fluid, electrolyte, and acid-base balance

Water percentage of body

60% of body

Compartments of fluid

separated by selectively permeable membranes, moving from one side to the other

• Extracellular fluid: plasma + interstitial fluid

• Intracellular fluid

Extracellular fluid

• plasma (in blood vessels)

• Interstitial fluid (on cell side)

Intracellular fluid

• in cells

Composition of body fluids

• solutes

• Electrolytes

• Nonelectrolytes

Solutes in body fluids

What is dissolved in water

Electrolytes in body fluids

Compounds that dissociate into ions in water

• has a greater osmotic power than nonelectrolytes

• Has a greater ability to cause fluid shifts

Nonelectrolytes in body fluids

Do not dissociate in water

• eg. glucose, lipids, creatine, and urea

• Do not really conduct electricity

Universal solvent

Can dissolve a lot of solutes (WATER!)

Comparison of Extracellular and Intracellular fluids

Opposite of each other due to cellular ATP dependent Na+/K+ pumps

• Extracellular: more sodium (Na+) and very little potassium (K+)

• Intracellular: more potassium (K+) and very little sodium (Na+)

Fluid movement in compartments

• between plasma and IF across capillary walls

• Between IF and ICF across cell membrane

Fluid movement between plasma and IF

Across capillary walls

Fluid movement between IF and ICF

Across cell membrane

• water: 2 way osmotic flow

• Nutrients, wastes, gases: unidirectional

• Ions: move selectively

Changes in solute concentration in any compartment…

Leads to net water flows

Major sources of water intake & output

Regulated by:

• sensory receptors (eg. baroreceptors): osmolarity, blood volume, blood pressure

• Hypothalamus: thirst center

• Hormones

• Kidneys

• Cardiovascular System: ANP hormone detect if water needs to one in

Regulations of water intake by hypothalamic thirst center

hypothalamic osmoreceptors detect ECF osmolality; activated by

• Increases plasma osmolality of 1-2%

• Dry mouth

• Decreased blood volume or pressure

• Angiotensin II or baroreceptor input

Maintenance of Body Fluid Osmolality

maintained at 300 mOsm

Rise in osmolality (dehydration)

Blood becomes salty

• stimulates this mechanism, ADH (antidiuretic hormone) release to kidneys

• Decreased BP → Renin-angiotensin-aldosterone mechanism from kidneys activated

• Increased thirst, decreased urine (to not waste water), restore Blood Pressure

Decrease in osmolality (hyperhydration)

• thirst inhibition

• ADH (antidiuretic hormone) inhibition (NOT released)

• Increased Blood volume/BP → Atrial Natriuretic peptide: stretch receptors in right atrium dilate blood vessels to decrease BP + increase urine output to decrease blood volume

Hypotonic Hydration

ECF is diluted (too much water)

Hyponatremia

ECF is low in solute concentration (low sodium)

Edema

Accumulation of fluid in interstitial space (pitting edema)

• causes Hyponatremia

Electrolyte balance

Includes salts, acids, and bases

Salts provide

• neuromuscular excitability

• Secretory activity

• Membrane permeability

Sodium imbalances

• Hypernatremia; Sodium excess

• Hyponatremia: Sodium deficit

Hypernatremia

Excess sodium

• caused by dehydration

• Consequences: thirsty, confused, lethargic, possible coma, twitching, convulsions

Hyponatremia

Sodium deficit

• caused by excess water retention, excess water intake, vomiting, diarrhea, burned skin, gastric suction, diuretics, less aldosterone, renal diseases, excess ASH release

• Consequences: decreased blood volume and blood pressure (excess water: confusion, coma, twitching, convulsions)

Potassium imbalances

Hyperkalemia: potassium excess

Hypokalemia: potassium deficit

Hyperkalemia

Potassium excess

• caused by renal failure, aldosterone deficit, burns or severe tissue injuries that cause K+ to leave cells

• Consequences: nausea, vomiting, diarrhea, bradycardia, cardiac arrest, skeletal muscle weakness, flaccid paralysis

Hypokalemia

Potassium deficit

• caused by GI tract disturbances (vomiting/diarhea), gastric suction, starvation, excess aldosterone, diuretic therapy

• Consequences: cardiac arrhythmias, flattened T wave on ECG, muscular weakness, confusion, nausea/vomiting

Calcium imbalances

• hypercalcemia: calcium excess

• Hypocalcemia: calcium deficit

Hypercalcemia

Calcium excess

• caused by hyperparthyroidism, excess vitamin D, prolonged immobilization, renal disease (decreased excretion)

• Consequences: decreased neuromuscular excitability leading to cardiac arrest, skeletal muscle weakness, confusion, coma, kidney atones, nausea/vomiting

Hypocalcemia

Calcium deficit

• Caused by burns in damaged tissues, hypoparathyroidism, Vit D deficiency, renal tubular diseases, renal failure, diarrhea

• consequences: increases neuromuscular excitability leading to tingling fingers, tremors, skeletal muscle cramps, convulsions,

Sodium balance

Most significant

• cotransport

• RMP

• Depolarization