Water & Electrolytes Flashcards
What are the functions of water?
- solvent
- transport
- lubrication
- protection
- regulation of body temperature
- involved in chemical reactions such as hydrolysis and condensation
- maintenance of acid-base balance
What is the distribution of water in the body?
- blood made up of 90% water
- muscle about 75%
- bone 25%
- adipocytes contain only about 10% water
We need to take in the same amount of water than we lose because?
- need to constantly intake water because we are losing it, and we cannot make it
How much water to we need a day?
- intake varies by individual and should let thirst guide your intake
- no scientific evidence to support the 8 glasses a day rule
- aim for around 1500 mL a day
How is water intake and loss regulated?
- thirst center in hypothalamus senses decreased blood volume and increased solute concentration
- stimulates thirst
- pituitary gland releases ADH to increase water reabsorption in kidneys
- this thirst center doesn’t work quite as well in elderly
Who is at higher risk fr dehydration?
- athletes
- infants
- overweight
- older adults
What is water intoxication?
- too much water consumed
- leads to hyponatremia, causes water to move out of blood into cells
- can cause edema in brain and increased ICP
- athletes can also be prone to this
What are food sources of water?
- water obtained from solid food sources as well as from drinks
- fruits, vegetables, and dairy products are especially high in water
What is the distribution of water in and between cells?
- 2/3 of body water is contained in cells
- 1/3 of body water is the ECF
- ECF includes blood, lymph, and interstitial fluid
What is osmosis, and how does it influence BP?
- water moves in direction of higher concentration of solutes
- high BP can push water out of capillaries
Why is acid-base balance important?
- narrow range of pH necessary to maintain life (7.35-7.45)
- maintained by kidneys and lungs to get rid of acids
- buffers include bicarbonate, phosphate, and hemoglobin
What are the principle electrolytes?
- sodium, potassium, chloride
In the western diet, which electrolyte is consume in excess, and which is too little?
- salt (sodium chloride) often consumed in excess, as it is in many processed foods
- not enough potassium consumed, found in unprocessed foods
What are the RDIs for the electrolytes?
- sodium AI: 1500 mg/day
- sodium UL: 2300 mg/day
- chloride AI: 2300 mg/day
- chloride UL: 3600 mg/day
- potassium AI: 4700 mg/day
Who is at higher risk for hypertension?
- African Americans and Hispanics
Are people meeting the AI of sodium and potassium?
- No; most Canadians consume over the UL of sodium at 2500-3500 mg/day
- only about 5-10% of people consuming enough potassium, which is due to lack of fruits and vegetables in diet
How does excess sodium cause hypertension?
- water moves from cells to vessels, where there is a higher concentration of solutes
- sodium mostly extracellular
- increased blood volume
What is the sodium-potassium pump?
- maintains resting membrane potential for APs by keeping potassium inside and sodium outside
- uses about 20-40% of REE to maintain
What is the main mechanism by which BP is controlled?
- RAA system – decreased BP leads to release of renin, angiotensin II constricts blood vessels, also increases aldosterone, which causes fluid retention
- net effect is increased BP
What is hypertension?
- ideally BP<120/80
- BP>140/90 defines hypertension
- hypertension increases risk of CVD, MI, stroke
How can electrolyte deficiency occur, and what are the risks?
- deficiency may occur due to heavy sweating, chronic diarrhea, vomiting or kidney disorders
- medications such as thiazide diuretics, used for hypertension or heart failure, may cause potassium loss, potassium supplements may be prescribed
- deficiencies can lead to acid-base imbalance, confusion, apathy, muscle cramps, constipation, poor appetite and eventually irregular heartbeat
How strong is the correlation between hypertension and salt intake?
- there is a relationship, but high intakes of fibre, potassium, calcium and magnesium are protective
- high intake of salt is often accompanied by other bad habits that raise BP
What is the DASH diet?
- dietary approaches to stop hypertension
- NIH compared reduced salt intake and DASH intake to effect on BP
- more fruit, vegetables, less processed foods
- combination of the DASH diet and low sodium intake lowered BP the most
- proves not just sodium, also lack of other nutrients
