LMP301 Lecture 3: Fluid Balance Flashcards
How much ICF is there?
28L
ECF can be subdivided into…
- Plasma
- Interstitial fluid (ISF)
How much ECF is there?
14L
How much plasma is there?
3.5L
How much ISF is there?
10.5L
ACE inhibitor = ?
angiotensin converting enzyme inhibitor
What are ACE inhibitors used for and how do they work?
Used for hypertension
Work by dilating blood vessels
What are the common electrolytes measured?
Na+ K+ Bicarbonate Ca++ Potassium phosphate
Where are electrolytes measured from?
Plasma
Plasma and electrolytes are most abundant in…
ICF
Is it harder to do ECF or ICF measurement?
ICF
What are extracellular ions?
Na+
Cl-
HCO3-
Ca++
What are intracellular ions?
K+
PO4
Anions
Define: concentration
amount of solute in a solvent
Define: osmolality
amount of solute particles in a solvent (weight)
mmol/kg
mOsm/kg
How to estimate osmolality?
Measure the most abundant solutes:
2[Na+] & [Glucose] & [Urea]
Define: osmolarity
amount of solute particles in 1kg of water (WATER IS SOLVENT)
When measuring dilute aqueous solutions, the appropriate unit is…concentration / osmolality / osmolarity
osmolarity
One weakness of concentration measurements
Must take into account total volume of solvent (dehydrated might affect measurement of electrolytes)
Osmolarity is a passive / active process?
passive
Define: oncotic pressure
Pressure in the capillaries
Walls of capillaries act as semi-permeable membrane, and proteins pull water into plasma.
Define: hydrostatic pressure
Pressure exerted by the heart when it pumps
Pushes fluid in vessels into ISF.
Oncotic pressure is balanced by…
Hydrostatic pressure
Hydrostatic pressure is balanced by…
Oncotic pressure
What might affect oncotic pressure?
- Injury: cause proteins in plasma to leak out
Typical input of water?
0.5 - 5L per day
Amount of output of water through renal processes?
0.5 - 4L per day
Amount of output of water through GI tract?
< 0.1 L per day
Amount of output of water through insensible loss?
0.5 - 1L per day
Define: insensible loss
Loss of fluid through sweat & respiration
Most of body fluids are lost through…
Renal processes (kidney)
Define: dehydration
Releasing more fluid than you’re consuming
Define: overhydration
Taking in more fluid than you’re releasing
Define: polyuria
A lot of pee
Define: polydipsia
Consuming a lot of water
Define: oligouria
Small amount of urine output
Define: anuria
no urine output
What medical term falls under dehydration?
polyuria
What medical terms fall under overhydration?
- polydipsia
- oligouria
- anuria
Features of dehydration (physical)
- increased pulse
- dry mucous membranes
- soft / sunken eyeballs
- decrease bld pressure
- decreased urine
- decreased skin turgor
Biochemical signs of dehydration
- increased plasma sodium
- increased bld urea
- increased hematocrit
Define: hematocrit
volume of RBC in blood
What is edema?
Accumulation of fluid in the ISF of your cells
Edema is a symptom of…
overhydration
Features of overhydration (physical)
- normal pulse
- normal mucous memb
- normal eyeballs
- normal / incr bld pressure
- normal / decr urine
- incr skin turgor
Symptoms of overhydration (biochem)?
- normal / decr plasma sodium
- normal / decr bld urea
- normal / decr hematocrit
How is water regulated in the body?
- Control osmolality
2. Control bld volume
Which is the direct route of water regulation?
control of osmolality
which is the indirect route of water regulation?
control of bld volume
How is osmolality controlled in the body? (via ADH)
- Hypothalamus senses bld osmolality
- Hypothalamus tells p. pituitary to make ADH
- ADH goes to kidney collecting tubules
- Kidney absorbs more water
more Na+ in the bld indicates… (in terms of osmolality)
higher bld osmolality
Less Na+ in the bld indicates ____ osmolality
lower
How is osmolality controlled in the body?
- ADH
2. Thirst
How is osmolality controlled in the body? (Thirst)
- Hypothalamus tells you to drink water
2. When homeostasis is reached, hypothalamus tells p. pituitary to stop secreting ADH
SIADH
syndrome of inappropriate ADH secretion
What does SIADH do?
Secrete too much ADH
Too much water reabsorbed
DI
Diabetes Insipidus
What is the symptoms of DI?
Not enough ADH secreted
Water not reabsorbed-> dehydration
How is sodium stored in the body?
25% in bones / tissues
75% in ECF
How is sodium regulated?
- Aldosterone
2. ANP
Aldosterone is secreted by…
adrenal gland
Aldosterone is secreted in response to…
ATII (angiotensin II)
What does aldosterone cause?
Na+ resorption in kidney (but H+ and K+ secreted as a result)
ANP
atrial naturetic peptide
ANP is secreted by…
atria of heart
What stimulates ANP secretion?
Amount of stretch of tissues in the heart (incr. stretch stimulates release)
ANP causes…
Na+ secretion in kidney (also get rid of water because it carries the Na+)
How is bld volume controlled?
- Renin (from kidney) converts angiotensinogen -> ATI
- ACE converts ATI -> ATII
- ATII causes vasoconstriction, Na+ resorption in kidney, aldosterone release
- Aldosterone stimulate Na resorption
What is renin?
enzyme secreted by kidney
What stimulates renin secretion?
low blood pressure
What converts ATI -> ATII?
ACE (angiotensin converting enzyme)
Aldosterone increases plasma Na+ at the expense of…
K+
What are the effects of aldosterone on K+?
- Decrease bld K+
- Increase urine K+
What is the effect of aldosterone on Na+?
- Increase bld Na+
- Decr. urine Na+
Define: hypernatremia
Increased serum [Na+]
What is the value for hypernatremia?
> 145 mmol/L
What are some causes of hypernatremia?
- Decr. body water
- Water loss > Na+ loss (hypotonic)
- Excess Na+ intake
What causes decreased body water?
- Decreased water intake
2. Excess water loss (DI)
What causes water loss > Na+ loss?
.
What is osmotic diuresis?
Things that draw water out along with it
e.g. excretion of glucose in urine will cause water to also be excreted
What causes excess Na+ intake?
- Diet
- IV
- Hyperaldosteronism (Conn’s syndrome, Cushing’s syndrome)
Conn’s syndrome
too much aldosterone
Cushing’s syndrome
Too much cortisol
act like aldosterone in terms of Na+ reabsorption
What is hyponatremia?
Low serum [Na+]
What causes hyponatremia?
- Increased water in body
- Na+ loss > water loss (hypertonic urine)
- Decreased Na+ in body
What causes increased water in body?
- excess water intake
- SIADH
- Renal failure
- Edema (nephrotic syndrome, heart failure)
- IV
2 things that cause edema
- Nephrotic syndrome
2. Heart failure
What is nephrotic syndrome?
Non-specific kidney disease
???
What causes Na+ loss > water loss in urine?
- Diarrhea
- Sweating
- Burns
- Diuretics
What causes decreased body Na+?
- Adrenal insufficiency / not enough aldosterone (Addison’s disease)
Addison’s disease
Too little aldosterone
Which symptom of hyponatremia & hypernatremia is the same?
Na+ loss > or < than water loss
Sweating, diarrhea
What happens if the kidney can’t respond to aldosterone?
Problems with Na+ reabsorption
What does kidney disease cause?
Kidney can’t respond to aldosterone
What does diuresis cause?
kidney secreting more Na+ / secreting more Na+ and K+
-> diuretics
What is the effect of adrenal disease?
Too much / little production of aldosterone
ADH and aldosterone have the [same / different] effects in terms of Na+?
Same
How does the body respond to edema?
- Release aldosterone
2. Release ADH
Edema causes a ___ in effective circulating volume
decrease
Things that may cause edema:
- heart failure
2. hypoalbuminemia
How does heart failure contribute to edema?
Fluid in vessels accumulate instead of pumped by the heart-> goes into ISF
How does hypoalbuminemia contribute to edema?
Less albumin -> less oncotic pressure -> more fluid in ISF
How to examine Na+ disorders?
- Examine serum [Na+] (hypo / hypernatremia)
- Examine bld volume (de / overhydrated)
- Examine input / output of water & Na+
- Consider organ dysfunction (kidney, p. pituitary, adrenal gland)
Aldosterone is secreted by…
adrenal gland
IV
Intravenous Fluid Therapy
What is IV used for?
correct imbalances in the body
IV can contain…
- 5% dextrose
- 0.9% saline (NaCl)
- Plasma
Dextrose in IV
- Correct overall dehydration (ECF & ICF)
- Isotonic w/ plasma, glucose quickly metabolized so only water remains
Why can’t water be directly given as IV to rehydrate someone?
Water is very hypotonic, and will cause cells to explode
Saline (NaCl) in IV
- For dehydration in ECF
- Isotonic to plasma
Plasma in IV
- Correct dehydration in vessels (vascular compartment)
- Given by donor
- Contains electrolytes & protein
- Protein -> oncotic pressure -> more water in vessels
Role of potassium?
- Maintain membrane potential
- Heart beat & contraction
- Acid-base balance
What role does K+ play in acidosis?
- H+ may get in cells
- K+ has same charge-> pushed out of cells int vessels
- High K+ in bld = hyperkalemia
Severe kyperkalemia causes…
Irregular heart beat
Death
How is K+ stored?
99% in ICF
1-2% in ECF
Main loss of K+?
Renal
What causes hyperkalemia?
- Acidosis
- Cells break
- Excess intake
- Renal failure
- Mineralocorticoid deficiency
What is the cutoff for hyperkalemia?
> 6 mmol/L
How does mineraldocorticoid deficiency lead to hyperkalemia?
- Adrenal gland doesn’t produce aldosterone
2. Drugs that inhibit aldosterone production
What is the cutoff for hyponatremia?
< 135 mmol/L
What is the cutoff for hypokalemia?
< 3 mmol/L
What causes hypokalemia?
- alkalosis
- renal loss
- drugs
- gastrointestinal loss (diarrhea & vomiting)
Define: alkalosis
Bld pH is basic
How does alkalosis affect K+?
K+ goes into cells -> hypokalemia
[More / less] aldosterone causes hypokalemia
More
What drugs causes hypokalemia?
Thiazide diuretics
Corticosteroids
What does thiazide diuretics do?
Excrete Na+ and K+
What is pseudohyperkalemia?
Falsely high plasma K+
What leads to pseudohyperkalemia?
- Hemolysis during venipuncture
- Too long tourniquet
- Disease (too much WBC, platelets)
What is released during clotting?
K+
What is tourniquet?
Tying off the arm when getting a shot
What is venipuncture?
getting a shot
Renin and aldosterone are sensitive to ____
Posture
What is something you have to make sure when doing a recumbent sample?
Compare with the right range (recumbent range)
Recumbent
Sample lying down
