Download MBBS Physiology Presentations 5 Tubular Processes Lecture Notes

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To understand

Terminology to know processes of handling tubular fluid ?

Renal Tubular Reabsorption or Secretion- Transcellular & paracellular pathway

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Tubular Cells ?Tight Junctions

To calculate secretion or reabsorption rate of any solute

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Nephron Terminology

Various transport mechanisms in proximal convoluted tubules

Glomerulo-tubular balance, and it's physiologic importance

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Glucose transport maximum
Terminology to know processes of handling tubular fluid

Tubular Reabsorption or Secretion in Renal Tubules

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PTCp

1. Reabsorption:

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1

2. Secretion:

TF

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2.
Tubular Cells ?Tight Junctions

PTCp

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Tight junctions

1

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Tight junctions ? claudins and occludins.

TF

2.

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Tubular Reabsorption/Secretion - Routes/Pathways

PTCp

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Transcel ular pathway:

1

Paracellular pathway:

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TF

2.
Pressures favoring reabsorption by bulk flow into peritubular Cps

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bulk

flow

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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):

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Solvent drag-
Nephron : Tubular Segments

Three major segments:

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These segments determine the composition & volume of the urine by the

Reabsorption and Secretion Rates of substances in renal tubules
Nephron Terminology

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TF/P ratio

2. TF/Pinulin

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3. [TF/P]x /[TF/P]inulin ratio

Exercise questions
Segment - Proximal Convoluted Tubule ?

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Tubule Characteristics --TF handling as per Permeability

+ADH/ - ADH

AQP1

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Transport mechanisms of different solutes of TF ? PxCT
First half of Px CT

Active NaCl Transport

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H2O

NaCl

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Urea

++

Early Part of Proximal Convoluted Tubule PxCT

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++

+

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+

H2O

Na+ Reabsorption

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Active NaCl Transport

H2O

NaCl

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Urea

++

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Early Part of Proximal Convoluted Tubule PxCT

++

+

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+

H+ secretion and

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H2O

HCO3-Reabsorption

Early Part of Proximal Convoluted Tubule

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Active NaCl Transport

H2O

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NaCl

Urea

PxCT

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++

++

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+

+

Glucose

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reabsorption
Applied-

Mutations in the GLUT2 gene

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Active NaCl Transport

H2O

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NaCl

Urea

++

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Early Part of Proximal Convoluted Tubule PxCT

++

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+

+

Ca++, Mg++, K+ , Urea

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Paracellular

H

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reabsorption

2O
Second half of Px CT

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Active NaCl Transport

H2O

NaCl

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Urea

++

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Second half of PxCT

PxCT

++

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+

+

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Na+ and Cl-

reabsorption
Active NaCl Transport

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H2O

NaCl

Urea

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++

Second half of PxCT

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PxCT

++

+

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+

(Mechanism: Na+H+ - Cl-Anion Antiporters)

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Second half of PxCT

Na+-glucose symporter (SGLT1)
Second half of Proximal Convoluted Tubule

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Water reabsorption

Urea reabsorption

Pinocytosis--An Active Transport Mechanism for Reabsorption of

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large molecules such as Proteins in PxT
Summary of handling of % of water & solutes ? Px CT

Summary of Transporters in Px CT

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Osmolality of TF Leaving PxCT

Clinical Relevance ? Acute Tubular Necrosis (ATN )
Transport Maximum (Tm)

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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.

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Cause of difference of TmG and Renal threshold for glucose

Phenomenon of SPLAY

ideal

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(or glucose amount filtered)

Regulation of Tubular processes

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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

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reabsorption.
Glomerulo-tubular Balance

Glomerulo-tubular balance - Mechanism

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Tubuloglomerular feedback vs Glomerulo-tubular balance

N
aC
l

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Self Assessment

Percentage of filtered urea, reabsorbed by Px CT is about :

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1. 00-25
2. 50 -65

3. 70-95

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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.

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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

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Water channel present in proximal convoluted tubule is:

1. Aquaporin 1
2. Aquaporin 2

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3. Aquaporin 3

4. Aquaporin 4

At the leaving end of PxCT, percentage of filtered solute

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and water is approximately:

1) 35% solute and 35% water

2) 45% solute and 45% water

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3) 35% solute and 45% water
4) 45% solute and 35% water
Thank you