Fluid & Electrolytes Nerd Notes

what kind of control is the water content of our bodies under?

homeostatic control

what is the percentage of water in skeletal muscle as an adult? what influences the percentage of body water?

Skeletal muscle is typically 78% water as an adult, but age and sex influence the percentage of body water

what is the percentage of water of infants and geriatric patients

Infants have lower percentages of body water ~73% and geriatric patients may have as little as 45% body water

what is the percent difference in body water between sexes

adult males have 60% and females have 50%

why is there a difference in body water between sexes

this difference is due the ratio between muscle and fat composition, as adipose tissue is the least hydrated of all tissues

what is within the multiple fluid compartments of the human body

differing solute compositions

what 2 components is the total body water divided into

extraceulluar fluid (ECF) and intracellular fluid (ICF)

what is the extracellular fluid ratio

roughly 1/3 total volume

what is the intracellular fluid ratio

roughly 2/3 total volume

what percentages is the extracellular fluid divided into

divided into blood plasma 20%, and interstitial fluid 80%

does solute composition vary within all fluid compartments

yes

what does the biological solvent water contain

includes both electrolytes and nonelectrolytes

what do electrolytes do? what do they include?

in general conduct electrical current and include salts, acids/bases, and proteins

what are nonelectrolytes and what do they include

noncharged molecules including glucose and lipids

the extracellular fluid has a decreased concentration of what? what are the major ions in the extracellular fluid?

decreased concentration of proteins with major ions as Na+ and Cl-

the intracellular fluid has a increased concentration of what? what are the major ions in the intracellular fluid?

increased protein concentrations with major ions as K+ and HPO4-.

what drives the direction of water outside and inside of cells and fluid compartments.

Osmotic power

what is osmolality? how is it changing?

the concentration of solutes in a solution, e. number of K+ particles in water, it changes as one fluid compartment affect another’s osmolality.

what drives cellular water movement? what kind of transport system is this?

extracellular osmolality, passive transport

what is the passive transport system of extracellular osmolality defined as

tonicity of a solution

what do hypertonic and hypotonic solutions do

Hypotonic solutions moved water into the cell and Hypertonic solutions moved water out of the cell

decribe how hypertonic and hypotonic solutions relate to extracellular fluid osmolality

We observe an increased extracellular fluid osmolality (Hypertonic solution) moves water out of cell and decreased extracellular fluid osmolality (Hypotonic solution) moves water into cell.

why is the osmotic strength/power of electrolytes greater? can nonelectrolytes do the same?

because the independent ions may disassociate into several components, i.e. MgCl2 (1 element) à 1 Mg + 1 Cl + 1 Cl (3 ions). Nonelectrolytes cannot disassociate into several components

how does water enter and leave the body

through multiple routes

what must water intake be equal to? how much should it be? how is this accomplished including percentages?

water output and should be 2.5 L a day,mainly through beverages 60% and food 30% with small amounts generated by the mitochondria 10% within cells

what is thirst regulated by? how does this work?

hypothalamic thirst center where there are receptors sensing osmolality of the extracellular fluid

what are osmoreceptors activated by

increased plasma osmolality of 1 or 2%, dry mouth, decreased blood volume or pressure, and angiotensin II or baroreceptor input

what else do the factors that activate osmoreceptors stimulate?

release of antidiuretic hormone (ADH).

what are the percent compositions of water output, include highest volume

the highest volume in urine 60% with insensible water loss 28% second.

what mechanisms regulate water intake and output

feedback mechanisms

describe how drinking water quenches thirst in the body

wets dry mouth and mechanically stretches (baroreceptor) intestines

what happens when water is absorbed in the small intestine ? how does this affect extracellular fluid osmolality? what is this sensed by? what is inhibited?

extracellular fluid osmolality decreases and is sensed by hypothalamic osmoreceptors that leads to inhibit ADH release

what is water reabsorption in collecting ducts of kidney nephrons proportional to

ADH release

what do decreased ADH levels equate to

decrease in the body water (urine output)

where are baroreceptors and what is their function

within blood vessels, maintain homeostasis of blood pressure also influence ADH levels

what causes an increase in antidiuretic hormone

when blood pressure decreases

Summarize the two origins of the negative feedback pathway for ADH

hypothalamic osmoreceptors and blood vessel baroreceptors both end at hypothalamic osmoreceptors.

what are the obligatory water losses are characterized by insensible

water loss from lungs and skin

what are the obligatory water losses are characterized by sensible

water loss from urine, sweat, and feces is more commonly known.

what conditions are outside the normal homeostatic range of body water and have severe consequences

Both dehydration and hypotonic hydration

why is dehydration an issue ? in what sicknesses would you consider it a concern?

when it comes to burns or viral and bacterial infections, e. the flu or cholera, because symptoms include prolonged vomiting or diarrhea

what may a dehydrated patient display? what may this lead to?

a ‘cotton’ mouth and have dry flushed skin; the condition may lead to weight loss, fever, mental confusion, and decrease of electrolytes

how does excessive loss of water from the extracellular fluid affect cells

cause cells to shrink from water loss.

what is hypotonic hydration

excessive water becomes intoxicating

why do patients with renal insufficiency need to be closely monitored

because symptoms include muscular cramping, cerebral edema, and possibly death

what is given to a patient experiencing hypotonic hydration

A hypertonic saline IV is used to counter act the condition

what is edema

the accumulation of interstitial fluid that can potentially impair tissue function

what could be the cause of edema

increased fluid flow out of blood capillaries or decreased return of fluid to blood (bulk flow in capillaries or lymphatic return [remember this requires muscle movement])

what is electrolyte balance commonly known as

salt balance

what do electrolytes include

acids, bases, and proteins

what do the several functions of salt balance inlclude

controlling fluid movements, providing minerals for excitability, secretory activity, and membrane permeability

describe how salts enter the body, how they are made, and how they exit the body

enter the body through ingestion and are made in metabolism and lost in sensible water loss

is electrolyte balance essential in mammals

yes

what do sodium imbalances provide

neurological dysfunctions that could lead to confusion, lethargy, coma, and disfunctions in neuromuscular junctions or provide circulatory shock (decreased blood volume and blood pressure).

what happens if potassium levels are low

may cause cardiac arrhythmias or flattened T-wave on ECG

what happens if calcium is low

may display as tingling fingers, tremors, or cramps in skeletal muscles

what may electrolyte deficiencies prompt? what is a disease that does the same and why?

cravings of salty or sour foods, e. pickles or smoked meats. Addison’s disease is a disorder that may cause these cravings because ADH is low therefore many electrolytes are lost in urine.

what is the purpose of sodium

key electrolyte regulating blood volume and blood pressure

what is the percent composition of sodium in the ECF? why is it important to osmotic pressure?

greater than 90% of total cations within extracellular fluid, consequently sodium is the only cation exerting a significant osmotic pressure.

what do changes in sodium levels affect

plasma volume, blood pressure, and volumes of extracellular fluid

what happens to Sodium that diffuses into cells ? where does it move?

pumped out against its electrochemical gradient and moves back and forth between extracellular fluid and body secretions.

is Sodium integral to renal acid-base homeostasis

yes

what does the concentration of sodium determine? why does it remain stable?

localized responses, e. osmolality of ECF and consequently excitability at gap junctions, but remains stable because of water following the salt into and out of intracellular fluid

what does the content of sodium also determine

global (organismal) responses, i.e. extracellular fluid volume and consequently blood pressure (baroreceptors)

what is the sodium content or sodium-water balance regulated by

neural and hormonal controls in response to blood pressure

what hormone plays the biggest role in regulating sodium ? where is sodium reabsorbed

Though aldosterone plays the biggest role in regulation of sodium by kidneys, 90% of sodium is reabsorbed in nephron

what does increased aldosterone translate to and why

increased extracellular volume because when sodium is reabsorbed in DCT and CT of nephron water follows

what is aldosterone’s release is dependent on? what is the RAAS system composed of?

Renin-angiotensin-aldosterone system (RAAS); RAAS is mainly comprised of three hormones renin, angiotensin II, and aldosterone

what happens in the first stage of RAAS

the release of renin in response to sympathetic nervous system stimulation and decreased stretch (baroreceptors) of granular cells (these guys release renin) from decreased blood pressure

what happens in the second stage of RAAS

Renin cleaves angiotensinogen, a precursor protein in the liver, to produce angiotensin I; this process continues, mainly in the lungs, as angiotensin converting enzyme (ACE) converts angiotensin I to angiotensin II.

what happens in the fourth stage of RAAS

Angiotensin II stimulates aldosterone release from adrenal cortex

what happens in the last stage of RAAS

the increase in aldosterone increases sodium reabsorption and water always follows

what else triggers the RAAS pathway (renin release).

increased Potassium levels

what is the release of renin (beginning of RAAS pathway) is inhibited by

atrial natriuretic peptide (ANP)

what triggers ANP release

triggered by stretch (baroreceptors – monitoring blood pressure) of atrial cells

what else does ANP inhibit? what does this do?

ADH and aldosterone, which increases excretion of Sodium and water

what does ANP promote and how

vasodilation directly and through the decrease of angiotensin II (known vasoconstrictor)

in regards to ANP what do the stretched baroreceptors of the cardiovascular system do to affect GFR

transfer signal to CNS and CNS transmits signal to kidneys causing increased glomerular filtration rate

what happens in potassium disruption in the heart

vital in heart and may interfere with electrical conduction, which leads to sudden death

how does potassium disruption affect resting membrane potential ? what does an increase in potassium in the ECF cause?

potassium affects resting membrane potential (RMP) in excitable cells (neurons and muscle). Increased potassium in extracellular fluid decreases RMP causing depolarization and reduced excitability.

where is the second vital function of potassium

within the buffer system, where H+ and K+ cross the plasma membrane in opposite directions

what does acidosis do

raises the levels of Potassium in extracellular fluid

how does potassium control its own extracellular fluid levels

by feedback regulation of aldosterone release; increased potassium in adrenal cortex causes release of aldosterone, which increases potassium secretion

how is calcium homeostasis is controlled

parathyroid hormone (PTH) and rarely deviates from normal limits

how is calcium released

With 99% of calcium being stored in the bones as calcium phosphate salts, breakdown of bone matrix by osteoclasts releases both calcium and phosphate into the blood

what does PTH increase and decrease

increases calcium reabsorption and decreases phosphate ion reabsorption

describe the realtionship between sodium and chloride , what occurs under acidosis

The anion Cl- is the partner of Na+ in extracellular fluid and 99% of Cl- is reabsorbed under normal pH but acidosis very few Cl- are reabsorbed due to HCO3-

what is the most important buffer system in the body and where is it located

bicarbonate and hydrogen regulation in the body located in the kidneys

how does a chemical buffer system acts

acts to resist pH changes when strong acids or strong bases are added to a solution, and includes one or more compounds/molecules; in short, the buffer system binds H+ if pH decreases (becomes acidic) or releases H+ if pH increases (becomes alkaline).

what are the three major buffer systems in the body ? why is the focus on bicarb?

bicarbonate, phosphate, and protein; however, the focus will be on the bicarbonate system because it is the ONLY important buffer system of the extracellular fluid but also buffers the intracellular fluid

The bicarbonate buffer system is a mixture of what two molecules

a weak acid H2CO3 and salts HCO3-.

describe what heppsn when extra H+ or OH- is added to a solution

When extra H+ is introduced in solution then HCO3- attaches to them creating a weak acid that decreases pH minimally; when extra OH- are introduced in solution then H2CO3 dissociates and attaches H+ to OH- producing water

where is the limitless supply of H2C03 from

from the CO2 released by respiration

if Chemical buffers do not function to eliminate excess acids or bases from body how are they eliminated

acids are eliminated, it is the lungs that eliminate volatile H2CO3 by expelling CO2 and the kidneys eliminate nonvolatile acids to prevent metabolic acidosis

what else do the kidneys regulate blood levels of

alkaline substances, refreshing storehouse of chemical buffers

summarize how the kidneys regulate acid base homeostasis

by adjusting amount of bicarbonate (HCO3-) in blood; to keep (reabsorb) HCO3- kidneys secrete H+ and to secrete HCO3- kidneys keep H+. The tubule cells of the kidneys use secondary active transport to exchange intercellular H+ for extracellular Na+ ions and extracellular CO2 may be imported back into tubule cell but not HCO3-; consequently, the rate of H+ secretion changes with extracellular fluid CO2 levels.Shifting to bicarbonate ion generation, the tubule cells generate new HCO3- by ridding body of H+ through two routes (1) excretion of H+ (2) NH4 excretion. (1) excretion of H+ is coupled with phosphate buffer system, HPO4- picks up H+, to produce H2PO4- in urine. (2) NH4 excretion is dependent on the breakdown of glutamine (most abundant amino acid in body) and produces not one but two new bicarbonate ions.

what are metabolic acidosis and alkalosis caused by

several factors and can be problematic and life threatening in a patient

what may metabolic acidosis be caused by

ingestion of too much alcohol, persistent diarrhea (bicarb lost from intestines), or accumulation of acid due to exercise (lactic acid buildup), ketosis, or starvation

what may metabolic alkalosis be caused by

less common but causes include ingestion of excess base (antacids) or excess vomiting (removing stomach acids).

what are the important issues of acidosis? pH?

issue of acidosis is blood pH below 6.8 causes depression of CNS (that can lead to coma and death)