Body Fluids (2)

8/3/2019 Body Fluids (2)

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Body fluid

The maintenance of a relatively constantvolume and a stable composition of the body

fluids are essential for homeostasis.

[Most important problems in clinical medicinearise because of abnormalities in the controlsystems that maintain this constancy of thebody fluids] .



During steady-state conditions intake and outputmust be balanced, despite the continuous exchange of

fluid and solutes with the external environment as wellas within the different compartments of the body

Intake 2.3 L/day : Output 2.3 L/day :

-Ingested water 2.1 L/d - Insensible loss 700water, food evaporation, diffusion

-Synthesis 200 - Sweat 100 , hot moreoxydation- Feces 100 ml/d

- Urine 1.4 , 0.5-20L



Table 14-3, p. 451



Table 14-2, p. 447



Body fluid compartments 60% of body weight

IntravascularExtravascular

a. Plasmaa. Extracellular 20% b. Interstitial

c. Transcellular : in

synovial, peritoneal, pericardial , CSF.

b. Intracellular 40%



Body fluid compartments

Percentage of fluids determines by age.Gender, and degree of obesity.

ICF : 28 L, around 40% of body weight.

ECF : 14 L around 20% of body weight.Interstitial is 75%, plasma is 25%.



• contains both ICF (RBCs) & ECF (plasma)

• considered as a separate compartment because it’s

contained in the circulatory system.

7% of body weight: 5 L, 60% plasma, 40% blood cells.

• hematocrit :(packed red cell volume) the fraction of blood

composed of RBCs (in men: 0.4 , in women: 0.36).

in anemic patients the hematocrit is lower. patients with polycythemia have higher hematocrit


http://slidepdf.com/reader/full/body-fluids-2 8/59Table 14-1, p. 445


http://slidepdf.com/reader/full/body-fluids-2 9/59Fig. 14-2, p. 446

C a p i l l a

r y w a l l

P l a s m a m

e m b r a n e

PlasmaInterstitialfluid

Intracellularfluid(skeletal muscle)



Composition of ECF

Donnan effect: Plasma proteinsnegatively charged, so attract morecations in plasma, and repel negatively

charged out. 2% cations more iside. ICF: small quantities of sodium, chloride,

almost no calcium, but large amount of

potassium, phosphate, sulfate ions, andlarge amount of proteins (4 times morethan plasma)



Measurement of fluidvolumes

Indicator-diluting-principle:

indicator: - evenly distributed in targetedcompartment. - not metabolized, or

excreted. - not toxic -easy to use.

Analyze concentration of indicator:

- chemically - photo electrically

-radioactivity.

Injected mass = mass after dispersion

Vi . Ci =Vf . Cf



Measurement of fluid volumes :

- Indicator-dilution principle Vi Ci = Vf Cf

a. Total body water: tritium H2O, deuterium H2O,Antipyrine

b. ECF : Labeled Na , Cl, thiosolfate , iothalmate, and

inuline

c. ICF = TBW - ECF (calculated)

d. Plasma : I - serum albumin, Evans blue dye

e. Interstitial = ECF - plasma (calculated)

f. Blood vol. = plasma vol. g. RBC: chromium1 - Hct



Regulation of fluid exchange

b/w intra-and extracellular fluid



egu a on o uexchange

Distribution b/w plasma & interstitial isdetermined by balance of hydrostatic &colloid forces across capillary.

Distribution b/w IC and ECF isdetermined by osmotic effect of thesmaller solutes acting across cell

membrane.




Relation b/w moles and osmoles: waterconcentration in a solution depends onthe # of solute particles in solution, so a

concentration term is needed todescribe the total concentration of soluteparticles, regardless of their exact

composition. Total # of particles in solution is

measured in osmoles.




Osmotic pressure: Precise amount ofpressure required to prevent theosmosis.

The higher the osmotic pressure of asolution, the lower the waterconcentration and the higher the solute

concentration of the solution.



1 osmole = 1 mole of solute particles (6.02 x10).

1 mole glucose = 1 osm.

1 mole NaCl = 2 osm.1 mole Na2SO3 = 3 osm.

Relation between moles andosmoles



•Osmotic pressure : pressure thatprevents the osmosis .

•The higher the osmotic pressure of asolution, the lower its [H2O] but the higherits [solute].

•According to Van’t hoff’s law: π = CRTπ= 19300 mm Hg for 1 osmole/liter at

body temp.

π(osmotic pr.) C(solute con. In osmole/liter)

R (ideal gas const.) T(absolute temp.)



Osmolarity of body fluids

In ECF more than 80-90% related tosodium chloride concentration.

In ICF 50% related to potassium

concentration.

ECF & ICF osmolarity almost 300mOsm/L.

Plasma has one mOsm/L more becauseof plasma proteins effect.



Osmolarity of body fluids

If particles exert interionic &intermolecular attraction, that causingslight decrease of osmotic activity.

If particles repel each other, that causesa slight increase in osmotic activity.

Plasma = 282 mOsm/L

ECF & ICF = 281 mOsm/L



-Frequent problem in the treatment ofseriously ill patients is the difficulty of

maintaining adequate fluids in one orboth of the intra- and extracellularcompartments.



- Osmotic effect of electrolytes (NaCl)determines the distribution of fluidsb/w intra- and extracell. comp.

(because the membrane is permeablefor H2O but not for Na and Cl)



- Osmolality and osmolarity inhuman fluids are equal.



• osmotic pr. = osmolarity(mOsm/L) X 19.3 mmHg

• the calculated value is not 100% correct due to intraionic

and intermolecular interactions between the particles andit has to be multiplied by the “osmotic coefficient” of the

particles to reach the true value.

• the osmolarity of the body fluids is around 300 mOsm/L,

the plasma being 1mOsm/L higher because of the osmotic

effect of plasma proteins



Osmotic equilibrium

Small changes in concentration of impermeantsolutes in the ECF can cause tremendous

changes in cell volume .

Isotonic Hypertonic HypoticIsosmotic Hyperosmotic Hypoosmotic



Osmotic Equilibrium

Isotonic, hypotonic and hypertonicsolutions depend on how cells behavein the solution, whether they swell or

shrink or do not change their volume.

Iso-smotic, hyper-osmotic, and hypo-

osmotic : determine the level ofosmolarity regardless of weather solutecan penetrate cell membrane.



Osmotic equilibrium

Transfer of fluid across membraneoccurs rapidly, so osmolariteis b/w IC &ECF are corrected w/in seconds, or at

the most, minutes. After drinking water we need only 30

min. to reach equilibrium everywhere in

the body.



1. Osmolarity of ECF and ICF remain

almost exactly equal, except for a fewminute after a change in onecompartment.

2. Cell membrane almost impermeable tomany solutes so # of osmoles is constantunless solutes are aded to or lost from the

ECF.



1. Calculation of H2O deficit in

dehydration

- 70 Kg pt. dehydrated unconscious.Plasma osm. 320 mOsm.

- How much water needed to restoreplasma osmolarity to 280 mOsm/L .



First step: assuming ECF 20% of body wt.

ICF 40% ____

ECF ICF Total

Vol. 14 L 28 L 42 LOsmoles 4480 896 13440

(because osm. = 320)



Second step: determine the volume

needed to reduce osmol. to 280 mOsm/L.Knowing that # of mosmoles is constantthen volume = # mosmoles

osmolarity

ECF ICF Total

Vol. 16 32 48 LOsm. 280 280 280# osm. 4480 8960 13440



Third step : Calculate the fluid volume

needed.

48 L - 42 L = 6 L water



Volume & osmolarity inabnormal states

-Ingestion of water

- Dehydration

-I.V infusion

-Loss of fluids:

From GI : diarrhea, vomiting.

Sweating : during hot weather, or heavyexercise.

From kidneys: diabetes insipidus, andneprogenic.



What is the effect of infusing 2 liters of ahypertonic 3.0 per cent sodium chlorideinto the ECF compartment of a 70Kgpatient whose initial plasma osmolarity is

280mOsm/L?



Table 14-4, p. 453



Glucose and other solutionsadministered for nutritive purposes

• given to patients who can not otherwise take

adequate amounts of nutrition.

• the osmotic ally active substances’concentrations are adjusted nearly to isotonicity,or they are given slowly enough in order not todisturb the osmotic eq. of the body.

• after they are metabolized what is left is only

water that is excreted by the kidneys in the formof very dilute urine.



2- Hyponatremia :

(a). Water excess in ECF :(hypoosmotic overhydration)- Excess secretion of ADH

(b). Loss of NaCl ( hypoosmoticdehydration)

-Excessive sweating, diarrhea, vomiting- Overuse of diuretics- Addison’s disease hypoaldosterone dedcreases Na reabsorption in kidneys



3. Hypernatremia :

a. Loss of water from ECF hyperosmotic dehydration.

-No ADH (diabetes insipidus,nephrogenic diabetes insipidus)- Heavy sweating.

b. Excessive NaCladdedhyperosmoticoverhydration. Hyperaldosterone.

St li ill



Starling capillarycirculation

-Balance of hydrostatic and colloidosmotic forces across the capillarymembrane determines the

distribution of ECF b/w plasma andinterstitial fluids.

EndothelialC ill



Fig. 10-16a, p. 292

Endothelialcell

Pores

Capillary



Starling capillary circulation

- 3 mmHg - 3 mmHg8 mmHg 1 8 mmHg ____________________________

130 mmHg 1 28 mmHg

1 10 mmHg

______________________________

Mean capillary pr. 17.3 mmHgNegative interstitial pr. 03.0 mmHg

Osmotic interstitial pr. 08.0 mmHgPlasma colloid pr. 28.0 mmHg

____

Net filtration 0.3 mmHg



Fig. 10-18 (middle), p. 294

11 mm Hg

(ultrafiltration)

Interstitial fluid

From arteriole To venule

9 mm Hg

(reabsorption)

Initial lymphaticvessel

Blood capillary(See next slide)



Fig. 10-19, p. 295

Capillarypressure

(mm Hg) Transitionpoint

Fluidmovement

Inward pressure

( pP + PIF)

Outward pressure

(PC + pIF)

Beginning Capillary length End

= Ultrafiltration = Reabsorption

Edema



Edema

A- Intracellular : causes

1. depression of the metabolic system of thetissues.

2. Lack of adequate nutrition to the cell.

3. Ischemia, inflammation.

Na-K pump stopped - Na lacks insideH2O follows.

T j



B- Extracellular : Two major causes

(1). Abnormal leakage of fluid from theplasma to the interstitial spaces acrossthe capillaries.

(2). Failure of the lymphatic to returnfluid from the interstitial back into theblood.

Filtration = Kf x (Pc -Pif - π c + π if )

Causes of extracellular edema



Causes of extracellular edema

1.Increased capillary pressure :

A. Excessive kidney retention of salt and water1. Acute or chronic kidney failure2. Mineral corticoid excess

B. High venous pressure :

1. Heart failure 2. venous obstruction3. Failure of venous pumps:

- muscle paralysis - Immobilized part- Venous valve failure

C. Decreased arteriolar resistance:1. Heat 2. Insufficiency of symp. S.

3. vasodilators



•edema caused by heart failure:

the heart fails to pump blood from the veins

to the arteries which causes:↑venous pr. ↑ capillary pr. ↑capillary

filtration.

↓arterial pr. ↓excretion of salts ↑blood

volume ↑ capillary hydrostatic pr. . ↓blood flow to the kidneys ↑aldosterone ↑salt & water retention.

2 Decreased plasma proteins:



2. Decreased plasma proteins :

A. Nephrotic syndrome: increase proteinleakage.

B. Protein loss : Wounds , burns

C. Failure to produce proteins:

- Liver disease, cirrhosis- Malnutrition



•edema caused by decreased plasma proteins:

Can be caused by:

1- plasma proteins’ leakage, and this can benoted in nephrotic syndrome

2- failure to produce normal amounts ofproteins such as in liver cirrhosis

cirrhosis also causes edema by compressingthe abdominal portal venous drainage beforeentering the general circulation↑ capillary

hydrostatic pr. In the GI area transudationof fluid and proteins to the abdominalcavity this is known as ascites



•edema caused by decreased kidney

excretion:Diseased kidney fails to excrete water andsalts accumulation of water and salts in

the blood and the interstitial space thiscauses:

1- extracellular edema

2- hypertension



3.Increased capillary permeability :

A. Immune rxnshistamine releaseB. Bacterial infiction.C. Toxins

D. Vitamin C deficiencyE. BurnsF. Prolong ischemia



4.Blockage of lymph Return :

A. Cancer

B.Infections (filari)C.SurgeryD. Congenital abnormality of lymphatic

vessels



C-Safety factors that prevent edema :

1.Low tissue compliance of the

interstitium when pres. is (-). 3mmHg

2.Ability of lymphatic flow to increase 10-

50 times. 7mmHg

3.Washout proteins from interstitium.7mmHG



Interstitial low compliance

Large change in pressure will causesmall change in volume. This is onlywhen interstitial space has negative

pressure. Compliance increases markedly, once

interstitial pressure rises above zero.

Protoglycan creates gel form of fluidprevents flowing “no free fluid spaces”.

When + pressure pitting edema.





Lymphatic flow

Lymphatic vessels able to increase theirflow ten to fifty folds.

This increase will be significant whenthe interstitial pressure is zero andabove.



Fluid pressure on the outside of the vessel



Fig. 10-20b, p. 296

Fluid pressure on the outside of the vesselpushes the endothelial cell’s free edge inward, permitting entrance of interstitial fluid(now lymph).

Fluid pressure on the inside of the vesselforces the overlapping edges together sothat lymph cannot escape.

Interstitialfluid

Overlapping

endothelial cell

Lymph



Edema in potential spaces

These type of edema called “Effusion”

Accumulation of fluids in transcellularspaces.

Ascites: collection of fluids in theabdominal cavity, huge 20 liters.

All transcellular spaces have negative

pressure: - pleural=7-8mm Hg- synovial=3-5mm Hg

- pericardial=5-6mm Hg.

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Body Fluids (2)