Lecture 9: Fluid, Electrolyte, and Acid-Base Balance Flashcards
What is total body water?
The amount of water in the body
We have a range of total body water % and can be affected by…
age and gender
Through the normal lifespan of a human, that normal range is…
45-75%
A newborn is going to have the highest TBW percentage. This is about…
75%
It will gradually decrease. We don’t see gender differences in TBW until
we get to puberty. Reproductive Hormone levels will be very high.
When we get to puberty, we start to see differences in TBW. How?
Primarily, bc those who have estrogen go up, we get blessed w/ more fat. Those that have testosterone go up, they get more muscle.
Once we hit puberty, males will have a TBW than females bc…
they have a higher muscle mass and a lower total body fat
A young non-obese male, who is post-puberity and not yet elderly, they will have a TBW of
about 60%
A woman of the same age would be about 50%. It doesn’t matter if we have a size difference between a young non-obese male and female, bc
it’s what percentage of THEIR body weight is made up of water.
What is the difference between those two?
Due to the effect of the reproductive hormones, women will have more adipose tissue and less water. Men will have more muscle mass and more water.
In an elderly man and an elderly woman, they will both have a TBW of ~ 45%. Why?
Our elderly male has lost muscle mass and replaced it with fat. Our elderly woman has lost muscle mass and replace it with fat.
We have 3 places in the body where we can have water. What are they?
- outside of cells (extracellular fluid)
- inside of cells (intracellular fluid)
- plasma
Extracellular fluid can be divided into different categories
- interstitial fluid *
- plasma *
- aqueous humor in eyeballs
- cerebrospinal fluid
- synovial fluid in joints
if we’re talking about this young but post-pubscent, non-obese male, who has total of 40 L of TBW, the breakdown is what?
intercellular fluid volume = 25 L
interstitial fluid volume = 12 L
Plasma = 3 L
Intercellular fluid volume is…
the biggest compartment
Smallest compartment of the 3 major compartment is
Plasma
What is the major difference between Plasma vs. Interstitial fluid?
Plasma has a lot more proteins.
What are the similarities between plasma and ECF?
ECF and plasma has the main cation is sodium. The main anion in both is chloride. They have the same amount of concentration of bicarb in each. There’s the same concentration of potassium in each.
IF looks a lot like plasma why?
IF comes from plasma.
If we look at the ICF and compare it to plasma, we see differences.
- main cation in ICF is K
- little bit of Na and a lot of K in ICF (opposite is true in plasma)
- A lot more Mg in ICF than plasma
- A lot more protein in ICF than ECF
Mg is used a lot by enzymes…
inside cells as a cofactor to help enzymes work more effectively.
Why is there a lot more protein in I.F than E.F ?
Membrane protein, structural proteins, carriers inside cell, cytoskeleton, lots of phosphate
4 things you need to keep in mind when talking about water balance?
- can adjust ECF and NOT the ICF
- Receptors measure plasma volume & osmotic concentration
- a. Water always moves by osmosis
b. Water follows Na - Balance depends on water in.vs. out
We don’t have any way to measure how much fluid is in a specific fluid compartment.What we’re looking at ALWAYS is the osmotic concentration….
We monitor the osmotic concentration of cerebrospinal fluid of our brain bc it’s a reasonable reflection of the osmotic concentration of the blood. We don’t have any way to monitor these things.
What are the primary regulating hormones that are going to affect fluid and electrolytic balance?
- ADH
- Aldosterone
- Angiotensin II
- ANH
Where does ADH come from?
Posterior Pituitary gland
When is ADH released?
When osmotic concentration of body fluids is higher than it should be
What are the effects of ADH?
- ^ water reabsorption ( in the DCT in the kidney)
- stimulate thirst center
- vasoconstrictor
If you drink more water and lose less water and vasoconstrict, what do you wind up with in respect to water?
higher bp and higher TBW
Where does Aldosterone come from?
Zona Glomerulosa of adrenal cortex
What’s the MAIN stimulus of Aldosterone release?
Angiotensin II
Another stimulus of Aldosterone would be…
low sodium concentration
What are the effects of Aldosterone?
- ^ Na secretion
- ^ K secretion
- ^ H ion secretion
Besides stimulating Aldosterone secretion, Ang. II also stimulates the thirst centers. How?
If i get dehydrated enough to lower my bp, i’m going to trigger RAAS and ultimately get more Ang. II. That’s gonna make me drink more water.
If I hemorrhage enough, to lower my Bp, it’s gonna activate…
RAAS and eventually get Ang. II which would make me thirsty and I will drink more water.
Generally speaking, the things that are gonna make me thirsty are…
- ADH
- Ang. II
- Dry Mouth
- Talking about things that make you thirsty
ANH is the one hormone we secrete more of to lower TBW. Where does ANH come from?
Atrium
What is the stimulus for ANH?
High Blood pressure
What is ANH gonna do?
- decrease Na reabsorption at kidney
- blocks Aldosterone release
- blocks ADH
- block epinephrine and norepinephrine so i can’t vasoconstrict
If water can ONLY move bc of osmosis, we look at the 4 pressure associated with those pressures.
CHP = out pressure
COP = in
IFHP = in
IFOP = out
Those 4 pressures determine…
how much water is in the plasma compartment vs how much is in the I.F compartment.