UWorld_2.28

Question 1

Calculation of GFR & RPF

Answer 1

• creatinine or inulin clearance
  
  • C = (( [urine] x urine flow rate)) / [plasma]
• starling equation
  
  • GFR = K_f ((P_G - P_B) - (π_G - π_B))
    
    • K_f = filtration coefficient
    • P_G = hydrostatic pressure @ GC
    • P_B = hydrostatic pressure @ bowmans
    • π_G = oncontic pressure @ GC
    • π_B = oncotic pressure @ bowman’s
• RPF = PAH clearance

Question 2

Common cause of gas gangrene + mechanism of infection

Answer 2

• clostridium perfingens
  
  • gram (+) bacillus
• C. perfingens = abundant @ soil, spores enter penetrating injuries
  
  • germinate in anaerobic environment ==> toxin-producers
• toxin = phospholipase that attacks cell membranes ==> cell death
  
  • metabolizes carbs ==> gas
• ==> extensive tissue damange, necrosis, reduction of blood supply to affected area

Question 3

C. perfringens presentations

Answer 3

• late-onset food poisoning ==> transient watery diarrhea
• gas gangrene

Question 4

Characteristics of caudal regression syndrome

Answer 4

• rare
• associated w/poorly controlled maternal DM
• pt. born w/agenesis of sacrum and lumbar spine
• flaccid paralysis of legs, dorsiflexed contractures of the feet
• urinary incontinence

Question 5

Wristdrop ==> dx?

Answer 5

• radial n. injury

Question 6

Characteristics of radial n. injury

Answer 6

• common causes
  
  • improperly-fitted crutches
  • midshaft humerus fracture
• radial n. = C5 - T1 spinal n.
  
  • branch of posterior cord of brachial plexus
  • can be injured due to superficial location @ axilla
• ==> weakness of forearm, wrist and finger extensors

Question 7

Attachment sites for complement and phagocytic cells to immunoglobulin

Answer 7

• C1 ==< hinge region of constant segment
• phagocytes ==< Fc receptor/initial segment

Question 8

Causes of Down’s sydnrome

Answer 8

1. Meiotic nondisjxn ==> trisomy
2. Robertsonian translocation = extra arm of chromosome 21 translocated to another chromosome
3. Mosaicism

Question 9

Sections of adrenal gland + products

Answer 9

• angiotensin II ==> zona glomerulosa ==> mineralocorticoids (aldosterone)
• ACTH ==> zona fasciculata ==> glucocorticoids (cortisol)
• zona reticularis ==> androgens
• preganglionic sympathetic neurons ==> ACh ==> medulla ==> epinephrine + norepinephrine

Question 10

Most common gallstone + risks

Answer 10

• caucasian
• female sex hormones/OCPs ==> increased synthesis of cholesterol via increased activity of hepatic HMG-CoA reductase
• hypomotility of gallbladder
  
  • preg., adv. age, fasting
• drugs: fibrates, octreotide, ceftriaxone
  
  • fibrates ==> reduced 7a-hydroxylase activity ==> less conversion of cholesterol to bile acids
• obesity or rapid weight loss