndrome?

Presentation?

Answer 4

Autoantibodies against presynaptic Ca2+ channels leads to decreased ACh release

Presents with proximal muscle weakness, autonomic symptoms (dry mouth, impotence)

Symptoms improve with muscle use

Question 5

What are the malignancies associated with Myasthenia gravis vs. Lambert-Eaton?

Answer 5

MG - Thymoma, thymic hyperplasa

Eaton-Lambert - Small cell lung cancer

Question 6

Are sodium levels high or low in DKA?

Answer 6

Low - hyponatremia due to sodium loss via diuresis

Question 7

What is the defect in Dandy-Walker malformation?

Answer 7

Failure of the cerebellar vermis to develop leading to cystic dilation of the 4th ventricle

Question 8

What is an intraventricular hemorrhage of infants called?

Answer 8

Germinal matrix hemorrhage

The germinal matrix is a dense cellular and vascular layer of the subependymal zone of the brain from which neurons and glial cells develop in utero; begins to involute by 28 weeks

The germinal matrix is weak and lacking stuctural support

Hemorrhage begins between the caudate nucleus and thalamus, and the extends to lateral, third, and fourth ventricle

Patients may be asymptomatic or develop seizures, AMS, and apnea

Question 9

What type of cancers are the vast majority of head and neck cancers?

And where do they tend to develop

Answer 9

Squamous cell

Tend to develop in the oral cavity

Question 10

What is the defect in Marfan syndrome

Answer 10

Autosomal dominant mutation in fibrillin gene (FBN1) which codes for a proten responsible for the produciton and maintenance of elastic fibers

Question 11

Describe the effects of nitrates on heart rate and end-diastolic LV volume

Answer 11

Nitrates lead to vasodilation

Venodilation leads to dereased venous return (decreased preload) and thus decreased end-diastolic LV volume

Nitrates can also cause arteriodilation and drop in blood pressure can lead to reflex tachycardia

Question 12

Describe the different effects of CFTR and mutated CFTR on chloride channels in epithelial cells of sweat glands, respiratory, and intestines

Answer 12

Sweat glands:

Normal CFTR - luminal Cl- ion reabsorption and enhanced sodium reabsorption

Mutated CFTR - decreased NaCl reabsortion

Respiratory and Intestinal epithelium:

Normal CFTR - passive luminal Cl- secretion

Mutated CFTR - reduced luminal Cl- secretion and increased luminal sodium absorption (decreased water content = dehydrated, viscous mucus)

Question 13

What is the defect and presentation in pseudohypoparathyroidism

Answer 13

Due to end-organ resistance to PTH due to defects in teh PTH receptor

Patients have hypocalcemia, hyperphosphatemia, and elevated PTH

Pseudohypoparathyroidism type 1a (Albright hereditary osteodystrophy) is an autosomal dominant disorder due to defets in GNAS1, characterized by short stature, short metacarpal and short metatarsal bones

Question 14

What is the cause behind DNA loops forming when hybridized with their complementary mature mRNA?

Answer 14

Mature mRNAs have already had their introns spliced out

Question 15

Describe the difference between allelic, genetic, and phenotypic heterogeneity

Answer 15

Allelic heterogeneity - different mutations at the same genetic locus cause similar phenotypes

Genetic heterogeneity - mutations of different genes cause similar phenotypes

Phenotypic heterogeneity - mutations at the same gene result in different phenotypes

Question 16

What is hemochromatosis anad what are common manifestations?

Answer 16

Excess iron

Presentation depends on tissues involved with iron deposition:

Liver - cirrhosis

Pancreas - DM

Skin - bronze (due to hemosiderin deposition in macrophages)

Heart - arrhythmias

Testes - atrophied

Question 17

What is achondroplasia and what is the mutated gene?

Answer 17

Most common cause of dwarfism

Autosomal dominant disorder caused by gain-of-funciton, point mutation in the fibroblast growth factor receptor 3 (FGFR3) gene

FGFR3 is normally responsible for inhibition of cartilage proliferation, particularly in the long bones - so gain-of-function would lead to restricted chondrocyte proliferation

Question 18

What is the defect and presentation of maple syrup urine disease?

Answer 18

Defect in the branched-chain alpha-keto acid dehydrogenase complex resulting in the inability to degrade branched chain amino acids (leucine, isoleucine, and valine)

Accumulation of branched amino acids causes CNS toxicity and sweet odor in the urine

The defective enzyme requires thiamine (Vitamin B1) as a coenzyme

Question 19

What is the mechanism behind seminiferous tubules maintaining higher concentrations of testosterone relative to circulation

Answer 19

Androgen-binding protein (ABP) within the seminiferous tubules binds testosterone and DHT to make them less lipophilic and reduce diffusion out of the luminal fluid

ABP is synthesized by Sertoli cells in response to FSH

Sertoli cell dysfunction may manifest as normal serum testosterone (hypothalamus, pituitary, and Leydig cells are fine) with low concentration of testosteron in the seminiferous tubules due to inadequate ABP production

Question 20

What type of tissue is stained by red safranin O

Answer 20

Cartilage (Type II collagen)

Question 21

What is the embryologic function of the round ligament of the uterus?

Answer 21

The round ligament is a vestige of the gubernaculum (ligamentous band that attaches to inferior gonad in both sexes and causes gonads to descend when it shortens)

Forms the scrotal ligament in adult males

Forms the round ligament in females (connects the uterus to the labia majora)

Question 22

What is vanillylmandelic acid

Answer 22

The inactive breakdown product of metanephrine and normetanephrine (metabolites of epi and norepi) produced by monamine oxidase

Will be elevated in patients with a catecholamine-secreting tumor

Question 23

What are the effects of a PE on pO2, pCO2, and arterial pH?

Answer 23

PE causes hypoxemia (low pO2)

Body tries to compensate for hypoxemia with hyperventilation and increased excretion of CO2 which causes a respiratory alkalosis (high pH and low pCO2)