Body fluids

BODY FLUIDSBODY FLUIDSBODY FLUIDSBODY FLUIDS

Composition of the human bodyComposition of the human body::11--Water → 60% of the Water → 60% of the

body weightbody weight..22--Proteins → 18% of the Proteins → 18% of the

body weightbody weight..33--Fats → 18% of the Fats → 18% of the

body weightbody weight..44--Minerals → 4% of the Minerals → 4% of the

body weightbody weight..

Body WaterBody Water

--Water constitutes about 60% of body Water constitutes about 60% of body weight in young adult maleweight in young adult male..

--The amount of body HThe amount of body H22O decline with O decline with ageage : :

--The new born has about 82%of body The new born has about 82%of body weight as Hweight as H22O at birth and elderlyO at birth and elderly about 52%about 52%..


--Loss of body HLoss of body H22O is a common cause of O is a common cause of death in children who suffer from death in children who suffer from dehydrationdehydration..

--The amount of HThe amount of H22O in the body is affected O in the body is affected by the quantity of body fatby the quantity of body fat....

Lean subjects have a higher percentage of Lean subjects have a higher percentage of HH22O than those with more body fatO than those with more body fat..

This is because adipose tissue contains far This is because adipose tissue contains far less Hless H22O than muscle, skin, and other soft O than muscle, skin, and other soft tissuestissues . .


Variation of body HVariation of body H22O with age and O with age and sex as % of body weightsex as % of body weight

Male Female

At birth 82% 82%Children&adolescence 70% 70%

18-20 years 59% 57%20-40 years 56% 51%40-60years 55% 47%Over 60 years 52% 46%


A man who is weighing about 65 kg, the A man who is weighing about 65 kg, the total body water (TBW) is equal to 40 total body water (TBW) is equal to 40 Liters it is subdivided intoLiters it is subdivided into::

11--IntracellularIntracellular :(inside the cells)ICF: It :(inside the cells)ICF: It is about 2/3 of total body water(25 is about 2/3 of total body water(25 liters)liters)

22 - -Extracellular:(Extracellular:(outside the outside the cells)ECF:It is about 1/3 of the total cells)ECF:It is about 1/3 of the total body water(15liters)body water(15liters)


The extracellular fluid is further subdivided The extracellular fluid is further subdivided intointo::a)Intravasculara)Intravascular(inside the blood vessels): (inside the blood vessels): It is the blood plasma(3 liters)It is the blood plasma(3 liters)..b)Interstitialb)Interstitial(between the cells) in the (between the cells) in the tissue spaces(12 liters), it is similar to the tissue spaces(12 liters), it is similar to the plasma but with low protein contentplasma but with low protein content..c)Transcellularc)Transcellular(500 ml):It found in special (500 ml):It found in special compartments in the body such as the compartments in the body such as the pleural cavity, peritoneal cavity, spaces pleural cavity, peritoneal cavity, spaces between the lining of the brain and spinal between the lining of the brain and spinal cord (CSF)and the joint cavitiescord (CSF)and the joint cavities..


There is continuous exchange between There is continuous exchange between the intravascular and interstitial fluid the intravascular and interstitial fluid to supply the nutrients needed by to supply the nutrients needed by the cells and removing the waste the cells and removing the waste products. This exchange keeps the products. This exchange keeps the internal environment constantinternal environment constant

Comparison of ECF&ICF Comparison of ECF&ICF solutessolutes::

ECF ECF contains large amount of Na+ and contains large amount of Na+ and Cl- but only small amounts of Cl- but only small amounts of

K+,Mg++ and PO4K+,Mg++ and PO4----

In contrast, ICF contains large In contrast, ICF contains large quantities of K+,PO4--,moderate quantities of K+,PO4--,moderate amounts of Mg++ and exceedingly amounts of Mg++ and exceedingly

few Cafew Ca.++.++

Osmolality of body fluidsOsmolality of body fluids::

Because the cell membrane is highly Because the cell membrane is highly permeable to water, the osmolarity permeable to water, the osmolarity of ECF&ICF compartments are of ECF&ICF compartments are normally the same, about normally the same, about 290milliosmol/L290milliosmol/L

The plasma osmolality is calculated by The plasma osmolality is calculated by using the following formulausing the following formula::

Osmolality =2[Na+] +0.055[Glucose] +0.36[ Urea]Osmolality =2[Na+] +0.055[Glucose] +0.36[ Urea]

mEq/L mg% mgmEq/L mg% mg%%

Mechanism of water Mechanism of water balancebalance::

Normally ,total body water remains Normally ,total body water remains constant, therefore over 24-hours constant, therefore over 24-hours period, intake and loss of water must period, intake and loss of water must balance exactly to precisely regulate balance exactly to precisely regulate ECF osmolality and Na+ ECF osmolality and Na+ concentrationconcentration..Maintenance of TBW balance involves Maintenance of TBW balance involves regulation of both water excretion by regulation of both water excretion by the kidneys and regulation of water the kidneys and regulation of water intake by the thirst mechanismintake by the thirst mechanism..


Water intakeWater intake::

11--Drinks and food → supply about Drinks and food → supply about 2100 ml/day2100 ml/day..

22--Oxidation of carbohydrates, Oxidation of carbohydrates, produces about 300ml/dayproduces about 300ml/day..


Water lossWater loss::11--Urine: about 1.5L/dayUrine: about 1.5L/day..

22--Sweat: variable amount depending on the Sweat: variable amount depending on the environmental temperature and physical environmental temperature and physical activity. The volume of sweat is normally activity. The volume of sweat is normally 100ml/day.In hot weather or during heavy 100ml/day.In hot weather or during heavy exercise, water loss may increase up to 1-2 exercise, water loss may increase up to 1-2 liters/hourliters/hour..

33--Insensible water loss by evaporation Insensible water loss by evaporation through skin and respiratory system. It is through skin and respiratory system. It is termed insensible water loss because we termed insensible water loss because we are not consciously aware of it. It is about are not consciously aware of it. It is about 0.5 L/day0.5 L/day..


Regulation of water intakeRegulation of water intake::

--It is controlled by thirst sensationIt is controlled by thirst sensation..

--Thirst sensation: It is the conscious desire Thirst sensation: It is the conscious desire for waterfor water..

--The thirst center is found in the lateral The thirst center is found in the lateral nuclei of the hypothalamusnuclei of the hypothalamus..

--This center is connected to the This center is connected to the osmoreceptors in the anterior nuclei of the osmoreceptors in the anterior nuclei of the hypothalamushypothalamus..

Regulation of water Regulation of water intakeintake::

Water intake is stimulated byWater intake is stimulated by::11--Inceased effective osmotic pressure of the Inceased effective osmotic pressure of the

plasmaplasma:: It acts via osmoreceptors located in the anterior It acts via osmoreceptors located in the anterior

hypothalamus. When the Na+ concentration hypothalamus. When the Na+ concentration increases about 2 mEq/L above normal, the thirst increases about 2 mEq/L above normal, the thirst mechanism is activated causing a desire to drink mechanism is activated causing a desire to drink water .This is called the threshold for drinkingwater .This is called the threshold for drinking..

22--Decreased extracellular fluid volumeDecreased extracellular fluid volume:: Hemorrhage or hypotension caused increased Hemorrhage or hypotension caused increased

drinking even though there is no change in drinking even though there is no change in osmolality of the plasmaosmolality of the plasma


MechanismMechanism::

a)Renin-Angiotensin Systema)Renin-Angiotensin System::

Hypovolemia stimulates Rennin secretion→ Hypovolemia stimulates Rennin secretion→ resulting in rise of Angiotesin II in the resulting in rise of Angiotesin II in the circulationcirculation..

Angiotensin II stimulates thirst & acts on the Angiotensin II stimulates thirst & acts on the kidney to reduce fluid and electrolyte kidney to reduce fluid and electrolyte excretionexcretion..

b)Baroreceptors in the heart and blood b)Baroreceptors in the heart and blood vesselsvessels::

Regulation of H2O Regulation of H2O excretion by kidneyexcretion by kidney::

--Urine output is regulated and is one of Urine output is regulated and is one of the primary contributions to the primary contributions to maintaining water balancemaintaining water balance..

--Daily urine output can be as high as Daily urine output can be as high as 20L or as low as 500mL depending 20L or as low as 500mL depending on the water intakeon the water intake


MechanismMechanism::33--Other factorsOther factors::

--Dryness of the pharyngeal mucous Dryness of the pharyngeal mucous membrane→ thirst sensationmembrane→ thirst sensation..

--Prandial drinking: The intake of liquids is Prandial drinking: The intake of liquids is increased during eatingincreased during eating::

a-Increased plasma osmolality as food a-Increased plasma osmolality as food is absorbedis absorbed..

b-Gastro-instinal hormones may b-Gastro-instinal hormones may stimulate the thirststimulate the thirst . .

Regulation of H2O Regulation of H2O excretion by kidneyexcretion by kidney

a-In conditions of Ha-In conditions of H22O excess: as a result of O excess: as a result of excess fluid intake: The renal response is excess fluid intake: The renal response is to increase water excretion. In conditions to increase water excretion. In conditions of maximal water excretion urine volume of maximal water excretion urine volume can increase to 18-20L/daycan increase to 18-20L/day..b-Conditions of fluid depletion: as a result of b-Conditions of fluid depletion: as a result of restricted intake or inappropriate losses, restricted intake or inappropriate losses, the renal response is to reduce water the renal response is to reduce water excretion. The urine volume can be excretion. The urine volume can be reduced to as little as 500ml/dayreduced to as little as 500ml/day. .

Regulation of HRegulation of H22O excretion O excretion by kidneyby kidney

--The ability of the kidney to excrete The ability of the kidney to excrete urine of variable volume and urine of variable volume and osmolality is absolutely dependent osmolality is absolutely dependent on the action of ADHon the action of ADH..

Regulation of HRegulation of H22O excretion O excretion by kidneyby kidney

ADH secretion is triggered byADH secretion is triggered by::11--Rise in plasma osmolality,which are Rise in plasma osmolality,which are

detected by hypothalamic osmoreceptorsdetected by hypothalamic osmoreceptors..22--Decrease in ECF volume: This is detected Decrease in ECF volume: This is detected

by baroreceptorsby baroreceptors..The osmoreceptors mechanism is the most The osmoreceptors mechanism is the most important for minute to minute control of important for minute to minute control of ADH secretionADH secretion..ADH increases water reabsorption by the ADH increases water reabsorption by the collecting duct and therefore minimizes collecting duct and therefore minimizes water losswater loss..

FORCES AFFCTING FORCES AFFCTING EXCHANGE OF BODY EXCHANGE OF BODY

FLUIDSFLUIDS11--DiffusionDiffusion::

It is the net movement of particles through It is the net movement of particles through the cell membranethe cell membrane from high from high concentration to low concentrationconcentration to low concentration. . Also from Also from positively charged ions to positively charged ions to negatively charged ionsnegatively charged ions i.e. diffusion i.e. diffusion governed by either chemical or electrical governed by either chemical or electrical gradientgradient..

--Net movement of particle /unit time =fluxNet movement of particle /unit time =flux..

FORCES AFFCTING FORCES AFFCTING EXCHANGE OF BODY EXCHANGE OF BODY

FLUIDSFLUIDSII-FiltrationII-Filtration::

It is forced passage of fluid through a It is forced passage of fluid through a membrane due to difference in the membrane due to difference in the hydrostatic pressure on the two hydrostatic pressure on the two sidessides..

--The rate of filtration depends on the The rate of filtration depends on the pressure difference, surface area of pressure difference, surface area of the membrane and its permeabilitythe membrane and its permeability

FORCES AFFECTING FORCES AFFECTING EXCHANGE OF BODY EXCHANGE OF BODY

FLUIDSFLUIDSIII-OsmosisIII-Osmosis::

It is the movement of solvent It is the movement of solvent molecules across a membrane to the molecules across a membrane to the other side in which there is higher other side in which there is higher concentration of solute to which the concentration of solute to which the membrane is impermeablemembrane is impermeable..


FLUIDSFLUIDSIV-Active transportIV-Active transport::

It is the transport of particles It is the transport of particles from low from low concentration to high concentration concentration to high concentration across the cell membrane. This type of across the cell membrane. This type of transport occurs against the laws of transport occurs against the laws of physical chemistry(uphill) it requires energy physical chemistry(uphill) it requires energy derived from adenosine derived from adenosine triphosphate(ATP).The particles may be triphosphate(ATP).The particles may be transported against chemical, electrical or transported against chemical, electrical or pressure gradient. good example for active pressure gradient. good example for active transport is Natransport is Na++-K-K++ pump and calcium pump and calcium pumppump..


FLUIDSFLUIDSMechanisms of fluid exchangeMechanisms of fluid exchange::

The forces which govern this exchange The forces which govern this exchange of fluid between the plasma and the of fluid between the plasma and the interstitial fluid areinterstitial fluid are::

11--Hydrostatic pressure due to fluid Hydrostatic pressure due to fluid tension within the circulationtension within the circulation..

22--The colloid osmotic pressure of the The colloid osmotic pressure of the plasma proteinsplasma proteins..


FLUIDSFLUIDSThe hydrostatic pressure is much The hydrostatic pressure is much higher in the capillaries than in the higher in the capillaries than in the tissue spaces and tends to drive fluid tissue spaces and tends to drive fluid out of the capillaries by filtration. The out of the capillaries by filtration. The osmotic pressure is much higher in osmotic pressure is much higher in the blood plasma than in the the blood plasma than in the interstitial fluid and tend to draw interstitial fluid and tend to draw back into the capillaries by osmosisback into the capillaries by osmosis..These two forces act in opposite These two forces act in opposite directionsdirections . .


FLUIDSFLUIDSWhile the osmotic pressure is uniform While the osmotic pressure is uniform throughout the capillary length, the throughout the capillary length, the hydrostatic pressure falls from the arteriolar hydrostatic pressure falls from the arteriolar to the venular end. At the arteriolar end of to the venular end. At the arteriolar end of the capillary the hydrostatic pressure is the capillary the hydrostatic pressure is greater than the colloid osmotic pressure greater than the colloid osmotic pressure and, therefore, fluid tends to pass out of the and, therefore, fluid tends to pass out of the capillaries. At the venous end of the capillaries. At the venous end of the capillaries, the hydrostatic pressure is less capillaries, the hydrostatic pressure is less than the colloid osmotic pressure and than the colloid osmotic pressure and therefore, H2O is reabsorbed into the therefore, H2O is reabsorbed into the capillaries at this end of the capillarycapillaries at this end of the capillary..


FLUIDSFLUIDSAPPLIED PHYSIOLOGY OF TISSUE FLUID APPLIED PHYSIOLOGY OF TISSUE FLUID EXCHANGEEXCHANGEEdema: Edema is defined as the abnormal Edema: Edema is defined as the abnormal collection of fluid in the interstitial spaces. collection of fluid in the interstitial spaces. There are three main causes which occur There are three main causes which occur frequently in clinical practicefrequently in clinical practice::

11--Increased capillary hydrostatic pressureIncreased capillary hydrostatic pressure22--Decrease in the plasma colloid osmotic Decrease in the plasma colloid osmotic

pressurepressure33--Obestruction of lymph vesselsObestruction of lymph vessels..

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Body fluids