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بسم الله الرحمن الرحيم. Counter Current Multiplication. And Micturition Reflex . Dr.Mohammed Sharique Ahmed Quadri Assistant professor physiology Al Amaarefa College. Objectives . Describe the factors that determine the ability of loop of Henle to creat osmotic medullary gradient

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counter current multiplication and micturition reflex

بسم الله الرحمن الرحيم

Counter Current Multiplication. And Micturition Reflex

Dr.Mohammed Sharique Ahmed Quadri

Assistant professor physiology

Al Amaarefa College

objectives
Objectives
  • Describe the factors that determine the ability of loop of Henle to creat osmotic medullary gradient
  • Identify countercurrent multiplier and countercurrent exchange systems in concentrating and diluting urine
  • Explain changes in osmolarity of tubular fluid in the various segments of the loop of Henle when concentrated urine is being produced.
  • Describe the role of ADH on the ability of the kidney to produce either a dilute or a concentrated urine.
  • Discuss the micturition reflex.
urine excretion
Urine Excretion
  • Depending on the body’s state of hydration, the kidneys secrete urine of varying concentrations.
  • Too much water in the ECF establishes a hypotonic ECF.
  • A water deficit establishes a hypertonic ECF.
  • This function is determined by the amount of water reabsorption in the renal tubules.
urine concentration dilution
Urine Concentration & Dilution
  • Water reabsorption is obligatory in the proximal(65%) tublues and Loop of Henle(15%).
  • The final adjustment of the urine volume and osmolarity depends on the extent of facultative water reabsorption in the Collecting Ducts, which is depends on:-
    • The blood level of antidiuretic hormone (ADH).
    • The Medullary interstitium (MI) hypertonicity (Medullary concentration gradient).
urine concentration
Urine Concentration

Requirements for forming a concentrated urine are:

  • High level of ADH (increase permeability)
  • High osmolarity of the renal medullary interstitial fluid (osmotic gradients)
driving force for h2o reabsorption
Driving force for H2O reabsorption
  • Driving force for water reabsorption throughout the entire length of tubules is an osmotic gradient between tubular lumen and surrounding interstitial fluid.
urine excretion1
Urine Excretion
  • A large, vertical osmotic gradient is established in the interstitial fluid of the medulla

(from 100 to 1200 mosm/liter)

  • This osmotic gradient exists between the tubular lumen and the surrounding interstitial fluid.
urine concentration dilution1
Urine Concentration & Dilution

What is the process by which renal medullary

interstitial fluid becomes hyperosmotic?

This process involves the operation of the

medullary countercurrent system

medullary countercurrent system
Medullary Countercurrent system
  • Juxta medullary nephrons
    • long loop of henleestabilishes a vertical osmotic gradient (Countercurrent multiplier) ,
    • their vassa recta preserve this gradient while providing blood to renal medulla,( Countercurrent exchanger)
    • collecting ducts of all nephrones use the gradient in conjunction with the hormone vassopressin, to produce urine of varying concentration (osmotic equilibrating device) .
  • Collectively this entire functional organization is known as medullary countercurrent system
countercurrent multiplication
Countercurrent Multiplication
  • Comparing the descending and ascending limbs of the loop of Henle
  • The descending ling is highly permeable to water but does not extrude sodium for reabsorption.
  • The ascending limb actively transports NaCl out of the tubular lumen into the surrounding interstitial fluid. It is impermeable to water. Therefore, water does not follow the salt by osmosis.
  • There is a countercurrent flow produced by the close proximity of the two limbs.
benefits of countercurrent multiplication
BENEFITS OF COUNTERCURRENT MULTIPLICATION
  • It establishes a vertical osmotic gradient in the medullary interstitial fluid. This gradient, in turn, is used by the collecting ducts to concentrate the tubular fluid so that a urine more concentrated than normal body fluids can be excreted.
  • Second, the fact that the fluid is hypotonic as it enters the distal parts of the tubule enables the kidneys to excrete a urine more dilute than normal body fluids.
role of vasopressin
Role of Vasopressin
  • Vasopressin-controlled, variable water reabsorption occurs in the final tubular segments.
  • 65 percent of water reabsorption is obligatory in the proximal tubule. In the distal tubule and collecting duct it is variable, based on the secretion of ADH.
  • The secretion of vasopressin increases the permeability of the tubule cells to water. An osmotic gradient exists outside the tubules for the transport of water by osmosis.
  • Vasopressin works on tubule cells through a cyclic AMP mechanism.
  • During a water deficit, the secretion of vasopressin increases. This increases water reabsorption.
  • During an excess of water, the secretion of vasopressin decreases. Less water is reabsorbed. More is eliminated.
renal failure
Renal Failure
  • Causes of renal failure
    • Infectious organisms
    • Toxic agents
    • Inappropriate immune responses
    • Obstruction of urine flow
    • An insufficient renal blood supply
micturition
Micturition
  • Urine stored in bladder is eliminated by micturition
  • Urine in bladder stimulates stretch receptors
  • Stimulated stretch receptors signal smooth muscle in bladder wall by parasympathetic neurons
  • Contraction of bladder pushes urine out of the body
  • Micturition reflex
    • Relaxation of external urethral sphincter muscle allowing urine to pass through urethra and out of the body
  • Under voluntary control but cannot be delayed indefinitely
  • Urinary incontinence
    • Inability to prevent discharge of urine
abnormalities of micturition
Abnormalities of micturition

Atonic Bladder Caused by Destruction of Sensory Nerve Fibers.

  • Micturition reflex cannot occur if the sensory nerve fibers from the bladder to the spinal cord are destroyed.
  • Person loses bladder control
  • Instead of emptying periodically, the bladder fills to capacity and overflows a few drops at a time through the urethra. This is called overflow incontinence.
  • A common cause of atonic bladder is crush injury to the sacral region of the spinal cord.
  • Certain diseases can also
slide29

Automatic Bladder Caused by Spinal Cord Damage Above the Sacral Region.

  • Typical micturition reflexes can still occur.
  • They are no longer controlled by the brain.
  • During the first few days to weeks the micturition reflexes are suppressed because “spinal shock” (sudden loss of facilitative impulses from the brain stem and cerebrum).
  • Gradually typical micturition reflexes return; then, periodic (but unannounced) bladder emptying occurs.
  • Some patients can still control urination in this condition by stimulating the skin (scratching or tickling) in the genital region, which sometimes elicits a micturition reflex.
slide30

Uninhibited Neurogenic Bladder Caused by Lack of Inhibitory Signals from the Brain.

  • Which results in frequent and relatively uncontrolled micturition.
  • From partial damage in the spinal cord or the brain stem that interrupts most of the inhibitory signals.
  • Facilitative impulses passing continually down the cord -even a small quantity of urine elicits an uncontrollable micturition reflex, thereby promoting frequent urination.
references
References
  • Human physiology by Lauralee Sherwood, seventh edition
  • Text book physiology by Guyton &Hall,11th edition
  • Text book of physiology by Linda .s contanzo,third edition
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