fluid, electrolyte and acid base balance

describe a humans body content

• between 45-75% fluid

• depends on age and amount of adipose and muscle tissue in body

• infants 73% or more of water

• adult males ~60% water

• adult females ~50% water

• water content is going to decline ~45% in old age

what fluids make up your total body fluid of 40 L

intracellular fluid (ICF) compartment

• 2/3 or 25 L in cells

• enclosed by the plasma membrane

extracellular fluid (ECF) compartment'

• 1/3 or 15 L

• fluid outside the cells

what fluids are going to make up the ECF compartment

plasma

• 3 L

• within the blood vessels

• seperated from interstitial fluid by capillary beds

interstitial fluid (IF)

• 12 L

• in spaces between cells

• 2/3 of ECF

other ECF, usually considered part of IF

• lymph, CSF, humors of the eye, synovial fluid, serous fluid and gastrointestinal secretions

what are the electrolytes in ICF

major cations

• potassium and Mg+

major anions

• PO4-(phosphate) and negatively charged ions

what are electrolytes in ECF

major cations

• sodium and Ca2+

major anions

• Cl- (chloride), HCO3- (bicarbonate)

describe how fluid is going to move through the compartments

• they move constantly due to osmotic and hydrostatic pressure

• water moves from hypotonic ot hypertonic solution, will continue until concentrations are equal

describe how drinking water plays a part in the movement of substances across the compartments

• water will enter blood from digestive system

• it decreases plasma osmolarity

• water moves to IF first then to cells

when you are dehydrated

• blood plasma osmolarity decreases, becomes hypotonic to both IF and cells

• water moves from cells to interstitial fluid, then to plasma

to remain properly hydrated what needs to be equal

water intake must equal water output, about 2500 ml/day

describe what your water intake consists of

• overall should be 2500 mL/day

• food and beverages, 2300 mL/day

• metabolic water, water that is produced through reactions happening in your cells and dehydration synthesise. 200 mL/day

describe how water output happens

• 2500 mL/day

insensible water loss

• breathing

• evaporation of water through skin

• perspiration

• depends on physical activities, environment and internal conditions

sensible water loss

• urine, 60%

• feces

what is obligatory water loss

water loss regardless of hydration level, you lose it no matter what

• all of water from lungs, skin and feces

• water loss in urine to excrete wastes

• minimum daily loss of 500 ml

what is facultative water loss

the controlled water loss in your urine

• depends on hydration of the body

• is hormonally regulated by kidney nephrons

• the nephrons are the only way to control fluid output, can decrease fluid if body is dehydrated

describe the disorder of water balance, severely dehydrated

you have a loss of H20 from ECF, so ECF osmotic pressure rises, cells lose H20 to ECF by osmosis and cells shrink

what are signs of someone being severely dehydrated

• thirst

• decrease urine output

• mental confusion

• fever

• BP decreased tremendously

describe hypotonic hydration

• water intoxication

• excess H20 enters the ECF, ECF osmotic pressure falls, H2O moves into cells by osmosis causing swelling and possible lysis

• can cause cerebral edema

describe edema

• atypical accumulation of IF fluid resulting in tissue swelling, not cell swelling

• increased formation of IF or decreased removal of IF

how is water intake going to be regulated

thirst mechanism

• the driving force for water intake

• activated by increased in plasma osmolarity of 2-3%, a dry mouth, and sustainable decrease in blood volume or pressure

hypothalamic thirst center

• hypothalamic osmoreceptors detect ECF osmolarity, governs the thirst mechanism

what does drinking water inhibit

the thirst center

inhibitory feedback mechanisms to stop thirst reflex include

• relief of dry mouth

• activation of stomach and intestinal stretch receptors

• decreased blood osmolarity, but comes later after the first two

• increased BP

what is fluid output mainly regulated by

through the kidneys by controlling urine output

four hormones involved

• angiotensin II, ADH, aldosterone. they all decrease urine output and increased blood volume and pressure

• ANP will increase urine output, decrease blood volume and pressure

describe electrolyte balance

electrolytes are your,

• salts, acids and bases

dissociate into ions when dissolved in a solution and conduct a electric current

this is usually referred to only salt balance

describe sodium balance

• the MOST abundant ion in ECF, only 1% in ICF

• controls ECF volume and water distribution because water follows sodium

• changes in sodium levels affect plasma volume, blood pressure, ECF and IF volumes

what is retention of sodium and water going to lead to

increase in blood volume and blood pressure

what is a loss of sodium and water going to lead to

decrease in blood volume and blood pressure

what is the amount of sodium loss in urine going to be regulated by

aldosterone, ADH and ANP

what is hypernatremia

high sodium

what is hyponatremia

low sodium

describe potassium balance

• 98% in ICF and 2% in ECF, maintained by Na/K pump

• potassium affects RMP in neurons and muscle cells, especially cardiac muscle cells

• regulated by aldosterone

what is hyperkalemia

too much potassium

what is hypokalemia

too little potassium

how is the balance of H2O, Na+ and K+ balance controlled

• angiotensin II

• ADH

• aldosterone

• ANP

describe the renin angiotensin system

1) liver always makes and releases inactive angiotensinogen

2) drop in BP

3) renin released, acts on angiotensinogen

4) angiotensin I still inactive is made

5) ACE acts on angiotensin I

6) angiotensin II is made, is now active

7) stimulate release of ADH

8) stimulate release of aldosterone

describe calcium and phosphate in the body

• 99% are in bone as calcium phosphate salts

• in sarcoplasmic reticulum and synaptic bulbs of neurons

• calcium is important for initiating muscle contraction, releasing neurotransmitters and blood clotting

• calcium balance controlled by parathyroid hormone and calcitrol

what is hypercalcemia

high calcium

what is hypocalcemia

low calcium

what are the effects of PTH and calcitrol

bones

• osteoclasts break down matrix, releasing calcium and phosphate into blood

kidneys

• increases calcium ion reabsorption, decrease phosphate ion reabsorption

small intestine

• increase calcium absorbtion

describe the chloride ion

associated with sodium

• follows sodium by electrostatic interactions

• regulated by same mechanisms as sodium

found in lumen of stomach as HCI

participants in chloride shift within RBC’s

obtained in a diet from table salt and processed foods

lost in your

• sweat, stomach secretions and urine

what is the normal pH of arterial blood

7.4

what pH is alkalosis or alkalemia

more than 7.45

what pH is acidosis or acidema

less than 7.35

pH is inversely related to what

H concentration

• increase in pH, decrease in H

• decrease in pH, increase in H

the amount of what to the blood varys

acids and bases

• usually more H added to blood as it will decrease pH

• to maintain acid base balance it required elimination of excess H

what is pH altered by

physiological buffering systems

• kidneys

• lungs

chemical buffering systems

describe renal regulation of pH

kidneys will

• eliminate excess acid (H) or base (HCO3-)

• is slower, takes several hours to days

• MOST powerful method to maintain blood pH

how would blood H+ be increased

• acid from GI tract

• waste products from metabolic processes

• excessive prolonged diarrhea, causing loss of bicarbonate

how are the kidneys going to react to an increase in H+

• excrete H+ in urine

• synthesize and absorb new bicarbonate

how would blood H+ be decreased

• vegetarian diet

• antacid ingestion

• vomiting with loss of HCI

• this is rare, increase of H+ is more common

how do the kidneys respond to decreased H+

secrete bicarbonate from blood into filtrate

reabsorb H+

describe the respiratory regulation of pH

lungs are going to act as a physiological buffer system

• CO2 normally eliminated from lungs at same rate it is produced

• the CO2, H+ and O2 levels will be regulated by chemoreceptors

• levels of these ions are relayed to respiration center to alter breathing rate

• the change in CO2 is the MOST important variable

how are lungs going to regulate concentration of H+

• alters amount of CO2 being eliminated

• CO2 +H2O arrows H2CO3 arrows H+ + HCO3-

• CO2 levels in blood directly related to H+ levels

• CO2 levels in blood inversely related to pH

how are the lungs going to respond to increased H+

the high H+ stimulates respiratory center, respiratory rate and depth will increase

how are the lungs going to respond to decreased H+

the decreased H+ depresses respiratory center, respiratory rate and depth decreases

• more CO2 stays in blood and is converted to H+

describe the chemical buffering system

• acts in minutes

• will temporarily prevent pH changes

• composed of a weak acid and a weak base

• weak base binds to excess H+

• weak acid release H+

what are the three major chemical buffering systems

protein buffering system

• ICF and the blood

phosphate buffering system

• ICF

bicarbonate buffering system

• ECF

describe the protein buffering system

• helps to minimize pH changes throughout body, intracellular and in blood

• they are your intracellular proteins, plasma proteins and hemoglobin

• protein molecules are amphoteric, functions as a weak acid and weak base

describe carboxylic acid (-COOH) in the protein buffering system

• acts as a weak acid to buffer base

• when pH rises, these groups release H+

describe the amine group (-NH2) in the protein buffering system

• acts as a weak base to buffer acid

• when pH falls, it binds to H+

describe the bicarbonate buffer system

• the most important buffering system in ECF

• composed of a weak acid, carbonic acid (H2CO3)

• composed of a weak base. bicarbonate (HCO3-)

in the bicarbonate buffering system, what happens when a strong acid is added

• HCO3- binds to H+ and forms H2CO3

• net result is strong acid buffered to produce a weak acid, pH decreases only slightly

in the bicarbonate buffering system, what happens when a strong base is added

• H2CO3 dissociate and releases H+, H+ binds to the base

• net result is strong base buffered to produce a weak acid, pH rises only slightly

describe the phosphate buffering system

• found in ICF

• buffers metabolic acid produced by cells

• composed of a weak acid, dihydrogen phosphate (H2PO4-)

• composed of a weak base, hydrogen phosphate (HPO42-)

• net result is a strong acid buffered to produce a weak acid and vise versa

what are abnormalities of acid base balance

• change in H+ resulting in a change in pH beyond normal range

• can be life threatening

• physiological buffering systems respond

how are acid base abnormalities classified

respiratory acidosis, metabolic acidosis, respiratory alkalosis, meatbolic alkalosis

how can the respiratory system cause an imbalance

• it can correct the acid base imbalance but if it is not funcitoning as it should, that is when it can cause acid base imbalances

• it is indicated by abnormal Pco2 levels

• kidneys will have to compensate

describe hyperventilation

abnormal increase in respiratory rate

caused by

• excess CO2 expired

• blood Pco2 decreases

• severe anxiety

• condition in which person is not getting enough oxygen

• aspirin overdose

causes

• blood H+ to decrease

• blood pH to increase

• respiratory alkalosis

describe respiratory alkalosis

• caused by an increase in inhalation, CO2 is being eliminated faster than it is being produced

• Pco2 lower than 35mmHg

describe hypoventilation

• abnormal decrease of respiratory rate

causes

• increase in amount of CO2 beign retained

• blood CO2 rises

• blood H+ increases

• blood pH decreases

• respiratory acidosis

describe respiratory acidosis

• the most common acid base disturbance

• due to impaired elimination of CO2 by respiratory system

• accumulation of CO2 and increase in h+ concentration

• Pco2 above 45 mmHg

causes

• decreased airflow, airway obstruction

• decreased gas exchange, reduced surface area or thickened width of membrane

• hypoventilation

what is metabolic acidosis

• low pH and low bicarbonate

• may happen from loss of bicarbonate or gain of H+, but more commonly gain of H+

what are causes of metabolic acidosis

increased production of metabolic acids

• diabetic ketoacidosis

• accumulation of lactic acid

• acetic acid from excessive alcohol intake

decreased acid elimination due to renal dysfunction

• certain kidney diseases

excessive loss of bicarbonate

• persistant diarrhea

describe metabolic alkalosis

• much less common

• indicated by high blood pH and high bicarbonate

what are causes of metabolic alkalosis

• vomiting of acid contents

• increase loss of acids by kidneys with diuretic overuse

• intake of excess base

how do we compensate for different types of alkalosis and acidosis

respiratory system correct metabolic imbalances, and kidneys correct respiratory imbalances

what is respiratory compensation

lungs try to compensate for metabolic pH problems by changing respiratory rate and depth

metabolic acidosis

• high levels of H+ stimulate respiratory centers

• rate and depth elevated

• Co2 levels lowered

metabolic alkalosis

• slower and shallow breathing

• CO2 levels increased

describe renal compensation to acidosis

• in response to elevated blood H+

• intercalated cells excrete H+ and reabsorb HCO3

• urine pH lower than normal

describe renal compensation to alkolosis

• in response to decreased H+

• intercalated cells reabsorb H+ and excrete HCO3-

• urine pH higher than normal