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BODY FLUIDS AND ELECTOLYTES

DR. ZAHOOR ALI SHAIKHLecture--5

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HUMAN BODY COMPOSITION

Human Body Composition: Water ---- 60% Protein --- 18% Fat -------- 15% Mineral --- 07 %

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BODY WATER

Body water makes 60% of body weight.

Therefore body water is about 42 liters in 70 kg person.

Body water is distributed between TWO major compartments:

1. INTRACELLULAR FLUID (ICF) 2. EXTRACELLULAR FLUID (ECF)

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BODY WATER DISTRIBUTION

We will see how this 42 liters of water is distributed between ICF and ECF

Total Body Water (TBW)--- 42 liters - Intracellular fluid (ICF)----- 28

liters - Extracellular fluid(ECF)-----14

liters

( ECF IS DIVIDED INTO INTERSTITIAL FLUID AND PLASMA ).

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EXTRA CELLULAR FLUID

Extracellular fluid (ECF)- 14 lit is divided into:

- Interstitial fluid --- 11 liters - Plasma -------------- 3 liters

Note-- Interstitial fluid is the fluid which is distributed between the cells or surrounding the cells.

Plasma – It is fluid portion of blood.

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TOTAL BODY WATER

SUMMARY

TOTAL BODY WATER (TBW) – 42 liters - Intracellular fluid – 28 liters - Extracellular fluid – 14 liters (i). Interstitial fluid – 11 liters (ii). Plasma - 3 liters

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OTHER EXTRACELLULAR COMPARTMENT

There are other TWO Minor Extracellular fluid compartments also:

1. Lymph 2. Transcellular fluid

1. Lymph It is fluid which is returned from the

interstitial fluid to plasma by means of Lymphatic System.

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Minor ECF Compartment (cont) 2. Transcellular Fluid It is small fluid volume secreted by specific cells

in the body, these cells perform special function Example of Transcellular fluid - Cerebrospinal fluid (CSF)- it surrounds the

Brain and Spinal cord - Intra ocular fluid - in the eye - Synovial fluid – lubricating joints - Pericardial fluid, Intra pleural fluid

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Extracellular Fluid[Plasma & Interstitial Fluid]

Plasma and Interstitial Fluid are separated by blood vessel wall.

Water and electrolyte are freely exchanged between plasma and interstitial fluid passively through pores of thin capillary membrane.

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Extracellular Fluid[Plasma & Interstitial Fluid] (cont)

But Plasma protein can not pass from plasma to interstitial fluid.

Therefore plasma and interstitial fluid are nearly same in composition except that plasma has protein and interstitial fluid doesn’t have protein.

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Extracellular Fluid [ECF] & Intracellular Fluid [ICF]

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Extracellular Fluid [ECF] & Intracellular Fluid [ICF]

ECF and ICF are separated by plasma membrane.

Plasma membrane is selectively permeable.

There is passive transport and active transport occurring through the plasma membrane.

There is difference between ECF and ICF.

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Extracellular Fluid [ECF] & Intracellular Fluid [ICF] Major Ionic Composition

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Important Differences Between ECF & ICF

INTRACELLULAR FLUID [ICF]

EXTRACELLULAR FLUID [ECF]

1. ICF has more protein 1. No protein in Interstitial Fluid. Protein present in Plasma.

2. More Potassium ion (145 mmol / l)

2. Less Potassium ion (4 mmol / l)

3. Less Sodium ion (10 mmol / l)

3. More Sodium ion (145 mmol / l)

4. More Phosphate ion

4. More Chloride ion

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Na+ and K+ Concentration In ECF & ICF

Q. Why Na+ is more in ECF and K+ more in ICF?

Ans: It is due to the Na+ - K+ ATPase pump which pumps Na+ outside the cell and K+ inside the cell.

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‘Important Things To Remember’

Both Interstitial Fluid and Plasma have same composition except that Plasma has more protein.

ICF and ECF are different as plasma membrane is selectively permeable and

Na+ - K+ ATPase pump is operating.

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‘Important Things To Remember’

ECF

Na+ 140 mmol / l (135-145 mmol / l)

K+ 4 mmol / l (3.5 – 5 mmol /

l) Cl- 105 mmol / l (100 – 110

mmol / l)

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Fluid Balance

Fluid Balance is regulated by: 1- ECF Volume

2- ECF Osmolarity

- ECF volume helps to maintain blood pressure and will be discussed later with blood pressure.

We will discuss ECF Osmolarity.

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Extracellular Fluid Osmolarity

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ECF OSMOLARITY

What is Osmolarity ? Osmolarity is the concentration of

solute particles dissolved in the fluid.

Increased Osmolarity means higher concentration of solute and less concentration of water.

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ECF Osmolarity (cont)

As Na+ is the main solute in ECF, it is responsible for ECF Osmolarity.

In ICF K+ is responsible for ICF Osmolarity.

Normally ECF and ICF are ISOTONIC (having same Osmolarity).

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Extracellular Fluid Osmolarity

Normally Osmolarity of ECF and ICF are the same (they are isotonic).

Why ? Because total concentration of Na+ and

other solutes in ECF is equal to total concentration of K+ and other solutes inside the cell.

Remember Osmolarity of ECF - 285 mmol/l (275 – 295)

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Importance of regulating ECF Osmolarity

PROBLEM

If there is water loss from the ECF , what will be its effect ?

Answer – ECF will become Hypertonic.

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Hypertonic Extracellular Fluid

ECF will become hypertonic if water is lost from it e.g. diarrhea, vomiting, sweating or less water intake.

If ECF becomes more hypertonic, water moves from the cells into ECF by osmosis (i.e. from ICF to ECF).

As water leaves the cell – cell will shrink.

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Clinical Application

In mild Dehydration (loss of water) and mild hyper tonicity --- There is dry skin, dry tongue thirst, sunken eyes.

In case of severe Hyper tonicity ( Hyper Osmolarity) of ECF, it may affect BRAIN CELLS and BRAIN FUNCTION --- person may become mentally confused.

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HYPOTONIC ECF

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HYPOTONIC ECF

PROBLEM What will happen if ECF becomes Hypotonic

(that is having less Osmolarity) ? Answer – When ECF becomes Hypotonic ,

water will enter the cell, and cell will swell ( get bigger).

NOTE – Usually Hypo tonicity does not occur because when we take more water, we loose water in urine, but it can happen in Abnormal conditions.

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Hypotonic Extracellular Fluid(cont) Clinical Application

In Renal failure, patient can not pass urine , therefore ECF will become hypotonic if water is added to it.

When ECF becomes hypotonic, water will enter into the cell by Osmosis and cells will swell (increase in size).

Swelling of BRAIN cells will cause Brain Dysfunction E.g. – headache, vomiting, confusion, drowsiness and coma. This is called WATER INTOXICATION.

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ISOTONIC SOLUTIONS

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ISOTONIC SOLUTIONS

What will happen if we give Is0tonic solution?

Answer – If we give ISOTONIC SOLUTION like o.9% saline (Isotonic saline) intravenously, ECF will remain ISOTONIC , there will be no net movement of water into or out of the cells. Only ECF volume will increase.

NOTE – In case of Diarrhea, vomiting ,

Isotonic saline is given intravenously .

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What Should You Know From This Lecture

Distribution of Body water – ICF, ECF [Interstitial Fluid in Plasma]

Define Tran cellular Fluid Compare Ionic composition of Plasma,

Interstitial Fluid and Intracellular Fluid What is Osmolarity of Plasma? Define Isotonic, Hypotonic, Hypertonic What are causes of ECF hyper tonicity

and hypo tonicity and its effects on body?

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Thank you