Counter-Current System
Regulation of Renal
Functions
Assoc. Prof. MUDr. Markéta Bébarová, Ph.D.
Department of Physiology
Faculty of Medicine, Masaryk University
This presentation includes only the
most important terms and facts. Its
content by itself is not a sufficient
source of information required to
pass the Physiology exam.
Water Transport in Tubules
substances
with
pronounced
secretion in
comparison
with H2O
substances
with
pronounced
reabsorption
in comparison
with H2O
GFR 180 l/day
UFR 1 l/day
UFR 0.5 l/day
(1400 mosm/l)
up to
UFR 23.3 l/day
(30 mosm/l)
Guyton  Hall. Textbook of Medical Physiology
Proximal Tubule
Intensive transport of solutes from tubules to interstitium osmotic
gradient - water reabsorption
Isoosmotic fluid, volume notably decreased (60-70% of
solutes and water reabsorbed)
Facilitated by water channels (aquaporin 1; not guided by
ADH!)
Water Transport in Tubules
Loop of Henle
Hypotonic fluid, volume decreased
1) thin descending part - passive reabsorption of water (osmosis)
2) thick ascending part – impermeable for water, intensive
reabsorption of solutes
Water Transport in Tubules
Distal Tubule
Tonicity of the outflowing fluid depends on the actual level of
ADH.
1) the first part – analogical to the thick ascending loop of
Henle – impermeable for water, reabsorption of solutes
(reabsorption of Na+ regulated by aldosteron)
2) the next part – analogical to the cortical part of collecting
duct – water reabsorption regulated by ADH (aquaporin 2)
Water Transport in Tubules
Collecting Duct
Tonicity of the outflowing fluid depends on the actual level of
ADH.
1) the cortical part – water reabsorption regulated by ADH
(aquaporin 2), isotonic intersticium
1) the medullar part – water reabsorption regulated by ADH
(aquaporin 2), hypertonic intersticium
Water Transport in Tubules
Counter-Current System in Kidneys
Counter-Current System in Kidneys
Guyton  Hall. Textbook of Medical Physiology
Hyperosmotic Renal Medulla – Role of Loop of Henle
1) Active transport of Na+, co-transport of Na+ with K+ and Clfrom
ascending loop of Henle; gradient even 200 mOsm/l
2) Impermeability of ascending loop of Henle for water
diuretics (e.g. furosemid)
Counter-Current System in Kidneys
3) Permeability of descending loop of Henle for water
Guyton  Hall. Textbook of Medical Physiology
Counter-Current System in Kidneys
Hyperosmotic Renal Medulla – Role of Loop of Henle
1) Active transport of Na+, co-transport of Na+ with K+ and Clfrom
ascending loop of Henle; gradient even 200 mOsm/l
2) Impermeability of ascending loop of Henle for water
Guyton  Hall. Textbook of Medical Physiology
Hyperosmotic Renal Medulla – Role of Loop of Henle
Counter-Current System in Kidneys
1) Active transport of Na+, co-transport of Na+ with K+ and Clfrom
ascending loop of Henle; gradient even 200 mOsm/l
2) Impermeability of ascending loop of Henle for water
3) Permeability of descending loop of Henle for water
Guyton  Hall. Textbook of Medical Physiology
Hyperosmotic Renal Medulla – Role of Loop of Henle
Counter-Current System in Kidneys
Ganong´s Review of Medical Physiology, 23rd edition
Hyperosmotic Renal Medulla – Role of Vasa Recta
Counter-Current System in Kidneys
Hyperosmotic Renal Medulla – Role of Vasa Recta
Guyton  Hall. Textbook of Medical Physiology
Counter-Current System in Kidneys
Hyperosmotic Renal Medulla – Role of Urea
Guyton  Hall. Textbook of Medical Physiology
Counter-Current System in Kidneys
passive
transport
following parts of
tubulus resistant
to urea
reabsorption
facilitated
diffusion
(through UT-A1 regulated
by ADH)
Water Diuresis
- after drinking of a higher amount of hypotonic fluid
- drinking itself  slightly ↓ ADH secretion
- water reabsorption  ↓ plasma osmolarity –
osmoreceptors in the hypothalamus  notable ↓
ADH secretion  ↓ water reabsorption in tubulus
 ↑ diuresis
Water Intoxication
Water Diuresis
- the water intake per time > the amount of water
which can be excreted (maximal diuresis ~16 ml/min)
-  cellular edema, symptoms of water intoxication
- iatrogenic
Osmotic Diuresis
- induced by presence of non-absorbed osmotically
active solutes in renal tubules (e.g. glucose diabetes
mellitus)
- non-absorbed solutes in the proximal tubule 
osmotic effect – retention of water in the tubulus
- ↓ transepithelial gradient for Na+  inhibition of
Na+ reabsorption in the proximal tubule  Na+
retained in the tubule ~ further osmotic load 
further retaining of water in the tubule
Osmotic Diuresis
- more isotonic fluid with higher total amount of Na+
into the loop of Henle  ↓ reabsorption of solutes
 ↓ hypertonicity of the renal medulla
- more fluid flows through other parts of tubulus + ↓
hypertonicity of the renal medulla  ↓ water
reabsorption in the collecting duct  ↑ diuresis,
urine with an increased amount of solutes
Regulation of Renal Functions
Regulation of Renal Blood Flow
Regulation of Renal Blood Flow
1) Myogenic Autoregulation
2) Neural Regulation
3) Humoral Regulation
Ganong´s Review of Medical
Physiology, 23rd edition
- dominates
- provides stable renal activity by maintaining
stable blood flow at varying systemic pressure
Regulation of Renal Blood Flow
1) Myogenic Autoregulation
2) Neural Regulation
- conformed to demands of systemic circulation
- sympathetic system - NE
light exertion (both emotional and physical) + upright
body posture   renal blood flow but without  GFR
higher  of sympathetic tone - during anesthesia and
pain - GFR may already 
Regulation of Renal Blood Flow
in healthy people – minor impact
3) Humoral Regulation
- contribute to regulation of systemic BP and
regulation of body fluids
- NE, E (from the adrenal medulla)
Regulation of Renal Blood Flow
constriction of aff. and eff. arterioles   renal blood
flow and GFR
(small impact with the exception of serious conditions, for
example serious bleeding)
3) Humoral Regulation
Regulation of Renal Blood Flow
- endothelin
constriction of aff. and eff. arterioles   renal blood
flow and GFR
released locally from the impaired endothel
(physiological impact - hemostasis; pathologically
increased levels at the toxemia of pregnancy, acute
renal failure, chronic uremia)
- contribute to regulation of systemic BP and
regulation of body fluids
3) Humoral Regulation
- NO
Regulation of Renal Blood Flow
- prostanglandins (PGE2, PGI2), bradykinin
continual basal production  vasodilation  stable
renal blood flow and GFR
 vasodilation
minor impact under physiological conditions
non-steroidal anti-inflammatory agents during stress!
- contribute to regulation of systemic BP and
regulation of body fluids
3) Humoral Regulation
- Renin-Angiotensine
System
Regulation of Renal Blood Flow
- contribute to regulation of systemic BP and
regulation of body fluids
Ganong´s Review of Medical
Physiology, 23rd edition
Renin-Angiotensine System
vasoconstriction
(more in eff. a.)
thirst, ADH
 Na+ in plasma
 blood pressure
 activity of sympathicus
( rec.)
Regulation of Renal Blood Flow
↓ renal blood flow but  GFR
(usually during  BP or fluid depletion – prevention
of  GFR +  tubular reabsorption of Na+ and
water due to  Pc in peritubular capillaries)
Regulation of Renal Blood Flow
Tubuloglomerular Feedback
3) Humoral Regulation
Ganong´s Review of Medical
Physiology, 23rd edition
Guyton  Hall.
Textbook of
Medical Physiology
Regulation of Renal Functions
Regulation of Glomerular Filtration
Regulation of Tubular Reabsorption
GFR = Kf  net filtration pressure
GFR = Kf  (PG + πB – PB – πG)
Regulation of Glomerular Filtration
• control of the glomerular filtration pressure:
constriction of vas aff.   glomerular pressure   filtration
constriction of vas eff.   glomerular pressure   filtration
1) Local Regulation
2) Neural Regulation
3) Humoral Regulation
1) Local Regulation
Regulation of Tubular Reabsorption
Glomerulotubular Balance
- controls balance between the glomerular filtration
and tubular reabsorption
Regulation of Tubular Reabsorption
Physical Forces in Peritubular Capillaries and in
Renal Intersticium
1) Local Regulation
TRR = Kf  net reabsorptive force
- ↑ Kf  ↑ TRR and vice versaKf
- rather stable under physiological conditions
Regulation of Tubular Reabsorption
1) Local Regulation
Physical Forces in Peritubular Capillaries and in
Renal Intersticium
TRR = Kf  net reabsorptive force
- BP (↑ BP  ↑ Pc  ↓ TRR)Pc
- resistance of aff. and eff. arterioles
πc
- fitration fraction (↑ FF  ↑ πc  ↑ TRR)
- π in plasma
Regulation of Tubular Reabsorption
Physical Forces in Peritubular Capillaries and in
Renal Intersticium
1) Local Regulation
Guyton  Hall.
Textbook of
Medical Physiology
Regulation of Tubular Reabsorption
Physical Forces in Peritubular Capillaries and in
Renal Intersticium – changes in intersticium (Pif, πif)
1) Local Regulation
Guyton  Hall. Textbook of Medical Physiology
↑ Pif
↓ πif
↑ reabsorption  ↓ Pif a ↑πif  ↓ backleak
Regulation of Tubular Reabsorption
Pressure Natriuresis and Pressure Diuresis
1) Local Regulation
- increased excretion of salt and water at ↑ BP
(physiologically slight effect on diuresis autoregulation
vs. impaired autoregulation at renal
diseases)
- mechanisms:
↑ GFR
↓ TRR
↓ formation of angiotensine II
(↑ BP  slight ↑ Pc  ↑ Pif  ↑ backleak  ↓ TRR)
Regulation of Tubular Reabsorption
2) Neural Regulation
Sympathicus
- small ↑ of its activity (α-rec. in epithelia):
 constriction of aff. and eff. arterioles  ↓ renal
blood flow  ↓ Pc  ↑ TRR
directly through ↑ reabsorption of Na+
- notable ↑ of its activity - indirectly:
 ↑ reabsorption of salt and water
Regulation of Tubular Reabsorption
3) Hormonal Regulation
- impact – separate regulation of
reabsorption/excretion of particular solutes (other
mechanisms are nonspecific – influence the total
TRR!)
Aldosteron
Angiotensine II
Natriuretic peptides (namely ANP)
Antidiuretic hormone
Parathormone
Urodilatin (renal NP)
Regulation of Tubular Reabsorption
3) Hormonal Regulation
Aldosteron
Angiotensine II
Regulation of Tubular Reabsorption
Natriuretic peptides
increased tension of atrial cardiomyocytes
 ↑ secretion of ANP:
 ↓ secretion of renin  ↓ angiotensine II  ↓
TRR
(congestive heart failure)
 ↓ reabsorption of salt and water directly
(namely in the collecting ducts)
3) Hormonal Regulation
Regulation of Tubular Reabsorption
Antidiuretic hormone (ADH)
- controls excretion of water
↑ osmolality of plasma (osmoreceptors)
 ↑ secretion of ADH – V2 receptors  water
channels (aquaporins 2)
 ↑ reabsorption of water by osmosis
3) Hormonal Regulation
Regulation of Tubular Reabsorption
Parathormone
- controls excretion of Ca2+
↓ calcemia
 ↑ secretion of parathormone:
 ↑ tubular reabsorption of Ca2+
(namely in the distal tubule)
 ↓ tubular reabsorption of phosphate in the
proximal tubule
 ↑ tubular reabsorption of Mg2+ in the loop
of Henle
3) Hormonal Regulation
Filling and emptying of the bladder
cystometrogram