Chapter 9 Water 1. Water Balance Introduction Water is the most vital nutrient to human existence....

Chapter 9 Water

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Water BalanceIntroduction

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

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ObjectivesDescribe the significant role of water and

water balance in the human bodyDescribe the human water balance systemDescribe body water requirementsDescribe the 2 collective body water

compartmentsDescribe the acid-base buffer system

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Water BalanceKey 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.

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Water: the Fundamental Nutrient

Three basic principlesA 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 sustainedThe skin provides a protective envelopeThis environment is controlled by solvents

within the water and membranes separating the compartments

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Water: the Fundamental NutrientThree 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

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Body Water FunctionsHomeostasis – 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 bodyTransport – Circulated through out the

body in the form of blood, various other secretions and tissue fluids

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Body Water FunctionsBody 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)

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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 sweat2. more water is needed for increased metabolic

demand9

Body Water RequirementsFunctional 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

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Body Water RequirementsAge

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 - 2900ml./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 medication11

Special Concerns related to Body Water RequirementsDehydration: excessive loss of total body

waterInitial sx. – thirst, headache, decreased

urine output, dry mouth, dizziness visual impairment, hypotension, loss of appetite, muscle weakness, kidney failure, seizures

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Adverse effects of dehydration

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Special Concerns related to Body Water RequirementsWater Intoxication:

from over consumption of water hyponatremia, serum Na+ levels fall below 136 mEq/L edema, lung congestion, muscle weakness

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Body Water: The SolventBody water: the solvent –

Solvent = a liquid that holds another substance in solution

Men: 55 – 65 % of body weight is waterWomen: 45 – 55 % of body weight is water

Total body water is divided into two compartments: Extracellular and intracellular

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Total water outside cells Extracellular fluid – 20 % of total body

weightAbout 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 circulationWater moving though the body in various tissue secretions (transcellular)

Body Water: the SolventTotal 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

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Water intake – enters the body in 3 main forms:Preformed water in liquids that are drunkPreformed water through foodsWater that is the product of cell oxidationEstimated average intake of an adult = 3L/day

Recommended minimum 1500-2000 cc/dayXerostomia = 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

Body Water: the SolventWater 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

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Body Water: the Solvent

Water Output cont.Optional Loss:

water loss varies according to the climate and physical activity

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Average daily adult I&O(see p 163, Table 9-4)

FORM OF H2O

INTAKE (ML/DAY)

BODY PART OUTPUT (ML/DAY)

Preformed -Liquids-FoodsMetabolism

Total

1500700200

2400

LungsSkin-diffusion-sweatKidneysPecesTotal

350

35010014002002400

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Solute Particles in SolutionThe 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, MgAnions – Carry a negative charge Cl, CO2, PO4,

SO425

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

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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

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Solute particles in solutionPlasma proteins – Mainly in the form of

albumin and globulin- organic compounds of large molecular size:Don’t move freely across membranesStay in blood vesselsControl 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

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Solute Particles in SolutionSmall 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 typesCapillary 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.

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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 ".

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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

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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

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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

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Forces moving water and solutes across membranes

Pinocytosis – Engulfing of a large molecule by the cell

Pinocytosis

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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

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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.

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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.

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The human water-balance system uses two other organ systems to control overall water balance:GI circulation which supports digestion

and absorption of nutrientsRenal 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 absorptionE.g. saliva, gastric juice, pancreatic

juice, intestinal juice


Clinical ApplicationsE.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

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Tissue Water CirculationE.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.

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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.


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)45

Mmmmm…. water

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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 basepH < 7 = acidpH > 7 = alkaline

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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

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Acid-Base Buffer SystemA 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

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Acid-Base Buffer SystemPhysiologic Buffer system –

respiratory/renal systems respond when the chemical buffers cannot reestablish equilibrium

Respiratory – increase rate and depth of respiration

release CO2 combating acidosisDecrease rate and depth of respiration

retaining CO2 alleviate alkalosisRenal – excretes more or less hydrogen ions

if the chemical and respiratory buffer systems do not re-est. blood pH.

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Chapter 9 Water 1. Water Balance Introduction Water is the most vital nutrient to human existence....

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Transcript of Chapter 9 Water 1. Water Balance Introduction Water is the most vital nutrient to human existence....