Physiology M02: Fluid, Electrolytes, and Acid-Base Balance

what percent of the body is intracellular fluid (ICF)

65%

what percent of the body is extracellular fluid (ECF)

35%

what percent of the body is tissue (interstitial) fluid

25%

what percent of the body is blood plasma and lymphatic fluid

8%

what percent of the body is transcellular fluid “catch-all” category

2%

electrolytes

the most abundant solute particles

osmosis is determined by the relative concentrations of

electrolytes, sodium salts in ECF, and potassium salts in ICF

electrolytes control the body’s

water distribution and total water content

fluid balance

when gains and losses are about equal ( around 2,500 mL per day)

fluid gains are due to

ingested food, ingested drinks, and metabolic water

only way to control water output is through

urine volume

kidneys slow the rate of water and electrolyte loss until

water and electrolytes can be ingested

as Na+ is reabsorbed or excreted,

water follows

water output is slowed by

antidiuretic hormone (ADH)

ADH secretion is triggered by

hypothalamic osmoreceptors in response to dehydration

ADH system is an example of

negative feedback

kidneys compensate well for

excessive fluid intake, but not inadequate fluid intake

hypotonic

larger concentration of water in the cell

hypertonic

higher concentration of solutes inside the cell

isotonic

same concentration of water and solutes inside the cell

volume depletion (hypovolemia)

total body water is reduced, osmolarity is isotonic

dehydration (negative water balance)

total body water is reduced, osmolarity is hypertonic

volume excess

total body water is elevated, osmolarity is isotonic

hypotonic hydration (positive water balance, water intoxication)

total body water is elevated, osmolarity is hypotonic

functions of Na+

responsible for resting membrane potential

sodium salts account for 90% - 95% of

osmolarity of ECF

sodium is the most important solute for determining

total body water and distribution of water among fluid compartments

Na+ gradient is a source of potential energy for co-transport of

glucose, potassium, and calcium

homeostasis sodium levels in humans

0.5g per day, typical diet is 3-7 g per day

sodium concentration coordinated by

aldosterone

aldosterone

“salt-retaining hormone”

aldosterone plays a primary role in

adjusting sodium excretion, hyponatremia/hyperkalemia, hypotension

elevated blood pressure inhibits the

angiotensin-aldosterone mechanism leading to sodium not being absorbed

anti-diuretic hormone modifies

water excretion due to high sodium concentration in the blood

ADH makes the kidneys

reabsorb more water

functions of K+

produces the resting membrane potentials and action potentials of nerve and muscle cells

most abundant cation of ICF

K+

K+ is the greatest determinant of

intracellular osmolarity and cell volume

the Na+ - K+ pumps is important for

thermogenesis

K+ is a cofactor for

protein synthesis and other metabolic processes

potassium imbalances are the

most dangerous

hyperkalemia effects depend on

whether the potassium concentration rises quickly or slowly

if potassium rises quickly there is an excess of K+ cells possibly leading to

cardiac arrest

slow onset of potassium inactivates

voltage gated Na+ channels (less excitable)

hypokalemia results from

sweating, chronic vomiting, diarrhea, excessive laxative use, aldosterone hypersecretion, and alkalosis

hypokalemia can lead to

muscle weakness and loss, arrhythmias

functions of chloride

most abundant in ECF, major contributions to ECF osmolarity, HCl, regulates body pH, chloride shift

Ca 2+ functions

strengthens skeleton, second messenger for hormones/neurotransmitters, factor in blood clotting

cells must pump Ca 2+ out of the cell to prevent

calcium phosphate crystal precipitation

calsequestrin

protein that binds Ca 2+ and keeps it unreactive

homeostasis is chiefly regulated by

PTH, calcitriol (vit. D), and calcitonin

functions of Mg 2+

cofactor for enzymes, transporters, and nucleic acids

intestinal absorption from food is regulated by

vitamin D

Mg 2+ is lost in

feces and urine, amount depending on reabsorption in nephron loop and parathyroid hormone

phosphate functions

activate metabolic pathways and act as a buffer in stabilizing pH

phosphates are components in

nucleic acids, phospholipids, ATP, GTP, cAMP, and creatine phosphate

pH of a solution depends on it’s

H+ ions

acids

any chemical that releases H+ in a solution

a strong acid like hydrochloric acid ionizes freely and

gives up most of H+ ions and lowers pH of a solution

a weak acid like carbonic acid ionizes very slowly and

keeps H+ chemically bonded and does nto really affect pH

normal pH range of blood and tissue fluid

7.35 - 7.45

buffer

any mechanism that resists changes in pH

physiological buffer

system that controls output of acids, bases, or CO2

the urinary system buffers the

greatest quantity of acid or base

chemical buffer

a substance that binds H+ and removes it from solution and either removes it or releases it into the solution, restoring the pH

three major chemical buffers

bicarbonate, phosphate, and protein systems

bicarbonate buffer system coordinates with the

lungs and kidneys to help control pH and CO2

more CO2 raises

the H+ ion concentration and lowers pH

the removal of CO2 decreases the

H+ ion concentration and increases the pH