Handling of water, organic compounds, and ions in LOH and Distal segment.
Different membrane proteins and osmolality of these segments.
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Nephron : Tubular SegmentsThree major segments:
Handling/Transport of different solutes in Loop of Henle
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PTCp
Segment ? Loop of Henle
Loop of Henle
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Segment - Loop of Henle Characteristics --TF handling as perPermeability
+ADH/ - ADH
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AQP1
Segment-Thin Descending Limb of LOH
Thin descending limb of Loop of Henle
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Since water and solutes are reabsorbed (65-67%)
in PxCT ? it receives: 1/3rd of the original volume
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and isosmotic to surrounding fluid (400 mosm/kg)Segment ? Thin descending limb of Loop of Henle
Water reabsorption
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Na+ - also reabsorbed.
300
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6001200
1200
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Segment ? Thin descending limb of Loop of HenleSecretion of urea
Segment Thin Ascending Limb of LOH
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Thin Ascending Limb of LOHThis segment is impermeable to water ? `NO' H2O reabsorption here.
Reabsorption of NaCl
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Small amount of Ca++ & HCO3- - reabsorbed
Secretion of urea
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Thick Ascending Limb of LOHThick ascending limb of LOH
NaCl reabsorption ?
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Thick ascending limb of LOHparacellular reabsorption of
Applied - Bartter Syndrome
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Mutations in the gene coding for the Na+-K+-2Cl-symporter (NKCC)
OSMOLALITY of TF leaving LOH-Diluting Segments
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Summary of Events- Handling of TF in LOHDistal Segment
Segment ? Distal Segment -Characteristics --TF handling as per
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Permeability+ADH/ - ADH
AQP1
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Distal Segment
DxT (Early and Late) and Col ecting Tubule (CLT)
Early segment of the distal tubule (DxT)
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Functionally, similar to thickALOLOH, This segment is also
impermeable to w ater.
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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+.
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2. Intercalated cells ? Imp for acid base balance and K+ balance.
Principal cells ?
Principal cells
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Aldosterone
Principal Cel s-Mechanism of action of Aldosterone
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Na+ - K+ ATPase pump onNa+ reabsorption and
K+ secretion
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Aldosterone
Principal Cells-Mechanism of action of Arginine Vasopressin (AVP) /ADH
V2 receptors
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Intercalated cel s (IC Cel s) ?
IC Cells ? Late segment of the DxT & C T
L (Cortical & Medul ary C T
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L )
Secretion of K+ and H+ based on body pH
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Medullary Collecting TubuleThere are special urea transporters ( UT A1
and UT A3) that facilitate urea diffusion across
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the luminal and BL memb.
Regulatory Control of Intercalated cells
Aldosterone and systemic acidosis -
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Aldosterone and alkalosis -
Summary of Events- Handling of TF in DxT
OSMOLALITY of TF leaving Dx Segment
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Hyposmotic fluid to ISF (100
mosm/kg H2O) enters the DxT
Undergoes water reabs and solutes
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reabs under the regulatory control of
hormones
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normally final fluid osmolality rangesfrom 50-1200 mosm/kg H2O
(isosmotic fluid to ISF ) when
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permeable to water (+ADH).
Hormones that regulate tubular reabsorption
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Site of actionEffects_____________________
Aldosterone
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DXCT, Col ecting tubule
NaCl, H2O reabs, K+ & H + secretion
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Angiotensin IIPxT, Thick ALOLOH , DxT and CT
NaCl, H2O reabs, H+ secretion
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Antidiuretic Hormone
D
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HXCT, Col ecting tubule
2O reabs
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Atrial natriuretic peptide
DXCT, Col ecting tubule
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NaCl reabsPara thyroid hormone
PxT, Thick ALOLOH , DxT
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Ca++ reabs, PO4- - - reabs
Self Assessment
About urea , all are true except :
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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
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d) causes osmotic diuresis when its blood concentration is increased .Aldosterone and systemic acidosis ?
proton pump in apical memb
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proton pump in BL membexpression of AE1 in BL memb
expression of AE1 in BL memb
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