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Fluid and Electrolyte Balance


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60% of the body's weight is made up of what? water
What are the three compartments that water is stored in in the body?
The intracellular, the extracellular and as a component of blood
What is interstitial fluid responsible for?
A medium for exchange between the cell and the outside, how things enter and exit cells
Total solute concentration in a solution- osmoles/liter
Which is more dilute a solution with an osmolarity of 100 or a solution with an osmolarity of 200?
Net movement of water through a selectively permeable membrane that seperates two solutions with different solute concentrations.
Elevated osmolarity is indicative of what?
Increased solute (sodium) and decreased fluid (water)
What are the two most important extracellular solutes?
Sodium and protein
What are the two most important intracellular solutes?
Potassium and protein
What would happen to a cell that has an intracellular osmolarity of 290 mOsM when it is placed in a solution with an osmolarity of 100 mOsM?
It will swell because the solution with 100 mOsM has more water than the cell that has an osmolarity of 290 mOsM
Where does all the exchange between plasma and interstitial space occur?
The capillary level
The goal of the body is to maintain what kind of osmolarity?
What does isosmotic mean?
Equal osmolarity
What are the two components of extracelluar fluid?
Plasma and interstitial fluid
What is water directly regulated by?
Antidiuretic hormone (ADH)
What is water indirectly regulated by and how is it regulated?
Aldosterone- because it regulates sodium and wherever sodium goes water follows
What organs regulate water balance?
Kidneys, GI tract, lungs, and to a lesser extent skin
How is fluid balance regulated?
By regulating intake (thirst) and output (kidneys)
What we take in should be... (Equal to, less than, or more than)what goes out
Equal to
What pressure does the blood enter the capillary at?
32 mmHg- hydrostatic pressure
As the blood moves through the capillary to the venous end hydrostatic pressure changes to what and why?
It decreases to 15 mmHg because of the loss of fluid to the interstitial spaces- remaining plasma solutes because concentrated.
At the venous end, the net flow of water is where?
Back into the capillary due to the increased osmolarity of the plasma at the venous end
What is the increased osmolarity of the plasma at the venous end due to?
Retained protein in the plasma- it does not leave the capillary
What is the most abundant plasma protein?
What does albumin do at the venous end of the capillary?
It draws fluid back in, and is responsible for the osmotic effect
Are the hydrostatic and osmotic pressures equal? (Meaning does all the fluid that goes in return?)
The excess fluid from the difference in pressures goes where?
Into the interstitial space
What happens to this excessive fluid in the interstitial space?
It is returned to circulation by the lympatic system
Excess fluid in the interstitial space and/or body cavities
What is exudate rich in?
Protein and blood cells
What is exudate type edema normally seen in?
What is purulent exudate?
What is transudate made of?
Little or no protein and very few cells, it is an ultrafiltrate of plasma and it has a water like consistency.
What is transudate normally found in?
Edema of right heart failure
What is the primary mechanism for formation of a transudate?
Increased pressure at the level of the capillary
True or False...

In transudate there is no vascular damage and there is no leakage of protein or cells into the interstitial space.
Transudate or exudate?

Increased hydrostatic pressure within blood vessels
Transudate or exudate...

Increase permeability of the vessel wall
What would happen if there was low albumin concentrations?
There would be nothing to pull the fluid back in so edema would result.
True or False...

Edema is usually multifactorial
Edema caused by chronic heart failure is usually a combination of what?
hydrostatic (HTN) and hypervolemic
Pitting edmea in right heart failure is prominent where and why?
In the lower extermities due to gravity
After a mastectomy patients may suffer from persistant edema for life- why?
Because in a mastectomy they take out the lymph nodes and therefore it is unable to drain anymore resulting in edema.
What is the principal regulator of water intake?
What is thirst regulated by?
The osmolarity of the plasma
What cells monitor the osmolarity of the plasma?
Increased osmolarity of the plasma activates what?
Neural pathways that result in the conscious perception of thirst.
Why are diabetics always thirsty?
Because there is an increased plasma osmolarity because of the increased glucose so the regulators are always being stimulated
What are the two mechanisms in the kidney that regulate output?
What is filtered at the glomerulus and what is reabsorbed or secreted by the tubules.
The amount of fluid filtered by the glomerulus is a function of what?
Hydrostatic pressure- the pressure of the pump
What are the tubules of the kidney are important for?
Reabsorption and secretion of substances- modifying the filtrate.
What is modified in the filtrate?
Both solute and water
What hormones are involved in the regulation of fluid balance?
ADH, aldosterone, and atrial natriuretic peptide
Where is ADH produced and stored?
Produced by the neurons in the hypothalamus and stored in the axon terminals of the posterior pituitary.
Increased osmolarity of the plasma causes what in regards to ADH?
Results in action potential within the hypothalamic neurons and release of ADH into the plasma
Where does ADH bind once it has been released?
A receptor on the collecting duct cell (Found only in the kidney)
When ADH binds to the receptor what does this stimulate?
the formation of membrane channels in the collection duct cells to increase permeability of water from the filtrate back to the plasma.
Lack of ADH secretion results in what?
Copious dilute urine
What is the only hormone that directly regulates water?
Where is aldosterone secreted?
The adrenal cortex
What does aldosterone act on?
The renal cortical collecting duct cells to promote the movement of sodium from the filtrate back into the blood
Movement of the sodium from the filtrate to the blood will result in what?
Increased water retention because water follows sodium
Where does atrial natriuretic peptide come from and what causes it to be released?
Atrial cells in the heart in response to increased stretch.
Increased stretch of the heart is caused by what?
Increased venous return to the heart, caused by excess fluid volume
What does ANP promote?
Water and sodium loss through the kidneys
Why is it important that aldosterone is a steroid hormone?
Because it is a lipid itself so it crosses the plasma membrane easily.
Where is the receptor for the aldosterone hormone?
In the nucleus
What stimulates the release of aldosterone?
low plasma sodium/
high plasma potassium
Does aldosterone directly regulate plasma postassium concentration?
What could cause hyperaldosterone secretion?
tumor in the adrenal cortex causing hypokalemia
Cardiac dysrhthmias from an inability of cells to conduct action potentials are associated with what electrolyte imbalance?
(low plasma postassium)
What could cause hypoaldosterone secretion?
Addison's disease causing hyperkalemia
What electrolye imbalance usually results from kidney dysfunction, and also results in cardiac dysfunction from hypoaldosterone secretion?
(high plasma postassium)
When blood pressure drops, baroreceptors stimulate cells in the afferent arteriole to the kidney to release this.
A protein that acts like an enzyme and converts a plasma protein termed angiotensinogen into angiotensin I.
Angiontensin I is converted into angiontensin II, how?
By an enzyme in the lung called the Angiotensin Converting Enzyme (ACE)
A potent vasoconstrictor, this causes an increase in peripheral vascular resistance thatt raises blood pressure.
It is a potent stimulus for the release of aldosterone.
Angiotensin II
What is the purpose of stimulating the release of aldosterone with low BP, in general or low pressure through the kidney, specifically?
To conserve water in order to increase plasma volume.
What is one treatment for patients with fluid overload and hypertension?
ACE inhibitors, diuretics
1.excretion of wastes
2.regulation of body water, sodium, potassium
4.secretion of hormones - erythropoetin, renin, vitamin D
These are the 4 functions of the kidneys.
What 2 major waste products are eliminated by the kidney?
Blood Urea Nitrogen (BUN)
A nitrogen waste product that is the end result of protein and nucleic acid catabolism.Breaks down into ammonia.
Normal range: 6-19 mg/dl
Blood Urea Nitrogen (BUN)
A product of creatine metabolism in muscle.
Normal range is 0.5 - 1.4 mg/dl
1. vary the acidity of urine - normal pH ranges from 4.5 - 8.0
2. make and release into the interstitial space bicarbonate ion
2 ways the kidney can help regulate pH
What is the normal pH required in the ECF?
1. the bicarbonate system
2. phosphate and protein buffering systems
How does the body maintain pH?
Kidney can excrete hiydrogen ion into urine and return bicarbonate to the ECF.
One mechanism to add new bicarbonate into blood.
H ion elevated/bicarbonate ion decreased.
H ion decreased/bicarbonate ion elevated.
In COPD - pt. cannot blow off CO2 as fast as it is produced. What can this cause?
respiratory acidosis
When CO2 is removed faster than it is produced (like in hyperventilation), it can cause this.
respiratory alkalosis
In the kidney, H ion is secreted and K ion is conserved.
In the kidney, H ion is retained and K is secreted.
1. correction - the cause of the disturbance is repaired
2. compensation - physiological adjustments are made
2 ways to return pH to normal
kidney cells sense reduced O2 carrying capacity of blood and release this to stimulate the bone marrow to produce more red blood cells
kidney activates this, which stimulates the GI tract to absord more dietary calcium
vitamin D
when blood pressure drops in the kidney, kidney cells release this, resulting in vasoconstriction, elevating BP
elevated BUN and creatinine (from inability to produce urine)
when azotemia becomes associated with clinical signs and symptoms, it is termed this.
uremia (urine in the blood)
prolonged signs and symptoms of uremia
chronic renal failure (scarring/irreversible)
kidney stone formation
a clinical syndrome in which kidneys are unable to excrete waste products frequently it is reversible
increased serum BUN and creatinine
caused by glomerular disease, ischemia, nephrotxicity, acute tubular necrosis
acute renal failure
characterized by destruction of tubular epithelial cells and clinically by acute suppression of renal function
most common cause of acute renal failure (when urine flow is <400 ml/day)
caused by ischemia from trauma, toxicity
acute tubular necrosis
1.initiation - 36 hours - decline in urine output, w rise in BUN/creatinine
2.maintenance - 3 weeks - urine output only 50-400 ml/day, fluid overload
3.recovery - take up to 6 mos. - steady increase in urine output - pt usually becomes anemic f
3 stages of acute tubular necrosis
Urinary outflow obstruction by renal stones.
More common in makes.
Most important fator: increased urine concetration of the stone's constituents that exceed their solubility in urine.
characterized morphologically by contracted kidneys with red-brown color and diffusely granular appearance
end-stage kidney disease
What electrolye imbalance usually results from kidney dysfunction, and also results in cardiac dysfunction from hypoaldosterone secretion?
(high plasma postassium)

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