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Water Balance

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Melanie Midkiff

on 9 August 2012

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Transcript of Water Balance

Key Concepts Water compartments inside and outside cells maintain a balanced distribution of total body water.
The concentration of various solute particles in water determines internal shifts and movement of water.
A state of dynamic equilibrium among all parts of the body's water balcance system sustains life. Objectives Water is the most vital nutrient to human existence. Humans can survive far longer without food than without water. Only the continuous need for air is more demanding. Basic Principles of Water A Unified Whole

Body Water Compartments

Particles in the Water Solution Homeostasis Body Water Functions Water acts as a solvent, serves as a means of transport, regulates temperature control, and provides lubrication for the body. The human body forms one continuous body of water contained by skin; this is where all processes to life are sustained. Water moves to all parts, controlled by solvents within the water and membranes separating the compartments. The body has a great capacity to use numerous finely balanced, homeostatic mechanisms to protect its vital water supply. The body's state of dynamic balance is called homeostasis. Body water can be thought of in terms of total body water as well as in separate individual locations throughout the body. The body's mechanisms constantly shift water to places of greatest needs to maintain equilibrium with all parts. The concentration and distribution of particles in the water solution determine the internal shifts and balances between compartments within the total body of water. As a solvent, water provides the basic liquid solvent for all the chemical processes in the body. In the circulating fluid, the many nutrients, secretions, metabolites (products formed from metabolism), and other materials can be carried about to meet the needs of all body cells. As the body temperature rises, sweat increases and evaporates from the skin, thus cooling the body. Water has a lubricating effect on moving parts of the body. Body Water Requirements P. 153 The body's requirement for water varies according to several factors: environment, activity level, functional losses, metabolic needs, age and other dietary factors. Factors To Body Water Requirement As the temperature rises, body water is lost as sweat in an effort to maintain body temperature. Activity Level Water is lost as sweat.
More water is needed for increased metabolic demand in physical activity. Environment Functional Losses Disease process affects water requirements. Metabolic Needs 1000 ml of water necessary for every 1000 kcal in the diet. Age Infants need 700 to 800 ml of water per day. Dehydration Excessive loss of total body water.
Relative severity can be measured in terms of percent total body weight loss with symptoms apparent after 2% of normal weight is lost, more than 20% is fatal. Some symptoms include:
Decreased Urine Output
Dry Mouth
Dizziness As the condition worsens... Symptoms can progress to:
Visual Impairment
Loss of appetite
Muscle weakness
Kidney failure
Seizures Dehydration in the Elderly Dehydration presents special concerns in older adults. The hypothalamus undergoes physiologic changes that accompany age such as:
Decreased thirst sensation and reduced fluid intake.
Diminishing kidney function, with additional losses of body fluid. Water Intoxication Not nearly as common, but water intoxication can occur.

Excessive intake of plain water may result in the dangerous condition of hyponatremia. Those at risk:
Psychiatric patients
Patients on psychotropic drugs
Endurance athletes Under normal situations, excess water consumed is lost by increased urine output and is not likely to pose a problem for a normal healthy person eating an otherwise typical diet. However, individuals with renal insufficiency or neurologic disorders affecting the thirst mechanism and those participating in heavy endurance exercise may not be able to dilute and/or excrete urine appropriately. As blood volume is diluted with excess water, the water moves to intracellular fluid spaces to reestablish equilibrium with sodium concentrations there, thus diluting intracellular fluid as well. This movement causes edema, lung congestion, and muscle weakness. Amount and Distribution Normal body water content ranges from 45% to 75% of the total body weight in adults.
Total body water is categorized into two major compartments. Extracellular Fluid Total body water outside cells
One quarter of extracellular fluid is blood plasma, in the intravascular compartment
Three quarters are the interstitial fluid, the transcellular fluid and the water within the lymphatic circulation Intracellular fluid
Total body water inside the cells
Twice the volume of that outside the cells Intracellular Fluid Total body water within the cells
Twice the number outside the cells P. 156 Overall Water Balance Water enters and leaves the body by various routes controlled by basic mechanisms such as thirst and hormones.
The average adult metabolizes 2.5 to 3 L of water per day in a balance between intake and output. Water Intake Water enters the body in three main forms;
1. Performed as water in liquids that are consumed
2. Preformed water in foods that are eaten
3. As a product of cell oxidation when nutrients are burned in the body for energy *Water Content in Food - P. 158* Conscious attention to adequate fluid intake is an important part of health maintenance and care. Water Output Obligatory Water Loss
Leaves the body through kidneys, skin, lungs, and feces.

Optional Water Loss
Varies according to climate and physical activity. table 9-4, p. 158 Particles in Body Water Two main types of particles control water balance in the body; electrolytes and plasma proteins. (cc) photo by medhead on Flickr Electrolytes Electrolytes are small, inorganic substances that break apart in solution and carry and electrical charge.
Because of their small size, electrolytes can freely diffuse across most membranes of the body, maintaining a constant balance between the intracellular and extracellular electrical charge.

Cations: Sodium (Na+), Potassium (K+), Calcium (Ca2+), Magnesium (Mg2+)

Anions: Chloride (Cl-), Bicarbonate (HCO3-), Phosphate (PO43-), Sulfate (SO42-) Plasma Proteins Plasma proteins are organic compounds of large molecular size, mainly in the form of albumin and globulin.
Usually retained in blood vessels, controlling water movement, called colloidal osmotic pressure. In addition to electrolytes and plasma protein, other small organic compounds are dissolved in body water. Plasma Proteins Plasma proteins are organic compounds of large molecular size, found mainly in the form of albumin and globulin.

They are retained in blood vessels, controlling water movement which is called colloidal osmotic pressure. Separating Membranes Two types of membranes separate and contain water throughout the body; the capillary membrane and the cell membrane. Capillary Membrane The walls of capillaries are thin and porous.

Water molecules and small particles can move freely across them. Cell Membrane Protect and nourish the cell contents.

Water is freely permeable, but other molecules or ions use channels for passage. Moving Forces A variety of forces are at work in the cell membrane to allow dynamic equilibrium, such as:
Facilitated Diffusion
Filtration The Capillary Fluid Shift Mechanism Pinocytosis Active Transport Osmosis Diffusion Facilitated Diffusion Filtration Active Transport Pinocytosis Osmosis is the movement from an area with low solute concentration to an area with high solute concentration.

Osmotic pressure moves water across the membrane to help equalize the solutions on both sides. Simple diffusion is 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. Have transporters assist particles in crossing the membrane. Water and small particles move back and forth between capillaries and cells according to shifting pressures to establish homeostasis. Drive necessary particles against their flow, "upstream" across separating membranes. Large molecules attach themselves to the thicker cell membrane and are then engulfed by the cell, carried across the membrane into the cell, the released so the cell enzymes metabolize the particles. Capillary Fluid Shift Mechanism This mechanism operates a balancing act between opposing fluid pressures to nourish the life of the cell. Purpose Process Organ Systems Involved Gastrointestinal Circulation Renal Circulation Acid-Base Balance System
The optimal degree of acidity or alkalinity must be maintained in body fluids to support human life. This vital balance is achieved by chemical and physiologic buffer systems. Acids and Bases The concept of acids and bases relates to hydrogen ion concentration.
Acidity is expressed in terms of pH.
An acid has more hydrogen ions, a base being one with fewer hydrogen ions.
Mechanisms to reestablish equilibrium within the body are constantly at work. Acid-Base Buffer System The body deals with degrees of acidity by maintaining buffer systems to handle an excess of either acid or base.

The human body contains many buffer systems because only a relatively narrow range of pH is compatible with life (7.35 to 7.45). Chemical Buffer System A chemical buffer system is a mixture of acidic and alkaline components, an acid and a base partner, that together protect a solution from wide variations in its pH, even when strong bases or acids are added to it.

The carbonic acid (H2CO3)/base bicarbonate (NaHCO3) buffer system is the body's main buffer system because the raw materials for producing carbonic acid are readily available and because the acid/base ratio is maintained well. Physiologic Buffer Systems When chemical buffers cannot reestablish equilibrium, the respiratory and renal systems will respond.

Respiratory Control - carbon dioxide leaves the body
Urinary Control - kidney monitors hydrogen ions Dietary Factors Kidney "laundering" of the blood helps maintain water balance and proper solution of blood

Hormonal controls of the Renal Circulation
Antidiuretic Hormone Mechanism
Aldosterone Hormone Mechanism Bibliography Gale Group. "Water and Nutrition." Enotes.com. Enotes.com. Web. 1 Apr. 2012. <http://www.enotes.com/water-nutrition-reference/water-nutrtion>.

Herlihy, Barbara L. The Human Body in Health and Illness. St. Louis, MO: Elsevier, 2011. Print.

Wissman, Jeanne, and Audrey Knippa. Nutrition for Nursing. Overland Park, KS: Assessment Technologies Institute, 2011. Print.

Nix, Staci, and Sue Rodwell. Williams. Williams' Basic Nutrition & Diet Therapy. St. Louis, MO: Mosby/Elsevier, 2009. Print. Student will be able to state the basic principles of water.

Student will be able to state the four functions of water.

Student will be able to state the factors in body water requirement.

Student will learn about medical conditions related to body water requirements such as, dehydration and water intoxication. More Objectives! Students will learn about amounts and distribution of water including intracellular and extracellular fluid, water intake and output and overall water balance.

Student will learn the solutes included in body water.

Student will learn the types of membranes that separate and contain water throughout the body.

Student will understand the different types of transportation forces involved in creating equilibrium.

Student will learn about tissue water circulation.
Student will understand the Acid-Base balance system. - Water from blood plasma is continually secreted into the gastrointestinal tract.
-In the latter portion of the intestine, most water and electrolytes are reabsorbed into the blood.
-Is maintained in isotonicity. Essential water, nutrients and oxygen must be pushed out of blood circulation into tissue circulation to distribute their goods throughout the body; then water, cell metabolites, and carbon dioxide must be pulled back into the blood circulation to dispose of wastes through the kidneys or lungs. The body maintains this constant flow of water through the tissues carrying materials to and from the cells by hydrostatic pressure and colloidal osmotic pressure. When blood first enters the capillary system from the larger vessels coming from the heart - the arterioles - the greater blood pressure from the heart forces water and small particles into the tissues to bathe and nourish the cells. When circulating tissue fluids are ready to reenter the blood capillaries, the initial blood pressure has diminished. COP draws water and its metabolites back into the capillary circulation after having served the cells and carries them to back to the heart. - Gastrointestinal Tract
- Kidneys In Summary Human body's percentage of water.
Primary functions of water.
Where body water is distributed.
The two types of solute particles that control water distribution.
How the acid-base system is controlled by the lungs and the kidneys. Chapter 9: Water Balance
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