Test 171  (MRCS Questions, 2003)

1. The corneal endothelium:

 a. is made up of 2-3 layers of cells

 b. are squamous stratified cells

 c. have tight junctions between cells

 d. has a bicarbonate pump

 e. may maintain clarity of the cornea even when only 
     50% of its cell population are left

Answera.F  b.F  c.F   d.T  e.T
The endothelium is the single layer of cuboidal cells located at the posterior of the cornea; it permits the passage of nutrients from the aqueous humour into the cornea. The requirement for a monolayer that is “leaky” to aqueous humour is met through the barrier function of the endothelium, formed by cell-to-cell contacts and interdigitating lateral membranes. The endothelium is the major cell layer responsible for maintaining the relatively low level of stromal hydration necessary for corneal transparency. Stromal hydration is controlled by the activity of ionic pumps in the plasma membrane of endothelial cells. The relatively high extracellular ion concentration produced by these pumps draws
water from the stroma, thus maintaining the highly organized collagen lamellar structure required for corneal transparency. At least two active transport systems appear to contribute to the pumping mechanism: an Na+,K+-ATPase pump and a bicarbonate-dependent Mg2+-ATPase pump.
The endothelium can enlarge to cover up loss endothelium.

2. Drugs that cause increased intracranial pressure:

a. steroids

b. azetazolamide 

c. vitamin A

d. ethambutol 

e. tetracyclin 
 

Answera.T  b.F  c.T  d.F  e.T
Acetazolamide is used to treat increased intracranial pressure.
Ethambutol causes optic neuritis.

3. Antibiotics that act on cell wall include:

a. chloramphenicol

b. vancomycin 

c. sulphonamid 

d. tetracyclin 

e. erythromycin 

 
Answer
a.F   b.T  c.F  d.F  e.F
Chloramphenicol is a bacteriostatic antibiotic that reversibly inhibits bacterial protein synthesis.
Vancomycin is a bactericidal antibiotic that inhibits bacterial cell wall synthesis through interference with glycopeptide polymerization.
Sulphonamide works by interfering with bacterial DNA synthesis.
Tetracycline antibiotics inhibit bacterial protein synthesis by binding to the 30-S ribosomes.
Erythromycin is a bacteriostatic inhibitor of bacterial protein synthesis and can be bactericidal in high concentrations.

4. Histamine is released by: 

a. macrophage 

b. lymphocytes 

c. mast cells 

d. basophils 

e. neutrophils 

 
Answer
a.F  b.F  c.T  d.T  e.F
Histamine, stored in granules of mast cells and basophils, is the central mediator of ocular allergy and inflammation. Histamine levels of 5ng/mL have been identified in normal human tears.
.

5. The following are true about HIV (human immunodeficiency 
    virus):

a. CD4 is a receptor for HIV 

b. it is a RNA virus

c. it can be transmitted through placenta

d. antibodies can be detected within 3 months of infection 

e. can cause tumours

Answer
a.T   b.T  c.T  d.T  e.T
The viral gp120 binds to the CD4 receptors on human T lymphocytes, and gp41 is required for fusion.
It is a RNA virus.
Seroconversion to HIV antibodies usually occurs between 4 to 12 weeks after acute infection.
HIV infection is associated with an increased incidence of tumour such as lymphoma.

 

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