Engineering of Global Health

Content Objectives

Drinking enough water everyday is one of the least conscious priorities that most people fulfill. The guidelines for the amount of water intake should be a half of ounce for every pound. So if you weigh 160 lb. your intake should be 80 ounces daily.² There is some controversy to this total daily amount within the medical community, however a number of researchers agree one should at the minimum drink 8 glasses daily. With the water content in our cellular structures being approximately 55-60% of total body weight³ we need to pay attention to this fact and make ingesting adequate amounts of water much more of a priority. Water makes up the majority weight of all our organs, tissues, and cells.  In our body, water is distributed between two main compartments – an intracellular one, and an extracellular one. The largest amount of water is contained in the intracellular domain - 65%. Extracellular compartments contain 35% water and a high percentage of that total finds solutions containing salts (such as Na, Mg, and K). ⁴

Intracellular fluid is primarily water based, and moves within the cell. Intracellular water is moved through, around, and out of the cell by osmotic forces. Extracellular fluid is saline based, and is stored outside the cell among the interstitial areas surrounding the cell.  It can also be found in intravascular areas, (within the blood vessels), and cavities surrounding structures.  CSF, G.I., synovial, pleural, peritoneal, and pericardial fluids are examples of extracellular.⁵

The type, location, and composition of intracellular / extracellular fluids are mentioned here to inform the reader of their important relationships in distributing and attaining water balance in the body.

Transport Systems

Diffusion

There are three passive transport mechanisms that our body employs to transmit and maintain fluid levels throughout our body - diffusion, osmosis, and filtration. In diffusion molecules move from an area of high concentration to a lower concentration to establish balance. Diffusion will continue until the concentration of substances is equal throughout a cell or tissue space. A few factors that influence diffusion rates are temperature and size of molecules in the solute.⁶  The higher the temperature of the solvent becomes, the quicker the rate of diffusion. The larger the molecules are, the slower the diffusion process happens.

Osmosis

Cells are made of water. Water is the solvent part of solutions that exists both inside and outside of the cell membrane. Osmosis is concerned with moving water in and out of two compartments that are separated by a semi-permeable membrane. Therefore, osmosis is an important driving force in moving water across the cell plasma membrane, which is semipermeable, and separates the intracellular and extracellular fluids. A solution will consist of water and solutes usually salts (Mg, Na, Ca, K). The water from a lower concentrated solution moves through a semipermeable membrane into a higher concentrated solution, in an attempt to balance the concentrations on both sides of the membrane. Osmotic pressure causes water and solute movement to go in opposite directions simultaneously with variation in solution concentration guiding the direction.⁷ The transmission of solid matter will go in one direction while the water component will move in the other direction. This helps quicken equilibrium to occur on both sides of the cell membrane. The passage of water-soluble molecules, minerals etc. will move through the membrane with ease, while other solutes will be kept out.

Another example of how absorption occurs through osmotic exchanges can be found in the intestine.  As water travels to the stomach the absorption rates there are quite weak so water can travel quickly to get to the intestines. The mucosal lining is covered with blood capillaries. The layer that separates the lining from the capillaries is .0030mm thick.⁸ Osmotic forces take place here because the digested food remains in communication with the mucosal layer over a period of time. Water is primarily absorbed in the small intestine.⁹ Water passes from the small intestine into the bloodstreams by way of the capillaries. The capillary wall is permeable and allows for the passage of water, nutrients, and toxins when released by the cell. Everything released by the structures especially the toxins are carried out and eliminated either by way of urination, or defecation.

Classification of aqueous solutions

Solutions can be classified as hypertonic, hypotonic, or isotonic. An isotonic solution has the same osmolarity as the fluid inside human cells: therefore an isotonic solution will maintain fluid balance in and out of the cell. A hypertonic solution will pull fluid out of the cell and into the extracellular space. A hypotonic solution will pull fluid back into the cell.¹⁰

Hypertonic solution has a higher osmotic pressure than the isotonic solution. A hypotonic solution has a lower osmotic pressure than isotonic. The importance of knowing the osmotic pressure in solutions is the effect they will have on cells. A red blood cell has a normal shape and volume when placed in an isotonic solution. The pressure on the membrane is balanced on both sides. A red blood cell that is immersed in a high concentration or hypertonic saline solution has water flow out of the cell in an attempt to balance osmotic pressure. If too much water leaves the cell, it takes on a shrunken appearance. A red blood cell placed in a low concentration of saline, or hypotonic solution takes in water from the extracellular space through the membrane increasing pressure and expanding the size of the cell. In addition knowing how solutions affect cells will beneficial to a patient faced with a medical need for intravenous therapy.

Filtration

Filtration moves solutes and solvents by hydrostatic pressure. Hydrostatic pressure is the force exerted by the weight of the solution and will move the solution from a high-pressure area to a lower one. However if you increase the pressure on one side of the membrane, or the fluid as a whole you force more water through the membrane. If enough pressure is applied to the side with the solute then it can overcome the pressure differences across the pores and reverse them causing water to flow against its concentration gradient.¹¹

pH Balance

The acid and alkaline levels of pH in your body is appraised on a scale from 1-14. A scale reading of one denotes an extremely high acidic state. A rating of fourteen labels it exceptionally basic. Pure water has a pH rating of 7. The pH of blood is carefully regulated in the body: a pH of blood test lower than 7 or above 7.8 has the potential to be fatal. When the pH scale of blood is lower than 7.35 this a medical condition called acidosis. Acidosis can have many causes, and can be either metabolic, or respiratory in nature. On the other end a pH of above 7.45 is said to be alkalosis.   Our blood is made up of, and carries acid and bases.  A medical state of alkalosis can either be caused by not having enough carbon dioxide (an acid in nature) in the blood or having too much base materials (bicarbonate etc.) blood levels.  Alkalosis can also have either metabolic, or respiratory connections.¹² It can be treated successfully if caught early.

Acid and Base

An acidic solution contains excess hydrogen ions. Acids can be either weak or strong depending on their location on the pH scale. A reading close to 7 indicates a weak acid while a strong acid will have a marker between 0 and 4 on the pH scale. A base is classified as being a solution having an excess of OH- ions. The same holds true for bases as mentioned above (for acids).  A weak base has a pH level close to 7.  A strong base will register 10 – 14. Every liquid will most likely have either acid or base characteristics due to pH levels, which focus on bondings with either hydrogen ions (H+) or hydroxide ions (OH-). ¹³The information on pH, acid /base readings from above paragraphs are cited to illustrate the seriousness of deficient water amounts and their effects on our bodies.

To maintain a stable pH reading of 7.40 – 7.45, a buffer is usually involved. 

Buffers in a solution minimize the effects of acid or base additions by binding or discharging hydrogen ions in response to concentration changes. They have the capabilities to provide a weak acid (proton donor) or a weak base (proton acceptor) and a salt of the acid or base to interact with the strong acid or base that was added to the solution. This process is termed the buffering effect.¹⁴

Chemistry - Electrolytes

Electrolytes are chemical compounds dissolved in body fluids. They contain small electrical charged particles (called ions). When electrolytes are added to pure water the solution will conduct an electrical charge. Electrolytes dissolved in water split apart and form electrical charges either positive or negative. The positively charged ion is called a cation. The negatively charge is called an anion.¹⁵

The following chart describes the important cations, and anions where they are found and what is their importance.

Water’s impact on body systems

Water is a building material for cell structure and function. It provides a transportation system for nutrients to enter and exit the cell. It is responsible for chemical and metabolic reactions such as breaking down of food particles into proteins, carbohydrates and lipids.¹⁶ Water is also classified as a lubricant taking the form of mucus. Mucus is 90% water and is required for many systems to function properly. The respiratory system relies on mucus to trap dust particles, allergens, and foreign pathogens along the entire airway preventing objects from entering the lungs. In the digestive tract mucus acts as a lubricant to have material move over membranes smoothly i.e. food moving through the esophagus. Mucus protects the stomach lining against the harsh ph of stomach acid.¹⁷ Mucus lines the colon and small intestine protecting them against inflammation by breaking down harmful bacteria.¹⁸

Water is imperative for the optimum maintenance and control of body temperature. The hypothalamus is the thermo-regulator center within our body. The blood and skin and skin are also important in the regulating process.  When the hypothalamus detects a rise in blood temperature it signals the smooth muscles and surrounding blood vessels to dilate so more blood flows to the body’s periphery thus moving heat away. Extra heat leaves the body through sweating. Water in the form of sweat will evaporate on the skin and cool the body down. When the skin and blood detect colder temperatures the hypothalamus sends neural signals to the smooth muscles and surrounding blood vessels to constrict and reduce blood flow. The hypothalamus also signals the endocrine glands to secrete hormones to speed up metabolism and conserve heat.¹⁹

A vital organ essential to the water input / output balance, the kidney, lies within the body just below the ribcage and in back of the abdomen. Everyone has two kidneys which are positioned on each side of, and attached to the aorta, and vena cava – the body’s two largest blood vessels. The kidneys’ are situated in a prime location where controlling fluid balance, regulating electrolyte balances, filtering waste out of the blood, and producing urine can be performed.²⁰

Kidneys can detect blood volume from the pressure in the vessels. If low the kidneys signal enzymes and proteins to signal the hypothalamus and adrenal glands surrounding the blood vessels to reestablish blood volume. The kidneys also regulate salt levels and the elimination of urea from the blood.  The water that is not reabsorbed by the body will be eliminated as urine.

Water is critical for the functioning and maintenance for all body systems. We unconsciously depend on all of our systems to be in synchronicity with each other. To maintain homeostasis water intake has to match water output. If there is a severe imbalance, dire consequences could emerge either from drinking too much, or not enough water.  Dehydration and toxicity come to mind.

Effect of Dehydration

“Water, it does a body good!” Instead of using the trademark saying from the milk commercial, I modified the saying to introduce this segment of my unit. Water has many positive effects on our lives when we keep our level of intake constant.  Water helps us think, is responsible for blood flow, and helps our muscles move. When everything is in synchronicity we have optimal health. Dehydration is a condition brought on by an insufficient level of water or salt in your body. For most of us we have a sensation of feeling thirsty, and drinking water will turn your deficit around. Sometimes the sensation gets ignored, and if it continues to be ignored the body will revert into backup mode. There is a belief that if you eat foods that contain a high water content (for example fruit), and feel that will satisfy your water and relieve hunger sensations at the same time, that is not what is occurring in the body at this time. Dehydration is still present and symptoms are not being relieved.

If the body can’t draw water from external compartments it must secure them from internal sources. Extracellular fluid sets up an immediate response. Blood continues to supply organs which forces the fluid from the interstitial compartment to give up its’ water. The interstitial fluid becomes thickened and no longer can guarantee a correct exchange between blood and cells.²¹ The body continues to look for water and will draw liquid from the intracellular fluid. Once this happens the cells will shrink because of the hypertonic effect of water leaving the cell causing the shrinkage, and the condition becomes irreversible.

Dehydration can lead to the following complications: kidney failure, shock, heat related illnesses, heart failure, and electrolyte imbalances. Kidney failure occurs when the volume of fluid decreases in the intravascular space, and blood pressure drops. Blood flow to vital organs like the kidney decreases and brings the potential for failure.²² Shock ensues when the blood loss overwhelms the body’s ability to correct the problem. Blood flow along with oxygen is severely decreased, and cell, tissue and organs start to fail. Heat related illnesses are caused when the body tries to cool down by sweating a may bring on dehydration to the point that muscles may go into spasms. If dehydration continues where sweat can no longer help, heat exhaustion or heat stroke will happen. Heart failure is brought on by the lack of blood flow to it causing it to fail. Electrolyte imbalances occur because important chemicals like sodium and potassium are lost through sweat. Potassium balance lost to sweating brings on muscle weakness, heart rhythm interruptions, and seizures.  Sodium that is lost will damage the kidneys and potentially cause renal failure, bring on seizures, and cardiac problems.²³ It is important to stress the point that if you sense thirst do something about it right away and you will be able to avoid the aforementioned consequences.

Waterborne Diseases

The World Health Organization says diarrheal diseases remain a leading cause of illness and death in the developing world. Every year, about 2.2 million people die from diarrhea; 90% of these deaths are among children, mostly in developing countries.²⁴ Coming in contact with stagnant pools of water, or having to draw drinking water from rivers where human and animal waste are dumped freely is unconscionable to many, but a stark reality to people who depend on the rivers for survival. Poor water quality and appalling sanitation are the main culprits that draw and support bacteria, viruses, insects, and parasites that cause dreaded diseases like cholera, malaria, diarrhea, dysentery, typhoid and schistosomiasis.²⁵ Humid regions are prime hotbeds for microorganisms to colonize and run rampant. Another place that hosts parasites, and microorganisms along with toxic chemicals are the agricultural wells found on land that indigent people call home.

Diarrheal diseases are major causes of death to infants and young children in developing nations. The children contract diarrhea from tainted water and become dehydrated from the water loss that occurs with diarrhea, potentially leading to death.²⁶  Cholera, typhoid fever, and schistosomiasis are the main diseases in most indigenous areas. Insects are another threat to people.  The insects develop in stagnant water ponds and acquire parasites like malaria, filaria, and trypanosomes that are waiting to infect ones who come in contact with them.

Most waterborne illnesses are preventable. Proper sanitation habits, hand washing, and treating contaminated water with bleach would reduce a sizable amount of deaths caused by them. Informing students of the potential hazards they face when traveling home will help them realize that they can become agents of health to their relatives and provide them with tools (their apparatuses) to improve their relatives health.

Service Learning

Service learning components are vital module to add to a curricular unit. They foster understanding of concepts on a deeper level. Students can finish a unit, study for the exam tied to that unit, and take the test. The next unit will start immediately after the test is taken. Three weeks later, while reviewing past units, I found recall from those units were considerably lacking. Service learning serves as an outlet for students to add to their knowledge bases. Knowledge of subject matter is somehow transformed from an abstract state into a more concrete foundation and comprehension becomes more solidified. One of the biggest advantages is the direct link to real life situations that service learning bestows on people.

In this unit students will be asked to keep an engineering notebook that will contain the information given to them throughout the unit. They will be designing, building, testing, and developing mechanisms that can either be used at their households, or going with them when they visit relatives.