Water
Most essential nutrient
o More important than any other nutrient
Needed in large quantities
o Can only survive without water for a few days
Aprox. 60% of adults body is water
o Makes ¾ of weight of tissue
o ¼ of the weight of fat
Percentage of water is lower in females, elderly
and obese people
Roles of Water in Body Fluids
Carries waste products and nutrients
Maintains structure of large molecules
o Protein
o Glycogen
Participates in metabolic reactions
o Hydrolysis
Serves as a solvent for vitamins and minerals, amino acids,
glucose
o Allows them to participate in metabolic reactions
Acts as a lubricant and cushion for joints
o Inside eyes, spine
Aids in regulation of body temperature
Maintains blood volume
o Body must maintain all water balance to support all of
these vital functions
Water Balance
Water intake and excretion is adjusted to ensure intracellular
fluid and interstitial fluid is maintained
o Within and in between cells
Intracellular Fluid – Within
o 2/3 of body’s water
o High in potassium and phosphate
Intravascular
Inside blood cells
Interstitial Fluid – Between
o Largest component of extracellular fluid
Outside of the cell
o High in sodium and chloride
Water Intake
Thirst
o Conscious desire to drink
o Thirst is only second behind the body’s actual need for
it Body’s need comes first, thirst comes after
o Beginning of dehydration
Influenced by response to changes
o Sensed by the mouth
o Hypothalamus
Blood becomes concentrated
Mouth becomes dry
o Nerves
Excessive water
o Stopped by stretch receptors in the stomach
o Volume receptors in heart signal drinking to stop
Dehydration
Water output exceed water input
o Thirst, dry mouth
o Dry skin and mucous membranes
o Weakness, exhaustion
o Rapid heart beat
o Low blood pressure
Symptoms
o Thirst, fatigue, weakness
1-2% body weight lost
o Impaired physically performance, dry mouth, reduction
in urine, flushed skin, impatience
3-4% body weight lost
o Difficult in concentrating, headache, sleepiness,
impaired temperature, increased breathing
5-6% body weight lost
o Dizziness, loss of balance, delirium, exhaustion,
collapse
7-10% body weight lost
Water Intoxication
Body’s water content are too high in all body fluid
compartments
o Occurs with excessive water consumption
o 10-20 litres in a few hours
Can lead to hyponatremia
Decreased sodium in the blood
Kidney disorders
Reduce urine production
Confusion
Convulsion
Death
Water Sournces Water + beverages
o 80-100% water
Fruits and vegetables
o 70-99% water
Meats and cheese
o 30-69% water
Butters and Oils
o 0-20%
Generated in metabolism
o 200-300ml a day
Energy yielding nutrients producing carbon
dioxide and water in their breakdown
Water Losses
Body must excrete at least 500 ml of urine per day to carry
out waste products
o More is usually excreted to adjust for intake
Water is lost in urine
Lungs as vapour (breath)
o 350ml
Skin as sweat
o 450-900ml
Gi tract as feces
o 150ml
Food Sources
o 700-1000ml
Metabolism
o 200-300ml
Insensible water loss (unnoticeable)
Lungs and skin
Half of daily water loss
Water Recommendations
Adequate Intake
o 3.7L for men
o 2.7L for women
DRI committee
o Total water intake includes
Food
Caffeinated and non caffeinated beverages
Reccomendations
o 1 – 1.5ml for every kcal energy expended for adults
o 1.5ml for every kcal energy expended athletes and
infants
Beverages ccount for more than 20% of energy intake
o Any beverage can meet water needs o With or without energy
Water is the best choice
Caffeine free way to quench thirst
Situations in which water needs exceed norm
o Sickness
o Blood donation, surgery
o Exercise
Lost during skin as sweat
Breathing as vapour
o Pregnancy
o Breastfeeding
o Environmental conditions
Extreme heat
Health Effects of Water
Water intakes have health benefits
o Can protect against stones and constipation
o Dehydration can affect physical and mental
performance
Hard Water
o Contains calcium and magnesium
Soft Water
o High sodium or potassium
o Prevents rings in bath tubs
o More easily dissolves contaminants such as lead
Toxic
Blood Volume and Blood Pressure
Fluid maintains blood volume
o Blood pressure
Kidneys regulate blood volume and blood pressure
o Filters that reabsorb needed nutrients
o Excrete waste products
Amount of urine and concentration is caused by
the kidneys
Based on food and beverage intake
Instructions on releasing or retaining substances come from
o ADH (Antidiuretic Hormone)
Water retention
Hypothalamus signals pituitary gland to
release ADH
When blood volume or blood pressure drops
low
Extracellular fluid becomes concentrated
ADH stimulates kidneys to reabsorb water Thirst is then triggered
Drinking water and retaining fluids restores
blood volume
ADH is water conserving
The more water you need
The less water kidneys excrete
o Renin
Sodium retention
Blood Pressure is low
Causes sodium reabsorption in the kidneys
Causes water retention
Water rentension increases blood pressure
and blood volume
Angiotensin
Inactive until converted into angiotension 2
Narrows blood vessels
Increases blood pressure
The smaller, the more pressure
Stimulates Aldosterone
Adrenal glands
Signals kidneys to retain more sodium
and more water
Regulates electrolytes
o Potassium, Sodium, Chloride
and other minerals
o Rehydration
Fluid maintains body temperature
o 2 factors on how water keeps us cool
Body has a high heat capacity
it takes a lot to actually make us hot
takes a large amount of heat to heat water
Body fluids cool body
Increases blood flow to area to cool under
the skin
Secrete more sweat when we are hot
Evaporates which releases heat
Fluid protects and Lubricates Other Tissues
o Water protects tissues and organs form injury
Saliva
Amniotic fluid
Synovial fluid
Joints
Tears
Spinal fluid Fluid balance and electrolyte balance
o Balance of water inside and outside cells is essential
2/3 of body’s water is inside the cells
1/3 outside the cells
o Movement in minerals has role in maintaining balance
Mineral salt
Creates positive and negative ions
Ca
More
Less
