Tubular Reabsorption
Figure 27-1;
Guyton and Hall
Copyright © 2006 by Elsevier, Inc.
Primary Active Transport of Na+
Figure 27-2;
Guyton and Hall
Copyright © 2006 by Elsevier, Inc.
Mechanisms of
Secondary
Active Transport
Copyright © 2006 by Elsevier, Inc.
Figure 27-3;
Guyton and Hall
Glucose Transport
Maximum
Figure 27-4;
Guyton and Hall
Copyright © 2006 by Elsevier, Inc.
Reasorption of Water and Solutes is
Coupled to Na+ Reabsorption
Tubular
Cells
Interstitial
Fluid
- 70 mV
Na +
K+
ATP
Na +
ATP
0 mv
Copyright © 2006 by Elsevier, Inc.
K+
Tubular
Lumen
H+
Na +
glucose, amino
acids
Na +
Urea
H20
Na +
Cl-
- 3 mV
Mechanisms by which Water, Chloride,
and Urea Reabsorption are Coupled with
Sodium Reabsorption
Figure 27-5;
Guyton and Hall
Copyright © 2006 by Elsevier, Inc.
Cellular Ultrastructure and Primary
Transport Characteristics of Proximal
Tubule
Figure 27-6; Guyton and Hall
Copyright © 2006 by Elsevier, Inc.
Cellular Ultrastructure and Transport
Characteristics of Thin and Thick Loop
of Henle
very permeable
to H2O)
not permeable
to H2O)
Figure 27-8;
Guyton and Hall
Copyright © 2006 by Elsevier, Inc.
Sodium Chloride and Potassium Transport in
Thick Ascending Loop of Henle
Figure 27-9;
Guyton and Hall
Copyright © 2006 by Elsevier, Inc.
Countercurrent Multiplier System
in the Loop of Henle
Figure 28-3; Guyton and Hall
Copyright © 2006 by Elsevier, Inc.
• Countercurrent multiplier animation
Copyright © 2006 by Elsevier, Inc.
Recirculation of Urea Absorbed from Medullary
Collecting Duct into Interstitial Fluid
Figure 28-5; Guyton and Hall
Copyright © 2006 by Elsevier, Inc.
Net Effects of
Countercurrent Multiplier
1. More solute than water is added to the renal medulla
(i.e., solutes are “trapped” in the renal medulla).
2. Fluid in the ascending loop is diluted.
3. Horizontal gradient of solute concentration established
by the active pumping of NaCl is “multiplied” by
countercurrent flow of fluid.
Copyright © 2006 by Elsevier, Inc.
The Vasa Recta Preserve
Hyperosmolarity of Renal Medulla
• The vasa recta
serve as
countercurrent
exchangers
• Vasa recta blood
flow is low
(only 1-2 % of
total renal
blood flow)
Figure 28-3; Guyton and Hall
Copyright © 2006 by Elsevier, Inc.
Sodium Chloride Transport in
Early Distal Tubule
Figure 27-10;
Guyton and Hall
Copyright © 2006 by Elsevier, Inc.
Cellular Ultrastructure and Transport
Characteristics of Early and Late Distal Tubules
and Collecting Tubules
• not permeable
to H2O
• not very
permeable to
urea
• permeability
to H2O
depends on ADH
• not very
permeable to
urea
Figure 27-11; Guyton and Hall
Copyright © 2006 by Elsevier, Inc.
Sodium Chloride Reabsorption and Potassium
Secretion in Collecting Tubule Principal Cells
Figure 27-12;
Guyton and Hall
Copyright © 2006 by Elsevier, Inc.
Cortical Collecting Tubules
Intercalated Cells
Tubular Cells
Tubular Lumen
H20 (depends on
ADH)
H+
K+
K+
ATP
ATP
Na +
K+
H+
ATP
ATP
ATP
Cl Copyright © 2006 by Elsevier, Inc.
Cellular Ultrastructure and Transport
Characteristics of Medullary Collecting Tubules
Figure 27-13; Guyton and Hall
Copyright © 2006 by Elsevier, Inc.
Normal Renal Tubular Na+ Reabsorption
7%
(16,614 mEq/day)
25,560
mEq/d
(1789 mEq/d)
65 %
25 %
2.4%
(6390 mEq/d)
(617 mEq/day)
0.6 %
(150 mEq/day)
Copyright © 2006 by Elsevier, Inc.
Summary of Water Reabsorption and
Osmolarity in Different Parts of the Tubule
• Proximal Tubule: 65% reabsorption, isosmotic
• Desc. loop: 15-20% reabsorption, osmolarity increases
• Asc. loop: 0% reabsorption, osmolarity decreases
• Early distal: 0% reabsorption, osmolarity decreases
• Late distal and coll. tubules: ADH dependent
water reabsorption and tubular osmolarity
• Medullary coll. ducts: ADH dependent water
reabsorption and tubular osmolarity
Copyright © 2006 by Elsevier, Inc.
Concentration and
Dilution of the Urine
• Maximal urine concentration
= 1200 - 1400 mOsm / L
(specific gravity ~ 1.030)
• Minimal urine concentration
= 50 - 70 mOsm / L
(specific gravity ~ 1.003)
Copyright © 2006 by Elsevier, Inc.
Obligatory Urine Volume
The minimum urine volume in which the excreted
solute can be dissolved and excreted.
Example:
If the max. urine osmolarity is 1200 mOsm/L,
and 600 mOsm of solute must be excreted each
day to maintain electrolyte balance, the
obligatory urine volume is:
600 mOsm/d
1200 mOsm/L
Copyright © 2006 by Elsevier, Inc.
= 0.5 L/day
Maximum Urine Concentration of
Different Animals
Animal
Max. Urine Conc. (mOsm /L)
Beaver
Pig
Human
Dog
White Rat
Kangaroo Mouse
Australian Hopping Mouse
Copyright © 2006 by Elsevier, Inc.
500
1,100
1,400
2,400
3,000
6,000
10,000
Late Distal, Cortical and Medullary
Collecting Tubules
Principal Cells
Tubular Lumen
H20 (w/o ADH)
Na +
Na +
K+
ATP
K+
Cl -
Aldosterone
Copyright © 2006 by Elsevier, Inc.
Abnormal Aldosterone Production
• Excess aldosterone - Conn’s syndrome
Na+ retention, hypokalemia, alkalosis,
hypertension
• Aldosterone deficiency - Addison’s disease
Na+ wasting, hyperkalemia, hypotension,
death if untreated
Copyright © 2006 by Elsevier, Inc.
Ang II Increases Tubular Na+ Transport
Tubular
Cells
Interstitial
Fluid
Tubular
Lumen
Ang II
Ang II
Na+
Na+
ATP
+
K
Copyright © 2006 by Elsevier, Inc.
H+
Effect of Angiotensin II on
Peritubular Capillary Dynamics
Glomerular
Capillary
Ra
Peritubular
Re Capillary
Arterial
Pressure
Ang II
Re
Pc (peritubular cap. press.)
renal blood flow
Copyright © 2006 by Elsevier, Inc.
FF
c
Ang II Constriction of Efferent Arterioles Causes Na+
Retention and Maintains Excretion of Waste Products
Na+ depletion
Ang II
Resistance efferent arterioles
Glom. cap. press
Prevents decrease
in GFR and
retention of
waste products
Copyright © 2006 by Elsevier, Inc.
Renal blood flow
Peritub. Cap. Press.
Filt. Fraction
Na+ and H2O Reabs.
Angiotensin II Blockade Decreases Na+
Reabsorption and Blood Pressure
• ACE inhibitors (captopril, benazipril, ramipril)
• Ang II antagonists (losartan, candesartin, irbesartan)
• decrease aldosterone
• directly inhibit Na+ reabsorption
• decrease efferent arteriolar resistance
Natriuresis and Diuresis +
Copyright © 2006 by Elsevier, Inc.
Blood Pressure
Formation of a Dilute Urine
• Continue electrolyte
reabsorption
• Decrease water
reabsorption
Mechanism:
decreased ADH
release and reduced
water permeability
in distal and
collecting tubules
Figure 28-1; Guyton and Hall
Copyright © 2006 by Elsevier, Inc.
Formation of a Concentrated Urine
• Continue electrolyte reabsorption
• Increase water reabsorption
Mechanism:
• Increased ADH release which increases water
permeability in distal and collecting tubules
• High osmolarity of renal medulla
• Countercurrent flow of tubular fluid
Copyright © 2006 by Elsevier, Inc.
Formation of a Concentrated Urine when
Antidiuretic Hormone (ADH) Levels are High
Figure 28-4; Guyton and Hall
Copyright © 2006 by Elsevier, Inc.
Osmoreceptor–
antidiuretic hormone (ADH)
feedback mechanism for
regulating extracellular
fluid osmolarity
Copyright © 2006 by Elsevier, Inc.
Figure 28-8;
Guyton and Hall
ADH synthesis in the
neurons of hypothalamus,
release by the posterior
pituitary, and action on the
kidneys
Copyright © 2006 by Elsevier, Inc.
Figure 28-9;
Guyton and Hall
Factors that Decrease
ADH Secretion
• Decreased osmolarity
• Increased blood volume (cardiopulmonary reflexes)
• Increased blood pressure (arterial baroreceptors)
• Other factors:
- alcohol
- haloperidol (antipsychotic, tics,Tourette’s)
Copyright © 2006 by Elsevier, Inc.
Stimuli for Thirst
• Increased osmolarity
• Decreased blood volume
(cardiopulmonary reflexes)
• Decreased blood pressure
(arterial baroreceptors)
• Increased angiotensin II
• Other stimuli:
- dryness of mouth
Copyright © 2006 by Elsevier, Inc.
Factors that Decrease Thirst
• Decreased osmolarity
• Increased blood volume
(cardiopulmonary reflexes)
• Increased blood pressure
(arterial baroreceptors)
• Decreased angiotensin II
• Other stimuli:
-Gastric distention
Copyright © 2006 by Elsevier, Inc.
Atrial Natriuretic Peptide (ANP)
Blood volume
ANP
Renin release
aldosterone
GFR
Ang II
Renal Na+ and H2O reabsorption
Copyright © 2006 by Elsevier, Inc.
Na+ and H2O excretion
Late Distal and Collecting Tubules
Tubular Cells
Tubular Lumen
H20 (depends
on ADH)
Aquaporin-3
H20
Aquaporins
ADH
cAMP
V2 receptor
Copyright © 2006 by Elsevier, Inc.
Vesicle
Aquaporin-2
H20
Sodium Chloride and Potassium Transport in
Thick Ascending Loop of Henle
Figure 27-9;
Guyton and Hall
Copyright © 2006 by Elsevier, Inc.
Sodium Chloride Transport in
Early Distal Tubule
Figure 27-10;
Guyton and Hall
Copyright © 2006 by Elsevier, Inc.
Sodium Chloride Reabsorption and Potassium
Secretion in Collecting Tubule Principal Cells
Figure 27-12;
Guyton and Hall
Copyright © 2006 by Elsevier, Inc.