SCIENCE

1. Water Imbalance
neelamz@unifiji.ac.fj

2. Body Water Content
 By weight, the average human adult male is
approximately 60% water and the average adult
female is approximately 55%.
 Percentage varies based on factors like age, health,
water intake, weight, and sex.
 E.g. 70 kg adult male has 42 liters of water on
average.(It depends on the person's body weight)

3. Body Water Content
 Normal water content of body
 75% at birth
 55 – 60% young adults : men slightly higher than
women (more fat, less water)
 45% in elderly, obese

5. Fluid Compartments
 Most of animal body water is contained in
various body fluids.
 Body fluids can be discussed in terms of their specific
fluid compartment, a location that is largely
separate from another compartment by some form of
a physical barrier.

6. Fluid Compartments
 Intracellular fluid (ICF) compartment includes all fluid
enclosed in cells by their plasma membranes.
 Extracellular fluid (ECF) surrounds all cells in the body.
 ECF :plasma and interstitial fluid (IF)
 Transcellular fluid - cerebrospinal, pericardial ,
synovial

7. 2/3 of body water
1/3 of body water
4/5 of ECF
Transcellular
Fluid

8. Composition of Body Fluids
ECF: major cation: Na+
major anion: Cl-, HCO3-
 Most body fluids are neutral in charge. Thus, cations
and anions are balanced in fluids.
 The composition of plasma and interstitial fluid are
virtually identical with the exception of the higher
protein content of the plasma.
 The concentration of sodium correlates closely with the
osmolality of ECF.

9.  ICF:
 Major cation : K+
 Major anion :
phosphate (HPO42−)
and protein

10. Fluid Movement between Compartments
 Hydrostatic pressure
 is the pressure exerted by blood against the walls of
the blood vessels by the pumping action of the heart.
 It drives fluid out of capillary (i.e. filtration).
 Higher at arterial end, lower at venial end.
 Fluid can also move between compartments along an
osmotic gradient.

11. (Oncotic pressure )
Colloid

13. Solute Movement between Compartments
 Active transport: require ATP ; against concentration
gradients
 Passive transport: depends on its ability to pass
easily through the membrane; concentration
gradient; no ATP.
 Chapter 2

14. Water Balance
 Total body water
 Enter:
osmosis from digestive tract (food, drink)
aerobic respiration; condensation etc.
 Exit: urinary, digestive, respiratory, sweating etc.
 Fluid gain = fluid loss

16. Water Loss
 Can vary greatly
 Increased respiratory loss in cold weather
 Increased sweat loss in warm weather
 Increased respiratory and sweat loss , decreased
urine output during physical exertion.

17. Water Loss
 Obligatory water loss
 Relatively unavoidable
 Expired air, cutaneous transpiration, sweat,
fecal moisture, minimum urine output
(~400mL/ day)

18. Regulation of Water Intake
 Governed by thirst
 Provoked by increased plasma osmolarity
 Provoked by blood loss
 Thirst center in hypothalamus
 Responds to signs of dehydration
 Angiotensin II
 Antidiuretic hormone (ADH)
 Signals from osmocenters
 Inhibits salivation

19. Regulation of Water Intake
 Inhibited salivation
 Dry mouth
 Sense of thirst
 Ingestion of water
 Cools and moistens mouth
 Distends stomach and intestines
 Rehydrates blood
 Thirst inhibited

21. Regulation of Water Output
 Controlled via alterations in urine
volume
 Urine volume affected by
 Sodium reabsorption
 Water follows sodium reabsorption
 Antidiuretic hormone (ADH)
 Blood volume , [Na+]  , osmoreceptors
stimulated, pituitary releases ADH
 Aquaporins produced in kidneys collecting ducts
 Facilitate water reabsorption
 Also works in reverse

23. Water Balance Disorders
 Disorders in water metabolism generally derived
from imbalance between water intake and water
output.
 Disorders in water metabolism appear as
dehydration and edema rather than overhydration.
 Na+ retention or excretion along with water is also
important in the homeostasis of water.

24. Water Balance Disorders
 Fluid deficiency
 Volume depletion (Hypovolemia)
 Dehydration
 Fluid excess
 Volume excess (Hypervolemia)
 Overhydration
 Fluid sequestration

25. Hypovolemia
 Fluid deficiency: Hypovolemia
 Caused by proportionate loss of water and sodium
without replacement
 Total body water decreased
 Osmolarity unchanged
 Causes
 Hemorrhage
 Severe burns
 Chronic vomiting or diarrhea
 Major cause of infant mortality

26. Dehydration
 Fluid deficiency: Dehydration
 Caused by loss of more water than Na+
 Total body water decreased
 ECF osmolarity increases
 Causes
 Lack of drinking water
 Diabetes mellitus
 ADH hyposecretion
 Profuse sweating
 Overuse of diuretics

27. Dehydration
 Affects all fluid compartments
 Infants more vulnerable than adults
o Higher metabolism more wastes  more urine
volume
 Immature kidneys
 Urine less concentrated
 Greater surface area-to-volume ratio
 Greater water loss by evaporation

28.  Effects of fluid deficiency
 Circulatory shock
 Due to loss of blood volume
 Neurological dysfunction
 Due to dehydration of brain cells
Dehydration

29. Water Balance Disorders
 Fluid excess
 Less common than fluid deficiency
 Kidneys are typically able to excrete more urine

30. Hypervolemia
 Fluid excess : volume excess: Hypervolemia
 Caused by proportionate retention of excess water and
sodium
 Total body water increased
 Osmolarity unchanged
 Causes
 Aldosterone hypersecretion
 Renal failure

31. Overhydration
 Fluid excess: Overhydration
 “Water intoxication”
 Caused by retention of more water than
sodium
 Total body water increased
 ECF osmolarity decreases
 Causes
 Replacement of water and salt with water
 Lack of proportionate intake of electrolytes
 ADH hypersecretion

32.  Effects of fluid excess
 Pulmonary edema
 Cerebral edema
(Na+)

33. Water Balance Disorders
 Fluid sequestration
 Excess fluid accumulates in a particular
location
 Total body water may be normal.
 Circulating volume may drop
 Examples
 Edema (in interstitial spaces)
 Hemorrhage (lost to circulation)
 Pleural effusion (in pleural cavity)

34. Edema
 Is a palpable swelling produced by
the accumulation of the interstitial fluid.
 Is a medical term for swelling caused by a collection
of fluid in the small spaces that surrounds the body’s
tissues and organs.
 Become evident when the interstitial fluid increased
by 2.5-3L.

37. Edema
Five factors contribute to the formation of edema:
 Increased hydrostatic pressure
 Decreased oncotic pressure within blood vessel
 Increased blood vessel wall permeability as in
inflammation
 Obstruction of fluid clearance via the lymphatic
system
 Changes in water retaining properties of tissues

38. Edema
Edema appears in the following conditions:
 Acute inflammation
 Venous and/or lymphatic obstructions
 Renal failure
 Heart failure
 Liver failure
 It may be local or systemic.

40. References
 John T. Hansen; Bruce M. Koeppen (2002). Netter's Atlas of Human Physiology.
Teterboro, N.J: Icon Learning Systems. ISBN 1-929007-01-9.
 Hellerstein S. Fluid and electrolytes: clinical aspects. Pediatr Rev. 1993
Mar;14(3):103-15
 Taylor SP, Karvetski CH, Templin MA, Heffner AC, Taylor BT. Initial fluid
resuscitation following adjusted body weight dosing is associated with improved
mortality in obese patients with suspected septic shock. J Crit Care. 2018 Feb;43:7-
12.
 https://www.slideshare.net/rajud521/balance-water
 Cheuvront SN, Kenefick RW, Sollanek KJ, Ely BR, Sawka MN. Water-deficit
equation: systematic analysis and improvement. Am. J. Clin. Nutr. 2013
Jan;97(1):79-85.
 https://opentextbc.ca/anatomyandphysiology/chapter/26-1-body-fluids-and-fluid-
compartments/
 https://www.merckmanuals.com/home/hormonal-and-metabolic-disorders/water-
balance/about-body-water
 Kaufman CE and Papper S (eds.) Review of Pathophysiology. Boston:
Little,Brown,1983,p.248.