4 (26) Water, Electrolyte, and Acid/Base Balance Flashcards
What is meant by “balance” in the body?
a state of equilibrium; substances are maintained in right amounts and in the right place in the body
Are substances always in a state of equilibrium?
nope, substances aren’t always in a state of equilibrium
By what process does water move within the body?
OSMOSIS => net movement of water molecules through a selectively permeable membrane from an area of high water concentration to an area of low water concentration
What determines the concentration of water?
- most concentrated form of water: liquid water
- to dilute water, you must add solutes to displace the water in a given volume
- the concentration of solutes determines the direction of water movement
What do we mean by “Where sodium goes, water follows”?
if we move sodium from one compartment to another, we are going to draw water after the sodium
Who has a greater amount of water, a baby or an adult? A man or a woman? Why?
there is about 40 L of body water
- baby = 75%
- male = 63% (men have more muscle = more water)
- female = 52% (women have more fat = less water bc water and oil don’t mix)
- elder = 45%
Who off these 3 is more susceptible to dehydration? Why?
- babies have a tendency to dehydrate very quickly
- they have more extracellular water than anyone else
What happens to body water content as we age?
body water content declines throughout life
What are the two main locations for water in the body? One of these can be broken down into two more compartments. What are they?
INTRACELLULAR => 2/3 (63%) of total body water
EXTRACELLULAR => 1/3 (27%)
- interstitial fluid = 80% of extracellular water
- blood plasma = 20% of extracellular water
Which of the three fluid compartments tends to vary the most?
interstitial fluid
Where would you find transcellular fluid?
- aqueous humor
- vitreous humor
- endolymph
- perilymph
- cerebral spinal fluid
- serous membranes
What are the two factors that control water movement between the three compartments? How do these two forces work?
HYDROSTATIC pressure => a pushing force of fluids; pushes outside a compartment
OSMOTIC pressure => a pulling force; draws water into the compartment where there are a lot of solutes (high solute concentration)
These two usually balance each other by pushing and pulling.
Where does the water we take in come from?
AVERAGE adult takes in ~2500 mL/day
preformed water = 2300 mL
- drinking water = 1500 mL (60%)
- moist food = 750 mL (30%)
water of metabolism = 250 mL (10%)
- cellular respiration
- dehydration synthesis
How do we prevent dehydration? (discuss thirst, blood osmolarity, and hormones)
DEHYDRATION (output > intake) => as little as 1% decrease in body water can cause:
- decreased production of saliva
- increased blood osmotic pressure (stimulates osmoreceptors in hypothalamus)
- main regulator of dehydration is the thirst center in the hypothalamus
- decreased blood volume (renin is produced)
- hypothalamus is the major regulator of the endocrine system (can put out ADH)
What stops us from taking in too much water?
- tongue gets wet, activates osmoreceptors and stretch receptors in the stomach and intestines
- stomach starts to stretch and prevents us from drinking more than we need and overdiluting our body fluids
- water is absorbed and blood osmotic pressure decreases
How do we lose water?
- through kidneys in urine = 1500 mL (60%)
- through intestines = 150 mL (6%)
- from skin (sweat) = 150 mL (6%)
- from lungs and skin = 700 mL (28%)
- insensible loss
What is insensible loss?
water that vaporizes out of the lungs in expired air or diffuses directly through the skin (menstruation)
What is the main way we control water loss?
main way to regulate our output to prevent dehydration is to decrease (or in some cases increases) urine production
What three hormones are involved in water loss, and how do they work? (Hint: all these hormones begin with “A”)
ADH => acts on distal convoluted tubules and collecting ducts of the kidney that permits reabsorption of water
ALDOSTERONE => if ADH is present, sodium (and water) to be reabsorbed
ANP => sodium and water losing hormone (causes sodium (and water) loss when pressure in right atrium is too high)
What is obligatory water loss?
- unavoidable output of certain amounts of water
- minimal amount of fluid loss from the body that can occur
What is water toxicity?
- water is drawn into cells, causing swelling (not a good thing)
- this increases ISF tonicity and water is drawn from the blood
- you need to add salt when replacing fluids like this
- an alternative to this would be Gatorade
How can overhydration occur?
- under normal circumstances will not occur bc we stop drinking when we need to
- occurs through excess hydration of IV fluids
- this extra fluid puts strain on the heart
