This chapter gives a brief overview of the physics and chemistry involved in homeostasis of the body. It also focuses on the fluid and electrolyte needs of clients over the lifespan and how a client’s wellbeing can be affected by alteration in fluid input or output. Nurses are required to assess, maintain and educate clients to maintain their fluid and electrolyte balance according to their specific needs. Fluid requirements vary according to age, height, sex, metabolism and the presence of any underlying conditions. Nurses must be able to accommodate for all these different factors when they plan, care and educate clients.

A basic knowledge of two sciences, physics and chemistry, is helpful in many aspects of nursing. This chapter therefore addresses some aspects of physics and chemistry that help to provide a valuable framework in the study of physiology and understanding of the rationale behind many nursing and medical practices. Although the boundary between the two sciences is often indistinct, physics may be defined as the study of the laws and properties of matter relating particularly to motion and force, while chemistry may be defined as the science dealing with the elements, their compounds, and the chemical structure and interactions of matter.

The concepts of atoms, atomic structure and bonding provide the link between physics and chemistry. Both physics and chemistry are interrelated and interdependent, and one action rarely happens in isolation. Therefore, this chapter outlines some of the physical and chemical principles that are commonly applied in nursing practice. This chapter also discusses the acid–base and the fluid and electrolyte balances that are essential components of the body’s homeostatic processes.


In health the body maintains a precise osmolarity and fluid balance within body compartments; the volume and constituents of body fluids varying only slightly in order to maintain a stable internal physical and chemical environment. When there is a disturbance in fluid and electrolyte balance, the body attempts to compensate by various adaptive mechanisms. If the imbalance is too great or prolonged, the body’s compensatory mechanisms may deplete the ability to maintain homeostasis and health.

The physiological processes involved in the maintenance of fluid, electrolyte and acid–base balance are:


An atom is composed of a central dense core of positively charged heavy particles termed protons and an equal number of lighter neutrons that bear little charge and are considered neutral. The nucleus is surrounded by a cloud of negatively charged electrons that are held in place by the positive electromagnetic force of the nucleus. The number of positively charged protons in each neutral atom normally equals the number of negatively charged electrons and therefore an atom is neither positive nor negative in its overall electrical charge under normal conditions. The number of neutrons may vary, but they do not affect the charge of the atom.

Atoms differ from each other in the number of particles they contain and, to aid in the identification of atoms, each one is assigned an atomic number. The atomic number of an atom is equal to the number of protons in its nucleus. For example, the hydrogen atom has one proton, so its atomic number is 1, the helium atom has two protons, so its atomic number is 2; thus, the larger the atomic number the larger and the heavier the atom is. Table 30.1 lists some common elements and their atomic numbers.


Name Symbol Atomic number
The first 20 elements, by increasing atomic weight
Hydrogen H 1
Helium He 2
Lithium Li 3
Beryllium Be 4
Boron B 5
Carbon C 6
Nitrogen N 7
Oxygen O 8
Fluorine F 9
Neon Ne 10
Sodium Na (Latin: natrium) 11
Magnesium Mg 12
Aluminium Al 13
Silicon Si 14
Phosphorus P 15
Sulphur S 16
Chlorine Cl 17
Argon Ar 18
Potassium K (Latin: kalium) 19
Calcium Ca 20
Some other well-known elements
Iron Fe (Latin: ferrum) 26
Copper Cu (Latin: cuprum) 29
Zinc Zn 30
Selenium Se 34
Silver Ag (Latin: argentum) 47
Tin Sn (Latin: stannum) 50
Iodine I 53
Barium Ba 56
Gold Au (Latin: aureum) 79
Mercury Hg (Latin: hydragyrum) 80
Lead Pb (Latin: plumbum) 82
Some heavier naturally radioactive elements
Radium Ra 88
Uranium U 92
Plutonium Pu 94


Matter that is composed entirely of the same kind of atoms — that is, each with the same number of protons — is known as an element. There are 112 different elements that are known to exist, some of which do not exist in nature but have only been observed in physics laboratories. Each is classified by its own individual atomic number and particular chemical properties. Every element (and thus each kind of atom) is named and has been given a unique symbol that is used as a ‘shorthand’ for that element (see Table 30.1). When arranged into a table with a series of rows (or ‘periods’) based on increasing atomic weights, from lightest to heaviest, elements with similar properties, such as being a metal or an inert gas, become grouped in vertical columns (see the periodic table of the elements in any chemistry textbook). Elements can combine naturally with each other to form new substances; for example, one atom of sodium (Na) combines with one atom of chlorine (Cl) to form a salt, sodium chloride (NaCl); similarly one atom of Carbon (C) combines with two atoms of oxygen (O2) to form carbon dioxide (CO2).

Table 30.2 lists the common elements that make up the human body and their relative concentration within it. More than 95% of the body is made up of the elements oxygen, carbon, hydrogen and nitrogen, while the remaining 5% is comprised mainly of calcium and phosphorus with other elements in very small quantities.


Element Atomic symbol Percentage of body mass (approximate)
Oxygen O 65
Carbon C 18
Hydrogen H 10
Nitrogen N 3
Calcium Ca 1.5
Phosphorus P 1
Potassium K 0.4
Sulphur S 0.3
Sodium Na 0.2
Magnesium Mg 0.1
Chlorine Cl 0.2
Iron Fe 0.1
Iodine I 0.1
Copper Cu Trace
Zinc Zn Trace
Cobalt Co Trace
Fluorine F Trace

Trace = less than 0.01%


An ion is an atom or molecule that has lost or gained one or more electrons. Elements or compounds that dissolve in a solvent, such as water, to form separate ions are known as electrolytes. By dissociating, an ion loses or gains an electron or electrons from the electron cloud and becomes electrically charged. If an electron is lost, the previously neutral atom becomes more positive, as the positively charged protons are no longer balanced by the same number of negatively charged electrons. Conversely, if an atom gains an electron, a previously neutral atom becomes more negatively charged. The number of electrons gained or lost is denoted by a number after the chemical symbol of the element or compound; for example, Ca++ is a calcium ion that has lost two electrons, while OH is a hydroxide ion that has gained one electron. Movement of positively and negatively charged ions across a membrane produces an electric current or potential, for example, the electrical nerve signals in the brain. Positively charged ions are called cations, and negatively charged ions are called anions.

Electrolytes are chemical substances that, when dissolved or melted, dissociate into ions and can conduct an electric current. Electrolytes are a major constituent of all body fluids and affect the functioning of many physiological processes. Electrolytes are essential to the normal function of all cells and are involved in metabolic activities, fluid homeostasis and in creating charge differences on which the functioning of nerves and muscles depend.

The maintenance of electrolyte balance in the body depends on homeostatic mechanisms that regulate the absorption, distribution and excretion of water and the solutes dissolved in it. Many conditions can cause an electrolyte imbalance; for example, prolonged diarrhoea may cause a loss of many electrolytes.


An acid is any substance that releases hydrogen ions (H+) when dissolved in water. Acids have chemical properties essentially opposite to those of bases. Examples of acids found in the body include hydrochloric, lactic, pyruvic, carbonic, citric, folic and fatty acids. A base is any substance that accepts hydrogen ions in chemical reactions. Alkalis are bases that are soluble in water. Examples of bases found in the body include hydrogen bicarbonate and sodium hydroxide.


Metabolic causes

Metabolic acidosis occurs when the body is unable to excrete enough acids because of a problem with malabsorption, such as diarrhoea; metabolism, for example, diabetes (ketone acids [see Clinical Interest Box 30.1]); or organ failure, such as kidney failure. (The lungs compensate, e.g. by increasing ventilation and increasing excretion of acidifying CO2.)

Metabolic alkalosis occurs when too much acid is lost, for example by vomiting, nasogastric drainage, or use of some diuretics. (The lungs compensate, e.g. by decreasing ventilation and decreasing excretion of acidifying CO2.)


Homeostasis is the term that refers to the processes by which the internal environment of the body is maintained within narrow physiological parameters. Homeostasis can also be defined as the tendency of the body to maintain the stability of the internal environment. Homeostasis is dynamic and active, as the body constantly and actively pursues the maintenance of a stable internal environment.

Homeostatic mechanisms are the mechanisms by which the body is able to control the state of the internal environment. They are the processes and means by which the body is able to adapt to stresses (anything that threatens or upsets homeostasis) and yet maintain its inner balance. Any stress situation that arises activates protective homeostatic mechanisms that endeavour to compensate for that stress. Without homeostatic mechanisms to maintain the internal environment, the body cannot survive. When the ability of the body to maintain homeostasis is overwhelmed, illness, and sometimes death, occurs.

Much of nursing practice is aimed at maintaining or restoring the client’s homeostasis. Many of the topics discussed in this and other chapters relate to the state of homeostasis; for example, acid–base balance in body fluids, energy production, fluid and electrolyte balance, and body temperature regulation. Homeostatic regulation of the body is achieved by the cooperative action of most organs and tissues, including the lungs, kidneys and cardiovascular system, and the pituitary, suprarenal and parathyroid glands.

For these mechanisms to maintain homeostasis, the body must be able to detect changes and to react appropriately to those changes. The ability of the body to detect changes is through the process of feedback. Two types of feedback exist. Negative feedback brings the body’s internal environment back to its optimal state. Negative feedback is a decrease in function in response to a stimulus; for example, if the blood glucose level rises above normal, action is instituted by several control systems (such as the islets of Langerhans in the pancreas) to restore the blood glucose level to normal.

Positive feedback directs the body’s internal environment away from its optimal state. Positive feedback is an increase in function in response to a stimulus; for example, during childbirth one uterine contraction induces further contractions, which continue to increase in intensity and frequency until the baby is born. Many positive feedback situations are undesirable and can, for example, result in the over-production of a normal body chemical, thus compounding the problem.

Feb 12, 2017 | Posted by in NURSING | Comments Off on MEETING FLUID AND ELECTROLYTE NEEDS

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