Ch 25 Learning Objectives

Fluid and Electrolytes

25.1.1 List the factors that influence the percentage of body fluid and explain its significance relative to fluid balance.

2 variables

age: infants have highest percentage of fluid, about 75% is fluid

• older adults have lowest percentage of fluid at 45%

• decreasing percentage of body fluid with increasing age

ratio of adipose ct to skeletal mt

• percentage of fluid in body at each age depends on ratio of adipose ct to skeletal mt

  • adipose ct is about 20% water

  • skeletal mt is about 75% water

lead adult females are about 55%

lead adult males are about 60%

25.1.2 Describe the two major body fluid compartments, and compare their chemical compositions.

intracellular fluid (ICF): fluid within our cells

• about 2/3 of total body fluid is within our cells

• 1/3 blood plasma

• contains: K, Mg, PO4, & neg charged proteins

extracellular fluid (ECF): fluid outside of cells

• includes both interstitial fluid & blood plasma

• ICF composes about 2/3 of ECF

• blood plasma compses 1/3

25.1.3 Explain how fluid moves between the major body fluid compartments.

25.2.4 Define fluid balance.

fluid balance: when fluid intake is equal to fluid output

• has normal distribution in fluid compartments

25.2.5 List both the sources of fluid intake and the categories of water loss.

fluid intake: addition of water to body

• ingested water: water absorbed from food/drink

  • taken to GI tract

  • 2300 mL per day

• metabolic water: water produced from aerobic cellular respiration & dehydration synthesis

  • 200 mL per day

fluid output: water loss from body

• breathing, sweating, defecation, urination

• sensible water loss: measurable

  • lost through urine/feces

• insensible water loss: not measurable

  • fluid lost in expired air or fluid lost from skin through sweat/transpiration

• obligatory water loss: loss of water that always occurs regardless of state of hydration

  • breathing

• faculatative water loss: controlled water loss through regulation of the amount; dependent on hydration

  • urination

25.2.6 Compare and contrast the different types of fluid imbalances.

fluid imbalance: occurs when fluid output doesn’t equal fluid intake

volume depletion: when isotonic fluid loss is greater than isotonic fluid gain

• severe burns, chronic vomiting, diarrhea

volume excess: when isotonic fluid gain is greater than isotonic fluid loss

• when fluid intake is normal but decreased fluid loss

dehydration: water loss greater than solute loss

• sweating, diabetes, hyposecretion of ADH

hypotonic hydration: water gain greater than solute gain

25.2.7 List and explain the stimuli that regulate fluid intake.

25.2.8 Identify the four hormones that are involved in regulating fluid output, and describe the general effects of each.

25.3.9 Describe the difference between a nonelectrolyte and an electrolyte.

25.3.10 Explain the general role of electrolytes in fluid balance.

25.3.11 List the six major electrolytes found in body fluids, other than H+ and HCO3–.

25.3.12 Explain why Na+ is a critical electrolyte in the body.

25.3.13 Describe the variables that influence K+ distribution.

25.3.14 Describe the main location, functions, and means of regulation for each of the common electrolytes.

25.4.15 Explain angiotensin II formation.

25.4.16 Describe the primary effects of angiotensin II following its formation.

25.4.17 Describe the stimuli that cause the hypothalamus to trigger release of antidiuretic hormone (ADH) from the posterior pituitary.

25.4.18 Explain the primary effects of antidiuretic hormone.

26.4.19 Describe the stimuli that cause release of aldosterone from the adrenal cortex.

low blood pressure / blood volume: activates RASS, causing aldo release

high blood potassium: directly stimulates adrenal cortex to release aldosterone

low blood sodium: can stimulate aldosterone indirectly through RASS

25.4.20 Explain the changes that occur in response to binding of aldosterone by kidney cells.

25.4.21 Describe the stimulus for the release of atrial natriuretic peptide (ANP) and its three actions.

25.4.22 Explain the ways in which the effects of atrial natriuretic peptide differ from the effects of angiotensin II, ADH, and aldosterone.

25.5.23 Distinguish between the two categories of acids in the body and name the physiologic buffering system that regulates each category.

fixed acid: wastes produced from metabolic processes

• regulated by the kidney

• ex: lactic acid from glycolysis

volatile acid: carbonic acid formed within the body

• regulated by respiratory rate & depth

• produced when CO2 combines with water

25.5.24 Compare and contrast the general concept of physiologic buffering systems and chemical buffering systems.

Physiologic buffering systems: uses body organs to regulate pH by removing acids or bases from body

• lungs regulate CO2

• kidneys regulate H+ & bicarbonate

Chemical buffering systems: uses chemicals that bind or release H+ ions to minimize changes in pH

• bicarbonate, phosphate, protein buffer systems

25.5.25 List the various sources of fixed acid.

protein metabolism

nucleic acid metabolism

phospholipid metabolism

anaerobic metabolism

fat metabolism

25.5.26 Describe how the kidneys counteract increasing blood H+.

when blood H+ increases, kidneys

1. secrete H+ into urine to remove

2. reabsorbes bicarbonate (HCO3-) to prevent it being lost in urine

3. makes new bicarbonate to help neutralize excess H+

overall: kidneys remove excess H+ & increase bicarbonate to raise blood pH

25.5.27 Explain how the kidneys function in response to decreasing blood H+.

when blood H+ decreases, kidneys

1. secrete less H+ into urine

2. reabsorb less bicarbonate, so more is lost in urine

3. excrete more bicarbonate to make pH more acidic

overall: kidneys conserve H+ & eliminate bicarbonate to lower blood pH

25.5.28 Explain the normal relationship between breathing rate and acid-base balance.

breathing rate helps regulate blood pH by controlling how much CO2 is removed from body

• faster breathing: removes more CO2 from blood, decreasing H+ & raising blood pH

• slower breathing: retains more CO2 in blood, increasing H+ & lowering blood pH

Fast breathing = less CO₂ = higher pH.

Slow breathing = more CO₂ = lower pH.

25.5.29 Describe the components of the protein buffering system and where and how they help prevent pH changes.

protein buffering system: uses amino acids in proteins to either accept or release H+ ions keeping pH stable

components: proteins with amino acid side groups

• if H+ is too high, proteins bind H+

• if H+ is too low, proteins release H+

25.5.30 Explain the reactions of the phosphate buffering system within the ICF.

mainly works inside cells (ICF) & in the kidneys

H2PO4^- (dihydrogen phosphate) = weak acid

• weak acid gives away H+ to raise H+ ions

HPO4^2- (hydrogen phosphate) = weak base

• weak base removes excess H+

25.5.31 Describe how the bicarbonate buffering system maintains acid-base balance in the ECF.

primary buffer of the extracellular fluid (ECF)

consists of:

• carbonic acid (H2CO3): weak acid

• bicarbonate (HCO3^-): weak base

When blood becomes too acidic:

• bicarbonate binds H+

• carbonic acid forms

• lungs exhale CO2, raising pH

when blood becomes too alkaline:

• carbonic acid releases H+

• lowers ph to normal

25.6.32 Define acid-base disturbance and list the four primary types.

respiratory acidosis: CO2 increases, blood pH decreases

respiratory alkalosis: CO2 decreases, blood pH increases

metabolic acidosis: bicarbonate (HCO3-) decreases or excess acid builds up, causing blood ph to decrease

metabolic alkalosis: bicarbonate increases or excess acid is lost, blood pH increases

25.6.33 Define respiratory acidosis, identify some of the causes of this type of acidbase disturbance, and explain how it occurs.

respiratory acidosis: when blood CO2 levels become too high

• causes blood pH to be below 7.35

causes:

• hypoventilation, airway obstruction, lung diseases, respiratory muscle weakness

how it occurs

• lungs dont remove enough CO2

• CO2 build up in blood

• CO2 combines with water to form carbonic acid

• carbonic acid releases H+ ions

• increased H+ lowers blood pH, causing acidosis

Overall: Too much CO₂ = too much acid = lower pH.

25.6.34 Explain why infants are more susceptible to respiratory acidosis.

25.6.35 Define respiratory alkalosis, identify some of the causes of this type of acidbase disturbance, and explain how it occurs.

25.5.36 Explain how metabolic acid-base disturbances differ from respiratory acid-base disturbances.

25.6.37 Define both metabolic acidosis and metabolic alkalosis, identify some of the causes of each type of acid- base disturbance, and explain how each occurs.

25.6.38 Describe renal and respiratory compensation.