ch24 acid base balance Flashcards
what are the three types of homeostatic balance?
–Water balance
–Electrolyte balance
–Acid–base balance
what is the normal total body water (TBW) of a 70 kg (150 lb) young male
is about 40 L
What are the major fluid compartments of the body?
–65% intracellular fluid (ICF)
–35% extracellular fluid (ECF)
How is water exchanged between the compartments?
by osmosis
How is Osmosis from one fluid compartment to another determined
by the relative concentrations of solutes in each compartment
Which are the most abundant solute particles?
Electrolytes
Where are sodium salts most abundant?
ECF
where are potassium salts most abundant?
ICF
what is Fluid balance?
when daily gains and losses are equal
What are the two main sources of fluid gain?
Preformed water from food and drink (2300ml per day)
Metabolic Water (200ml per day)
What is Sensible water loss?
is observable water loss
in urine, feces, sweat in resting adult
What is Insensible water loss?
is unnoticed water loss
expired breath, cutaneous transpiration
varies greatly with environment and activity
What is Obligatory water loss?
output that is relatively unavoidable
–Expired air, cutaneous transpiration, sweat, fecal moisture, and minimum urine output (400 mL/day)
What is the main regulator of fluid intake?
Thirst
what other regulators of fluid intake does the body have?
Dehydration
osmoreceptors in hypothalamus
How does the Hypothalamus regulate fluid balance
produces antidiuretic hormone promoting water conservation
How does the Cerebral cortex help regulate fluid balance?
produces conscious sense of thirst
what is the mechanism of short-term inhibition of thirst
–Cooling and moistening of mouth quenches thirst
–Distension of stomach and small intestine
–30-45 minutes of satisfaction
What is the long term inhibition of thirst mechanism?
–Absorption of water from small intestine reduces osmolarity of blood
- Stops the osmoreceptor response, promotes capillary filtration, and makes saliva more abundant and watery
- Changes require 30 minutes or longer to take effect
What is the body’s first reaction to dehydration?
Increased blood osmolarity
Reduced blood pressure leading to production of Renin and angiotensin II
What stimulates the hypothalamic osmoreceptors
Increased blood osmolarity
Reduced blood pressure leading to production of Renin and angiotensin II
What is the result of the hypothalamic osmoreceptors being stimulated
reduced salivation and the feeling of thirst
What does the feeling of thirst activate?
rehydration/ingestion of water
How does the body control water output
through variation in urine volume
What type of feedback loop is the ADH system?
negative feedback loop
How is water output slowed?
- ADH secretion is triggered by hypothalamic osmoreceptors
- Aquaporins synthesized
–Membrane proteins allowing water to diffuse back into renal medulla
–Na+ is still excreted
urine’s osmolarity increases
What is fluid imbalance?
abnormality of
- total volume
- concentration
- distribution of fluid among the compartments
what are the two types of fluid deficiency
–volume depletion and dehydration
What are the causes of Volume depletion (hypovolemia)?
Hemorrhage, severe burns, chronic vomiting, diarrhea, or Addison disease
What is dehydration?
A negative water balance
If the body loses 1 L of sweat: where does it come from?
–300 mL from tissue fluid, and 700 mL from ICF
What is the process of water loss through sweating
- Sweat produced by capillary filtration
- Blood volume and pressure drop, osmolarity rises
- Blood absorbs tissue fluid to replace loss
- Tissue fluid pulled from ICF
- Blood, ICF and tissue fluid all lose water
skin blood vessels are constricted when it is cold, how does the body maintain fluid balance
Raises blood pressure which inhibits ADH secretion and increases secretion of atrial natriuretic peptide
Urine output is increased and blood volume reduced
What could lead to fluid retention?
Renal failure
What are the two types of fluid excesses
–Volume excess
–Hypotonic hydration (water intoxication or positive water balance)
What are the most severe effects of fluid excess?
pulmonary and cerebral edema and death
What is Volume excess?
- Both Na+ and water retained
- ECF remains isotonic
- Caused by aldosterone hypersecretion or renal failure
What is Hypotonic hydration ?
- More water than Na+ retained or ingested
- ECF becomes hypotonic
–Can cause cellular swelling
What is fluid sequestration?
excess fluid accumulates in a particular location
What is the effect of fluid sequestration?
circulating blood volume may drop to a point causing circulatory shock
What is the most common form of fluid sequestration?
Edema
what is edema?
•abnormal accumulation of fluid in interstitial spaces, causing swelling of tissues
What is a hemorrhage?
–Blood that pools in the tissues is lost to circulation
What is pleural effusion?
•several liters of fluid can accumulate in the pleural cavity (Caused by some lung infections)
What are the three types of fluid sequestration?
- Edema
- Hemorrhage
- Pleural effusion
If the body is experiencing hypovolemia, What is the effect on total body water and osmolarity?
TBW=reduced
Osmolarity= isotonic (normal)
If the body is experiencing dehydration, What is the effect on total body water and osmolarity?
TBW= reduced
Osmolarity=Hypertonic (elevated0
If the body is experiencing volume excess, What is the effect on total body water and osmolarity?
TBW=Elevated
Osmolarity=Isotonic (normal)
If the body is experiencing hypotonic hydration, What is the effect on total body water and osmolarity?
TBW= Elevated
Osmolarity= Hypotonic (reduced)
what are the Physiological functions of electrolytes?
–Chemically reactive and participate in metabolism
–Determine electrical potential (charge difference) across cell membranes
–Strongly affect osmolarity of body fluids
–Affect body’s water content and distribution
name the Major cations
–Na+, K+, Ca2+, Mg2+, and H+
name the Major anions
–Cl−, HCO3− (bicarbonate), and PO43−
there is a large difference in electrolyte concentrations between blood plasma and intracellular fluid but they have the same…….
Osmolarity
What are the main function of Sodium (Na+)
- It is one of the principal Ions responsible for resting membrane potential
- It is the principal cation in extra cellular fluid (ECF)
- Most significant solute in determining total body water and distribution of water among fluid compartments
- •Na+ gradient is a source of potential energy for cotransport of other solutes such as glucose, potassium, and calcium
- •Na+–K+ pump
Sodium concentration is coordinated by
The hormone Aldosterone
where are the aldosterone receptors located?
- ascending limb of nephron loop,
- distal convoluted tubule
- cortical part of collecting duct
What are the primary effects of aldosterone?
urine contains less NaCl, but more K- and a lower pH
Which three imbalances stimulate the production of aldosterone?
Hypotension
hyponatremia
Hyperkalemia
What is the effect of elevated blood pressure on the aldosterone mechanism?
inhibits renin-angiotensin–aldosterone mechanism
Which hormone modifies water excretion independently of sodium excretion?
Anti diuretic hormone (ADH)
What is the effect of Natriuretic peptides on sodium reabsorption?
inhibit sodium reabsorption
How is sodium homeostasis achieved?
regulation of salt intake
What is the effect of estrogen on sodium regulation?
mimics aldosterone: Na+ and water retained
What is the effect of progesterone on sodium reabsorption?
reduces Na+ reabsorption and has a diuretic effect
What is the effect of glucocorticoids on sodium reabsorption?
promote Na+ reabsorption and edema
What sre the two types of sodium imbalance?
Hyponatremia
Hypernatremia
What is hyponatremia?
–Plasma sodium concentration less than 130 mEq/L
What is hypernatremia?
–Plasma sodium concentration greater than 145 mEq/L
What are the main functions of potassium
–Produces (with sodium) the resting membrane potentials and action potentials of nerve and muscle cells
–Most abundant cation of ICF
–Greatest determinant of intracellular osmolarity and cell volume
–Important for thermogenesis
–Essential cofactor for protein synthesis and other metabolic processes
What is the effect of aldosterone on the secretion of potassium?
Aldosterone stimulates renal secretion of K+
Which is the most dangerous type of electrolyte imbalance?
Potassium imbalance
What are the two types of potassium imbalance?
Hyperkalemia
Hypokalemia
What is hyperkalemia?
–Greater than 5.5 mEq/L
–If concentration rises quickly (crush injury), the sudden increase in extracellular K+ makes nerve and muscle cells abnormally excitable
•Can produce cardiac arrest
–Slow onset, inactivates voltage-regulated Na+ channels, nerve and muscle cells become less excitable
What is hypokalemia?
–Less than 3.5 mEq/L
–From sweating, chronic vomiting, diarrhea, excessive laxative use, aldosterone hypersecretion, or alkalosis
–Nerve and muscle cells less excitable
What are the main functions of Chloride Cl- in acid base balance?
–Most abundant anion in ECF
–Major contribution to ECF osmolarity
–Required for the formation of stomach acid (HCl)
–Chloride shift that accompanies CO2 loading and unloading in RBCs
–Major role in regulating body pH
What is Hyperchloremia?
–Result of dietary excess or administration of IV saline
What is Hypochloremia?
–Side effect of hyponatremia
–Sometimes from hyperkalemia or acidosis
What are the functions of Calcium Ca2+
–Lends strength to skeleton
–Serves as a second messenger for some hormones and neurotransmitters
–Activates exocytosis of neurotransmitters and other cellular secretions
–Essential factor in blood clotting
Do cells maintain very high or very low intracellular Ca2+ levels?
Low
What is Calsequestrin?
protein that binds Ca2+ and keeps it unreactive
How is calcium homeostasis regulated?
•by PTH, calcitriol (vitamin D), and calcitonin (in children)
what is Hypercalcemia?
calcium levels greater than 5.8 mEq/L
- Causes: alkalosis, hyperparathyroidism, hypothyroidism
- Reduces membrane Na+ permeability, inhibits depolarization of nerve and muscle cells
- Concentrations greater than 12 mEq/L cause cardiac arrhythmias
What is hypocalcemia?
Calcium levels less than 4.5 mEq/L
- Causes: vitamin D deficiency, diarrhea, pregnancy, acidosis, lactation, hypoparathyroidism, hyperthyroidism
- Very low levels result in tetany, laryngospasm, death
What are the main functions of magnesium?
–About 54% of Mg2+ is in bone; about 45% in intracellular fluid
–Mg2+ serves as a cofactor for enzymes, transporters, and nucleic acids
What is Hypomagnesia?
Plasma deficiency of Magnesium
What is Hypermagnesia?
Excess of magnesium in the blood
What is the main function of phosphates (Pi )?
–Relatively concentrated in ICF due to hydrolysis of ATP and other phosphate compounds
- Activates many metabolic pathways by phosphorylating enzymes and substrates such as glucose
- Buffers that help stabilize the pH of body fluids
Why is PH important to homeostasis?
–Metabolism depends on enzymes, and enzymes are sensitive to pH
–Slight deviation from the normal pH can shut down entire metabolic pathways
–Slight deviation from normal pH can alter the structure and function of macromolecules
How is the PH of a solution determined?
by its hydrogen ions (H+)
What is an acid?
any chemical that releases H+ (Hydrogen) in solution
Name a strong acid
hydrochloric acid (HCl), it gives up it’s hydrogen ions freely
Name a weak acid
carbonic acid (H2CO3) ionizes only slightly
What is a base?
•any chemical that accepts H+
Name a strong base
hydroxide ion (OH−),
Name a weak base
bicarbonate ion (HCO3−),
What is the normal PH range of blood?
7.35-7.45
What are the challenges to acid base balance in the body?
- Lactic acids from anaerobic fermentation
- Phosphoric acid from nucleic acid catabolism
- Fatty acids and ketones from fat catabolism
- Carbonic acid from CO2
What is a buffer?
any mechanism that resists changes in pH
What is a physiological buffer?
•system that controls output of acids, bases, or CO2
Which system takes hours or days to exert it’s effect and – buffers greatest quantity of acid or base?
Urinary system
Which system buffers within minutes but cannot alter pH as much as the urinary system
Respiratory system
What is a chemical buffer?
a substance that binds H+ and removes it from solution as its concentration begins to rise, or releases H+ into solution as its concentration falls
Name the three major chemical buffers?
– bicarbonate, phosphate, and protein systems
What is the bicarbonate buffer system?
a solution of carbonic acid and bicarbonate ions
•O2 + H2O ® H2CO3 ® HCO3− + H+
–Lowers pH by releasing H+
•CO2 + H2O ¬ H2CO3 ¬ HCO3− + H+
–Raises pH by binding H+
what does the above chemical equation represent?
The reversible reaction in the bicarbonate buffer system
What is the main role of the bicarbonate buffer system?
coordinates with the lungs and kidneys to help control pH and CO2
What is the Phosphate buffer system?
•Phosphate buffer system—a solution of HPO42− (hydrogen phosphate) and H2PO4− (dihydrogen phosphate)
What does the chemical equation below represent?
•H2PO4− « HPO42− + H+
The reversible reaction in the phosphate buffer system
What is the role of the phosphate buffer system?
Important buffering in the ICF and renal tubules
What differentiates the protein buffer system from the others?
Proteins are more concentrated than bicarbonate or phosphate systems, especially in the ICF
What is are the key elements of the proetein buffer system?
–Carboxyl (−COOH) side groups release H+ when pH begins to rise
–Others have amino (−NH2) side groups that bind H+ when pH gets too low
What proportion of the chemical buffering in the body does the protein buffer system account for?
about 3/4
which buffer system is the basis for the strong buffering capacity of the respiratory system
The Bicarbonate buffer system
What is the effect of Increased CO2 and decreased pH in the respiratory system?
stimulates pulmonary ventilation
What is the effect of increased PH in the respiratory system?
inhibits pulmonary ventilation
How do the Kidneys function to neutralize more acid or base than either the respiratory system or chemical buffers?
•Renal tubules secrete H+ into the tubular fluid
–Bound and free H+ are excreted in the urine actually expelling H+ from the body
What is acidosis?
pH of ECF below 7.35 leading to hyperkalemia and death
What is alkalosis?
• pH above 7.45
H+ diffuses out of cells and K+ diffuses in leading to hypokalemia and death
What are the two main categories of acid-base imbalances?
respiratory and metabolic
What is respiratory acidosis?
–Occurs when rate of alveolar ventilation fails to keep pace with the body’s rate of CO2 production
What is respiratory alkalosis?
–Results from hyperventilation
–CO2 eliminated faster than it is produced
what is metabolic acidosis?
–Increased production of organic acids such as lactic acid in anaerobic fermentation, and ketone bodies seen in alcoholism, and diabetes mellitus
–Ingestion of acidic drugs (aspirin)
–Loss of base due to chronic diarrhea, laxative overuse
What is metabolic alkalosis?
–Rare, but can result from:
- Overuse of bicarbonates (antacids and IV bicarbonate solutions)
- Loss of stomach acid (chronic vomiting)
What is compensated acidosis or alkalosis?
–Either the kidneys compensate for pH imbalances of respiratory origin, or
–The respiratory system compensates for pH imbalances of metabolic origin
what is uncompensated acidosis or alkalosis?
–A pH imbalance that the body cannot correct without clinical intervention
What is respiratory compensation?
•changes in pulmonary ventilation to correct changes in pH of body fluids by expelling or retaining CO2
how does the respiratory system compensate if there is hypercapnia, (excess CO2) ?
it stimulates pulmonary ventilation eliminating CO2 and allowing pH to rise
How does the respiratory system compensate if there is hypocapnia, (deficiency of CO2) ?
ventilation is reduced to allow CO2 to accumulate and thereby lowering pH
What is renal compensation?
adjustment of pH by changing rate of H+ secretion by renal tubules
How does renal compensation deal with acidosis?
urine pH may drop to 4.5 due to excess H+
How does renl compensation deal with alkalosis?
urine pH as high as 8.2 due to excess HCO3−
Why might we administer fluid therapy to a patient?
–Replenish total body water
–Restore blood volume and pressure
–Shift water from one fluid compartment to another
–Restore and maintain electrolyte and acid–base balance
What are the parentaral routes of fluid administration?
- Intravenous (I.V.) route is the most common
- Subcutaneous (sub-Q) route
- Intramuscular (I.M.) route
How is blood loss treated in fluid therapy?
giving normal saline (isotonic, 0.9% NaCl)
