Glomerular capillaries in the kidneys have unique structural and functional characteristics distinct from true systemic capillaries. Clarifying these differences is crucial for understanding renal physiology and the filtration process that initiates urine formation.

Statement Evaluation:

A. The hydrostatic pressure in GC is higher than that in TC

• True: Glomerular capillaries have higher hydrostatic pressure (~55-60 mm Hg) because blood enters and exits through arterioles, creating resistance and pressure buildup.

• True capillaries generally have lower pressure (~20-30 mm Hg) because blood flows from arterioles to venules.

B. The endothelial cells are fenestrated in GC but not in TC

• Partly Incorrect:

  • Glomerular capillaries are fenestrated to allow filtrate passage.

  • Some true capillaries (e.g., in endocrine glands, intestines) are also fenestrated.

  • However, many systemic true capillaries are non-fenestrated (continuous capillaries).

• The blanket statement is therefore inaccurate since many true capillaries can be fenestrated.

C. Both filtration and fluid movement into capillary takes place in TC but only filtration occurs in GC.

• Incorrect:

  • In glomerular capillaries, fluid filtration into Bowman’s capsule predominates; reabsorption usually does not occur within the glomerulus.

  • True capillaries have filtration at the arterial end and fluid reabsorption at the venous end due to pressure differences.

  • Hence, statement C is accurate.

D. The plasma colloid osmotic pressures in both the ends of GC or TC are similar.

• Incorrect:

  • Plasma colloid osmotic pressure in true capillaries increases toward the venous end because water is filtered out at the arterial end (concentrating proteins).

  • In glomerular capillaries, since filtration dominates, colloid osmotic pressure remains relatively constant along the capillary.

  • Thus, statement D is not correct.

What is NOT Correct?

• B is not fully correct because fenestrated endothelial cells can also be present in some true capillaries.

• D is not correct because plasma colloid osmotic pressure varies in true capillaries but not much in glomerular capillaries.

• Statements A and C are generally correct except the formulation in C where it might imply no fluid movement back in glomerulus, which is true.

Given answer choices, the least correct statements are:

(3) B and C is incorrect because C is true.
(4) Only D is definitely incorrect as explained.
(2) A and B includes B which is partly incorrect.
(1) Only A is incorrect because A is correct.

Hence, the answer is:

(4) Only D is the statement that is NOT correct.

Conclusion

The statement that the plasma colloid osmotic pressures in both ends of glomerular and true capillaries are similar is not correct. This contrast is important because it underlies differences in fluid exchange dynamics between these two capillary types.

Correct answer: (4) Only D