WEEK TEN - Water and electrolyte balance Flashcards
Name the major fluid compartments & explain how water moves from one to another
fluid compartments
- ICF - 65%
-
ECF = 35%
» 25% interstitial fluid
» 8% blood plasma
» 2% transcellular fluid [CSF, synovial fluid]
movement/distribution occurs due to **osmosis + capillary filtration **from blood tissues –> blood fluid
- net movement of water = determined by conc. of solutes in each compartment
List the body’s sources of water and routes of water loss
total body water for 70kgM = 40L [55-60% TBW]
women hold LESS water –> because they have more adipose tissue [free of water]
typically humans gain and lose water at **2500mL/day ** [fluid balance]
sources
1. performed water [ingested via **food - 700mL/day **+ drink - 1600 mL/day]
2. metabolic water [byproducts of aerobic metabolism eg glycogenesis and dehydration synthesis
- about **200mL/day **
**loss **
-urine = 1500mL/day
- cutaneous transpiration = 400mL/day
- expired air = 300mL/day
- faeces = 200mL/day
- sweat = 100mL/day
Describe the mechanisms of regulating water intake and output
**fluid INTAKE **
1. deydration = ^ blood osmolarity + v BP
2. ^ osmolarity stims hypothalamic osmoreceptors
3. v BP stims renin-angiotensin II system –> stims osmoreceptors
4. stims ADH secretion by post.pit
5. osmoreceptors inhibit salivary glands –> dry mouth
6. osmoreceptors + ADH stim. –> thirst –> ingestion of water
7. cools/moistens mouth = greater satiation
8. 6. distension of stomach/intestines = short term satiation [30-45 mins]
9. blood rehydration [long term resolution]
fluid OUTPUT
ADH
1. deydration = ^ blood osmolarity + v BP
2. ^ osmolarity stims hypothalamic osmoreceptors
3. stims ADH secretion by post.pit
4. stims DCT to increase water reab.
5. stims aquaporin synthesis in CD
6. by helping the kidneys retain water ADH reduces urine volume + slows decline in blood volume + slows rise in osmolarity = ADH –> NEGATIVE FEEDBACK LOOP
7. when hypertension –> ADH inhibted = body does not retain as much water = TBW declines
ALDOSTERONE
1. 1. deydration = ^ blood osmolarity + v BP
2. v BP = stims renin secretion from kidney
3. renin»_space; angiotensin I»_space; angiotensin II»_space; aldosterone
4. angiotensin II directly stims **PCT to reab water **
5. aldosterone stims **Na+/water reab in DCT and CD **
State some conditions where there is a fluid deficiency or a fluid excess amongst fluid compartments
deficiency
**1. hypovolemia **[volume depletion
- proportionate amounts of water and sodium lost = TBW declines, osmolarity NORMAL
- eg hemorrhage, burns, chronic vomiting, diarrhea
**2. dehydration **
- TBW decreased, osmolarity RISES
- eg lack of drinking water, diabetes, profuse diaphoresis, diuretics
- infants MORE vulnerable due to kidneys not being able to concentrate urine effectively, high metabolic rate demands high urine excretion
- affects all fluid compartments
fluid excess
**1. volume excess **
- both Na+/H20 are retained and ECF remains isotonic
- eg aldosterone hypersecretion, renal failure
2. hypotonic hydration/water intoxication
- more H20 than Na+ is ingested/retained and ECF –> hypotonic
- can occur if you lose large amounts of water through urine or sweat and replace it by drinking plain water = lack of electrolytes
- w/o proportionate intake of electrolytes, water dilutes ECF = hypotonic = causing swelling
- eg **pulmonary/cerebral edema **
3. fluid sequestration
- excess fluid conc. in particular location
- most common cause of sequestration = edema
- other causes = hemorrhage, pleural effusion
State the physiological roles of sodium and potassium [10]
Na+
- **conc. in ECF **as the major cation - accounts for 90-95% osmo. of ECF
- most SIGNIFICANT solute in **determining TBW **and distribution
- one of the prinicpal ions responsible for **RMP and nerve functioning **
- responsible for cell membrane **depol in AP **
- Na+ gradient = used to transport other solutes eg glucose, K+, Ca+
- MAJOR role as pH buffer in ECF
K+
- **conc. in ICF **as the most abundant cation
- GREATEST determinant of intracellular osmolarity and cell vol
- one of principal ions responsible for **RMP and nerve functioning **
- responsible for cell membrane **repol in AP **
- important for proper heart function
State the term for an excess or deficiency of sodium and describe consequences of these imbalances
Hypernatremia
- HIGH CONC Na+
- Plasma sodium > 145 mEq/L
- can result from IV saline administration
- causes edema, water retention, hypertension
Hyponatremia
- LOW CONC Na+
- Plasma sodium < 130 mEq/L
- results from excess BW eg hypotonic hydration
- generally is quickly corrected by excretion of excess water, but if untreated can result edema and death
State the term for an excess or deficiency of potassium and describe consequences of these imbalances
Most DANGEROUS electrolyte imbalances occur with K+
Hyperkalemia
- >5.5 mEq/L
- can have different effects depending on whether the K+ rises quick/slow
- quick influx eg crush injury/hemolytic anemia –> releases K+ from ruptured cells
- also caused by blood transfusion w/ outdated blood also causes
- ^ in K+ = makes cells MORE EXCITABLE –> cardiac arrythmias –> arrest
- **slow influx **eg aldosterone hyposecretion, renal failure, acidosis –> SLOW INFLUX = LESS EXCITABLE CELLS = affects AP production
Hypokalemia
- **<3.5 mEq/L **
- from sweating, chronic vomiting, diarrhea, aldosterone hypersecretion,
- nerve + muscle cells LESS excitable = muscle weakness, loss of muscle tone, decreased reflexes, cardiac arrythmias
Describe the hormonal and renal mechanisms that regulate the concentrations of sodium and potassium
HORMONAL **
aldosterone
- secreted by adrenal glands in response to low BP**, low Na+ or high K+ levels
- - stims DCT + CD to reab Na+ = ^ Na+ conc in blood
- simultanously stims release of K+ ions = ^ K+ conc in urine
ADH
- produced by hypothal - released by post.pit in response to ^ blood osmolarity/ v vol/ high Na+ conc
- indirectly affects Na+conc in blood by stim DCT to reab water and aquaporin synthesis in CD
- primarily affects water regulation
- low Na+ levels will inhibit ADH secretion
AtrialNP/BrainNP
- sec by atrial myocardium from ^BP –> acts to excrete more Na/water in urine = v BP
- inhibits sodium/water reab
- inhib renin/ADH/aldosterone secretion
RENAL
1. filtration
- Na+/K+ filtered from blood –> renal tubules
- reabsorption
- filtered Na+ reab in PCT, DCT,
- regulated by various hormones including aldosterone and ADH
- majority of K+ = reab in PCT, further in DCT - secretion
- K+ secretion primarily occurs in the DCT/ CD as reg by aldosterone
- K+ channels in DCT facilitate active transport of K+ ions from tubular fluid to –> tub.cells [^ K+ conc. in URINE = prevents hyperkalemia]
- in CD, principal cells/ inctercalated cells reg K+ reab/sec.
- principal cells have K+ channels, aldosterone stims insertion of more channels [^ K+ sec] –> when aldo. low = channels removed = allowing ^ K+ to be excreted.
Define and write chemical equations for the bicarbonate, phosphate, and protein buffer systems
bicarbonate
CO2 + H20 <–> H2co3 <–> HCO3- + H+
- optimal pH = 6.1
- equation to R = h2co3 releases H+ = v pH
- to L = HCO3 binds H+ = ^ pH
phosphate
H2PO4- <–> HPO42- + H
- H2PO4 = dihydrogen phosphate
- HPO42 = hydrogen phosphate
- optimal pH = 6.8
- equation to R = liberates H+ = v pH
- STRONGER buffering effect than bicarbonate but phospahtes less conc. in ECF = not as important
protein
**- COOH –> -COO- + H+ ** [v pH]
- COOH = carboxyl acid
- liberates H+ = v pH
-NH2 + H+ = -NH3+
- binds H+ = ^ pH
- ## proteins MORE conc than bicarbonates/phosphates esp ICF = accounts for 2/3 chemical buffering in body fluids
Discuss the relationship between pulmonary ventilation, pH of the extracellular fluids, and the bicarbonate buffer system
Respiratory Control of pH:
*Basis for the strong buffering capacity of the respiratory system
-The addition of CO2 to the body fluids raises the H+ concentration and lowers pH
-The removal of CO2 has the opposite effects
*Respiratory system neutralizes two or three times as much acid as chemical buffers
^ CO2 and decreased pH = stimulate pulmonary ventilation
^ pH inhibits pulmonary ventilation
bicarbonate buffer system
CO2 + H2O <–> H2co3 <–> HCO3 + H+
equation to right = H2CO3 releases H+ = v pH
equation to left = HCO3 binds H+ [removes free H+ ions from solution] = ^ pH
- optimum pH = 6.1
Explain how the kidneys secrete hydrogen ions and describe how these ions are buffered in the tubular fluid.
kidneys neutralise more acid or base than either respiratory/chemical buffers as it actually expels H+ from the body
Renal tubule cells secrete H+ into tubular fluid → Most bind to bicarbonate [HCO3] , ammonia [NH3] , and phosphate buffers / then both Bound/free H+ are excreted in the urine
can only occur with a steep H+ concentration gradient between tubule cells [high H+ conc] -tubular fluid [lower H+ conc]
- slight excess of free H+ in urine gives the pH of 5-6
- if tubular fluid pH lowers to 4.5 = H+ conc too HIGH = stops H+ secretion [pH of 4.5 is the limiting pH for tub.sec]
Name 4 disorders of acid-base balance and state possible causes of these disorders
normal blood pH = 7.23 - 7.45
pH < 7.35 = state of acidosis
pH > 7.45 = state of alkalosis
RESPIRATORY
respiratory acidosis [low pH]
- from HYPOventilation [rate of alveolar ventilation fails to keep pace w body’s rate of CO2 production]
- CO2 accumulates in ECF = ^ H+ = lower pH
- initial symptoms = headaches, dyspnea, lethargy
respiratory alkalosis [high pH]
- from HYPERventilation
- CO2 eliminated faster than it is produced
- ^ pH
- symptoms = hyper reflexes, cramping, anxiety, ^ irritability
METABOLIC
metabolic acidosis [low pH]
- ^ production of organic acids eg ketone bodies or HCO3 loss
- caused by = alcoholism, diabetes, starvation, kidney failure, ingestion of acidic drigs eg aspirin
**metabolic alkalosis ** - lose acid eg vomit
- rare - but can results from
- overuse of bicarbonates eg antacids or loss of stomach acid from chronic vomitting
- ^ pH
Explain how the respiratory and urinary systems compensates acidosis and alkalosis, and compare their effectiveness and limitations.
respiratory compensation [short-term corrections of pH imbalances]
- changes pulm ventilation to correct pH changes = expels/retains CO2
- low pH - Co2 excess [hypercapnia] –> stims pulm vent = expels CO2 = ^ pH
- high pH - CO2 deficiency [hypocapnia] –> reduces pulm vent = allows **accumulation of CO2 = lowering pH **
renal compensation [for pH imbalances that last for a few days/longer - SLOWER - but better at restoring a fully normal pH]
- acidosis urine pH may fall as low as 4.5 due to excess H+= renal tubules **^ rate of H+ secretion = ^ blood pH **
- alkalosis urine pH may rise as high as 8.2 from excess HCO3- = renal tubules v rate of H+ secretion = v pH
Define digestive tract (alimentary canal) & list in order the passage of food through the structures of this tract.
digestive system = organ system which processes food, extracts nutrients and eliminates waste
five stages
1. ingestion
2. digestion
3. absorption
4. compaction
5. defecation
digestive tract = 9m long tube in cadaver, 5m long in living person
order of food passage:
mouth
pharynx
esophagus
stomach
small intestine
large intestine
anal canal
Name & identify accessory organs & all parts of the digestive system
teeth/tongue
salivary glands
liver
gallbladder
pancreas
