Body fluid - Human Anatomy and Physiology B. Pharma 1st Semester

Body fluid


At the end of this lecture student will be able to

• Classify body fluid compartments

• Explain composition of body fluid

• Functions of different ions present in the body fluid

• Understand the importance of water balance in the body

• Enlist signs and symptoms associated with fluid loss

• Explain Treatment techniques for dehydration and water intoxication

• Enumerate different body fluid and their function

• Explain the physiological role of body fluids


• Body Fluids

• Body Fluid Compartments

• Composition of body fluids

• Concentration and tonicity of body fluids

• Applied Physiology of body fluid

• Specialized Fluids of the Body and functions

Body Fluids

• Total amount of fluid in the human body is approximately 70% of body weight

• Body fluid has been divided into two compartments –

– Intracellular fluid (ICF)

• Inside the cells

• 55% of total body water

– Extracellular fluid

• Outside the cells

• 45% of total body water

Body Fluid Compartments


Body Fluid Compartments

Extracellular fluid has 5 subunits

• Interstitial fluid: Present between the cells (App. 80% of ECF)

• Plasma: Present in blood (app– 20% of ECF)

• Fluid in bones

• Fluid in dense connective tissue: Cartilage

• Transcellular fluid

» Intraocular fluid 

» Digestive juices

» Fluid in urinary tract

» cerebrospinal fluid

» Synovial fluid in joints

» Serous fluid

Composition of body fluids

Organic substances

Inorganic substances



Amino acid


Fatty acid












   Most abundant cation - Na+,

– Muscle contraction

– Impulse transmission

– Fluid and electrolyte balance

– Regulation of pH

   Most abundant cation - K+

– Resting membrane potential

– Action potentials

– Maintains intracellular volume

   Most abundant anion - Cl-               

– Regulates osmotic pressure

– Forms HCl in gastric acid

• Anion are proteins and phosphates (HPO42-)

• Na+ /K+ pumps play major role in keeping K+ high inside cells and Na+ high outside cell

Measurement of body fluid volume

• Indicator dilution method or Dye dilution method

• Principle: A known quantity of marker substances or indicators such as a dye is administered into a specific body fluid compartment.

V = M – E / C

V = Volume of fluid in the compartment.

M = Mass or total quantity of marker substance injected.

E = Amount of dye excreted or lost from the body

C = Concentration of the marker substance in the sample fluid

Criteria for a suitable dye

• Must mix evenly throughout the compartment

• Non toxic

• Must have no effect of its own on the distribution of water

• Either it must be unchanged during the experiment or if it changes, the amount changed must be known.

• The material should be relatively easy to measure.

Biomarkers used for various fluids compartment

Fluid compartment

Marker substances

Total body water

1.       Deuterium oxide (D2O)

2.       Tritium oxide (T2O)

3.       3. Antipyrine

Extracellular fluid

1.       Radioactive sodium, chloride, bromide, sulfate and thiosulfate.

2.       Non-metabolizable saccharides like inulin, mannitol, raffinose and sucrose


1.       Radioactive iodine (131I)

2.       2. Evans blue (T-1824)


Concentration of body fluids

Concentration of body fluids is expressed in three ways:

1. Osmolality: Measure of a fluid’s capability to create osmotic pressure is called osmolality or osmotic (osmolar) concentration of a solution (osmoles/Kg)

2. Osmolarity:  Osmolarity is another term to express the osmotic concentration. It is the number of particles (osmoles) per liter of solution (osmoles/L)

3. Tonicity: is the measure of effective osmolality

Tonicity of solutions

According to the concentration of the solute (osmoles) present in the solution they can be classified as

1. Isotonic solution: has the same effective osmolality (tonicity) as body fluids

2. Hypotonic solution: has greater effective osmolality than the body fluids

3. Hypertonic solution: has less effective osmolality than the body fluids

Significance of body fluids

• Homeostasis: Body cells survive in the fluid medium called internal environment or ‘milieu interior’. Water not only forms the major constituent of internal environment but also plays an important role in homeostasis

• Transport mechanism: Body water forms the transport medium by which nutrients and other essential substances enter the cells; and unwanted substances come out of the cells

Metabolic reactions: Water inside the cells forms the medium for various metabolic reactions, which are necessary for growth and functional activities of the cells

Texture of tissues: Water inside the cell ensures cells texture

Temperature regulation: Water present inside the cell plays vital role in maintaining normal body temperature

Applied Physiology Maintenance of water balance


• Mild dehydration – Loss of 5% total body fluid

• Moderate dehydration – loss of 10% total body fluid

• Severe dehydration – loss of 15% total body fluid

Dehydration based on water and sodium ratio

• Isotonic dehydration

• Hypertonic dehydration

• Hypotonic dehydration


   Severe diarrhoea and vomiting due to gastrointestinal disorders

• Excess urinary output due to renal disorders, insufficient intake of water

• Endocrine disorders such as diabetes mellitus, diabetes insipidus and adrenal insufficiency

• Prolonged physical activity without consuming adequate amount of water in hot environment

• Excess sweating leading to heat frustration

• Use of laxatives or diuretics in order to lose weight quickly

Signs and Symptoms

Mild and moderate dehydration

Severe dehydration

Very severe dehydration

Dryness of the mouth         

Decrease in blood volume            

Damage of organs

Excess thirst                 

Decrease in cardiac output       

Mental depression and confusion

Decrease sweating                 

Low blood pressure                       

Renal failure

Decrease in urine formation

Hypovolemic shock








Cramps in legs and arms




Treatment of dehydration

• Treatment depends upon the severity of dehydration

• Mild to moderate dehydration can be reversed by drinking water and other fluids

• Incase of severe dehydration ORT is preferred to compensate salt loss along with water

• ORT involves oral administration of ORS formulated by WHO

• Incase of very severe dehydration IV route of administration is preferred

Water intoxication or over hydration 

Condition characterized by great increase in the water content of the body

• Heart failure

• Renal disorders

• Hypersecretion of antidiuretic hormone - syndrome of inappropriate hypersecretion of antidiuretic hormone

• Intravenous administration of unduly large amount of medications and fluids than the person’s body can excrete

• Swimmers

Signs and Symptoms

• Nausea, Vomitting, Blurred vision

• Anemia, acidosis, hemorrhage, shock

• Behvarioal changes – delirium, seizure, confusion, coma

• Muscular symptoms – cramps, twitching, paralysis


• Mild water intoxication requires only fluid restriction

• In very severe cases, the treatment includes:

1. Diuretics to increase water loss through urine

2. Antidiuretic hormone (ADH) receptor antagonists to prevent ADH-induced reabsorption of water from renal tubules

3. Intravenous administration of saline to restore sodium.

Specialized Fluids of the Body

• Lymph

• Milk

• Cerebrospinal fluid

• Amniotic fluid

• Aqueous humor

• Sweat

• Tears

Functions of Lymph


 • Return protein from tissue spaces into blood

• Redistribution of fluid

• Removal of bacteria, toxins and other foreign bodies from tissues

 • Maintain structural and functional integrity of tissue

• Route for intestinal fat absorption

• Transport lymphocytes

Functions of Milk

• Milk sugar provides galactose, a structural unit for growing infant.

• In intestine, it gets metabolized to lactic acid which eliminates harmful bacteria.

• Source of protein, mineral and vitamins

Functions of CSF

•Hydrolic shock absorber

• Regulation of intracranial pressure

• Influences the hunger sensation and eating behaviours

Functions of Amniotic Fluid

• Liquid produced by membranes and fetus

• Volume of fluid increases with gestational age

• Physical protection to the fetus

• Medium for exchange of various chemical

Aqueous Humor

• Fluid that fills the interior chamber of eye

• Secreted by ciliary body, enters anterior chamber

• Blockade in the flow of aqueous humor causes glaucoma due to increased intraocular pressure.

• Posterior chamber of eye is filled with vitrous humor which contains a gel (vitrous body of hyaluronic acid secreted by retina)


• Secretion of sweat gland

 • Regulates body temperature by cooling and evaporation

• Sweat glands controlled by ANS, Adrenal cortical steroid - which affect the quantity of electrolyte present


• Produced by lachrymal glands

• Isotonic but becomes hypertonic due to evaporation as fluid passes over the cornea

• Lysozyme – lyses the cells of a number of micro-organisms by breaking down the polysaccharides of their outer layer

Functions of Tears

• Lysozyme protects eye from infectious agents

• Lubricate the surface of the cornea

• Fill the irregularities of the corneal surface to improve optical properties

• Protects eyes from injury


Body fluids can be: Extracellular and Intracellular

Composed of: Organic and inorganic substances

Body fluids: Measured by using various bio markers

• Concentration (Osmolality, Osmolarity) and Tonicity (Iso,Hyper,Hypotonic) of body fluids play a vital role in homeostasis

• Maintenance of water balance in the body is very essential

• Dehydration treatment depends on the severity

• Mild water intoxication can be treated with water retriction

• Various specific functions are carried out by specialized fluids


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