Test 173 (modified from MRCOphth/MRCS Questions, 2003)

1. Intracellular messengers include: 

a. cyclic guanosine monophosphate (cGMP)

b. inositol triphosphate (IP3)

c. cyclic adenosine monophosphate (cAMP)

d. diacylglycerol

e. GABA
 

Answera.T   b.T  c.T   d.T  e.F
cGMP is generated by the activation of the guanylylcyclase enzyme whereas cAMP is through the activation of a G-protein and adenylyl cyclase. Diacyclglycerol is generated along with IP3 by activated phospholipase C. GABA is a neurotransmitter.

2. The following are true about inositol triphophate (IP3):

a. it is increased by activation of a1-adrenoreceptors

b. it is produced by the action of phospholipase C,
    a membrane bound enzyme

c. it acts as second messengers

d. it binds to the membrane of the endoplasmic reticulum 
    and opens the calcium channels

e. it causes smooth muscle contraction
 

Answera.T  b.T  c.T  d.T  e.T
IP3 binds to endoplasmic reticulum membrane and 
increases the intracellular calcium concentration and 
this in turn results in smooth muscle contraction, increased secretion from exocrine glands and the force and rate of cardiac contraction.
 
 

3. The following are true about antifungal medications:

a. polyene macrolids bind to the ergosterol in the 
    fungal cell membrane and produce pores

b. imidazoles prevents ergosterol synthesis by inhibiting 
    the enzyme squalene oxidase

c. allylamines inhibit fungal lipid synthesis in the cell 
    membrane

d. flucytosine inhibits fungal DNA synthesis

e. griseofulvin interferes with microtubule formation
 

Answer
a.T   b.F  c.F  d.T  e.T
Imidazoles such as clotrimaxole or fluconazole inhibit fungal lipid synthesis especially ergosterol in the cell membrane. Allylamines such as terbinafine prevents ergosterol synthesis by inhibiting the enzyme squalene oxidase. 
Griseofulvin interferes with microtubule formation, nuclei acid synthesis and polymerase in fungus.

 

. 4. With regard to the eye:

a. parasympathetic stimulation causes pupil constriction

b. pin-point pupil results from opiate overdose

c. inhibition of the parasympathetic pathway to the 
    ciliary muscle causes the lens to becomes thinner and 
    more elongated

d. the ciliary muscle contains muscarinic M1 receptors

e. pilocarpine causes miosis by relaxing the dilator muscle
   of the pupil
 

Answer
a.T  b.T  c.T  d.F  e.F
The ciliary muscle contains muscarinic M3 receptors. Pilocarpine contracts the sphincter muscle of pupil and gives rise to miosis.

5. Stimulation of a2-adrenoreceptors causes:

a. contraction of blood vessels

b. decreased intraocular pressure

c. relaxation of the iris dilator

d. eyelid retraction

e. platelet aggregation
 

Answer
a.T   b.T  c.F  d.T  e.T
Mydriasis is mediated by alpha1 adrenoreceptors.

 

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