Constituents of body fluid –
The human body consists mostly of water, and is a major constituent to the human body and vital organs; of this 90% include blood plasma, lymph, urine, saliva, digestive juices, bile, cerebrospinal fluid and tissue fluid. Water enables substances to be transported throughout the body, red blood cells for example, as wells as supplying the medium required for metabolic reaction to take place (respiration). Without water the progression of these fluids would not be possible. Water is constantly being transported between the fluid compartments of the body.
Water has five main functions in the body, of which includes:
‘Cell life – distribute nutrients to cells i.e. vitamins, minerals and glucose Chemical and metabolic reactions – removal of waste products (toxins) from the organs Transport of nutrients – participates in the breakdown of food Body temperature regulation – water has a large heat capacity that allows it to help limit any changes to an individual’s body temperature in a certain environment. For example the release of heat when the surrounding temperature is higher than body temperature Elimination of waste’
Urea is an organic molecule made up of carbon, nitrogen, oxygen, and hydrogen. Urea is a common constituent of blood and other various bodily fluids, and is formed from ammonia in the kidney and liver. Ammonia is produced through the breakdown of proteins during tissue metabolism. Metabolic reactions that take place within the body can produce a surplus of amino acids of which can be converted into the waste product otherwise known as urea through the process of deamination in the liver. Proteins obtained through an individual’s diet are broken down into amino acids. The excess amino acids made during this process are unable to be stored in the body as they can become toxic; therefore they would then have to be converted into a less toxic urea before ultimately being removed as a component of urine.
Acids, bases and salt –
Acids are a substance that has a pH less than 7. There are two different types of acid:
Weak acid – An organic compound with a minimal amount of dissociated molecules Strong acid – An organic compound with a large amount of dissociated molecules
Acids are a corrosive substance with a pH less than 7. Acidity is caused by a high concentration of hydrogen ions.
Bases are a substance with a pH higher than 7, and have a high concentration of hydroxyl ions. Bases can react with acids in order to neutralise them in order to form salt and water. Bases are normally metal oxides or metal hydroxides. Sodium hydroxide for example is a base.
Acids react with reactive metals in order to make a salt. Salts are a compound formed by the neutralisation of an acid by a base, for example metal oxide. This is a result of hydrogen atoms in an acid being replaced by positive ions.
Bases that have are able to dissolve into water are known as alkalis. Sodium hydroxide is an alkali as it dissolves in water, copper oxide cannot dissolve water therefore is not an alkali.
Hydrochloric acid is produced in the stomach, consisting of chloride and hydrogen. Carbonic acid is produced in red blood cells consisting of carbon dioxide and water, of which is why demanding exercise can lead to the increase in the acidity of the individual’s blood.
Control of osmosis –
Salts are a major constituent of blood, and the levels both inside and outside of the cell, of which can be controlled by ATP. The sodium salts and chloride ions are continuously pumped back out of the cell each time they enter a cell, whereas potassium are pumped back into the cell as they leave a cell. The movement of salts enable the individual in assisting osmosis through the cell membrane.
Osmotic pressure outside the cell is equal to that inside of the cell.
Water moving into and out of the cell is the same.
Osmotic pressure is lower.
Water moving into the cell is greater than that of which is moving out of the cell.
Osmotic pressure is higher.
Water moving out of the cell is greater than that of which is moving into the cell.
Role of electrolytes –
Electrolytes are compounds that dissociate into ions when they are dissolved in water, thereby causing them to become electrically charged particles, meaning that they have the ability to conduct electrical impulses. The electrical impulses created are what the body needs in order to make muscle cells contract. Electrolytes can become either cations (positively charged) or anions (negatively charged).
Essential minerals – Some electrolytes are considered essential minerals, meaning that they are unable to be made within the body and are an essential part of health.
The major constituent for a cell is potassium
The components of amino acids and proteins
Chloride is needed in order to produce hydrochloric acid in the stomach Magnesium of which can be found in bone and teeth, plays a key role in the contraction of muscles as well as an activator for various enzymes. Another component of bone and teeth is phosphorous and calcium, with calcium being required for blood clotting along with aiding in the contraction of muscles.
There are trace elements present in the body. These essential minerals are required in only small amounts.
The food and fluids consumed by an individual contain mineral salts, which are used to form electrolytes which dissolve in the fluids of the body. Electrolytes can be found in blood, urine, in the fluid contained in the body’s cells, and in the fluid surround the cells. Sodium, calcium, chloride, magnesium, potassium are the most commonly found electrolytes within the body. Electrolytes play a key role in helping the heart, nerves, and muscles to function. They also play role in keeping fluid levels normal in different body compartments.
Levels of electrolytes in the body’s fluid compartments are controlled through the movement of electrolytes moving into/ out of the compartments. The kidneys have a hand in filtering electrolytes from the blood in order to keep the levels constant. Hormones such as the antidiuretic hormone and parathyroid hormone for example, help to regulate electrolyte balance.
Acid-base balance –
In order to function properly the blood needs the right balance between acid and basic (alkaline) compounds. This is known as acid-base balance. The kidneys and lungs within the body work in order to maintain acid-base balance; the slightest of variations from its normal range can have detrimental effects to the body’s vital organs.
Acid and alkaline levels are measured on a pH scale. Increase in acidity can cause pH levels to fall, whereas an increase in alkaline levels causes pH levels to rise.
pH – pH measures the amount of hydrogen ions that are in a given solution. The pH scale ranges from the values of 1 to 14. Number 7 in the scale is known as neutral, water for example is a neutral substance. From 1 to 7, the lower the number on the scale the stronger the acid; whereas from 7 to 14 the higher the number the stronger the base.
Importance of maintaining hydrogen concentration in body fluid –
Hydrogen ion concentration is important to the structure and function of living systems. Slight changes can cause changes in ‘larger molecules and molecular complexes composing organisms.’ Buffer systems are put in place in order to maintain and stabilise the pH of body fluids.
Phosphate buffers – These chemical buffers are essential in order to maintain normal hydrogen concentration in intracellular fluids, as their concentration inside the cells are many times greater than the concentration of the bicarbonate buffers. Metabolic activities are controlled by enzymes, of which can also be known as organic catalysts.
Protein buffers – Are similar to the composition of phosphate buffers, as they include haemoglobin, are especially important within the cells. Chemical buffers of the body fluids are the first line of defence to prevent any changes in hydrogen ion concentration; any acid/base added to the body fluids immediately react with the buffers in order to prevent any changes in acid-base balance.
Buffer systems –
Chemical buffers are in place in order to resist changes in pH levels, and are the body’s first line of defence. A buffer solution is a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid; and is used to stabilize the pH of a liquid. The ability of an acid-base mixture resist sudden changes in pH is known as buffer action. Tissue cells and vital organs of the body are sensitive to the slightest of changes in the pH environment; and in high concentrations, acids and bases can be highly damaging to living cells.
Buffer solutions are put in place as a means of keeping pH at a nearly constant level in various chemical applications. One such buffer solution can be found in the blood. Several buffering agents bind hydrogen ions in order to stop any change in pH. Extracellular buffers include bicarbonate and ammonia, and intracellular buffers include proteins and phosphates.
Buffers are in place in order to work against sudden and large changes in the pH of body fluids by
Releasing hydrogen ions when the pH increases (acids)
Binding hydrogen ions when the pH decreases (bases)
There are three main chemical buffer systems in the body:
Carbonic acid-bicarbonate buffer system
Phosphate buffer system
Protein buffer system
Materials can be transported between the cytoplasm and the outside of the cell; this is known as the active transport process (ATP), whereas the movement of other molecules is known as passive transport which does not require energy. Active transport can be used in order to get the molecules to go against the concentration gradient; this can be done by either facilitated diffusion or osmosis.
Passive transport of molecule depends on its ability to be able to pass through the cell membrane, as well as that of the concentration gradient which allows molecules to diffuse from an area of high concentration to an area of low concentration. Molecules such as gases, lipids and water have the ability to pass through the cell membrane fairly easily.
However other molecules such as glucose, amino acids, and ions do not have the same ability. Some of these molecules can enter and leave the cell through the use of facilitated transport, where the molecules can move down the concentration gradient through protein channels in the membrane. This process does not require any form of energy.
Role of water in relation to properties –
Specific heat capacity – Water has a large heat capacity which aids in limiting any changes in an individual’s body temperature in a warm or cold environment. As a result of the high specific heat capacity of water, its role in temperature regulation is very important. Water enables the body to release heat when the ambient temperature is higher than that of the individual’s body temperature. The body starts to sweat, and the evaporation of water from the skins surface occurs, in order to cool the body down.
Surface tension – ‘Surface tension is a contractive tendency of the surface of a liquid that allows it to resist an external force. ‘For example the floating of some objects on the surface of water, even though they are denser than water, some insects however have the ability to run on the water’s surface. The cohesive forces of liquid molecules are responsible for surface tension, and are responsible for many of the behaviours of liquids. In addition, water has adhesive properties, so that the pleural fluid which covers the membrane of the lungs stops them from sticking to the inside of the ribcage.
Distribution of water –
There are two main fluid compartments in the human body:
Intracellular fluid (ICF)
Extracellular fluid (ECF)
Water is the major solvent of all body fluid compartments. Total body water averages around 60% body weight in young males and 50% of body weight in young adult females. The percentage of body weight that water occupies depends on the amount of adipose tissue (fat) an individual has.
The overall water in the body involves water inside of the cells known as intracellular fluid (ICF compartment), found inside the bilayered cell plasma membrane which is around 28 litres, which makes up around 60% to 67% of body water; and the extracellular water located outside of the cells which is around 14 litres makes up the other 33% to 40%. Tissue fluid also known as the intracellular and the interstitial fluid have the majority of the component of the extracellular fluid as it has 11 litres compared to 3 litres of plasma. The lymph has 10% of the tissue fluid that form in the remainders of the plasma.
ECF is composed of fluid outside of the cells and consists of three subdivisions:
Third space (transcellular fluid)
The interstitial compartment is the fluid space which surrounds the cells of a given tissue, and is filled with interstitial fluid. Interstitial fluid allows for the movement of ions, proteins, and nutrients across the cell membrane. The fluid is continuously recollected by the lymphatic channels. Excess fluid in the interstitial compartment causes oedema to develop. Intravascular plasma can be found within the vascular system and makes up a fourth of ECF. The third space is part of the ECF compartment and is otherwise known as transcellular fluid. Examples of third space include:
Renal tubular fluid
Intercellular fluid is the main component of extracellular fluid; ‘other components include plasma and transcellular fluid. Intercellular fluid surrounds the body’s cells, and provides a way for delivering materials to the cells, intercellular communication, and removal of metabolic waste. The fluid found in the intercellular spaces are made up of water, amino acids, sugars, fatty acids, coenzymes, hormones, neurotransmitters, salts and cellular products. ‘
Plasma makes up approximately 25% of the body’s total extracellular fluid. Plasma proteins serve several functions, of which include maintaining the proper distribution of water between the blood and tissues; transportation of nutrients, metabolites, and hormones throughout the body, defending against infection etc. Diseases can alter the amount of plasma proteins that are produced and their concentration in the blood.
Role of intercellular fluid in homeostasis –
In homeostasis, intercellular fluid also known as interstitial and tissue fluid, plays a vital role as the fluid is pushed out of the arterial end of the capillary by the blood pressure, after the blood has been pushed out through the muscular arterioles and capillaries. During this stage carbon dioxide is low. Tissue fluid flows around the cells and in between giving out raw materials through the use of osmosis, facilitated diffusion and diffusion etc. The metabolic waste is passed in the opposite direction to the cells and into the tissue fluid. However if the waste materials were allowed to accumulate, this could ultimately cause disruption and lead to the cells dying before death occurring.
http://www.nestle-waters.com, (2014). Functions of water in human body. [online] Available at:
http://www.nestle-waters.com/healthy-hydration/water-fonctions-in-human-body [Accessed 13 Oct. 2014].
Bbc.co.uk, (2014). BBC – GCSE Bitesize: Acids and bases. [online] Available at: http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/acids/acidsbasesrev1.shtml [Accessed 13 Oct. 2014].
Biology-online.org, (2014). Intercellular fluid – definition from Biology-Online.org. [online] Available at: http://www.biology-online.org/dictionary/Intercellular_fluid [Accessed 13 Oct. 2014].
Chemical Buffer Systems- Acid-Base Balance. (2014). Boundless. [online] Available at: https://www.boundless.com/physiology/textbooks/boundless-anatomy-and-physiology-textbook/fluids-and-acid-base-balance-26/acid-base-balance-248/chemical-buffer-systems-1217-4810/ [Accessed 13 Oct. 2014].
Healthline.com, (2014). Acid-Base Balance | Definition and Patient Education. [online] Available at: http://www.healthline.com/health/acid-base-balance#Overview1 [Accessed 13 Oct. 2014].
Inkling.com, (2014). Inkling. [online] Available at: https://www.inkling.com/read/medical-physiology-rodney-rhoades-david-bell-4th/chapter-23/fluid-compartments-of-the-body [Accessed 22 Oct. 2014].
Inkling.com, (2014). Inkling. [online] Available at: https://www.inkling.com/read/marks-medical-biochemistry-lieberman-marks-4th/chapter-45/i–plasma-proteins-maintain [Accessed 13 Oct. 2014]. Media.lanecc.edu, (2014). Chemical Buffer Systems and Acid-Base Balance. [online] Available at: http://media.lanecc.edu/users/driscolln/RT127/Softchalk/Acid_Base_Lesson/Acid_Base_Lesson4.html [Accessed 13 Oct. 2014].
Research.vet.upenn.edu, (2014). Milk Urea Nitrogen. [online] Available at: http://research.vet.upenn.edu/DairyPoultrySwine/DairyCattle/MUN/MilkUreaNitrogen/tabid/1596/Default.aspx [Accessed 13 Oct. 2014].
Ensminger, M. and Ensminger, A. (1993). Foods & Nutrition Encyclopedia, Two Volume Set. 2nd ed. CRC Press, 1993, p.4.
Cnx.org, (2014). OpenStax CNX. [online] Available at: http:[email protected]/Body_Fluids_and_Fluid_Compartm [Accessed 13 Oct. 2014].
Fastbleep.com, (2014). Chemical principles: Properties of water – Biochemistry | Fastbleep. [online] Available at: http://www.fastbleep.com/biology-notes/40/116/1166 [Accessed 13 Oct. 2014].
Howard Perlman, U. (2014). Surface Tension (Water Properties), USGS Water Science School. [online] Water.usgs.gov. Available at: http://water.usgs.gov/edu/surface-tension.html [Accessed 13 Oct. 2014].