Water

Question 1

Water

Answer 1

Water is the essen􏰀al nutrient with the highest daily requirement. We need water for the body’s structure but
it is also important as a solvent and in various physiological ac􏰀vi􏰀es. Water is so important to the body’s func􏰀on and structure that if we do not consume enough, our bodies tell us almost immediately to consume more. Since we do not store water in the body and we con􏰀nuously lose it, we need to consume a constant supply. Accordingly, our thirst is very sensi􏰀ve to reduc􏰀ons in the water content of blood and 􏰀ssues.

Question 2

Structure of water

Answer 2

A water molecule is composed of two hydrogen atoms a􏰁ached to an oxygen atom, giving it the chemical for- mula H2O. Geometrically, the molecule has a V-shape, due to the respec􏰀ve slightly posi􏰀ve (δ+), and slightly nega􏰀ve (δ–) charges of the hydrogen and oxygen atoms (Figure 4.1). The nega􏰀ve charge forms one pole of the molecule, while the posi􏰀ve charge forms the other pole. Water is thus aOpolar molecule. This charge arrangement allows water to be a􏰁racted to other water molecules, as well as other molecules that are polar. Polar molecules that are a􏰁racted to and dissolve easily in water are hydrophilic, or water loving. Those that are not polar and not a􏰁racted to water are hydro- phobic, or water ha􏰀ng. For instance, lipids are nonpolar, and therefore separate themselves from water when the two are combined.

Question 3

Extra cellular and intercellular

Answer 3

The human body is 60–70% water by weight (Mitchell et al., 1945). Approximately two thirds of this water is found within cells, or intracellularly, and the remainder is found outside of cells, or extracellularly (Figure 4.2).

Question 4

Water and cell

Answer 4

Cells have lipid walls, but are comprised mostly of cytoplasm, a gel-like substance that is 80% water. Given that the human body has more than 30 trillion cells (Bianconi et al., 2013), the water in cytoplasm therefore accounts for the majority of the body’s water. In healthy people, the water content of cells does not change substan􏰀ally. However, the extracellular water content is constantly being used for the body’s needs and must be regularly replenished.
Most extracellular water is found within blood. Red blood cells give blood its characteris􏰀c colour, however, more than 9E0% of the volume of blood is water. Extracellular water can also be found around the joints, in the lungs, lining certain 􏰀ssues and in the lymph. It is further found in the extracellular space around cells. Water can be exchanged between this extracellular space and the blood. Certain factors regulate this exchange and the content of water in the blood versus the extracellular space.

Question 5

Osmosis

Answer 5

Osmosis drives water to move across semi-permeable membranes, like blood capillaries, with the goal of eve- ning out concentra􏰀on differences. For instance, the blood carries many charged, polar substances, such as protein. These a􏰁ract water and draw it in to the blood from the extracellular space (Figure 4.3). That is one func􏰀on of protein: to maintain fluid balance and make sure that water doesn’t build up in the extracellular space. Conversely, blood pres- sure provides a force that pushes water out of blood and into the extracellular space.

Question 6

Functions of water

Answer 6

Structure solvent hydroliss defense infection protection injury temp regulation ,

Question 7

Structure

Answer 7

Water helps structures maintain their form. For instance, the water within cells gives them the three-di- mensional shape necessary for cellular organelle to func􏰀on properly. Another example is the water within synovial fluid found in sacs between joints. Not only do these synovial sacs promote joint structure, but they also allow bones to glide by each other more fluidly. The eye also maintains its structure because of the fluid, or huomour, found within it (Figure 4.4).

Question 8

Solvent

Answer 8

Water is the most important biological solvent because
of the variety of polar substances it can dissolve (Figure 4.5). This is important for moving things around the body via blood vessels or the diges􏰀ve tract. For instance, blood can transport oxygen, nutrients and other cellular needs to the 􏰀ssues while also Iremov-
i n g hE
armful waste products. The water within cells also allows certain material to move around the cell. It also brings the reac- tants of chemical processes together. Water is a fluid that is always in mo􏰀on and so the substances within water are also in mo􏰀on. Accordingly, when compa􏰀ble reactants are dissolved in water, there is an increased chance of them colliding and undergoing a chemical reac􏰀on.
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Question 9

Hydroliss

Answer 9

As we learned in Chapter 3, hydorolysis reac􏰀ons use water to split larger molecules into smaller ones. An exam- ple of a hydrolysis reac􏰀on is the breakdown of the double-sugar maltose into two molecules of single-sugar glucose

Question 10

Defence infection

Answer 10

Within the lymph you will find many immune
cells suspended within a watery environment. If an
infec􏰀ous agent gets into the body, it can be moved
it for removal. Furthermore, mucus, which is mostly water, helps trap and gather pathogeens together for removal. This is why doctors advise us to drink plenty of fluids when we have certain infec􏰀ons (Figure 4.7).

Question 11

Injury protection

Answer 11

Water can reduce the fric􏰀on and damage from
movement or trauma that can nega􏰀vely affect our 􏰀ssues.
For instance, the water found in synovial fluid helps protect
bones that ar􏰀culate from scrapping against each other (Fig-
ure 4.8). Also, the mucus found lining body 􏰀ssues, such as
the diges􏰀ve tract and respiratory system, can help protect
Ito
these 􏰀ssues from injuries. Around and within certain parts
of the brain and spinal cord is cerebrospinal fluid. This wa-
ter-based fluid helps to protect the brain from various forces

Question 12

Temp regulation

Answer 12

The human body’s temperature must be maintained at around 37 ̊C to func􏰀on properly. Even a 0.5 ̊C change in body temperature can nega􏰀vely affect body physiology. This presents a challenge, as the temperature of our external environments can change drama􏰀cally throughout the day. Also, without a way to regulate temperature, body tempera- ture can increase for other reasons such as increased physical ac􏰀vity (Figure 4.9). Our bodies accordingly use two main strategies to maintain internal temperature; both involve water.

Question 13

Sweating

Answer 13

Swea􏰀ng involves the release of watery sweat from our sweat glands. When this sweat evaporates, it cools down our skin and bodies. Swea􏰀ng in a humid environment compromises this process, as the air’s high water content does not let sweat evaporate. This leaves us feeling hot, s􏰀cky and uncomfortable. During the hot summer months in many Canadian ci􏰀es you may accordingly hear the phrase, “It’s not the heat that gets you, it’s the humidity.”
When body temperature increases, as is the case during strenuous exercise, the face o􏰂en becomes redder. This is because the body tries to maintain its temperature by opening blood vessels close to the skin. This allows blood to shunt some of the heat from the body’s core to the skin’s surface. As the skin heats up, this then triggers the sweat response, which can further cool the body.

Question 14

Heat illness

Answer 14

When the body is unable to regulate temperature, heat illness can occur. Symptoms of heat illness can range from minor heat cramping to heatstroke, which can be life-threatening. Heat stroke occurs when the body temperature rises above 40 ̊C (Bouchama & Knochel, 2002). It is accompanied by neurological symptoms such as delirium, confusion and convulsions and can lead to coma or death. This is more likely to occur in elderly individuals, or those with disease who have compromised temperature regula􏰀on physiology (Bouchama et al., 2007). As global temperatures con􏰀nue to rise, the incidence of heat illness and heat injury may also increase. Indeed, in the United States, heat waves result in more fatali􏰀es than any other extreme weather event (Na􏰀onal Weather Service, n.d.).

Question 15

Sources of water

Answer 15

Every day, we lose water through urine, feces and evapora􏰀on. Since the body does not store water, we must constantly replenish this water. Beverages account for most of the water we take in, though foods also provide water. The plants and animals we eat are made up of cells. When we eat them, we break down their cells and release the water from their cytoplasm. Water is also gained during certain metabolic processes. Recall from Chapter 3 that water is a by- product of cellular respira􏰀on. All three of these contribute to our daily water needs (Figure 4.10).

Question 16

Maintaining water balance

Answer 16

Water homeostasis is one of the body’s main priori􏰀es. To this end, there is a 􏰀ghtly regulated feedback process in place to make sure that water is maintained at desirable levels. When blood volume decreases, two main mechanisms are employed to help maintain water levels. First, our thirst increases. This is due to several body sensors that indicate to the brain that the concentra􏰀on of dissolved par􏰀cles in the blood is high, meaning that the concentra􏰀on of water
is low. Thirst is the body’s way of telling us it is deficient in water. The kidneys also play a key role in regula􏰀ng water levels. They decide what stays in the blood and what is excreted in urine (Figure 4.11). When blood volume is high, excess water is excreted at the kidneys. If there are a lot of waste products for the kidneys to remove, this also contrib- utes to water loss, since water is needed to help these materials pass outward. When blood volume and pressure is low, the kidneys decrease the produc􏰀on of urine. Individuals that are deficient in water will no􏰀ce that their urine is more darkly coloured, as it contains less water to dilute waste products.

Question 17

Dehydration

Answer 17

Most of us have experienced a degree of dehydra􏰀on in our lives. Dehydra􏰀on can be caused by not consuming enough water or by an excessive loss of water, poten􏰀ally due to swea􏰀ng, diarrhea or vomi􏰀ng. Mild dehydra􏰀on can be uncomfortable; extreme dehydra􏰀on can be deadly. Dehy- dra􏰀on is especially dangerous for young children and older adults and measures should be taken to prevent it.
Symptoms of dehydra􏰀on include increased thirst, dry mouth, headaches, fa􏰀gue, dizziness, irritability and dark urine (Figure 4.12). Chronic dehydra􏰀on can lead to more severe complica􏰀ons, including kidney damage, seizures and hypovolemic shock.

Question 18

Kidney disease

Answer 18

Dehydra􏰀on puts extra stress on the kidneys, as they do not have enough water to help secrete waste products. This increases the risk of urinary tract infec􏰀ons, kidney stones, and in extreme cases can lead to chronic kidney disease and even death (Roncal-Jimenez et al., 2015).

Question 19

Seizure

Answer 19

Excessive swea􏰀ng not only promotes water loss, but important electrolytes can also be lost in this process. Elec- trolyte imbalance can compromise the body’s electrical ac􏰀vity, poten􏰀ally promo􏰀ng seizures. Those with sodium and other electrolyte disorders are more suscep􏰀ble to these dehydra􏰀on-induced seizures (Nardone et al., 2016).

Question 20

Hypovolemic shock

Answer 20

ellular fluid. Excessively low blood volume can promote a significant drop in blood pressure. Low blood volume and
pressure can compromise oxygen and nutrient delivery to the 􏰀ssues. Symptoms of hypovolemic shock include increased heartrate, low blood pressure, blue skin colour, cool and clammy skin and mental status changes. The symptoms and severity depend on the health of the person and the length of 􏰀me the person stays in hypovolemic shock. If untreated, it can be fatal.

Question 21

Water intoxication

Answer 21

Water intoxica􏰀on, also known as water poisoning, is a poten􏰀ally fatal condi􏰀on where the content of water in the body is too high with respect to the level of electrolytes. Water intoxica􏰀on can occur when an individual consumes excessive amounts of water in a short period of 􏰀me and does not excrete it through urina􏰀on. However, most cases of water intoxica􏰀on occur when a significant amount of water is lost due to excessive swea􏰀ng, diarrhea or vomi􏰀ng. Both water and electrolytes are lost in sweat, diarrhea and vomit. If these losses are replaced by only drinking water, it dilutes the electrolytes in the body (Figure 4.13). This can result in a condi􏰀on called hyponatremia, or low sodium in the blood. decrease in the concentra􏰀on of sodium and other dissolved par􏰀cles nega􏰀vely impacts many body func- 􏰀ons. The brain is par􏰀cularly suscep􏰀ble to hyponatremia, where it can lead to an increase in intracranial pressure. Most symptoms of water intoxica􏰀on are accordingly neurological and include headache, confusion, personality changes, irritability and drowsiness. In extreme cases this can lead to malfunc􏰀on of the central nervous system and an increased risk for seizures, brain damage, coma and even death (Box 4.1). Extra electrolytes may be necessary in cases of extreme fluid loss. Endurance athletes such as marathon runners, for instance, o􏰂en consume electrolyte mixtures in addi􏰀on to replenishing water.

Question 22

Water intoxication and fatal radio

Answer 22

In 2007, a radio sta􏰀on in Sacramento, California held a contest called “Hold your Wee for a Wii” (ABC News, 2009). The premise: the person who could drink the most water without urina􏰀ng would win a Ninten- do Wii video game console, a hot commodity at the 􏰀me. One of the contestants, Jennifer Strange, report- edly drank almost eight litres of water in three hours. She died of water intoxica􏰀on. The disc jockeys had apparently been made aware before and during the compe􏰀􏰀on about the poten􏰀ally fatal outcome, but they were unphased and even joked about it on air. In 2009, the radio sta􏰀on’s parent company was ordered to pay US$16,577,118 in damages to Jennifer’s family.

Question 23

Diuretics

Answer 23

Diure􏰀cs are substances that promote water losses through urina􏰀on. Certain medica􏰀ons act as diure􏰀cs, as do
certain psychoac􏰀ve drugs like caffeine and alcohol.

Question 24

Caffeine

Answer 24

Caffeine is a psychoac􏰀ve drug found in certain foods and beverages. It is a compound found naturally in many seeds, nuts and leaves. Its most well-known source is coffee (Figure 4.14). While caffeine acts as a diuret-
ic, it is typically consumed for its effects on the central nervous system, as it can promote alertness, while reduc- ing fa􏰀gue and drowsiness., Caffeine has been studied for its poten􏰀al disease-reducing effects. A review of meta-analyses found that coffee
intake probably decreases risk of cardiovascular disease, Parkinson’s disease, type 2 diabetes and certain types of can-
cers (Grosso et al., 2017). Cau􏰀on should be taken in interpre􏰀ng these results, as this review looked at coffee and not
caffeine specifically. Coffee is believed to have an􏰀oxidant and an􏰀-inflammatory proper􏰀es that perhaps contribute to
the observed effects. While is it generally recognized as safe, caffeine has some poten􏰀al side effects. The authors of the
above study found an increased risk of miscarriage with coffee consump􏰀on. The diure􏰀c effects of caffeine may also
promote kidney problems. Indeed, a large prospec􏰀ve epidemiolocal study of more than 16 million people found that
caffeine consump􏰀on is associated with a higher risk of kidney stones, especially in women (Sun et al., 2019).

Question 25

Alcohol

Answer 25

Like caffeine, alcohol is a psychoac􏰀ve drug found in certain foods and beverages (Figure 4.15). It has diure􏰀c proper- 􏰀es and can affect hydra􏰀on levels if overconsumed. Alcohol also provides energy to the body; each gram provides 7 kcal.
Unlike caffeine, the side effects of alcohol use can be det- rimental to health. High alcohol intakes significantly increase the risk of liver cirrhosis and cancers of the liver and diges􏰀ve systems (Grønbaek, 2009). Alcohol also increases the risk of neurological deficits such as confusion and demen􏰀a. Further, individuals who chronically consume high levels of alcohol are at higher risk for nutri􏰀onal deficiencies, as alcohol impairs the absorp􏰀on of sev- eral micronutrients.
Interes􏰀ngly, epidemiological evidence suggests that light to moderate drinkers (1–2 servings of alcohol per day) have a lower risk of cardiovascular disease compared to non-drinkers (Corrao et al., 2000; Grønbaek et al., 2000; Poiko- lainen, 1995). The poten􏰀al posi􏰀ve effect is not fully understood, though it might be linked to alcohol’s ability to reduce the forma􏰀on of artery-blocking blood clots and increase HDL, the so-called good cholesterol. However, these effects are only seen at light to moderate levels of consump􏰀on. Higher levels of consump􏰀on are associated with a higher risk of all-cause mortality and are not recommended (Boffe􏰁a & Garfinkel, 1990; Piano, 2017).
The short-term effects of alcohol depend on several factors. For instance, factors that lead to quicker absorp􏰀on
lead to more pronounced short-term effects. Absorp􏰀on is quickest when alcohol is consumed on an empty stomach and
when the concentra􏰀on of alcohol in the product is 20–30%, as is the case with for􏰀fied wines like sherry (Paton, 2005).
Drinks with dissolved carbon dioxide, such as champagne and mixed drinks with pop, are also absorbed more quickly. A
person’s blood volume also contributes to how quickly and intensely alcohol’s effects are felt. Women and smaller indi-
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viduals have lower total blood volume; thus, alcohol is concentrated more quickly. Blood alcohol also tends to concen- trate more before menstrua􏰀on and during ovula􏰀on.

Question 26

Alcohol metabolism

Answer 26

Approximately 90% of alcohol is metabolized and eliminated at the liver. The enzymes alcohol dehydroge- nase and aldehyde dehydrogenase modify alcohol in a two-step process that leads to the forma􏰀on of acetate (Figure 4.16). Acetate can be used to synthesize acetyl CoA. Recall from Chapter 3 that acetyl CoA can enter the citric acid cycle and con􏰀nue through cellular respira􏰀on to create ATP, the body’s energy currency. Acetyl CoA can also be used to synthesize fa􏰁y acids, and this extra energy source is stored in fat 􏰀ssue. However, this is a minor pathway.
Certain people have varia􏰀ons in their genes that code for the enzymes alcohol dehydrogenase and alde- hyde dehydrogenase. These changes can affect the rate of alcohol metabolism. These varia􏰀ons may also increase or decrease risk for alcohol dependence. For instance, one gene􏰀c varia􏰀on of the enzyme aldehyde dehydrogenase leads to slower metabolism and lower risk for depen- dence. People with this gene􏰀c difference o􏰂en expe- rience facial redness, nausea, swea􏰀ng, dizziness and a racing heartrate due to the buildup of acetaldehyde. These uncomfortable symptoms are believed to be partly respon- sible for a lower risk for dependence in these popula􏰀ons (Chang et al., 2017).

Question 27

Hangovers

Answer 27

Many people experience hangovers several (6+) hours a􏰂er drinking – especially a􏰂er high levels of consump- 􏰀on. Symptoms of a hangover vary, but may include vomi􏰀ng, 􏰀redness, decreased a􏰁en􏰀on, decreased concentra􏰀on, stomach pain and disturbed sleep. The causes of hangovers are complex and not fully clear. Proposed reasons for hang- overs include acetaldehyde buildup, the direct effect of alcohol on the gastrointes􏰀nal and other systems and alcohol withdraweal. It is also proposed that it is not the alcohol itself that produces hangover symptoms, but the presence of congeners, substances added during the fermenta􏰀on process. Red wine, whisky, cognac and tequila, which are alcoholic beverages high in congeners, promote hangovers more than those low in congeners, such as rum, vodka or gin (Pawan, 1973).

Question 28

Treatment hangover

Answer 28

The treatments for hangovers are also not fully established. Some studies have found that certain products reduce symptoms, while others have not. A systema􏰀c review of six randomized control trials found that supplements
of the polysaccharide-rich extract Acanthopanax sen􏰀cosus, red ginseng, Korean pear juice, KSS formula and A􏰂er-Effect are associated with a decrease in hangover symptoms (Pi􏰁ler et al., 2005). Conversely, another meta-analysis of random- ized control trials found that supplemen􏰀ng propranolol, sugars, borage, ar􏰀choke and prickly pear had no effect to cure or prevent a hangover (Pi􏰁ler et al., 2005). The authors suggested that the best way to avoid hangovers is to moderate or abstain from alcohol consump􏰀on.

Question 29

Water recommendations

Answer 29

The exact amount of water an individual requires daily depends on various factors, including their sex, ac􏰀vity level and how muoch they sweat. An RDA for water hasn’t been determined, so an adequate intake (AI) level of 2.7oL/day for women and 3.7 L/day for men is typically used. One way to determine whether water intake is adequate is to look for signs and symptoms of dehydra􏰀on: thirst, headache and urine that is dark yellow.
The best source of water for most people is water itself. While most drinking water in Canada is safe to drink from the tap, there are s􏰀ll regions of the country where it is not. Unsafe drinking water dispropor􏰀onately affects com- muni􏰀es in the north of Canada, many of which are Indigenous. The risk of drinking unsafe water is that it may contain infec􏰀ous agents such as bacteria that can make an individual sick. In these situa􏰀ons, drinking bo􏰁led water or boil-
ing water is recommended. Boiling water kills most infec􏰀ous agents and renders water safer to drink, but it does not, however, remove all poten􏰀al contaminants or make it clear. While drinking bo􏰁led water is an op􏰀on in these cases, it is not always an economically feasible one. Accordingly, there is momentum towards using community-based research and engagement to help restore the quality of water in Indigenous communi􏰀es, where water is o􏰂en seen not only as a vital nutri􏰀onal and industrial resource, but also as a living being (Box 4.2).

Question 30

Indigenous lens