28: Regulation of Extracellular FluidOsmolarity and Sodium Concentration

By: Dr. FoadoddiniDepartment of Physiology & PharmacologyBirjand University of Medical Sciences

0.5 20 L

50 1200 mOsmol/L

Countercurrent Mechanism• Interaction between the flow of filtrate through the loop of Henle

(countercurrent multiplier) and the flow of blood through the vasa recta blood vessels (countercurrent exchanger)

• The solute concentration in the loop of Henle ranges from 300 mOsm to 1200 mOsm

Countercurrent MechanismProduces a Hyperosmotic Renal Medullary Interstitium

http://www.colorado.edu/intphys/Class/IPHY3430-200/countercurrent_ct.htmlhttp://www.cellphys.ubc.ca/undergrad_files/urine.swf

http://bio-alive.com/animations/anatomy.htm

Permeable 

to H2O if ADH

50%

Urea Contributes to Hyperosmotic Renal Medullary Interstitium and to a Concentrated Urine

Countercurrent Exchange in the Vasa Recta Preserves Hyperosmolarity of the Renal Medulla

• Medullary osmotic gradient

• H2O→ECF→vasa recta vessels

Countercurrent Multiplier and Exchange

Quantifying Renal Urine Concentration and Dilution:"Free Water" and Osmolar Clearances

2.1 * 142 = 298 mOsmol/L

29: Renal Regulation of Potassium, Calcium, Phosphate, andMagnesium;  Integration of Renal Mechanisms for Control of Blood Volume and Extracellular Fluid Volume

UOBPDirectly

Indirectly

Pressure Diuresis & Natriuresis importance in BV and ECF control

Pressure Natriuresis and Diuresis Are Key Components of a Renal‐Body Fluid Feedbackfor Regulating Body Fluid Volumes and Arterial Pressure

BV CO BP UO

Neural controlAgIIAldostroneADHANP

Factors Increase the Effectivenessof Renal-Body Fluid Feedback Control

Factors affect K secretion:[K]oAldostroneTubular flowAcidosis

30: Regulation of Acid‐Base Balance

Volatile acids: CO2

Non‐ Volatile acids:  H2SO4, H3PO4β‐hydroxybutyric acid, Acetoacetic acidLactic acidSalcylic acid, formic acidGycolic acid, oxalic acid

extremely low

pH: is not linear but logarithmic functionie, more change in acidemia

normal range of arterial pH: 7.37 to 7.42

carbonic anhydrase

Isohydric law

1

3

2

4

5

brush bordercarbonic anhydrase

Acetazolamide

no net secretion of H+

little change in tubular fluid pH

DT, CT

Acid-base nomogram

Micturition (Voiding or Urination)

• Bladder can hold 250 ‐ 400ml• Greater volumes stretch bladder walls initiates

micturation reflex:• Spinal reflex

– Parasympathetic stimulation causes bladder to contract– Internal sphincter opens – External sphincter relaxes due to inhibition

Urination: Micturation reflex

Figure 19-18: The micturition reflex

Micturition (Voiding or Urination)

Figure 25.20a, b