Download MBBS Physiology Presentations 61 Loh Dct Lecture Notes

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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