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Handling/Transport of different solutes in Loop of Henle and Distal Segm
Learning Objectives
To understand
Handling of water, organic compounds, and ions in LOH and Distal segment.
Different membrane proteins and osmolality of these segments.
Nephron : Tubular Segments
Three major segments:
Handling/Transport of different solutes in Loop of Henle
PTCp
Segment ? Loop of Henle
Loop of Henle
Segment - Loop of Henle Characteristics --TF handling as per
Permeability
+ADH/ - ADH
AQP1
Segment-Thin Descending Limb of LOH
Thin descending limb of Loop of Henle
Since water and solutes are reabsorbed (65-67%)
in PxCT ? it receives: 1/3rd of the original volume
and isosmotic to surrounding fluid (400 mosm/kg)
Segment ? Thin descending limb of Loop of Henle
Water reabsorption
Na+ - also reabsorbed.
300
600
1200
1200
Segment ? Thin descending limb of Loop of Henle
Secretion of urea
Segment Thin Ascending Limb of LOH
Thin Ascending Limb of LOH
This segment is impermeable to water ? `NO' H2O reabsorption here.
Reabsorption of NaCl
Small amount of Ca++ & HCO3- - reabsorbed
Secretion of urea
Thick Ascending Limb of LOH
Thick ascending limb of LOH
NaCl reabsorption ?
Thick ascending limb of LOH
paracellular reabsorption of
Applied - Bartter Syndrome
Mutations in the gene coding for the Na+-K+-2Cl-
symporter (NKCC)
OSMOLALITY of TF leaving LOH-Diluting Segments
Summary of Events- Handling of TF in LOH
Distal Segment
Segment ? Distal Segment -Characteristics --TF handling as per
Permeability
+ADH/ - ADH
AQP1
Distal Segment
DxT (Early and Late) and Col ecting Tubule (CLT)
Early segment of the distal tubule (DxT)
Functionally, similar to thick
ALOLOH, This segment is also
impermeable to w ater.
Late segment of the distal tubule and col ecting tubule
Late segment of the distal tubule and col ecting tubule
1. Principal cells reabsorb Na+ and water and secrete K+.
2. Intercalated cells ? Imp for acid base balance and K+ balance.
Principal cells ?
Principal cells
Aldosterone
Principal Cel s-Mechanism of action of Aldosterone
Na+ - K+ ATPase pump on
Na+ reabsorption and
K+ secretion
Aldosterone
Principal Cells-Mechanism of action of Arginine Vasopressin (AVP) /ADH
V2 receptors
Intercalated cel s (IC Cel s) ?
IC Cells ? Late segment of the DxT & C T
L (Cortical & Medul ary C T
L )
Secretion of K+ and H+ based on body pH
Medullary Collecting Tubule
There are special urea transporters ( UT A1
and UT A3) that facilitate urea diffusion across
the luminal and BL memb.
Regulatory Control of Intercalated cells
Aldosterone and systemic acidosis -
Aldosterone and alkalosis -
Summary of Events- Handling of TF in DxT
OSMOLALITY of TF leaving Dx Segment
Hyposmotic fluid to ISF (100
mosm/kg H2O) enters the DxT
Undergoes water reabs and solutes
reabs under the regulatory control of
hormones
normally final fluid osmolality ranges
from 50-1200 mosm/kg H2O
(isosmotic fluid to ISF ) when
permeable to water (+ADH).
Hormones that regulate tubular reabsorption
Site of action
Effects_____________________
Aldosterone
DXCT, Col ecting tubule
NaCl, H2O reabs, K+ & H + secretion
Angiotensin II
PxT, Thick ALOLOH , DxT and CT
NaCl, H2O reabs, H+ secretion
Antidiuretic Hormone
D
H
XCT, Col ecting tubule
2O reabs
Atrial natriuretic peptide
DXCT, Col ecting tubule
NaCl reabs
Para thyroid hormone
PxT, Thick ALOLOH , DxT
Ca++ reabs, PO4- - - reabs
Self Assessment
About urea , all are true except :
a) concentration rises in tubular fluid as the glomerular filtrate passes down the nephron.
b) is actively secreted by the renal tubular cells
c) concentration in the blood rises slightly after a high protein diet
d) causes osmotic diuresis when its blood concentration is increased .
Aldosterone and systemic acidosis ?
proton pump in apical memb
proton pump in BL memb
expression of AE1 in BL memb
expression of AE1 in BL memb
Thank you
This post was last modified on 08 April 2022