Fluid and Electrolyte Balance - Introduction - F and E Intro.PDF

Fluid and Electrolyte Balance Introduction 1 Copyright © 2016 by Elsevier Inc. All rights reserved.  Learning Objectives Fluid and Electrolyte Balance 1. List, describe, and compare the body fluid compartments and their subdivisions. 2. Discuss avenues b...

Fluid and Electrolyte Balance Introduction 1 Copyright © 2016 by Elsevier Inc. All rights reserved.  Learning Objectives Fluid and Electrolyte Balance 1. List, describe, and compare the body fluid compartments and their subdivisions. 2. Discuss avenues by which water enters and leaves the body and the forces that move fluids into and out of the blood. 3. Explain the mechanisms used by the body to maintain fluid balance. 4. Discuss the nature and importance of electrolytes in body fluids. 5. Describe examples of common fluid and electrolyte imbalances. 2 Copyright © 2016 by Elsevier Inc. All rights reserved.  Body Fluid Volumes Water is most abundant body compound – References to “average” body water volume based on a healthy, nonobese, 70-kg male – Water is 60% of body weight in males; 50% in females – Volume averages 40 L in a 70-kg male (154 pounds) 3 Copyright © 2016 by Elsevier Inc. All rights reserved.  Body Fluid Volumes (Cont.) Variation in total body water is related to: – Total body weight of individual – Fat content of body: The more fat the less water (adipose tissue is low in water content) – Gender Female body has about 10% less water than male body (Figure 19-2) – Age In a newborn infant, water may account for 80% of total body weight In older adults, water per pound of weight decreases (muscle tissue – high in water – replaced by fat, which is lower in water) 4 Copyright © 2016 by Elsevier Inc. All rights reserved. Relative Volumes of Three Body Fluids 5 Copyright © 2016 by Elsevier Inc. All rights reserved. Water in the Body 6 Copyright © 2016 by Elsevier Inc. All rights reserved.  Body Fluid Compartments Extracellular fluid (ECF) – Called internal environment of body – Surrounds cells and transports substances to and from them – Types Plasma: Liquid part of whole blood Interstitial fluid: Surrounds the cells Transcellular fluid: Lymph, joint fluids, cerebrospinal fluids, eye humors 7 Copyright © 2016 by Elsevier Inc. All rights reserved.  Body Fluid Compartments (Cont.) Intracellular fluid (ICF) – Largest fluid compartment – Serves as solvent to facilitate intracellular chemical reactions 8 Copyright © 2016 by Elsevier Inc. All rights reserved. Volumes of Body Fluid Compartments 9 Copyright © 2016 by Elsevier Inc. All rights reserved.  Mechanisms That Maintain Fluid Balance Overview of fluid balance Regulation of fluid output – Fluid output, mainly urine volume, adjusts to fluid intake – Antidiuretic hormone (ADH) from posterior pituitary gland acts to increase kidney tubule reabsorption of sodium and water from tubular urine into blood, thereby tending to increase ECF (and total body fluid) by decreasing urine volume 10 Copyright © 2016 by Elsevier Inc. All rights reserved.  Mechanisms that Maintain Fluid Balance (Cont.) Regulation of fluid intake – ECF electrolyte concentration influences ECF volume – Increase in ECF increases ECF volume by increasing movement of water out of ICF and by increasing ADH secretion, which decreases urine volume Exchange of fluids by blood – Capillary blood pressure pushes water out of blood, into interstitial fluid; blood protein concentration pulls water into blood from interstitial fluid; hence, these two forces regulate plasma and interstitial fluid volume under usual conditions 11 Copyright © 2016 by Elsevier Inc. All rights reserved. Aldosterone Mechanism 12 Copyright © 2016 by Elsevier Inc. All rights reserved.  TYPES OF FLUIDS/ IVF SOLUTION ISOTONIC FLUIDS An isotonic solution is one that has the same osmolarity, or solute concentration, as another solution. If these two solutions are separated by a semipermeable membrane, water will flow in equal parts out of each solution and into the other. A depiction of a cell in an isotonic solution can be seen above. Note that because there is the same concentration of solute molecules inside and outside of the cell that water molecules are simply exchanged through the cell membrane. Example: 0.9% Normal Saline (0.9% NaCl). Because the concentration of the IV fluid is similar to the blood, the fluid stays in the intravascular space and osmosis does not cause fluid movement between compartments  TYPES OF FLUIDS/ IVF SOLUTION HYPOTONIC FLUID A hypotonic solution is a solution with a lower concentration of solutes than another solution. In biology, hypotonic solutions carry across semipermeable membranes—plant cell walls and animal cells—to infuse the cells with fluids. In medicine, hypotonic solutions include: -Saline 0.45 percent (less than half the normal saline level found in blood) -Saline 0.25 percent with or without dextrose (a quarter of normal saline level) -5 percent or 2.5 percent dextrose -Pure distilled water  Hypertonic solutions Hypertonic solutions have a higher concentration of dissolved particles than blood. An example of hypertonic IV solution is 3% Normal Saline (3% NaCl). When infused, hypertonic fluids cause an increased concentration of dissolved solutes in the intravascular space compared to the cells. This causes the osmotic movement of water out of the cells and into the intravascular space to dilute the solutes in the blood.  MOVEMENTS OF FLUIDS Diffusion Diffusion is the process of movement of molecules under a concentration gradient. It is an important process occurring in all living beings. Diffusion helps in the movement of substances in and out of the cells. The molecules move from a region of higher concentration to a region of lower concentration until the concentration becomes equal throughout. Liquid and gases undergo diffusion as the molecules are able to move randomly. MOVEMENTS OF FLUIDS Example: Take water in a beaker. Add a few copper sulfate crystals in one place and leave it as it is for some time without disturbing it. After some time we can see that the beaker contains a uniformly colored solution. Here, both water and copper sulfate diffuse independently. With this experiment, we can infer that solutes move from a higher concentration to a lower concentration in a solution.  MOVEMENTS OF FLUIDS Active Transport It is defined as a process that involves the movement of molecules from a region of lower concentration to a region of higher concentration against a gradient or an obstacle with the use of external energy. The diagram shows the process of active transport, which uses an external energy ATP for the movement of the molecules. The uptake of glucose in the intestine of the human body and also the uptake of minerals or ions into the root hair cells of the plants are some of the examples of active transport. MOVEMENTS OF FLUIDS Osmosis It is a process by which the molecules of a solvent pass from a solution of low concentration to a solution of high concentration through a semi- permeable membrane. Osmotic pressure is the pressure required to stop water from diffusing through a membrane by osmosis. It is determined by the concentration of the solute. Water diffuses into the area of higher concentration from the area of lower concentration. MOVEMENTS OF FLUIDS MOVEMENTS OF FLUIDS Osmosis is of two types: Endosmosis– When a substance is placed in a hypotonic solution, the solvent molecules move inside the cell and the cell becomes turgid or undergoes deplasmolysis. This is known as endosmosis. Exosmosis– When a substance is placed in a hypertonic solution, the solvent molecules move outside the cell and the cell becomes flaccid or undergoes plasmolysis. This is known as exosmosis.  Fluid Imbalances Dehydration – Total volume of body fluids less than normal – Interstitial fluid volume shrinks first, and then if treatment is not given, ICF volume and plasma volume decrease – Dehydration occurs when fluid output exceeds intake for an extended period Overhydration – Total volume of body fluids greater than normal – Overhydration occurs when fluid intake exceeds output – Various factors may cause this (e.g., giving excessive amounts of intravenous fluids or giving them too rapidly may increase intake above output) 26 Copyright © 2016 by Elsevier Inc. All rights reserved.  Fluid Imbalances (Cont.) Overhydration – Water intoxication may result from rapidly drinking large volumes of water or giving hypotonic solutions to persons unable to dilute and excrete urine normally 27 Copyright © 2016 by Elsevier Inc. All rights reserved.  Fluid Imbalances (Cont.) Water output by the body Testing for dehydration. From Fritz S: Mosby’s fundamentals of therapeutic massage, under varying conditions. ed 5, St Louis, 2013, Mosby. 28 Copyright © 2016 by Elsevier Inc. All rights reserved.  Importance of Electrolytes in Body Fluids Electrolytes and nonelectrolytes – Nonelectrolytes Organic substances that do not break up or dissociate when placed in water solution (e.g., glucose) – Electrolytes Compounds that break up or dissociate in water solution into separate particles called ions (e.g., ordinary table salt or sodium chloride) 29 Copyright © 2016 by Elsevier Inc. All rights reserved.  Importance of Electrolytes in Body Fluids (Cont.) Ions – The dissociated particles of an electrolyte that carry an electrical charge (e.g., sodium [Na+]) – Positively charged ions (e.g., potassium [K+] and sodium [Na+]) – Negatively charged particles (ions) (e.g., chloride [Cl–] and bicarbonate [HCO3–]) 30 Copyright © 2016 by Elsevier Inc. All rights reserved.  Importance of Electrolytes in Body Fluids (Cont.) Electrolyte functions – Electrolytes are required for many cellular activities, such as nerve conduction and muscle contraction – Sodium (Na+) Most abundant and important positively charged ion of plasma – Normal plasma level: 142 mEq/L – Average daily intake (diet): 100 mEq – Chief method of regulation: Kidney Aldosterone increases Na+ reabsorption in kidney tubules – Sodium-containing internal secretions (Figure 19-10) 31 Copyright © 2016 by Elsevier Inc. All rights reserved. Sodium-Containing Internal Secretions 32 Copyright © 2016 by Elsevier Inc. All rights reserved.  Electrolyte Imbalances Homeostasis of electrolytes – Electrolyte balance related to “intake” and “output” of specific electrolytes Sodium imbalance – Hypernatremia: Blood sodium level >145 mEq/L – Hyponatremia: Blood sodium level 5.1 mEq/L – Hypokalemia: Blood potassium level