1. Chapter 9 Water

2. Water Balance Introduction
Water is the most vital nutrient to human existence. Human life depends on a constant supply of water. Humans can survive far longer without food than water. Only the need for air is more demanding.
One of the most basic nutritional tasks is ensuring a balanced distribution of this water to all body cells is a primary physiologic function

3. Objectives
Describe the significant role of water and water balance in the human body
Describe the human water balance system
Describe body water requirements
Describe the 2 collective body water compartments
Describe the acid-base buffer system

4. Water Balance Key Concepts:
Throughout the body, water exists as a unified whole with constant ebb and flow among its interfacing parts
Collective water compartments, inside and outside of cells, maintain a balanced distribution of total body water
The concentration of various solute particles in the body’s water solution determines internal shifts and movement of water
A state of dynamic equilibrium (e.g. homeostasis) among all parts of the body’s water-balance system sustains life.

5. Water: the Fundamental Nutrient
Three basic principles A unified whole – The human body forms one continuous body of water – every space within and outside the cells are filled with water-based body fluids. In this warm, watery, chemical environment all the processes necessary to life are sustained The skin provides a protective envelope This environment is controlled by solvents within the water and membranes separating the compartments

6. Water: the Fundamental Nutrient
Three basic principles cont. Body water compartments – Water does not slosh around in the body. The body moves water where it is needed in the body (dynamic system) – intracellular or extracellular Particles in the water solution – the concentration and distribution of particles in the water solution determine all of the internal shifts and balances between compartments

7. Body Water Functions
Homeostasis – the body’s state of dynamic balance; the capacity built into the body to maintain its life systems Gk. Homeo = similar / Stasis = balance The body has a great capacity to employ numerous homeostatic mechanisms to protect its vital water supply. Body Water Functions: Solvent – Basic liquid for all chemical reactions in the body Transport – Circulated through out the body in the form of blood, various other secretions and tissue fluids

8. Body Water Functions
Body form and structure – helps to give form and structure by filling in spaces within body tissues Body temperature – Helps regulate temperature – as the temperature rises, sweat increases and evaporates, thus cooling the body Body lubricant – water has a lubricating effect on moving parts of the body (eg. Synovial fluid in joints)

9. Body Water Requirements
The body’s requirement for water varies according to several factors: temperature, activity level, functional losses, metabolic needs, age, and other dietary factors.
See Table 9-1, p.159
Surrounding environment–As temp increases water loss as sweat increases
Activity level- Heavy or extensive physical activity increases the water requirement for 2 reasons:
1. more water is lost as sweat
2. more water is needed for increased metabolic demand

10. Body Water Requirements
Functional losses – When any disease process interferes with the normal functioning of the body, water requirements are affected. E.g. prolonged diarrhea increase water loss Metabolic needs – the work of body metabolism requires water. General rule: 1000cc is needed for every 1000 Kcal in the diet

11. Body Water Requirements
Age Infants needs are higher – the content of water of an infant’s body is 70-75% sedentary adults: female should consume about 2200ml/day; male ml./day Special concern: dehydration in the elderly (thirst mechanism diminishes with age) Moderate to severe dehydration is associated with delirium, UTIs, respiratory infections, skin breakdown, and constipation Other dietary factors – additives and medication can affect water requirements. E.g. diuretics in the form of caffeine, alcohol, and medication

12. Special Concerns related to Body Water Requirements
Dehydration: excessive loss of total body water Initial sx. – thirst, headache, decreased urine output, dry mouth, dizziness  visual impairment, hypotension, loss of appetite, muscle weakness, kidney failure, seizures

14. Special Concerns related to Body Water Requirements
Water Intoxication: from over consumption of water  hyponatremia, serum Na+ levels fall below 136 mEq/L  edema, lung congestion, muscle weakness

15. The Human Water Balance System

16. Body Water: The Solvent
Body water: the solvent – Solvent = a liquid that holds another substance in solution Men: 55 – 65 % of body weight is water Women: 45 – 55 % of body weight is water Total body water is divided into two compartments: Extracellular and intracellular

17. Body Water: the Solvent
Total water outside cells
Extracellular fluid – 20 % of total body weight
About 25% of ECF is contained in the blood plasma (intravascular)
The remaining 75% is composed of the following:
Water surrounding the cells and bathing tissues
(interstitial fluid)
Water in lymphatic circulation
Water moving though the body in various tissue secretions (transcellular)

18. Body Water: the Solvent
Total water inside cells Intracellular fluid 40-45% of total body weight Overall water balance – water enters and leaves the body by various routes, controlled by basic mechanisms such as thirst and hormones. Body metabolism 2.5 to 3 liters a day in a balance between I & O

19. Body Water: the Solvent
Water intake – enters the body in 3 main forms:
Preformed water in liquids that are drunk
Preformed water through foods
Water that is the product of cell oxidation
Estimated average intake of an adult = 3L/day
Recommended minimum cc/day
Xerostomia = dry mouth due to aging, meds, disease, radiation tx.
Nursing: don’t depend on a sense of thirst – check for clinical signs of dehydration and I&O

20. Body Water: the Solvent
Water output – Leaves the body through kidneys, skin, lungs, and feces Largest amount of water exits through the kidneys Obligatory Loss: compulsory for survival and must occur daily for health – e.g. water loss as urine through kidneys

21. Body Water: the Solvent
Water Output cont. Optional Loss: water loss varies according to the climate and physical activity

23. Average daily adult I&O (see p 163, Table 9-4)
FORM OF H2O
INTAKE (ML/DAY)
BODY PART
OUTPUT (ML/DAY)
Preformed
-Liquids
-Foods
Metabolism
Total
1500
700
200
2400
Lungs
Skin
-diffusion
-sweat
Kidneys
Peces
350
100
1400

25. Solute Particles in Solution
The solutes in body water are a variety of particles in varying concentrations Two main types of particles control water balance: electrolytes and plasma protein Electrolytes – small, inorganic substances that can break apart in a solution and carry an electrical charge. These charged particles are called : ions [from the Gk. word meaning “wanderer”]. Ions are free to wander through a solution to maintain its chemical balance. Cations – Carry a positive charge NA,K, or C, Mg Anions – Carry a negative charge Cl, CO2, PO4, SO4

26. Solute Particles in Solution
The constant balance between the two major electrolytes – Na+ outside the cell, and K+ inside the cell, maintains water balance between these 2 water compartments Because of their small size, electrolytes can diffuse freely across most membranes of the body,  maintaining a constant balance between the intracellular and extracellular water

27. Solute particles in solution
Electrolytes cont. Electrolyte concentration in body fluid is measured in terms of milliequivalents – mEq The number of electrolytes per unit of fluid is expressed as mEq/L

28. Solute particles in solution
Plasma proteins – Mainly in the form of albumin and globulin- organic compounds of large molecular size: Don’t move freely across membranes Stay in blood vessels Control water movement and maintain blood volume by influencing the shift of water in and out of capillaries. In this function, plasma proteins are called colloids and exert colloidal osmotic pressure (COP) to maintain the integrity of the blood volume

29. Solute Particles in Solution
Small organic compounds – Along with electrolytes and plasma protein, are dissolved in body water. Their concentration is too small to influence shifts in water. Separating membranes: 2 types Capillary membrane –capillary walls are thin and porous; water molecules and small particles pass through, plasma protein can not pass through Cell membrane – thicker; specially constructed to protect and nourish the cell contents. Structured in a sandwich-like fashion of outer layers with penetrating channels of protein and inner structure of fat material.

30. Forces Moving Water and Solutes Across Membranes
The presence of separating membranes requires certain physical and chemical forces to control the movement of body water and particles in solution across them Osmosis – Gk. Word: osmos meaning " a driving or pushing force, and impulse ".

31. Forces Moving Water and Solutes Across Membranes
Osmosis cont.
In human physiology, osmosis is the force that moves water molecules from an area of greater concentration to an area of lesser concentration of water molecules
When solutions of different concentration exist on either side of a selectively permeable membrane, the osmotic pressure moves water across the membrane to help equalize the solution on both sides

33. Forces Moving Water and Solutes Across Membranes
Diffusion –applies to particles in solution (Osmosis applies to water) The force by which these particles move outward in all directions from an area of greater concentration of particles to an area of lesser concentration of particles. Movement of water molecules and solute particles by osmosis and diffusion effectively balance solution concentrations and pressure on both sides of the separating membrane

34. Forces Moving Water and Solutes Across Membranes
Filtration – Water is forced through the pores of membranes when the pressure outside the membrane is different Active transport – Particles in a solution are moved across the membrane throughout the body at all times even when the pressures are against their flow. Accomplished by means of a "ferry" or carrier partner Pinocytosis: for absorption of larger particles such as proteins and fats « cell drinking » - the larger molecules attach themselves to the thicker cell membrane and are then are engulfed by the cell

37. Forces moving water and solutes across membranes
Pinocytosis – Engulfing of a large molecule by the cell

38. Forces Moving Water and Solutes Across Membranes
Pinocytosis cont.
The larger molecule is encased in a vacuole, which is a small space or cavity formed in the protoplasm of the cell. In this small space, nutrient particles are carried across the cell membrane into the cell.
Once inside the cell, the vacuole opens and the cell enzymes metabolize the particles

39. Tissue Water Circulation
Tissue water circulation: the capillary fluid shift mechanism – One of the body’s most important controls in maintaining overall water balance is the capillary fluid shift mechanism 1. Purpose – essential water, nutrients and oxygen must be pushed out of blood circulation into tissue circulation to distribute their goods through out the body, and water metabolites and carbon dioxide must be pulled back into circulation to dispose of metabolic wastes through the kidneys or lungs.

40. Tissue Water Circulation
2. Process – Blood enters the capillary system from the vessels coming from the heart. Thus forcing water and small particles from the blood into the tissues to bathe and nourish the cells. The force of blood pressure is an example of hydrostatic pressure The colloidal osmotic pressure draws water and metabolites back into the capillary circulation after serving the cells, and carries them on to larger vessels and back to the heart.

41. Tissue Water Circulation
The human water-balance system uses two other organ systems to control overall water balance:
GI circulation which supports digestion and absorption of nutrients
Renal circulation which maintains normal blood levels of various nutrients and metabolites
Gastrointestinal circulation
Secretions – which are predominantly water- aid in the process of digestion and absorption
E.g. saliva, gastric juice, pancreatic juice, intestinal juice

42. Tissue Water Circulation
Clinical Applications E.g. What would happen if a patient undergoing gastric suctioning drank water? The water would cause the stomach to produce more secretions containing electrolytes, which would be lost in the suctioning. The plasma, from which the electrolytes were supplied, would be gradually depleted of these electrolytes and unable to supply them to tissue cells

43. Tissue Water Circulation
E.g. What would happen if a patient being fed by tube were given the formula too rapidly at too concentrated a dilution?
The concentrated solution would cause water to shift into the intestine to dilute the solution, thus rapidly shrinking the surrounding blood volume. This condition would produce S/S. of shock, reflecting the body’s effort to restore blood volume.

44. Tissue Water Circulation
Renal circulation – Kidneys maintain the appropriate levels of all constituents of blood by filtering it and then selectively reabsorbing water and needed materials to be carried through out body
Through this continual “laundering” of the blood by the millions of nephrons in the kidneys, water balance and the proper solutions of blood are maintained.
When disease occurs in the kidneys, this filtration process does not operate normally, and water imbalances occur.

45. Tissue Water Circulation
Hormonal controls – operate in the kidneys to help maintain constant water balance: Antidiuretic hormone (ADH) mechanism – vasopressin is produced by the pituitary gland, water conserving effect that works on the kidneys’ nephrons to induce reabsorption of water Aldosterone mechanism – Produced by the adrenal glands, which are located on top of each kidney. It triggers the kidneys’ nephrons to reabsorb sodium, a ‘sodium-conserving’ mechanism ( also, exerts a secondary control over water resorption because water follows sodium)

46. Mmmmm…. water

47. Human Acid-Base Balance System
The optimal degree of acidity or alkalinity that must be maintained in body fluids  to support life. This is achieved by a chemical and physiological buffer system Acids and bases – related to hydrogen ion concentration. acidity is expressed in terms of “pH” pH of 7 = neutral point between and acid and a base pH < 7 = acid pH > 7 = alkaline

48. Human Acid-Base Balance System
Acid – a compound that has increased hydrogen ions – enough to release extra when in solution Base – a compound with fewer hydrogen ions. In solution, accepts hydrogen ions to decrease the solution’s acidity

49. Acid-Base Buffer System
A chemical buffer system is a mixture of acidic and alkaline components, and acid and a base partner, that together protect a solution from wide variations in its pH Main buffer system – NaHCO3 is the main buffer system of the body = base bicarbonate

50. Acid-Base Buffer System
Physiologic Buffer system – respiratory/renal systems respond when the chemical buffers cannot reestablish equilibrium Respiratory – increase rate and depth of respiration release CO2  combating acidosis Decrease rate and depth of respiration  retaining CO2  alleviate alkalosis Renal – excretes more or less hydrogen ions if the chemical and respiratory buffer systems do not re-est. blood pH.