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Body Fluids and Electrolyte Balance

Terms in this set (45)

how much of body weight is water content
50-60%
how much of water weight is intracellular
2/3 (40% of body weight)
how much of water weight is extracellular
1/3 (20% of body weight
how much of fluid volume is intravascular
-¼ of extracellular fluid volume is intravascular
What is the best measure to track fluid status?
Body Weight
how much does a gallon of water weigh
8.34 pounds
What are the ways to track fluid status
- body weight
•Careful history
•Physical Exam
•Serum and Urine Electrolytes
•Serum Osmolality
How do you assess fluid status?
•Orthostatic hypotension
•Urine output
•24 hour urine sodium: fluid status
•Skin Turgor
•Cap refills
•Breath sounds
•Mucus membranes
•Serum SODIUM!
What makes up the starling forces
1.Capillary Hydrostatic force
2.Capillary Osmotic force
3.Tissue Hydrostatic force
4.Tissue Osmotic
what are hydrostatic forces
•pressure placed on the fluid in the blood vessels or the tissue
how is arterial blood pressure determined
by vascular smooth muscle in the precapillary arteriole
Where is pressure highest and lowest in capillary bed
•There is considerable fluid pressure at the arterial end of a capillary
•There is very little actual pressure by the venous end of the capillary - but the blood is flowing - just slowly
Negative pressure is needed to do what
•in order to drain towards a vein or a lymph channel
Oncotic/osmotic pressure
a force that attempts to pull fluid from the interstitial and intracellular spaces into the capillary
- There is a pressure for water to move into dilute a concentrated solution
what attracts water
•Solutions and suspensions
what is considered the oncotic force
- cell membrane or selectively permeable membrane
- creates the osmotic (solution) or oncotic (colloid) force
Osmolarity
measure of total concentration of solute particles
osmolality
the solute concentration in the serum
normal osmolarity of blood
285-295 mosm/kg
what is the major ion influencing osmolality?
sodium
Osmolar Gap
•the difference between the measured Osmolality and the Predicted
what causes osmolar gap
- caused by very high concentrations of small molecules (often toxic) that can exert Osmotic pressure
- ex)
-Mannitol
-Ethanol
-Methanol
-Ethylene glycol
-Propylene Glycol/Benzos
hypovolemia
- too little
- Represents a decrease in total body water
-This is dehydration
hypervolemia
- Too Much
- Intravascular would be venous pooling
-causes back pressure
-inevitably it becomes an extracellular issue EDEMA
uvolemia
- just right
Reasons for Increased Interstitial Fluid
1.Increased Osmotic Pressure of the Interstitial Fluid
2.Deceased Oncotic Pressure of the Plasma Protein
3.Increased Venous Hydrostatic Pressure of the Intravascular Fluid
4.Obstruction of Lymphatic Drainage (lymphedema)
5.Increased Endothelial Permeability
Increased Osmotic Pressure of the Interstitial Fluid
an increase in total body sodium
•excessive salt intake
•increased renal tubular sodium absorption
•decreased renal tubular sodium excretion
reduced renal profusion can lead to generalized edema
Deceased Oncotic Pressure of the Plasma Protein
- A decrease in serum albumin may also produce a generalized edema
- due to a failure of albumin synthesis (liver disease, malnutrition)
- excessive albumin loss (glomerulopathy, enteropathy
- consequence of excessive alcoholism
Increased Venous Hydrostatic Pressure of the Intravascular Fluid
- localized edema
- usually involves increased hydrostatic pressure on the venous (rather than arterial) side of the vascular bed
- Due to interference with (or obstruction to) venous blood flow
- Back up
Obstruction of Lymphatic Drainage (lymphedema)
•also produces a localized edema (chase this)
•usually the result of lymphatic obstruction
•Cancer
•scarring (post-inflammatory, post-radiation, etc.)
•parasitic disease (filarial)
•lymphadenectomy
Increased Endothelial Permeability
•localized edema caused by vascular issues
•Inflammation
•immunologic reactions
•tissue injury
histamine
causes leaky capillaries
- capillary endothelial cells allow fluid to pass through
Liver Disease
•cirrhosis, hepatocellular damage leads to hepatic injury
•Decreased synthesis of plasma protein
•Decrease in the easy of blood flowing through the liver
•Hence, Portal vein has increased hydrostatic pressure
•Pooling of blood in portal venous circulation
•Hepatic lymphatic obstruction which is really important in nutrient absorption
Renal Disease
•Glomerulopathy and tubular dysfunction
•may result in loss of plasma protein
•Or increased sodium retention
•Nephrotic syndrome
-wholes in the filtration membrane
-protein loss to urine
- level of the nephron
GI Disease
•plasma protein deficiencies may result from:
-Starvation
-Malabsorption
-Any enteropathy
•This decreases intravascular osmotic pressure
•And increased interstitial fluid
minimum calories in diet
- 800-1000
Inflammatory or Allergic inflammation
•Inflammatory cells leave the vascular space
•Release mediators of inflammation
•Capillaries become "leaky"
•Fluid accumulates where ever there is loose connective tissue
•Eyes are usually early
- caused by lymphatics
- loose lymphatic tissue can cause edema
Hyperemia as a Local Volume Expansion
•Refers to increased blood flow through dilated arteries, arterioles, and capillary beds
•Clinically, this results in increased warmth and redness on affected tissue.
•This is a reflexive mechanism (neutrally and/or chemically mediated) that allows greater blood flow to areas of inflammation
•Also seen in tissues needing more oxygen
•A mechanism of heat dissipation
•Prominent in reperfusion after cold
Congestion as a Localized Tissue Expansion
•Decreased blood flow to veins, venules, and capillaries
•due to impaired venous drainage
•Clinically, results in a bluish discoloration of tissue (cyanosis) due to accumulation of reduced hemoglobin
•Since impaired venous drainage also leads to increased hydrostatic pressure, edema is a common accompaniment of congestion.
Acute congestion
•This produces heavier, bloodier organ or tissue which may or may not lead to clinical signs and symptoms.
Chronic congestion
•This leads to impaired tissue oxygenation and may result in "degeneration" or necrosis of the affected tissue. The effects of chronic passive congestion are most often seen in the lungs, liver, and spleen.
what should we think of the liver and spleen as
- just another vein
excitable cells in the body
- muscle and neurons
What drives depolarization?
- sodium
what drives hyperpolarization
-If serum level is low Potassium leaves the intracellular space and the cell is hyperpolarized (this is usually a chloride thing)
-If serum level is too high it goes into cells and depolarizes them
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