water and life
1. Life on Earth began in water and evolved there for 3 billion years
- Modern life still remains tied to water
- Your body is 60% water
- Your cells￼ are composed of 70%-95% water
Water: the most indispensable nutrient (9)
- Carries nutrients throughout the body
- Serves as the solvent for chemicals in the body
- Cleanses the tissues and blood of wastes
- Participates in chemical reactions
- Acts as a lubricant ￼ around joints
- Serves as a shock absorber inside eyes, spinal cord, joints, and amniotic sac
- Aids in maintaining the body's temperature
- Human life begins in water
- The proper amounts of water and dissolved proteins and minerals is crucial to maintaining cells an life itself
Structure of water (3)
1. Studied in isolation, the water molecule is deceptively simple
2. Its two hydrogen atoms are joined to one oxygen atom by single covalent bonds
3. But the electrons of the covalent bonds are not shared equally between oxygen and hydrogen
- this unequal sharing makes water a polar molecule (+ & - pole, Oxygen hogs the electrons)
water: polarity (2)
1. The polarity of water results in weak electrical attractions between neighboring water molecules
2. These interactions are called hydrogen bonds
• Interaction of oppositely "charged" atoms from two
different polar (b) covalent bonds
water: characteristics (5)
1. Made of 2 hydrogen atoms and 1 oxygen atom
2. Needs no digestion and is easily absorbed
3. Makes up 50 to 75% of body weight
- Elderly ~50% Infants ~75%
4. Major solvent
5. Very essential—without water, death can occur within 1 to 2 weeks
Water: Functions (9)
2. major component of blood, saliva, sweat, tears, mucus, joint fluid
3. removes wastes
4. helps transport substances
5. lubricates tissues
6. regulates body temperatures
7. helps digest food
8. participates in many chemical reactions
9. helps maintain proper blood pH
1. Water-soluble substances may move within watery solutions by simple diffusion
- movement from a region of higher to lower concentration.
movement from a region of higher to lower concentration. movement of a solute down a concentration gradient
Osmosis is movement of WATER through a Selectively Permeable membrane, due to solute concentration
-water moves from an area that has less material (solute) dissolved in it (dilute)
body water distribution (3)
1. Intracellular Water = Water inside the cells
~ 2/3 of body water is intracellular
2.Extracellular Water (aka Interstitial fluid) = Water surrounding the cells or in the fluid portion of blood (plasma)
3. Balance between intra- and extracellular fluid is maintained by concentration of ions (part of minerals), particularly sodium, potassium, chloride, and phosphate ions
water balance (3)
1. To maintain water balance, a person must consume at least the same amount lost each day to avoid life- threatening losses.
- balance btw water intake & water excretion
• Keeps the body's water constant
• Maintains dissolved mineral (electrolytes) balance
2. A change in body's water content can bring about a temporary change in body weight.
3. Body water varies by pounds
- Approximately 8.34 pounds per gallon
- 1 kilogram per liter
maintaining proper hydration (2)
1. Hydration refers to water status.
2. Shifts in ion concentration can affect proper hydration.
Sources of water (2)
1. includes water in beverages & foods
- Water weight of fruits and vegetables typically ranges from 60 to 95%.
2. Metabolic water = water formed by cells as a metabolic byproduct (generated by the chemical breakdown of energy nutrients during digestion)
Output of water: sources in order (5)
2. insensible perspiration & sweat
3. expired air
essential balancing act (3)
1. Body water is lost through:
-urine, perspiration, exhaled air, feces & insensible perspiration
2. Insensible perspiration = body water that passes through the skin and is not from sweat glands.
3. Typical fluid intake = fluid lost
- Average is ~2.5 qt/d
- ￼1 quart = 0.95 liters ~2.4 L/d
how much water is needed? (4)
1. Adequate Intake (AI) for total water (including water in foods) is:
►Young Women = 11 cups/d (2.7 L)
►Young Men = 15.5 cups/d (3.7 L)
2. Urine output is best indicator of adequate fluid (water) intake.
3. Exercise, sweating, and high temperatures, among other causes, increase the need for water
4. Both Caffeine and alcohol increase excretion of water by the kidneys
- They act as diuretics
• Any substance that causes increased urinary water excretion. A "water pill".
quenching thirst & balance losses (3)
1. Thirst behind lags a lack of water (need of water)
- To ignore thirst is to invite dehydration
• When a person is thirsty, they may already have lost up to 2 cups of total fluid
2. Thirst and satiety govern water intake
3. Some organs involved in thirst = Hypothalamus, pituitary gland, kidneys
Kidneys & hydration (3)
1. Kidneys are the major regulator of body's water content & ￼ concentration.
2. Maintain proper hydration by filtering excess ions from the blood.
• Remove excess sodium ions; water follows sodium.
3. Remove drugs & metabolic wastes.
• Urea & uric acid — waste products of protein metabolism.
water conservation (2)
1. Water conservation occurs when a person is hot & perspires heavily.
2. Hormones that participate in sodium & water conservation include:
-Antidiuretic hormone (ADH) -Aldosterone
water homeostasis: maintaining salt-water balance (2)
1. Anti-diuretic hormone ￼ (ADH) released by the posterior lobe of the pituitary plays a role in water reabsorption.
2. Body "low" on water = Blood solute concentration high -->
• More ADH released by pituitary
• More water reabsorbed from collecting duct into capillaries/blood
• Less urine
• Blood volume/pressure go up - blood concentration goes down
salt (Na+) homeostasis: reabsorption of salt
1. Hormones regulate the reabsorption of sodium at the distal convoluted tubule.
- Aldosterone - from adrenal￼ cortex
- Excretion of K+
- Reabsorption of Na+
1. Diuretics — substances that increase urine output
2. Two common dietary diuretics:
• Caffeine - In coffee, tea, "energy" drinks, and caffeinated soft drinks
• Alcohol - In beer, wine, and spirits
3. Diuretics inhibit ADH resulting in urinary water losses that are > than amount of fluid consumed
dehydration effects (5)
Dehydration = Loss of water from the body
dehydration definition (2)
1. When the body's fluid losses are greater than its fluid input, dehydration occurs.
• Weight loss can be a sign of dehydration.
2. Every 16 oz of water lost by the body represents 1 lb of body weight.
people at risk for dehydration (3)
1. Older adults - do not sense thirst as quickly as younger people.
2. Sick people - especially sick children with fever, vomiting, and diarrhea.
3. Athletes and people who work or exercise outdoors in hot weather.
water intoxication & signs & symptoms
1. too much water consumed at a time or conditions in which kidneys have difficulty filtering water from blood
• Excess water ￼ sodium concentration of blood, disrupting water balance
• Can occur if several gallons of water are consumed in a few hours' time
2. Signs & symptoms:
• Dizziness, headache, confusion, poor coordination, bizarre behavior, seizures, muscular weakness, poor concentration & memory, loss of appetite, death
bottled water definition
Water intended for human consumption that is sealed in containers and has no added ingredients other than a substance that prevents growth of microbes, such as bacteria.
bottled water: general (4)
1. A consumer group tested bottled water, however, and disproved the notion of superior safety
- Standards for bottled water are rigid than those for tap water
• Many only apply if bottled water is sold across state lines
- About 1/3 were contaminated with bacteria,
arsenic, or synthetic organic chemicals
2. Concerns about the type of plastics water is stored in
- Some release synthetic chemicals into the water • BPA - bis-phenol-A, acts like synthetic estrogen in the
3. Bottled water is unpredictable in its content of fluoride￼, a mineral important to the health of teeth and bones.
4. Vitamin-fortified bottled waters are simply liquid supplements.
hard water (3)
Hard water - high concentrations of calcium and magnesium ions
- Leaves deposits (replace Ca & Mg w/Na+)
- Doesn't lather as easily
- Both are valuable minerals in the diet
soft water (3)
Soft water - high sodium
- A water softener is a system that exchanges sodium ions for the calcium and magnesium in hard water
- and it dissolves cadmium and lead from pipes
- Most people in developed nations get too much sodium in their diet
• Implicated in hypertension - high blood pressure
safety of public water (4)
1. The Environmental Protection Agency (EPA) is responsible for ensuring that public water systems meet minimum standards for protection of health.
2. Public water systems remove some hazards
- treatment includes the addition of a disinfectant (usually chlorine ) to kill most microorganisms.
3. Some concerns about cancer and chlorine
- Chlorine is easily removed by boiling or letting water set out in an open container for a day
4. Local municipal water companies must test for and make available to the public what is in their water