Question

1. Why are blood cells and proteins not a normal constituent of urine?

2. What happens if the TM for glucose is exceeded in the PCT?

3. Where in the urinary tract (not kidneys) would the following shed cells have originated?

Squamous (more common):

Transitional:

4. The specific gravity of pure water is 1.000. Urine Specific Gravities range from 1.001-1.035. With regards to the solute, how does urine with a specific gravity of 1.006 differ from urine with a specific gravity of 1.024?

5. Casts are formed in the collecting duct and can be acellular or cellular. When filtrate flow is low, proteins and cells accumulated and concentrated in the tubules. When the flow increases the casts are pushed out of the tubules.

Decreased urine pH contributes to the formation of casts. Explain why a decreased filtrate pH promotes cast formation.

Answer 1

Q. 1. As size or RBC and most of the proteins is more than 8nm and also proteins are negatively charged they are not fitered through glomerulus. Hence does not appear in urine.

Glomerular Filteration Membrane :::
1) Glomerular endothelial cell layer: Fenestrated
capillary with a gap of 70–90 nm in between
endothelium cells
2) Basement membrane: A gel-like acellular meshwork

Visceral epithelial layer of Bowman’s capsule called podocyte has many foot processes form fltration slits.
The slits are approximately 25 nm wide and are closed
slit diaphragms which bridge the slits between
the pedicels.

Glomerular Membrane Permeability Depends on
1) Size of particle: Neutral substances which are < 4 nm
are freely fltered; > 8 nm are not fltered.
2) Charge of the particle: as fltration membrane are negatively charged, fltration of positively charged particles is facilitated and negatively charged particles are repelled.

Q. 2. TM (tranport maxima) - For most substances that are actively reabsorbed or secreted, there is a limit to the rate at which the solute can be transported, often referred to as the transport maximum. This limit is due to saturation of the specifc transport systems involved when the amount of solute delivered to the tubule exceeds the capacity of the carrier proteins and specifc enzymes involved in the transport process.

Hence if Tm of Glucose is Increased the capacity of maximum reabsorbtion.

Q.3. Squamous Epithelium - external urethral orifice

Transitional epithelium - Urinary bladder, ureter

Q.4. Specific gravity depends on solute Concentration. Urine with a specific gravity of 1.006 will have less solute compared to urine with a specific gravity of 1.024

Q.5. Decreased filteration decreses the flow of fluid in tubules. This leads to stagnation of filterate and hence protein accumulation occur ans lead to formation of cast.