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
Why do substances move in and out of capillaries in the body (how do forces differ at the arteriole and venous ends of the capillary)?
ARTERIOLE END
- outward pressure + hydrostatic pressure = 41.3 mm Hg
- inward force of osmotic pressure = 28 mm Hg
- net OUTWARD pressure = 13.3 mm Hg
VENOUS END
- outward pressure + hydrostatic pressure = 21.3 mm Hg
- inward force of osmotic pressure = 28 mm Hg
- net INWARD pressure = 6.7 mm Hg
water that moves back into capillaries depends on concentration of plasma proteins (produced by liver)
What is edema, and how does it occur?
EDEMA => large amounts of fluid in intercellular spaces, leading to tissue swelling
caused by:
(1) low plasma protein concentration
(2) obstruction of lymph vessels
(3) increased venous pressure
(4) inflammation
What are electrolytes? What are anions? What are cations?
- Electrolytes => inorganic compounds which dissociate into ions in solution (help control fluid balance in the body)
- Cations => positively charged ions
- Anions => negatively charged ions
What do electrolytes do in the body – your notes should have 4 functions.
1 - certain ions control the OSMOSIS of water between compartments
2 - ions help maintain the ACID-BASE BALANCE necessary for cellular activity
3 - ions carry ELECTRIC CURRENT, which allows for action potentials and secretion of neurotransmitters
4 - several ions are COFACTORS needed for the optimal activity of enzymes
(do NOT act as energy storage molecules within the body)
Are most of the solutes in our body fluids mostly electrolytes, or non-electrolytes?
MOSTLY electrolytes
Review the pH scale. Know what pH is. What is an acid? What is a base?
pH = negative log of H+ concentration
ACID => pH < 7
BASE => pH > 7
Be able to list the three major ways the body handles acids and bases.
1 - Buffer systems
2 - Exhalation of carbon dioxide (respiratory mechanisms)
3 - Kidney excretion (renal mechanisms)
Which is the bigger problem, acids or bases? Why?
ACIDS, because we have to control excess H+
What acids does our body form?
- carbonic acid
- lactic acid
- sulfuric acid
- acidic ketone bodies
- phosphoric acid
What is a buffer system? How does it work?
“pairs of chemical substances that prevent a sharp change in the pH of a solution”
- buffers exchange strong acids for weaker acids that do not release as much H+ and thus change the pH less
What are the three main buffer systems of the body?
1 - phosphate buffer system
2 - protein buffer system
3 - bicarbonate buffer system
How much more bicarbonate ion than carbonic acid does the blood contain?
blood contains a 20:1 ration of bicarbonate ion to carbonic acid
How does a protein act as a buffer?
- carboxyl and amino groups of proteins act as buffers
- carboxyl group => H+ donor
- amino group => H+ acceptor
- proteins are also amphoteric molecules, meaning they can act as either an acid or a base
What is a volatile acid? What is a fixed acid?
VOLATILE ACID => an acid produced from carbon dioxide
- can be eliminated by breathing out CO2
FIXED ACID => an acid that accumulates in the body as a result of digestion, disease, or metabolism
- cannot be eliminated from the body by ventilation, but can by other organs such as the kidneys
What happens to blood pH when we hyperventilate? When we hypoventilate?
HYPERVENTILATION
excessive loss of CO2 => decrease in concentration of H2CO3 => decrease in concentration of H+ => respiratory alkalosis ===> blood pH becomes more alkaline
HYPOVENTILATION
accumulation of CO2 => increasing in concentration of H+ => respiratory acidosis ===> blood pH becomes more acidic
Why are kidneys the most efficient and important of the acid-base regulatory systems?
- can eliminate larger amounts of acids than the lungs
- can also excrete bases
- can excrete acids while conserving bicarbonate ion and produce more bicarbonate ion
- kidneys are the most effective regulators of pH: if the kidneys fail, pH balance fails
What are the good aspects and down-sides for each of the three ways our bodies regulate acids?
- chemical buffers are the first line of defense because they work almost INSTANTLY
- respiratory mechanisms and renal mechanisms take longer to work
- respiratory take several minutes to hours
- renal take several days
What do we mean by acidosis or alkalosis? Does blood ever get very acidic?
ACIDOSIS => any blood pH below 7.35
ALKALOSIS => any blood pH above 7.45
What is the normal range of blood pH?
7.35 - 7.45
What can cause respiratory acidosis? Respiratory alkalosis? How would the body compensate?
RESPIRATORY ACIDOSIS => carbonic acid EXCESS
- blood CO2 is too high
- decreased rate/depth of breathing
- obstruction of air passages
- decreased gas exchange
RESPIRATORY ALKALOSIS => carbonic acid DEFICIT
- blood CO2 is too low
- fever, anxiety, poisoning, high altitude
!! compensation would occur through the KIDNEYS
What can cause metabolic acidosis? Metabolic alkalosis? How would the body compensate?
this refers to the kidneys!
METABOLIC ACIDOSIS => bicarbonate DEFICIT
- kidney failure to excrete acids (drinking too much alcohol)
- excessive acidic ketones in diabetes mellitus
- prolonged diarrhea with loss of alkaline intestinal secretions
METABOLIC ALKALOSIS => bicarbonate EXCESS
- vomiting the acidic contents of the stomach
- intake of excess base (too many antacids)
!! compensation would occur through changes in depth and rate of respiration
Water that moves back into capillaries depends on concentration of _____ _____ (produced by liver).
plasma proteins
SODIUM ION
- chemical symbol
- found in greater concentrations inside or outside a cell
- what does it do for the body
- how is its concentration regulated
Sodium ion (Na+)
- 90% of extracellular cations
- Necessary for action potentials in nerve and muscle cells
- Aldosterone decreases blood volume and extracellular Na+
- ANP causes loss of Na+
POTASSIUM ION
- chemical symbol
- found in greater concentrations inside or outside a cell
- what does it do for the body
- how is its concentration regulated
Potassium ion (K+)
- Most numerous intracellular cation
- Regulates membrane potential and repolarization
- Controlled by aldosterone—causes loss of K+ in urine
CALCIUM ION
- chemical symbol
- found in greater concentrations inside or outside a cell
- what does it do for the body
- how is its concentration regulated
Calcium ion (Ca++)
- An extracellular cation
- Most abundant mineral in the body
- Used for blood clotting, nerve and muscle function
- PTH causes reabsorption of bone and increases reabsorption from G.I. tract and glomerular filtrate
- Calcitonin inhibits osteoclasts and stimulates osteoblast, so calcium is removed from the blood
CHLORIDE ION
- chemical symbol
- found in greater concentrations inside or outside a cell
- what does it do for the body
- how is its concentration regulated
Chloride ion (Cl-)
- Most common extracellular anion
- Diffuses between compartments and can help balance charges
- Aldosterone indirectly adjusts Cl- when it increases the reabsorption of Na+ because Cl- follows the Na+
BICARBONATE ION
- chemical symbol
- found in greater concentrations inside or outside a cell
- what does it do for the body
- how is its concentration regulated
Bicarbonate ion (HCO 3-)
- Extracellular (most abundant anion in ECF)
- Part of the body’s chief buffer system and transports CO2 in blood stream
- Regulated by the kidneys (Form bicarb when levels are low and excrete it when levels are high)
PHOSPHATE ION
- chemical symbol
- found in greater concentrations inside or outside a cell
- what does it do for the body
- how is its concentration regulated
Phosphate ion (HPO4 2- )
- Intracellular
- Mostly found in the bones
- Part of the phosphate buffer system
- PTH causes phosphate to be released from bones and to be excreted by the kidneys; calcitonin removes phosphate by encouraging bone formation
What is THE equation?
CO2 + H20 <=> H2CO3 <=> HCO3- + H+
What is the pH of venous blood? Arterial blood?
VENOUS => 7.35
ARTERIAL => 7.45
_____ _____ is the most abundant acid in the body.
Carbonic acid
Explain the bicarbonate buffer system.
MAJOR extracellular buffer system
sodium bicarbonate + carbonic acid
NaHCO3 + H2CO3
- addition of a strong acid
HCl + NaHCO3 => H2CO3 + NaCl - addition of a strong base
NaOH + H2CO3 => NaHCO3 + H2O
Metabolic (kidney) reactions can produce large amount of _____ _____.
fixed acids
_____ can eliminate larger amounts of acids than the _____.
Kidneys; lungs
Kidneys can excrete acids while conserving _____ _____.
bicarbonate ion
