#PHYSIOLOGY(NEET-PG)
Q- A politician is shot in the back during a rally at level of T8 vertebral immediately after the shot he loses all the sensation below level of lesion. Chance of regeneration of spinal cord due to the fact that injured nerve is not able to regenerate is due to reason all except:
A. Lack of endoneural tubes
B. Lack of growth factors
C. Presence of glial scar
D. Lack of myelin inhibiting substance
Answer is D. Lack of myelin inhibiting substance
Following CNS injuries several events which provide inappropriate environment for regeneration are:
-Activation of microglia
-Scar formation
-Inflammation
Invasion of immune cells
-CNS neurons do not have the growth promoting chemical needed for the regeneration
-CNS myelin is a potent inhibitor of axonal growth
Axon Regeneration in CNS:
-The proximal stump of a damaged axon in the CNS will form short sprouts, but distant stump recovery is rare, and the damaged axons are unlikely to form new synapses. This is because:
-CNS neurons do not have the growth promoting chemical needed for the regeneration
-CNS myelin is a potent inhibitor of axonal growth.
That is why treatment of brain and spinal cord injuries frequently focuses on rehabilitation rather than reversing the nerve damage.
Following CNS injuries, several events which provide inappropriate environment for regeneration are:
-Astrocytic proliferation
-Activation of microglia formation
-Inflammation
-Invasion of immune cells
New research is aiming to identify ways to initiate and maintain axonal growth, to direct regenerating axons to reconnect with their target neurons and to reconstitute original neuronal circuit.
Q- Clamping of the carotid arteries below (proximal) the carotid sinus is likely to produce:
A. Increase in Blood pressure and increase in Heart Rate
B. Decrease in Blood pressure and decrease in Heart Rate
C. Increase in Blood pressure and decrease in Heart Rate
D. Increase in Blood pressure and decrease in Heart Rate
Answer is A. Increase in Blood pressure and increase in Heart Rate
▪️Stretching of carotid sinus baroreceptors [d/t clamping of bilateral carotid arteries above (distal to) carotid sinus] stimulate their firing which leads to peripheral vasodilation decreased heart rate, decreased the strength of contraction, decreased cardiac output and decreased blood pressure (BP) by excitation of vagal parasympathetic center.
▪️Clamping of carotid arteries proximal (below) the carotid sinus, decreases pressure within the sinus reducing its
discharge. This intum stimulates vasomotor center in the medulla and inhibits vagal parasympathetic center. This induces reciprocal compensatory response causing peripheral vasoconstriction, increased heart rate, increased strength of contraction, increased cardiac output and increased blood pressure (BP).
▪️When bilateral vagotomy is also performed the BP rise 300/200mmHg and is unstable.
▪️Bilateral destruction of visceral afferent nucleus ie nucleus tractus solitaries (NTS), which is the site of termination of baroreceptor afferents, also causes a marked (severe maybe even fatal) hypertension.
Q- What is the effect of constriction of efferent arteriole and dilatation of afferent arteriole on glomerular filtration rate?
A. Increases GFR
B. Decreases GFR
C. No change to GFR
D. First increase then decreases GFR
Answer is A. Increases GFR
▪️Increase in renal blood flow increases GFR.
▪️Afferent arteriole brings blood to the nephron hence its dilation will increase renal blood flow, and efferent arteriole takes blood away from the nephrons, hence its constriction will cause increase filtration, hence increase in GFR.
▪️Constriction of afferent arteriole: decreases both renal blood flow and GFR, without change in filtration fraction.
▪️Dilatation of afferent arteriole : increases both renal blood flow and GFR, without change in filtration fraction.
▪️Constriction of efferent arteriole: decreases the renal blood flow and increases GFR and filtration fraction.
▪️Dilatation of efferent arteriole: increases the renal blood flow and decreases the GFR and filtration fraction.
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