DR. ZAHOOR ALI SHAIKH Lecture--5 1

 Human Body Composition:  Water %  Protein %  Fat %  Mineral % 2

 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) 3

 We will see how this 42 liters of water is distributed between ICF and ECF  Total Body Water (TBW) liters - Intracellular fluid (ICF) liters - Extracellular fluid(ECF) liters ( ECF IS DIVIDED INTO INTERSTITIAL FLUID AND PLASMA ). 4

 Extracellular fluid (ECF)- 14 lit is divided into: - Interstitial fluid liters - Plasma liters  Note-- Interstitial fluid is the fluid which is distributed between the cells or surrounding the cells. Plasma – It is fluid portion of blood. 5

 SUMMARY  TOTAL BODY WATER (TBW) – 42 liters - Intracellular fluid – 28 liters - Extracellular fluid – 14 liters (i). Interstitial fluid – 11 liters (ii). Plasma - 3 liters 6

 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. 7

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 8

9

 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. 10

 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. 11

12

 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. 13

14

INTRACELLULAR FLUID [ICF] EXTRACELLULAR FLUID [ECF] 1. ICF has more protein1.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 15

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. 16

 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. 17

 ECF Na+ 140 mmol / l ( mmol / l) K+ 4 mmol / l (3.5 – 5 mmol / l) Cl- 105 mmol / l (100 – 110 mmol / l) 18

 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. 19

20

 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. 21

 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). 22

 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 mmol/l (275 – 295) 23

PROBLEM  If there is water loss from the ECF, what will be its effect ? Answer – ECF will become Hypertonic. 24

 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. 25

 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. 26

27

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. 28

 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. 29

30

 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. 31

32

 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? 33

34