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Tubular Processes ? Handling of TF
Learning Objectives
To understand
Terminology to know processes of handling tubular fluid ?
Renal Tubular Reabsorption or Secretion- Transcellular & paracellular pathway
Tubular Cells ?Tight Junctions
To calculate secretion or reabsorption rate of any solute
Nephron Terminology
Various transport mechanisms in proximal convoluted tubules
Glomerulo-tubular balance, and it's physiologic importance
Glucose transport maximum
Terminology to know processes of handling tubular fluid
Tubular Reabsorption or Secretion in Renal Tubules
PTCp
1. Reabsorption:
1
2. Secretion:
TF
2.
Tubular Cells ?Tight Junctions
PTCp
Tight junctions
1
Tight junctions ? claudins and occludins.
TF
2.
Tubular Reabsorption/Secretion - Routes/Pathways
PTCp
Transcel ular pathway:
1
Paracellular pathway:
TF
2.
Pressures favoring reabsorption by bulk flow into peritubular Cps
bulk
flow
GENERAL PRINCIPLES OF MEMBRANE TRANSPORT ? across cell membranes
Passive transport of substances (without expenditure of energy):
Active transport of subtances (with the expenditure of energy):
Solvent drag-
Nephron : Tubular Segments
Three major segments:
These segments determine the composition & volume of the urine by the
Reabsorption and Secretion Rates of substances in renal tubules
Nephron Terminology
TF/P ratio
2. TF/Pinulin
3. [TF/P]x /[TF/P]inulin ratio
Exercise questions
Segment - Proximal Convoluted Tubule ?
Tubule Characteristics --TF handling as per Permeability
+ADH/ - ADH
AQP1
Transport mechanisms of different solutes of TF ? PxCT
First half of Px CT
Active NaCl Transport
H2O
NaCl
Urea
++
Early Part of Proximal Convoluted Tubule PxCT
++
+
+
H2O
Na+ Reabsorption
Active NaCl Transport
H2O
NaCl
Urea
++
Early Part of Proximal Convoluted Tubule PxCT
++
+
+
H+ secretion and
H2O
HCO3-Reabsorption
Early Part of Proximal Convoluted Tubule
Active NaCl Transport
H2O
NaCl
Urea
PxCT
++
++
+
+
Glucose
reabsorption
Applied-
Mutations in the GLUT2 gene
Active NaCl Transport
H2O
NaCl
Urea
++
Early Part of Proximal Convoluted Tubule PxCT
++
+
+
Ca++, Mg++, K+ , Urea
Paracellular
H
reabsorption
2O
Second half of Px CT
Active NaCl Transport
H2O
NaCl
Urea
++
Second half of PxCT
PxCT
++
+
+
Na+ and Cl-
reabsorption
Active NaCl Transport
H2O
NaCl
Urea
++
Second half of PxCT
PxCT
++
+
+
(Mechanism: Na+H+ - Cl-Anion Antiporters)
Second half of PxCT
Na+-glucose symporter (SGLT1)
Second half of Proximal Convoluted Tubule
Water reabsorption
Urea reabsorption
Pinocytosis--An Active Transport Mechanism for Reabsorption of
large molecules such as Proteins in PxT
Summary of handling of % of water & solutes ? Px CT
Summary of Transporters in Px CT
Osmolality of TF Leaving PxCT
Clinical Relevance ? Acute Tubular Necrosis (ATN )
Transport Maximum (Tm)
Blood glucose level and corresponding Glucose tubular load
This glucose blood concentration (200 mg/dl) and the filtered load of 250 mg/min are
termed as the renal threshold for glucose.
Cause of difference of TmG and Renal threshold for glucose
Phenomenon of SPLAY
ideal
(or glucose amount filtered)
Regulation of Tubular processes
Because it is essential to maintain a precise balance between tubular
reabsorption and glomerular filtration, there are multiple nervous,
hormonal, and local control mechanisms that regulate tubular
reabsorption.
Glomerulo-tubular Balance
Glomerulo-tubular balance - Mechanism
Tubuloglomerular feedback vs Glomerulo-tubular balance
N
aC
l
Self Assessment
Percentage of filtered urea, reabsorbed by Px CT is about :
1. 00-25
2. 50 -65
3. 70-95
4. 80-100
If there is increased load of NaCl and water, what wil happen in Px CT
1) There wil be an increase in NaCl and water reabsorption.
2) There wil be a decrease in NaCl and water reabsorption.
3) There wil be an increase in NaCl but water reabsorption wil decrease
4) There wil not be any change
Water channel present in proximal convoluted tubule is:
1. Aquaporin 1
2. Aquaporin 2
3. Aquaporin 3
4. Aquaporin 4
At the leaving end of PxCT, percentage of filtered solute
and water is approximately:
1) 35% solute and 35% water
2) 45% solute and 45% water
3) 35% solute and 45% water
4) 45% solute and 35% water
Thank you
This post was last modified on 08 April 2022