الأحد، 14 يناير 2018

Body Fluids

Body Fluids 

Body compositions :

  • In the average young adult male:

  1. Water      60% ( TBW)
  2. Protein    18%.
  3. Fat           15%.
  4. Minerals    7 %
  5. carbohydrates < 1 %
  • The cells of the body live in fluid environment  .The interstitial fluid which represent the internal environment.
  • The function of all organ system is to ensure that the physical characteristics of the tissue fluids remain constant within narrow limits.
  • So pH, temp, concentration of chemical components of the internal environment are precisely regulated

Body fluids :

  • Represent 60% of body weight = 40 liters
  • Factors affect body fluids
  1. age: amount varies with age new born  73-82%, adult 60% , old age 45-50%.
  2. loss of body water is a common cause of death in children
  3.  body fats: lean subject more water than obese
  4. sex: women more fat and less water 

Body fluid compartment :

  • Body fluids are distributed into two compartments:
  1. intracellular fluid compartment .
  2. Extracellular fluid compartment .

  • Intracellular fluid :
  •  2/3 of body water
  •  40% of body weight = 25 liters

  • Extracellular fluid :
  •  1/3 of body water
  •   20% of body weight=15 liters
  •   Further divided into 3 compartment:
  1. interstitial fluids:
  • surround the cells
  • comprises ¾ of  ECF = 15% of Body Weight =12 liters
  • include lymph which cannot be measured separately
  1. Plasma:
  • intravascular fluids
  • comprises ¼ of ECF = 5% of BW =   3liters
  1. Transcellular fluid:
  • Fluid which are found out side normal compartment
  • Secreted by epithelium lining eg cerebrospinal fluid, GIT and urinary fluids, fluids in potential spaces eg joint cavities, and in pleural and peritoneal spaces
  • Total amount is small (.5 L) but large volumes can be formed in disease state eg ascites.
 VOLUME OF BODY FLUIDS IN 70 kg MAN TOTAL VOLUME 40 L .




  • ECF:  ICF 
  • Is  larger in infants and children than in adults but the absolute  ECF volume is smaller in children than in  adults. 
  • That’s why children tend to dehydrate more  rapidly  and  more  sever.

  • TBW : BW
  • The  ratio varies with  the  amount  of fat  present.   this variable   leads   to the   variation  due to age   and  gender
.

Many functions of body fluid :

  1. Lubrication
  2. Medium for cellular activities
  3. Transport of nutrients
  4. Temperature regulation
  5. Elimination/excretion of waste

Measurement of body fluids :

  • Volumes in various compartments measured using dilution method

V (Volume) = Q (Quantity) - E (excreted) /C (Concentration)


Ficks Principle :

  • Amount = vol. X conc.
  • Vol. = A/C  (in plasma)

Measurement of body fluid compartment:

  • Using indicator (dye)dilution method.
  • A known quantity of substance(e.g. a dye) Is injected and allowed to distribute in the compartment of interest.
  • measure the final concentration of the dye from the compartment then the volume of compartment(=volume of distribution of the dye ) .Calculated using the formula: volume of distribution =Q-e /c

Characteristic of substance :

  1. Not toxic
  2. Distribute itself in the certain compartment to be measured
  3. Should distribute it self uniformly in all part of the fluid to be measured
  4. No effect of its own on distribution of water or other substances in the body
  5. Must be unchanged  by the body during mixing or amount changed must be known
  6. Easy to measure   

Measurement of total body water :

  • Using dilution method by injecting a substance which diffuse freely in all fluid compartment Substance used :

  1. Deuterium oxide (D2O)
  2. Tritiated water 3(H2O)
  3. antipyrine and amino-antipyrine

  • Sample of plasma obtained to measure concentration=Q/C

Measurement of ECF :


  • Two types of substance used:

  1. Saccharides: eg inulin, sucrose, manitol
  2. diffusable ions: eg chloride, bromide, Na+

Measurement of ICF :

  • No substances can diffuse only in ICF
  • Total body water – ECF

 Measurement of plasma :

  • Substance used

  1. Evans blue; which bind to plasma protein
  2. Albumins labeled with radioactive iodine

Measurement of blood :

  • Dilution method using red blood cells labeled with radioactive chromium 51(Cr) By use of plasma volume 

Interstitial fluid :


  • Interstitial fluid = ECF – plasma volume

Factors affecting the body fluids :

  1. Osmosis: Movement of solvent molecules into a region in which there is a higher concentration of solute to which the membrane is  semi permeable.   
  2. Diffusion: It is expansion of a gas or substance through a cell membrane, due to continuous random movement of its molecules. Water will follow this  molecules into or out of the cell 
  3. Gibbs Donnan effect: the presence of non diffusible anions like proteins and organic phosphate within the cell will affect distribution of diffusible Anions –ve charged and Cations +ve charged .  [K+ X] [Cl-X] = [K+Y ] [Cl-Y ]




About Mohammed Abd Alkariem Ahmed

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