Functions of the Urinary System 1.Excretion. 2.Regulation of blood volume and pressure. 3.Regulation...

Functions of the Urinary Functions of the Urinary SystemSystem

Functions of the Urinary Functions of the Urinary SystemSystem

1. Excretion.2. Regulation of blood volume and

pressure.3. Regulation of the concentration of

solutes in the blood.4. Regulation of pH of extracellular fluid.5. Regulation of red blood cell

synthesis.6. Vitamin D synthesis.

1. Excretion.2. Regulation of blood volume and

pressure.3. Regulation of the concentration of

solutes in the blood.4. Regulation of pH of extracellular fluid.5. Regulation of red blood cell

synthesis.6. Vitamin D synthesis.

Internal Anatomy of the Internal Anatomy of the KidneyKidney


Cortex – outer area Medulla – inner area Renal pelvis Ureter

Cortex – outer area Medulla – inner area Renal pelvis Ureter



Cortex – outer area Medulla – inner area Renal pelvis Ureter Urinary Bladder Urethra

Cortex – outer area Medulla – inner area Renal pelvis Ureter Urinary Bladder Urethra

NephronNephronNephronNephron

Glomerulus Bowman’s capsule Proximal Tubule Loop of Henle

Descending limb, Ascending limb Distal Tubule Collecting Duct

Glomerulus Bowman’s capsule Proximal Tubule Loop of Henle

Descending limb, Ascending limb Distal Tubule Collecting Duct

Glomerular Filtration RateGlomerular Filtration RateGlomerular Filtration RateGlomerular Filtration Rate

Volume filtered per unit time Averages 180 l/day = 125 ml/min Total plasma volume = 3 l Therefore total plasma filtered 60x

/ day

Volume filtered per unit time Averages 180 l/day = 125 ml/min Total plasma volume = 3 l Therefore total plasma filtered 60x

/ day

MicturitionMicturitionMicturitionMicturition

Urination Kidney → Ureter → Bladder →

Urethra Detrusor muscle Internal Urethral Sphincter External Urethral Sphincter

Urination Kidney → Ureter → Bladder →

Urethra Detrusor muscle Internal Urethral Sphincter External Urethral Sphincter

Micturition ProcessMicturition ProcessMicturition ProcessMicturition Process

As bladder fills, ↑ pressure ↑ pressure → stimulates stretch

receptors Sensory fibers enter the spinal cord Parasympathetic neurons are

stimulated Sympathetic neurons are inhibited

As bladder fills, ↑ pressure ↑ pressure → stimulates stretch

receptors Sensory fibers enter the spinal cord Parasympathetic neurons are

stimulated Sympathetic neurons are inhibited


Stimulation of parasympathetic neurons → contraction of detrusor muscle

Inhibition of sympathetic neurons relaxes → internal urethral sphincter

Somatic input to external urethral sphincter is also inhibited by a reflexive action

Stimulation of parasympathetic neurons → contraction of detrusor muscle

Inhibition of sympathetic neurons relaxes → internal urethral sphincter

Somatic input to external urethral sphincter is also inhibited by a reflexive action


Result … Result …


Result … urination! Result … urination!


Result … urination! All of these actions are reflexive Central nervous system does have

a certain degree of control (thankfully!)

We can also voluntarily initiate or prevent urination

Result … urination! All of these actions are reflexive Central nervous system does have

a certain degree of control (thankfully!)

We can also voluntarily initiate or prevent urination

Sodium (NaSodium (Na++) & ) & Water (HWater (H22O) ReabsorptionO) Reabsorption




Both Na+ and H2O are freely filterable into Bowman’s space.

Most Na+ and H2O is reabsorbed. Most reabsorption takes place in the

proximal tubule (65%). Na+ reabsorption is an active process. H2O reabsorption is a passive process.

Both Na+ and H2O are freely filterable into Bowman’s space.

Most Na+ and H2O is reabsorbed. Most reabsorption takes place in the

proximal tubule (65%). Na+ reabsorption is an active process. H2O reabsorption is a passive process.

Sodium (NaSodium (Na++) ) ReabsorptionReabsorptionSodium (NaSodium (Na++) ) ReabsorptionReabsorption

2 phases: Diffusion down concentration

gradient across luminal membrane.

Active transport across basolateral membrane by Na+/K+ pump.

2 phases: Diffusion down concentration

gradient across luminal membrane.

Active transport across basolateral membrane by Na+/K+ pump.

Water (HWater (H22O) ReabsorptionO) ReabsorptionWater (HWater (H22O) ReabsorptionO) Reabsorption

Relies on the movement of Na+. Na+ moves from tubule to interstitial

fluid. Osmolarity of tubular fluid decreases

(↑ water concentration). Osmolarity of interstitial fluid

increases(↓ water concentration).

Relies on the movement of Na+. Na+ moves from tubule to interstitial

fluid. Osmolarity of tubular fluid decreases

(↑ water concentration). Osmolarity of interstitial fluid

increases(↓ water concentration).


As a result, water will move from an area of high concentration to an area of low concentration.

Therefore, there will be a net diffusion of water out of the tubule.

As a result, water will move from an area of high concentration to an area of low concentration.

Therefore, there will be a net diffusion of water out of the tubule.


The permeability of the tubular wall varies throughout the nephron.

Due to the presence of protein water channels called aquaporins.

The permeability of the tubular wall varies throughout the nephron.

Due to the presence of protein water channels called aquaporins.


Example: Collecting Duct Permeability depends on the peptide hormone

produced by the posterior pituitary known as vasopressin (aka anti-diuretic hormone).

Vasopressin stimulates the insertion of aquaporins into the luminal membrane of the collecting duct. (↑ H2O reabsorption).

Example: Collecting Duct Permeability depends on the peptide hormone

produced by the posterior pituitary known as vasopressin (aka anti-diuretic hormone).

Vasopressin stimulates the insertion of aquaporins into the luminal membrane of the collecting duct. (↑ H2O reabsorption).

Urine ConcentrationUrine ConcentrationUrine ConcentrationUrine Concentration

Hypoosmotic: Total solute concentration less than that of normal extracellular fluid.

Isoosmotic: Having the same solute concentration as extracellular fluid.

Hyperosmotic: Total solute concentration greater than that of normal extracellular fluid.

Hypoosmotic: Total solute concentration less than that of normal extracellular fluid.

Isoosmotic: Having the same solute concentration as extracellular fluid.

Hyperosmotic: Total solute concentration greater than that of normal extracellular fluid.


When vasopressin is high, urine volume is small.

The urine is also very concentrated (hyperosmotic).

How does the kidney do this? Answer:



How does the kidney do this? Answer:




How does the kidney do this? Answer: Countercurrent Multiplier

System.



How does the kidney do this? Answer: Countercurrent Multiplier

System.

Urine ConcentrationUrine Concentration(Countercurrent Multiplier System)(Countercurrent Multiplier System)Urine ConcentrationUrine Concentration(Countercurrent Multiplier System)(Countercurrent Multiplier System)

Urine concentration takes place in the medullary collecting ducts.

Interstitial fluid surrounding these ducts is very hyperosmotic.

When vasopressin is present, water diffuses out of the ducts into the interstitial fluid and then enters the blood.

Urine concentration takes place in the medullary collecting ducts.

Interstitial fluid surrounding these ducts is very hyperosmotic.

When vasopressin is present, water diffuses out of the ducts into the interstitial fluid and then enters the blood.


How does the interstitial fluid become hyperosmotic?

Answer:


Answer:



Answer: The Loop of Henle.


Answer: The Loop of Henle.



Answer: The Loop of Henle. The opposing flow in the two limbs

of the Loop of Henle (countercurrent) creates the hyperosmotic interstitial fluid.


Answer: The Loop of Henle. The opposing flow in the two limbs

of the Loop of Henle (countercurrent) creates the hyperosmotic interstitial fluid.


Ascending Limb Sodium (Na+) and Chloride (Cl-) (i.e. salt) are

reabsorbed in the ascending limb. Ascending limb is also relatively

impermeable to water, so little water follows the salt.

Result: Interstitial fluid becomes hyperosmotic when compared to fluid in ascending limb.

Ascending Limb Sodium (Na+) and Chloride (Cl-) (i.e. salt) are

reabsorbed in the ascending limb. Ascending limb is also relatively

impermeable to water, so little water follows the salt.

Result: Interstitial fluid becomes hyperosmotic when compared to fluid in ascending limb.


Descending Limb Descending limb is not permeable to

sodium (Na+) and chloride (Cl-) (i.e. salt).

Descending limb is also highly permeable to water.

Result: Net diffusion of water out of the descending limb to the more concentrated interstitial fluid.

Descending Limb Descending limb is not permeable to

sodium (Na+) and chloride (Cl-) (i.e. salt).

Descending limb is also highly permeable to water.

Result: Net diffusion of water out of the descending limb to the more concentrated interstitial fluid.


Descending Limb The diffusion will continue until the

osmolarities inside the descending limb and the interstitial fluid are equal.

This osmolarity is also greater than the osmolarity in the ascending limb.

This is the essence of the system.

Descending Limb The diffusion will continue until the

osmolarities inside the descending limb and the interstitial fluid are equal.

This osmolarity is also greater than the osmolarity in the ascending limb.

This is the essence of the system.

Urine ConcentrationUrine Concentration(Countercurrent Multiplier System)(Countercurrent Multiplier System)

MultiplicationMultiplication

Urine ConcentrationUrine Concentration(Countercurrent Multiplier System)(Countercurrent Multiplier System)

MultiplicationMultiplication Multiplication refers to the fact that

the osmolarity difference at each horizontal level is “multiplied” to a much higher value at the bend in the loop.

Result: Concentrated medullary interstitial fluid.

Multiplication refers to the fact that the osmolarity difference at each horizontal level is “multiplied” to a much higher value at the bend in the loop.

Result: Concentrated medullary interstitial fluid.

Urine ConcentrationUrine ConcentrationDistal TubuleDistal Tubule

Urine ConcentrationUrine ConcentrationDistal TubuleDistal Tubule

The fluid entering the distal tubule is more dilute (hypoosmotic) than the plasma.

The fluid becomes even more dilute while it passes through the distal tubule because sodium and chloride are pumped out and the tubule is relatively impermeable to water.

The fluid entering the distal tubule is more dilute (hypoosmotic) than the plasma.

The fluid becomes even more dilute while it passes through the distal tubule because sodium and chloride are pumped out and the tubule is relatively impermeable to water.

Urine ConcentrationUrine ConcentrationCollecting DuctCollecting Duct


The hypoosmotic fluid then enters the cortical collecting duct.

From here on, vasopressin is crucial. When vasopressin is present, water

is reabsorbed until it becomes isoosmotic to the plasma in peritubular capillaries (300 mOsmol/L).

The hypoosmotic fluid then enters the cortical collecting duct.

From here on, vasopressin is crucial. When vasopressin is present, water

is reabsorbed until it becomes isoosmotic to the plasma in peritubular capillaries (300 mOsmol/L).



The tubular fluid then enters the medullary collecting duct.

In the presence of vasopressin, water diffuses out of the duct into the interstitial fluid due to the high osmolarity set up by the countercurrent multiplier system.

This water eventually ends up in the blood.

The tubular fluid then enters the medullary collecting duct.

In the presence of vasopressin, water diffuses out of the duct into the interstitial fluid due to the high osmolarity set up by the countercurrent multiplier system.

This water eventually ends up in the blood.



The final urine is hyperosmotic. The kidneys retain as much water

as possible, minimizing the rate at which dehydration occurs during water deprivation.

Remember, the kidney relies on vasopressin for its function.

The final urine is hyperosmotic. The kidneys retain as much water

as possible, minimizing the rate at which dehydration occurs during water deprivation.

Remember, the kidney relies on vasopressin for its function.



If vasopressin concentration is low, cortical and medullary collecting ducts are relatively impermeable to water.

Result:


Result:




Result: Large volumes of hypoosmotic urine is excreted.


Result: Large volumes of hypoosmotic urine is excreted.

Sodium RegulationSodium RegulationSodium RegulationSodium Regulation

Sodium is freely filterable into Bowman’s Space.

Total body sodium levels varies by only a few percent.

The body controls the sodium levels reflexively.

Sodium is freely filterable into Bowman’s Space.

Total body sodium levels varies by only a few percent.

The body controls the sodium levels reflexively.


No specific receptors for sodium. Instead, the cardiovascular

baroreceptors provide feedback for sodium control.

Baroreceptors respond to pressure changes in the cardiovascular system.

Pressure changes in cardiovascular system are linked to sodium levels.

Low cardiovascular pressures are sensed by baroreceptors.

No specific receptors for sodium. Instead, the cardiovascular

baroreceptors provide feedback for sodium control.

Baroreceptors respond to pressure changes in the cardiovascular system.

Pressure changes in cardiovascular system are linked to sodium levels.



Low total-body sodium leads to low cardiovascular pressures.


Result:



Result:




Result: Lower GFR and increase sodium reabsorption.



Result: Lower GFR and increase sodium reabsorption.

Control of Sodium Control of Sodium ReabsorptionReabsorption

Control of Sodium Control of Sodium ReabsorptionReabsorption

More important for long-term regulation of sodium levels.

Major factor in control of sodium levels is the hormone aldosterone.

More important for long-term regulation of sodium levels.

Major factor in control of sodium levels is the hormone aldosterone.

AldosteroneAldosteroneAldosteroneAldosterone

Steroid hormone produced in the adrenal cortex.

Stimulates reabsorption of sodium by the cortical collecting ducts.

When a person eats a lot of sodium, aldosterone secretion is low, and vice versa.

Steroid hormone produced in the adrenal cortex.

Stimulates reabsorption of sodium by the cortical collecting ducts.

When a person eats a lot of sodium, aldosterone secretion is low, and vice versa.


What controls the secretion of aldosterone?

Answer:


Answer:



Answer: Another hormone called angiotensin II.






Angiotensin II acts directly at the adrenal cortex, stimulating the secretion of aldosterone.



Angiotensin II acts directly at the adrenal cortex, stimulating the secretion of aldosterone.

Renin-Angiotensin SystemRenin-Angiotensin SystemRenin-Angiotensin SystemRenin-Angiotensin System

Figure 26.19 (page 991) Renin is an enzyme secreted by

the juxtaglomerular cells. Renin splits a small peptide

(angiotensin I) from a larger protein called angiotensinogen (produced by the liver).

Figure 26.19 (page 991) Renin is an enzyme secreted by

the juxtaglomerular cells. Renin splits a small peptide

(angiotensin I) from a larger protein called angiotensinogen (produced by the liver).

Renin-Angiotensin SystemRenin-Angiotensin SystemRenin-Angiotensin SystemRenin-Angiotensin System

Angiotensin I is converted to angiotensin II by another enzyme called angiotensin converting enzyme.

Angiotensin II then stimulates the adrenal cortex to secrete aldosterone.

Therefore, the main determining factor in the production of angiotensin II is renin.

Angiotensin I is converted to angiotensin II by another enzyme called angiotensin converting enzyme.

Angiotensin II then stimulates the adrenal cortex to secrete aldosterone.

Therefore, the main determining factor in the production of angiotensin II is renin.

Juxtaglomerular cellsJuxtaglomerular cellsJuxtaglomerular cellsJuxtaglomerular cells

Juxtaglomerular cellsJuxtaglomerular cellsJuxtaglomerular cellsJuxtaglomerular cells

Three inputs to the juxtaglomerular cells: Renal sympathetic nerves Intrarenal receptors Macula densa

Three inputs to the juxtaglomerular cells: Renal sympathetic nerves Intrarenal receptors Macula densa

Renal Sympathetic NervesRenal Sympathetic NervesRenal Sympathetic NervesRenal Sympathetic Nerves

↓ plasma volume↓

↓ cardiovascular pressure↓

↑ renal sympathetic nerve activity↓

↑ renin secretion


↓ cardiovascular pressure↓

↑ renal sympathetic nerve activity↓

↑ renin secretion

Intrarenal BaroreceptorsIntrarenal BaroreceptorsIntrarenal BaroreceptorsIntrarenal Baroreceptors

↑ blood pressure in kidneys↓

↑ stretching of juxtaglomerular cells↓

juxtaglomerular cells secrete less renin

↑ blood pressure in kidneys↓

↑ stretching of juxtaglomerular cells↓

juxtaglomerular cells secrete less renin

Macula DensaMacula DensaMacula DensaMacula Densa

Located near the end of the ascending loops of Henle and the distal tubule.

Senses the sodium concentration in the tubular fluid flowing past it.

Located near the end of the ascending loops of Henle and the distal tubule.

Senses the sodium concentration in the tubular fluid flowing past it.

Macula DensaMacula DensaMacula DensaMacula Densa

↓ arterial blood pressure↓

↓ GFR↓

↓ salt concentration (Na+ & Cl-) in tubular fluid↓

↑ renin secretion

↓ arterial blood pressure↓

↓ GFR↓

↓ salt concentration (Na+ & Cl-) in tubular fluid↓

↑ renin secretion

SummarySummarySummarySummary

Renal Water RegulationRenal Water RegulationRenal Water RegulationRenal Water Regulation

Total-body water levels are regulated mainly by reflexes

The reflexes alter the secretion of vasopressin.

Total-body water levels are regulated mainly by reflexes

The reflexes alter the secretion of vasopressin.

VasopressinVasopressinVasopressinVasopressin

Vasopressin is produced by a group of neurons in the hypothalamus that terminate in the posterior pituitary.

Vasopressin is then released into the blood from the posterior pituitary.

The most important inputs for this release are from baroreceptors and osmoreceptors.

Vasopressin is produced by a group of neurons in the hypothalamus that terminate in the posterior pituitary.

Vasopressin is then released into the blood from the posterior pituitary.

The most important inputs for this release are from baroreceptors and osmoreceptors.

Baroreceptor Control of Baroreceptor Control of VasopressinVasopressin

Baroreceptor Control of Baroreceptor Control of VasopressinVasopressin


↓ blood pressure↓

↓ firing rate of cardiovascular baroreceptors↓

↑ vasopressin secretion (posterior pituitary)↓

↑ plasma vasopressin↓

↑ H2O reabsorption (collecting ducts)↓

↓ H2O excretion


↓ blood pressure↓

↓ firing rate of cardiovascular baroreceptors↓

↑ vasopressin secretion (posterior pituitary)↓

↑ plasma vasopressin↓

↑ H2O reabsorption (collecting ducts)↓

↓ H2O excretion

Osmoreceptor Control of Osmoreceptor Control of VasopressinVasopressin


Osmoreceptors are responsive to changes in osmolarity.

Located in the hypothalamus.

Osmoreceptors are responsive to changes in osmolarity.

Located in the hypothalamus.



↑ H2O ingested↓

↓ body-fluid osmolarity (↑ H2O concentration)↓

↓ firing rate of hypothalamic osmoreceptors↓

↓ vasopressin secretion (posterior pituitary)↓

↓ plasma vasopressin↓

↓ H2O reabsorption (collecting ducts)↓

↑ H2O excretion

↑ H2O ingested↓

↓ body-fluid osmolarity (↑ H2O concentration)↓

↓ firing rate of hypothalamic osmoreceptors↓

↓ vasopressin secretion (posterior pituitary)↓

↓ plasma vasopressin↓

↓ H2O reabsorption (collecting ducts)↓

↑ H2O excretion

Hydrogen Ion RegulationHydrogen Ion RegulationHydrogen Ion RegulationHydrogen Ion Regulation

Kidneys are ultimately responsible for balancing hydrogen ion gains/losses.

Kidneys excrete excess hydrogen ions or retain hydrogen ions to replenish supplies.

Uses bicarbonate to do this.

Kidneys are ultimately responsible for balancing hydrogen ion gains/losses.

Kidneys excrete excess hydrogen ions or retain hydrogen ions to replenish supplies.

Uses bicarbonate to do this.

Hydrogen Ion RegulationHydrogen Ion RegulationHydrogen Ion RegulationHydrogen Ion Regulation

Excretion of bicarbonate in urine results in an increase in plasma H+.

This occurs during alkalosis. Addition of bicarbonate to plasma

decreases plasma H+. This occurs during acidosis.

Excretion of bicarbonate in urine results in an increase in plasma H+.

This occurs during alkalosis. Addition of bicarbonate to plasma

decreases plasma H+. This occurs during acidosis.

Fluid Replacement During Fluid Replacement During ExerciseExercise


During prolonged exercise in the heat, people can become dehydrated at a rate of 1-2 L every hour (about 2-4 lbs of body weight loss per hour).

Even a slight amount of dehydration causes physiological consequences.

During prolonged exercise in the heat, people can become dehydrated at a rate of 1-2 L every hour (about 2-4 lbs of body weight loss per hour).

Even a slight amount of dehydration causes physiological consequences.



For example, every liter (2.2 lbs) of water lost will cause: Heart rate to be elevated by about

eight beats per minute

Cardiac output to decline by 1 L/min

Core temperature to rise by 0.3o C when an individual participates in prolonged exercise in the heat.

For example, every liter (2.2 lbs) of water lost will cause: Heart rate to be elevated by about

eight beats per minute

Cardiac output to decline by 1 L/min

Core temperature to rise by 0.3o C when an individual participates in prolonged exercise in the heat.



People should attempt to drink fluids at close to the same rate that they are losing body water by sweating.

People should attempt to drink fluids at close to the same rate that they are losing body water by sweating.



Unfortunately, runners generally drink only 300-500 mL of fluids per hour and thus allow themselves to become dehydrated at rates of 500-1,000 mL/h.

Dehydration compromises cardiovascular function and places the runner at risk for heat-related injury.

Unfortunately, runners generally drink only 300-500 mL of fluids per hour and thus allow themselves to become dehydrated at rates of 500-1,000 mL/h.

Dehydration compromises cardiovascular function and places the runner at risk for heat-related injury.



So, the runner must ask him/herself the question…

Will the time I lose by drinking larger volumes of fluid be compensated for by the physiological benefits the extra fluid produces that may cause me to run faster during the last half of the race?

So, the runner must ask him/herself the question…

Will the time I lose by drinking larger volumes of fluid be compensated for by the physiological benefits the extra fluid produces that may cause me to run faster during the last half of the race?



The prevalent thinking from the turn of the century until the 1970's was that participants in endurance sports did not need to replace fluids lost during exercise.

However, we know now that drinking fluids reduces the increase in body temperature (hyperthermia) and the amount of stress on the cardiovascular system, especially when exercising in hot environments.

The prevalent thinking from the turn of the century until the 1970's was that participants in endurance sports did not need to replace fluids lost during exercise.

However, we know now that drinking fluids reduces the increase in body temperature (hyperthermia) and the amount of stress on the cardiovascular system, especially when exercising in hot environments.



However, many do not appreciate the extent to which even a slight degree of dehydration adversely affects bodily function during exercise.

Adding carbohydrate and salt to water provides added benefit.

The volume of fluid that most athletes choose to drink voluntarily during exercise replaces less than one-half of their body fluid losses.

However, many do not appreciate the extent to which even a slight degree of dehydration adversely affects bodily function during exercise.

Adding carbohydrate and salt to water provides added benefit.

The volume of fluid that most athletes choose to drink voluntarily during exercise replaces less than one-half of their body fluid losses.

Fluid Replacement During Fluid Replacement During Prolonged ExerciseProlonged Exercise


Undoubtedly, the most serious consequence of inadequate fluid replacement, i.e., dehydration, during exercise is hyperthermia.

When severe, hyperthermia will cause heat exhaustion, heat stroke, and even death.

Undoubtedly, the most serious consequence of inadequate fluid replacement, i.e., dehydration, during exercise is hyperthermia.

When severe, hyperthermia will cause heat exhaustion, heat stroke, and even death.



The risks of too much fluid ingestion are:

Gastrointestinal discomfort.

Reduced pace during competition associated with the physical difficulty of drinking large volumes of fluid while exercising.

The benefits of fluid ingestion are:

Reduced cardiovascular stress.

Reduced hyperthermia which could improve exercise performance.

The risks of too much fluid ingestion are:

Gastrointestinal discomfort.

Reduced pace during competition associated with the physical difficulty of drinking large volumes of fluid while exercising.

The benefits of fluid ingestion are:

Reduced cardiovascular stress.

Reduced hyperthermia which could improve exercise performance.

Difficulties in Drinking Large Difficulties in Drinking Large Volumes of Fluids While Volumes of Fluids While

RunningRunning


RunningRunning Large gastric volumes will no

doubt cause discomfort in some runners.

Therefore, in runners, it remains to be determined if the performance benefits of high rates of fluid replacement outweigh the discomfort it may cause.

Large gastric volumes will no doubt cause discomfort in some runners.

Therefore, in runners, it remains to be determined if the performance benefits of high rates of fluid replacement outweigh the discomfort it may cause.


RunningRunning


RunningRunning Many marathon runners allow

themselves to become dehydrated to some extent because they feel their stomachs cannot tolerate the large volumes of fluid that must be drunk to totally offset sweat losses.

In general, most runners drink less than about 500 mL of fluid per hour.

Many marathon runners allow themselves to become dehydrated to some extent because they feel their stomachs cannot tolerate the large volumes of fluid that must be drunk to totally offset sweat losses.

In general, most runners drink less than about 500 mL of fluid per hour.


RunningRunning


RunningRunning Sweat rates often average 1,000-

1,500 mL/h.

Marathon runners commonly become dehydrated at a rate of 500-1,000 mL/h, although dehydration rates can be much higher when the fastest runners compete in hot environments.

Sweat rates often average 1,000-1,500 mL/h.

Marathon runners commonly become dehydrated at a rate of 500-1,000 mL/h, although dehydration rates can be much higher when the fastest runners compete in hot environments.


RunningRunning


RunningRunning Unfortunately, drinking large volumes of

fluid cost the runner additional seconds in approaching the aid-station table and in attempting to drink and breathe while running.

Furthermore, the added gastrointestinal discomfort may cause the competitor to run at a slower pace until the discomfort subsides.

Unfortunately, drinking large volumes of fluid cost the runner additional seconds in approaching the aid-station table and in attempting to drink and breathe while running.

Furthermore, the added gastrointestinal discomfort may cause the competitor to run at a slower pace until the discomfort subsides.


RunningRunning


RunningRunning The runner is faced with the same

important question…

Will the time lost while drinking larger volumes of fluid will be compensated for by the physiological benefits the extra fluid produces that may cause me to run faster during the last half of the race?

The runner is faced with the same important question…

Will the time lost while drinking larger volumes of fluid will be compensated for by the physiological benefits the extra fluid produces that may cause me to run faster during the last half of the race?


RunningRunning


RunningRunning However, if the goal is safety,

which means minimizing hyperthermia, it is clear that the closer that the rate of drinking can match the rate of dehydration, the better.

However, if the goal is safety, which means minimizing hyperthermia, it is clear that the closer that the rate of drinking can match the rate of dehydration, the better.

Low Intensity Exercise and Low Intensity Exercise and Fluid ReplacementFluid Replacement


It has been known for over 60 years that fluid ingestion during prolonged low-intensity exercise such as walking and stair stepping controlled deep body (core) temperature and improved exercise performance.

It has been known for over 60 years that fluid ingestion during prolonged low-intensity exercise such as walking and stair stepping controlled deep body (core) temperature and improved exercise performance.



Fluid ingestion equal to the rate of sweating was more effective than voluntary or partial fluid replacement.

Furthermore, voluntary fluid ingestion during low-intensity exercise is more effective in attenuating hyperthermia than when fluid intake is totally prohibited or is restricted to small volumes.

Fluid ingestion equal to the rate of sweating was more effective than voluntary or partial fluid replacement.

Furthermore, voluntary fluid ingestion during low-intensity exercise is more effective in attenuating hyperthermia than when fluid intake is totally prohibited or is restricted to small volumes.



Thus, during prolonged, low-intensity, intermittent exercise, the optimal rate of fluid replacement for reducing hyperthermia appears to be the rate that most closely matches the rate of sweating.

Thus, during prolonged, low-intensity, intermittent exercise, the optimal rate of fluid replacement for reducing hyperthermia appears to be the rate that most closely matches the rate of sweating.

Hyponatremia in AthletesHyponatremia in AthletesHyponatremia in AthletesHyponatremia in Athletes

Hyponetremia is a fluid-electrolyte disorder that occurs when the sodium level in blood drops below normal.

The proper blood (plasma) sodium level is critical for the body to function normally.

Hyponetremia is a fluid-electrolyte disorder that occurs when the sodium level in blood drops below normal.

The proper blood (plasma) sodium level is critical for the body to function normally.


Sodium plays a key role in body fluid balance and in the conduction of electrical impulses along nerves and across cardiac and skeletal muscle.

For those reasons, the body is well equipped with mechanisms that control blood sodium.

Sodium plays a key role in body fluid balance and in the conduction of electrical impulses along nerves and across cardiac and skeletal muscle.

For those reasons, the body is well equipped with mechanisms that control blood sodium.


When these mechanisms are overwhelmed, blood sodium can drop. If blood sodium falls below an acceptable level, the individual is considered to be hyponatremic.

When these mechanisms are overwhelmed, blood sodium can drop. If blood sodium falls below an acceptable level, the individual is considered to be hyponatremic.

Is Hypernatremia Is Hypernatremia Dangerous?Dangerous?


Hyponatremia is dangerous and can be deadly.

The danger of hyponatremia is that it disrupts the fluid balance across the blood-brain barrier, resulting in a rapid influx of water into the brain.

Hyponatremia is dangerous and can be deadly.

The danger of hyponatremia is that it disrupts the fluid balance across the blood-brain barrier, resulting in a rapid influx of water into the brain.



This causes brain swelling and a cascade of increasingly severe neurological responses (headache, malaise, confusion, seizure, coma) that, in some cases, can lead to death.

The faster and lower the blood sodium falls, the greater the risk of fatality.

This causes brain swelling and a cascade of increasingly severe neurological responses (headache, malaise, confusion, seizure, coma) that, in some cases, can lead to death.

The faster and lower the blood sodium falls, the greater the risk of fatality.



A decrease in plasma sodium concentration to 125-135 mEq/L is often benign, with either no noticeable symptoms or relatively modest gastrointestinal disturbances such as bloating or mild nausea.

A decrease in plasma sodium concentration to 125-135 mEq/L is often benign, with either no noticeable symptoms or relatively modest gastrointestinal disturbances such as bloating or mild nausea.



Below 125 mEq/L, symptoms include throbbing headache, vomiting, wheezy breathing, swollen hands and feet, restlessness, unusual fatigue, confusion and disorientation.

Below 125 mEq/L, symptoms include throbbing headache, vomiting, wheezy breathing, swollen hands and feet, restlessness, unusual fatigue, confusion and disorientation.



Below 120 mEq/L, seizure, permanent brain damage, respiratory arrest, coma and death become more likely. However, some athletes have survived hyponatremia of <115 mEq/L, whereas others have died at >120 mEq/L.

Below 120 mEq/L, seizure, permanent brain damage, respiratory arrest, coma and death become more likely. However, some athletes have survived hyponatremia of <115 mEq/L, whereas others have died at >120 mEq/L.

What Causes What Causes HypernatremiaHypernatremia

in Athletes?in Athletes?


in Athletes?in Athletes? In athletes, hyponatremia is

usually caused by

excessive drinking.

sodium loss in sweat.

kidney’s limited capacity to excrete water.

the combination dilutes the sodium content of the extracellular fluid (ECF).

In athletes, hyponatremia is usually caused by

excessive drinking.

sodium loss in sweat.

kidney’s limited capacity to excrete water.

the combination dilutes the sodium content of the extracellular fluid (ECF).




in Athletes?in Athletes? The ECF contains most of the

sodium in the body.

Large sodium losses in sweat can increase the risk for hyponatremia by reducing the sodium content of the ECF.

The ECF contains most of the sodium in the body.

Large sodium losses in sweat can increase the risk for hyponatremia by reducing the sodium content of the ECF.




in Athletes?in Athletes? However, it is the combination of

excessive drinking and large sweat sodium losses that poses the greatest threat.

Excessive drinking increases the risk of developing hyponatremia in both athletes and non-athletes.

However, it is the combination of excessive drinking and large sweat sodium losses that poses the greatest threat.

Excessive drinking increases the risk of developing hyponatremia in both athletes and non-athletes.




in Athletes?in Athletes? Some athletes may drink large volumes

of fluid in a misguided attempt to stay well hydrated.

For example, Eichner (2002) reports that a woman who experienced hyponatremia during a marathon drank 10 liters (10.6 quarts) of fluid the previous night.

Some athletes may drink large volumes of fluid in a misguided attempt to stay well hydrated.

For example, Eichner (2002) reports that a woman who experienced hyponatremia during a marathon drank 10 liters (10.6 quarts) of fluid the previous night.




in Athletes?in Athletes? Hyponatremia has occurred in people

who have tried to dilute their urine (to escape being detected for drugs) by drinking large amounts of fluid.

The kidneys' limited capacity to excrete water can increase the risk of hyponatremia.

Hyponatremia has occurred in people who have tried to dilute their urine (to escape being detected for drugs) by drinking large amounts of fluid.

The kidneys' limited capacity to excrete water can increase the risk of hyponatremia.




in Athletes?in Athletes? Most adults can drink 2 quarts of fluid or

more an hour, but the most we can lose in urine is usually less than 1 quart/hour.

Researchers have shown that plasma sodium levels can quickly plummet when resting subjects overdrink water.

Most adults can drink 2 quarts of fluid or more an hour, but the most we can lose in urine is usually less than 1 quart/hour.

Researchers have shown that plasma sodium levels can quickly plummet when resting subjects overdrink water.




in Athletes?in Athletes? During exercise, it is even easier

for an overzealous drinker to overwhelm the kidneys' ability to excrete excess water because urine production normally declines 20 to 60 percent from resting values due to a decrease in kidney blood flow.

During exercise, it is even easier for an overzealous drinker to overwhelm the kidneys' ability to excrete excess water because urine production normally declines 20 to 60 percent from resting values due to a decrease in kidney blood flow.




in Athletes?in Athletes? This response helps conserve vital

water, but increases the risk that excessive drinking will lead to hyponatremia.

This response helps conserve vital water, but increases the risk that excessive drinking will lead to hyponatremia.

Symptoms and Treatment Symptoms and Treatment of Hypernatremiaof Hypernatremia


Watch for a combination of these symptoms, especially if you or somebody you know is at risk for the condition:

Watch for a combination of these symptoms, especially if you or somebody you know is at risk for the condition:



Rapid weight gain Severe fatigue

Bloated stomach Lack of coordination

Swollen hands & feet Restlessness

Nausea & vomittingConfusion & disorientation

Throbbing headache Wheezy breathing

Dizziness Seizure



Seek emergency care for hyponatremia victims. In most cases, they will be treated with some combination of:

An IV of a concentrated sodium solution

A diuretic medication to speed water loss

An anticonvulsive medication in the case of seizure.

Seek emergency care for hyponatremia victims. In most cases, they will be treated with some combination of:

An IV of a concentrated sodium solution

A diuretic medication to speed water loss

An anticonvulsive medication in the case of seizure.

What Can Be DoneWhat Can Be Doneto Prevent to Prevent

Hypernatremia?Hypernatremia?


Hypernatremia?Hypernatremia? Educate athletes to avoid

excessive drinking of any beverage and make sure they have enough sodium in their diets.

Educate athletes to avoid excessive drinking of any beverage and make sure they have enough sodium in their diets.




Hypernatremia?Hypernatremia? The goal of drinking during exercise is

to: Keep weight loss (dehydration) to a

minimum. (Losing weight during exercise means athletes are not replacing their fluids properly and are at risk for dehydration.)

Make sure athletes don't gain weight during exercise, which is a sure sign of drinking too much.

The goal of drinking during exercise is to: Keep weight loss (dehydration) to a

minimum. (Losing weight during exercise means athletes are not replacing their fluids properly and are at risk for dehydration.)

Make sure athletes don't gain weight during exercise, which is a sure sign of drinking too much.





to: An athlete who weighs more after exercise

than when he or she started has had too much fluid and needs to cut back during the next time.

Assure they're getting enough sodium to replace what they're losing in sweat.

The goal of drinking during exercise is to: An athlete who weighs more after exercise

than when he or she started has had too much fluid and needs to cut back during the next time.

Assure they're getting enough sodium to replace what they're losing in sweat.





to: Provide athletes with salty foods and

snacks. During workouts and competitions, athletes

should favor a sports drink containing at least 100 mg of sodium/8-oz serving, (Gatorade), over water to assure an additional intake of sodium that will help stabilize the sodium content of the ECF.

The goal of drinking during exercise is to: Provide athletes with salty foods and

snacks. During workouts and competitions, athletes

should favor a sports drink containing at least 100 mg of sodium/8-oz serving, (Gatorade), over water to assure an additional intake of sodium that will help stabilize the sodium content of the ECF.

Functions of the Urinary System 1.Excretion. 2.Regulation of blood volume and pressure. 3.Regulation...

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